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thesis entitled
THE PATTERN OF VOLATILE CHANGES DURING THE MODIFIED
ATMOSPHERE PACKAGING (MAP) STORAGE OF APPLE
presented by

We imin Deng

has been accepted towards fulﬁllment
of the requirements for

Masters degree in Horticulture

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1/” COMM“

THE PATTERN OF VOLATILE CHANGES DURING THE MODIFIED
ATMOSPHERE
PACKAGING (MAP) STORAGE OF APPLE
BY

Weimin Deng

A THESIS
Submitted to
Michigan State University

in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1999

ABSTRACT

PATTERN OF VOLATILE CHANGES DURING THE MODIFIED ATMOSPHERE
PACKAGING (MAP) STORAGE OF APPLE

By

Weimin Deng

A simple sampling method was developed to measure volatiles produced
by apple (Malus xdomestica Borkh cv. Golden Delicious) fruit in modiﬁed
atmosphere packages. The sampling system incorporated GC column segments
installed in gas tight syringes and used as needles for volatile analysis. The
number of times the syringe plunger was pumped required to maximize GC
response for each needle/volatile combination was determined. The pump
number for maximal GC response was greatest (~40) for the larger more
lipophilic molecules and lowest (~5-10) for the smaller, more polar molecules that
did not readily partition into the column coating. A capillary needle resulted in an
increase in GC response of 3- to 15-fold relative to an uncoated stainless steel
needle. By using the capillary needle, at least 10 volatile compounds and their
perrneabilities to be measured under the real storage condition. This
methodology was used to determine the dynamic relationship between ﬂavor

volatile synthesis and package atmosphere for packaged apple.

Dedicated to my father and mother

iii

ACKNOWLEDGMENTS

I would like to express my sincere appreciation to Dr. Randolph M.
Beaudry for his guidance, patient training, continued encouragement, help and
support throughout my years of graduate study. The opportunity to study under
his tutelage has been enlightening and gratifying.

I would like to express my special thanks to the member of my guidance
committee: Dr. Art Cameron, Dr. Jerry N. Cash and Dr. Ruben Hernandez for
their valuable advice, help, and critical review of this thesis.

i wish to thank Drs. David R. Dilley, Frank Dennis, Robert C. Herner,
Muraleedharan G. Nair, John Everard, Zhenyong Wang, Jun Song, Nazir Mir,
Dina Kadyrzhanova for their assistance and encouragement.

I also wish to thank Hongying Jiang; Yali Zhu, Cathy S. Roth, Silvanda
Silva, Jennifer Dwyer, Stacie Wee, Jessica Townsend, Rujida Leepipattanawit,
Ruﬁno Perez, Michael Wendorf, Costas Vlachonasios, TJ McCully and all
colleagues in the post-harvest lab for their help, friendship and encouragement.

I am grateful to Joyce Jackson, Lorri K. Busick, Sherry Mulvaney and all
the people in the Department Ofﬁce for their assistance.

Finally, l express my deep love and appreciation to my wife Yuan Dong,
daughter Lu Deng, brothers and sisters for their love, understanding, support

and encouragement.

TABLE OF CONTENTS

LIST OF TABLES ............................................................................... vi

LIST OF FIGURES ......................................................................................... vii

CHAPTER 1

INTRODUCTION ............................................................................................. 1

CHAPTER 2

LITERATURE REVIEW .................................................................................. 1O
Importance of volatile compounds in food ............................................ 11
Importance of aroma volatiles in apple fruit ......................................... 12
Progress in apple volatile research ...................................................... 12
Biogenesis of apple ﬂavor components ............................................... 23
Factors affecting volatile production of apple ....................................... 27

Preharvest factors ..................................................................... 27
Postharvest factors .................................................................... 28

The methods of volatile collection, isolation and analysis .................... 34
References ........................................................................................... 39

CHAPTER 3

OVERCOMING GAS SAMPLING PROBLEMS: ANALYSIS

OF VOLATILES USING CAPILLARY COLUMN NEEDLES ........................... 50
Abstract ................................................................................................ 51
Introduction .......................................................................................... 52
Materials and Methods ......................................................................... 55
Results and Discussion ........................................................................ 57
Conclusion ........................................................................................... 62
References ........................................................................................... 65

CHAPTER 4

A PACKAGING SYSTEM FOR RIPID MEASUREMENT OF VOLATILE

SYNTHESIS AND PERMEABILITY ................................................................ 89
Abstract ................................................................................................ 90
Introduction .......................................................................................... 92
Materials and Methods ......................................................................... 94
Results and Discussion ........................................................................ 98
References .......................................................................................... 105

CHAPTER 5

SUMMARY AND CONCLUSIONS ................................................................. 142

LIST OF TABLES

CHAPTER 2
Table 1. Volatile components isolated from apple ................................ 15

CHAPTER 3

Table 1. The effect of pump number, needle types, and volatile
compounds on GC response ................................................................ 67

vi

LIST OF FIGURES

CHAPTER 2

Figure 1. Number of volatiles identiﬁed to be produced by
apples since 1920 ................................................................................... 15

Figure 2. Some possible routes for the synthesis of ﬂavor
compounds in apple ................................................................................ 25

CHAPTER 3

Figure 1. Standard Jar: The jar was specially-designed glass chamber
with a volume of 4-L, ﬁtted with a Mininert value. The standard
concentration was generated by evaporating sub-micro liter amount
of the liquid of each of the volatile compounds of interest ...................... 69

Figure 2. GC response as a function of number of times a syringe
plunger is pumped for 50 uL injections of hexyl acetate (1.673 Pa)
from glass, gas-tight syringes ﬁtted with a stainless steel needle
and needles made from capillary column (glass and steel)
segments. Arrows denote estimated saturation point. Bars represent
SE of more than 10 randomized replicates. Each data point
represents the mean of 10 to 20 injections of a single standard ............. 71

Figure 3. GC response as a function of number of times a syringe plunger
is pumped for 50 uL injections of 6-methyI-5-hepten-2-one (1.847 Pa)
from glass, gas-tight syringes ﬁtted with a stainless steel needle
and needles made from capillary column (glass‘and steel) segments.
Arrows denote estimated saturation point. Bars represent SE of more
than 10 randomized replicates. Each data point represent mean of
10 to 20 injections of a single standard. .................................................. 73

Figure 4. GC response as a function of number of times a syringe plunger
is pumped for 50 uL injections of butanoi (3.051 Pa) from glass,
gas-tight syringes ﬁtted with a stainless steel needle and needles
made from capillary column (glass and steel) segments. Arrows
denote estimated saturation point. Bars represent SE of
more than 10 randomized replicates. Each data point represents
mean of 10 to 20 injections of a single standard. .................................... 75

vii

Figure 5. GC response to injection volume of butanoi using a
gas-tight syringes fitted with a stainless steel needle and needles
made from capillary column (glass and steel) segments. Note
the fitted line dose not extrapolate through the origin. Dotted
line segment represents extrapolation to zero injection volume
(reflects contribution of needle volume, material adhering
to the interior of the needle and effect of pressure of carrier
gas). Syringe pump number: 20; Needle length: 5.7 cm;
Temperature: 22°C. .................................................................. 77

Figure 6. G0 response to injection volume of hexyl acetate, ethyl 2-
methylbutyrate, and butanoi using a gas-tight syringes ﬁtted with
a needle made from steel capillary column segments. Note the
ﬁtted line dose not extrapolate through the origin. .................................. 79

Figure 7. Effect of needle length on 60 response to 50 uL injections of
6-methyI-5-hepten-2-one from glass, gas-tight syringes ﬁtted with a
stainless steel needle and needles made from capillary column
(glass and steel) segments. .................................................................... 81

Figure 8. Coefficient of variation for injection volume of butanoi
using a gas-tight syringes fitted with a stainless steel needle
and needles made from capillary column (glass and steel)
segments. ................................................................................ 83

Figure 9. Effect of needle length on Coefficient of variation to 50 pL
injections of 6-methyl-5—hepten-2-one from glass, gas—tight
syringes fitted with needles made from capillary column (glass
and steel) segments ................................................................... 85

Figure 10. Effect of temperature and concentration of hexyl acetate vapors
on GC response to 50 pL injections from glass, gas-tight syringes
ﬁtted with a needle made from steel capillary column segments
(length: 5.7 cm). ...................................................................................... 87

CHAPTER 4

Figure. 1. Package-in-a-jar system. Apples (1 10-240 9) were sealed in
a 2-mil (0.00508 cm) thick LDPE package with an area of 0.06-0.07
m’. Packages were placed in a 2-L glass jar ventilated at 6-7 mL/min
with air. The package and jar headspaces were sampled for aroma
volatile analysis. The permeability of packaging ﬁlm was calculated
by the gradient of aroma volatiles across the ﬁlm, the rate of
production by product was simultaneously calculated based on

viii

the ﬂux of volatile compounds .............................................................. 107

Figure 2. The standard jar was a specially-designed, 4-L Erlenmeyer ﬂask

having a ground-glass stopper ﬁtted with a Mininert valve. Volatile
concentrations were generated by evaporating sub—microliter

Amounts of the liquid of each of the volatile compounds

of interest. ............................................................................................ 109

Figure 3. Glass permeation cell used for measurement of steady-state

permeability of plastic ﬁlm to single volatile perrneants ........................ 111

Figure 4. Effect of temperature on the permeability of LDPE ﬁlm to

Hexyl acetate, 6-methyI-5-hepten-2-one, butyl acetate, Ethyl 2-
methylbutyrate, hexanal, and butanoi. Test ﬁlm area was 7.55 cm2

and thickness was 0.00508 cm (2-mii). Four replicates were

performed and 10 measurements were made for each permeation

ceﬂ ....................................................................................................... 113

Figure 5. Effect of storage duration on the ‘apparent’ permeability of

LDPE ﬁlm to volatiles during MAP storage of apple at 22°C as
measured by the package-in-a-jar system. Each symbol
represents 5 replications :l: SE. ............................................................ 115

Figure 6 Permeability of LDPE to ethylene during MAP storage at

22°C as measured by the package-in-a-jar system. Each
symbol represents 5 replications iSE ........................................ 1 17

Figure 7. Permeability of LDPE to selected volatiles as measured by the

permeation cell and package-in-a-jar systems. .................................... 119

Figure 8. Effect of storage duration on 02, C02, ethylene and volatile

partial pressures in packages that maintained approximately
10 kPa 02 during MAP storage of apple at 0°C. Each symbol
represents 5 replications :I: SE ............................................................. 121

Figure 9. Effect of storage duration on 02, COZ, ethylene and volatile

partial pressures in packages that maintained approximately
8 kPa 02 during MAP storage of apple at 0°C. Each symbol
represents 5 replications 1 SE. ............................................................ 123

Figure 10. Effect of storage duration on Oz, 002, ethylene and volatile

partial pressures in packages that maintained approximately
4 kPa 02 during MAP storage of apple at 0°C. Each symbol
represents 5 replications 1: SE. ............................................................ 125

Figure 11. The effect of O2 partial pressure and storage duration on
ethylene production rate during MAP storage of apple fruit at
0°C. Each symbol represents 5 replications :l: SE. .............................. 127

Figure 12. Effect of storage temperature and storage duration on
ethylene production rate of apple fruit during MAP storage
(10% 02). Each symbol represents 5 replications 3: SE ...................... 129

Figure 13. Changes in hexyl acetate, butyl acetate, and 2—methyl-
butyl acetate production rate during MAP storage of apple
under different package atmosphere and storage duration.
Storage temperature was 0°C. Each symbol represents
5 replications t SE. ................................................................ 131

Figure 14. Concentration of 2-methylbutyl acetate in the headspace.
of packages containing apple fruit, which were further enclosed
in jars, in the headspace of those same jars and in the
headspace of jars containing apple fruit not enclosed in
packages. The storage temperature was 22°C. Each
symbol represents 5 replications t SE ....................................... 133

Figure 15. Concentration of hexyl acetate in the headspace of
packages containing apple fruit, which were further enclosed
in jars, in the headspace of those same jars and in the
headspace of jars containing apple fruit not enclosed in packages.
The storage temperature was 22°C. Each symbol represents
5 replications t SE. .............................................................................. 135

Figure 16. Concentration of a-farnesene in the headspace of
packages containing apple fruit, which were further enclosed
in jars, in the headspace of those same jars and in the
headspace of jars containing apple fruit not enclosed in packages.
The storage temperature was 22°C. Each symbol represents
5 replications t SE. .............................................................................. 137

Figure 17. The ﬂux of volatiles released from the package-in-a-jar and
jar only system during MAP storage of apple. The 02 level
in the package was similar to that in glass jars with no package.
Storage temperature was 22°C. Each symbol represents
5 replications :I: ................................................................ 139

CHAPTER I: INTRODUCTION

The methodologies for organic volatile compounds analysis include
solvent extraction, distillation, and headspace sampling. For the analysis of
odorous volatile compounds of apple fruits, headspace analysis is considered
the most suitable and widely used technique "since it reveals the identity and the
concentration in the vapor phase of those compounds that are directly
responsible for the odor of the product" (Maarse, 1991). Headspace sampling
involves taking the sample from vapor phase above the food. This technique
offers the possibility of volatile isolation without sample destruction or artifact
formation (Land, 1975; Olafsdottir et al., 1985). Therefore, the volatiles that are
measured by headspace analysis are more representation to the odor in the
concentration and ratios presented to the human nose if compared with other
analysis techniques (Bemelmans, 1978).

Of the various headspace techniques, direct or static headspace analysis
is the simplest and fastest for studying the aroma properties and quality of food
materials (Weurman, 1961; Martin, 1969; Guadagni et al., 1971; Yamashita et
al., 1977; Mcnaily and Grob, 1985). Direct headspace analysis is that in which a
volume of the atmosphere containing the volatiles of interest is removed from the
system and directly introduced into a gas chromatograph (GC) or other detection
device. However, aroma volatiles are often produced at very low levels by
almost all produce and therefore accumulate to low concentrations in most
sampling systems. Direct headspace sampling often does not deliver enough of
the molecules of interest to permit detection by ﬂame ionization or mass

spectrometry following separation by gas chromatograph (Reineccious, 1983).

The lack of sufﬁcient analyte in the gas phase has lead to techniques
that increase sample amount by concentrating volatiles using absorptive and
adsorptive surfaces or devices (Bertsch et al., 1975; Buckholz et al., 1980;
Fawvell et al., 1979; Murray, 1977; Olafsdottir et al., 1985). In many cases,
volatile compounds are removed from the headspace of a sampling chamber by
carrier (N2) gas purging and trapped onto a porous polymer (Hirvi and Honkanen,
1982; Shamaila et al., 1992; Song and Bangerth, 1994), hence the term ‘purge-
and-trap’ is used to refer to this approach. The volatile compounds are extracted
from the trapping material by heating (Dirinck et al., 1981; Mattheis et al., 1991a,
1991b) or by various liquid extraction techniques (Clark and Cronin, 1975;
Guadagni et al., 1971; Olafsdottir, 1985; Shamaila, et al., 1992; Song and
Bangerth, 1994). Tenax-GC (2,6-diphenyl-p-phenylene oxide polymer) and
Tenax-TA are two popular and effective sorbants that have been widely used for
the adsorption of a variety of aroma volatiles from foods. The purge-and-trap
technique in which a gas is used to sweep volatiles onto a sorptive surface is
speciﬁcally termed the dynamic headspace technique (Dirinck et al., 1981;
Mattheis et al., 1991a, 1991b; Olafsdottir et al., 1985; Shamaila et al., 1992;
Song, 1994; Song and Bangerth, 1994).

Dynamic headspace sampling is arguably the most suitable method for
volatile analysis for apple fruit after CA storage or during ripening. However, it is
incompatible with low-volume sealed systems such as packages or small vials.
In addition, these kinds of methods are generally time and labor intensive. In

many cases, research often requires the analysis of only a few of the more

plentiful volatiles but from many samples of food. The relationship between
aroma biosynthesis and aroma accumulation in packages of produce for some
major volatile compounds is not well understood. It would be useful, therefore, to
have a sampling technique that is simple, fast, and accurate speciﬁcally for this
system.

Modiﬁed-atmosphere packing (MAP) "has the potential to provide low
Ozlhigh CO2 regimes similar to those of CA storage" (Beaudry et al., 1992). It is a
widely used technique for storage fresh and lightly processed fruits and
vegetables. However, the loss or change of ﬂavors by packing material during
storage are "the greatest problems in providing high quality food" (Matsui et al.,
1994). The ﬂavor proﬁle of apple in MAP can be affected by the production rate,
which is related to O2 and CO2 concentration in the packaging and storage
temperature and also by the interaction of ﬂavor compounds with the package
polymer (Debeaufort and Voilley, 1994; Mason et al., 1992; Matsui et al., 1994;
Nielsen and Giacin, 1994; Osajima and Matsui, 1993). Loss of ﬂavor
constituents or changes their proﬁle may due to sorption into packaging material
or permeation through the package to the environment (Nielsen and Giacin,
1994) or due to the acquisition of ﬂavor volatiles directly from the packing or
indirectly by permeation from the environment through the package to the food
(Mason et al., 1992).

Low-density polyethylene (LDPE) is a commonly used polymer ﬁlm for the
construction of MAP for fresh and lightly processed produce. Its high

perrneabilities to O2 and CO2 (Beaudry et al., 1992; Beaudry and Dube, 1994)

and water vapor (Debeaufort and Voilley, 1994) are well studied and make LDPE
especially amenable to packaging of fresh produce. However, only a few studies
on the permeability of LDPE ﬁlm to aroma volatiles have been published
(Delassus et al., 1988; Fukamachi et al., 1994).

Aroma volatile biosynthesis by apple fruit is well studied under various
conditions, including following CA storage (Brackmann et al., 1993; Mattheis et
al., 1991a; Song and Bangerth, 1994; Willaert et al., 1983) and during ripening
(Song and Bangerth, 1994; Seifabad, 1988). To our knowledge, however, aroma
volatile changes during MAP storage have not been studied.

Apple volatiles are produced in minute quantities, making study difﬁcult
and requiring the use of specialized equipment to concentrate, separate and
detect these compounds in the atmosphere. Under actual conditions of apple
storage such as low 02, high 002, and low temperature, volatile emanation is
reduced even further making in situ studies even more problematic. These are
some of the reasons why most investigators have chosen to removed the fruit
from the storage environment and place them under conditions of higher
temperature and 02. Studies employing these practices likely have masked the
responses to the modiﬁed atmospheres. In order to understand the inﬂuence of
the storage environment on the physiology and the biochemistry of aroma
production, it is important to study the aroma biosynthesis of apples within their
storage environment.

The purpose of this investigation was three-fold: 1. to develop a simple,

rapid, and accurate system for measuring volatiles; 2. employ a package system

for the simultaneous measurement of volatile production by plant organs and the
permeability of the packaging ﬁlm to those volatiles; and 3. measure the

production of volatiles as affected by package 02 and storage duration.

Literature Cited:

Beaudry, R. M., A. C. Cameron, A. Shirazi and D. Dostal Lange. 1992. Modiﬁed-
atmosphere packaging of blueberry fruit: Effect of temperature on
package oxygen and carbon dioxide. J. Amer. Soc. Hort. Sci. 117

Beaudry, R. M. and N. Dube. 1994. A permeable membrane respirometer.
HortScience 29 (5)2132 (Abstr).

Brackmann, A., J. Streif and F. Bangerth. 1993. Relationship between reduced
aroma production and lipid metabolism of apples after long-term
controlled-atmosphere storage. J. Amer. Soc. Hort. Sci. 118 (2): 243-247.

Clark, R. G. and D. A. Cronin. 1975. A new technique for trapping and sensory
evaluation of ﬂavor volatiles. J. Sci. Food Agric. 26: 1009.

Debeaufort, F. and a. Voilley. 1994. Aroma compounds and water vapor
permeability of edible ﬁlms and polymeric packaging. J. Agric. Food
Chem. 42:2871-2875.

DeLassus P. T., J. C. Tou, M. A. Babinec, D. C. Rulf, B. K. Karp, and B. A.
Howell. 1988. Transport of apple aromas in polymer ﬁlms. In Food and
Packaging Interactions, J. H. Hotchkiss,(ed.)ACS SymposiumSeries No.
365.

Dirinck, P. J., H. L. De Pooter, G. A. Willeart and N. M. Schamp. 1981. Flavor
quality of cultivated strawberries: The role of the sulfur compounds. J.
Agric. Food Chem. 29:319.

Fukamachi, M., T. Matsui, M. Shimoda, and Y. Osajima. 1994. Derivation of
thermodynamic sorption equation of ﬂavors with packaging ﬁlms. 2. J.
Agric. Food Chem. 1994 42:2893-2895.

Guadagni, D. G., J. L. Bomben and J. 8. Hudson. 1971. Factors inﬂuencing the
development of aroma in apple peels. J. Sci. Food Agric. 22:110-115.

Hirvi, T. and E. Honkanen. 1982. The volatiles of two new strawberry cultivars,
"Annelie" and "Alaska Pioneer," obtained by backcrossing of cultivated
strawberries with wild strawberries, Fragan'a vesca, Rugen and Fragan'a
virginana. Z. Lebensm. Unters. Forsch. 175:113-116.

Land, O. G. 1975. Techniques for assessing odour: uses and limitations. Proc.
Int. Symp. Aroma Research. Pudoc., Wageningen, The Netherlands.

Martin, J. M. 1969. Gas chromatographic qualitative and semiqualitative
analysis of apple aroma by means of retention indexes. J. Anal. Chem.
Acta. 48:169.

Mason R. C., P. T. Delassus, G. Strandburg, and B. A. Howell. 1992. Diffusion
of ﬂavors in polymers: effect of permeant size and shape. Tappi Journal.
75 (6):163-168.

Matsui, T., M. Fukamachi, M. Shimoda, and Y. Osajima. 1994. Derivation of
thermodynamic sorption equation of ﬂavors with packaging ﬁlms. 1. J.
Agric. Food Chem. 42(12):2889-2892.

Mattheis, J. P., D. A. Buchanan, and J. K. Fellman. 1991a. Change in apple fruit
volatiles after storage in atmospheres inducing anaerobic metabolism. J.
Agri. Food Chem. 39:1602-1605.

Mattheis, J. P., J. K. Fellman, P. Chen, and M. Patterson. 1991b.
Changes in headspace volatiles during physiological development of
bisbee delicious apple fruit. J. Agric. Food Chem. 39:1902-1906

McNalIy, M. E. and R. L. Grob. 1985. Current application of static and dynamic
headspace analysis. A review. Part II: non environmental applications. J.
Amer. Lab. Febz106.

Nielsen, T. G. and J. R. Giacin. 1994. The sorption of Limonene/ethyl acetate
binary vapor mixture by a biaxially oriented polypropylene ﬁlm. Packaging
technol. and Sci. 72247-256.

Olafsdottir, G., J. A. Steinke and RC. Lindsay. 1985. Quantitative performance
of a simple Tenax-GC adsorption method for use in the analysis of aroma
volatiles. J. Food Sci. 50:1431-1436

Osajima, Y. and T. Matsui. 1993. Dynamic Approach to the Sorption of ﬂavors
into a food packaging ﬁlm. Anal. Sci. 9:753-763.

Reineccious, G. 1983. Determination of ﬂavor components. 43th Annual Meeting
Inst. Food Technologists, New Orleans, LA.

Seifabad, T. C. 1988. Effect of harvest date and ethylene concentration in
controlled atmosphere storage on the quality of empire apple. PhD.
Thesis, Michigan State Univ.

Shamaila, M., W. D. Powrie and B. J. Skura. 1992. Analysis of volatile
compounds from strawberry fruit stored under modiﬁed atmosphere
packaging (MAP). J. Food Sci. 57:1173-1176.

Song J. and F. Bangerth. 1994. Production and development of volatile aroma
compounds of apple fruits at different times of maturity. Act Horticulturae.

357.

Weurman, C. 1961 Gas-liquid chromatographic studies on the enzymatic
formation of volatile compounds in respberries. J. Food Technol. 15:531.

Willaert, Dirinck, De Pooter, and Schamp. 1983. Objective measurement of
aroma quality of golden delicious apple as a function of controlled-
atmosphere storage time. J. Agric. Food Chem. 31:809-813.

Yamashita, l., Y. Nemoto and S. Yoshikawa. 1977. Studies on ﬂavor
development in strawberries. 4. Biosynthesis of volatile alcohol and esters
from aldehyde during ripening. J. Agric. Food Chem. 25: 1165.

CHAPTER II: LITERATURE REVIEW

"Biogenesis is the natural process by which ﬂavor develops with progressive

ripening, reaches an optimum value corresponding to the perfect ripening stage

and subsequently exhibits a generalized rapid decay" (Feranoli, 1973).

10

IMPORTANCE OF VOLATILE COMPOUNDS IN FOOD

Volatile compounds are often present in small amounts in food. The
concentration of the major volatile compounds varies from 10‘1 to 10'3 ppm, while
those of the trace constituents may be as low as 10'7 ppm (Bemelmans, 1978).
Despite these low content levels, the ﬂavor characteristics of a food are derived
mainly from its volatile components. The degree to which volatiles contribute to
the ﬂavor is dependent on their threshold value and their concentration (Mulders,
1973). The concentration, ratio, and mixture of volatiles make the aroma speciﬁc
to each type of food. Aroma as a component of ﬂavor is one of the most
important quality factors of food. It has been estimated that aroma comprises
70% of what we perceive of as ﬂavor. Product re-purchase is highly dependent
upon possession of acceptable ﬂavor. In some cases, consumers are attracted
to test a particular food solely from its aroma (Seifabad, 1998).

Volatiles have properties other than aroma that may confer value to their
presence. For instance, some plant volatiles have been identiﬁed having
antimicrobial activity. Red raspberries and strawberries possess some antifungal
volatile compounds, which when applied at high concentrations, can completely
inhibit postharvest decay fungi (Fries, 1973; Farag et al., 1989; Vaughn et al.,
1993; Wilson et al., 1987). Davis and Smoot (1972) found Penicillium digitatum
was inhibited by volatile Cs-Cgaldehydes in mature citrus fruit. Hexanal was
reported to inhibit fungal growth on apple slices and artiﬁcial media (Song et al.,
1996). Importantly, this antifungal volatile is actively converted to hexylacetate

by the apple itself such that no residues of the active compounds remain only

11

hours after application.
IMPORTANCE OF AROMA VOLATILES OF APPLE FRUIT

Aroma comprises the major component of ﬂavor and directly affects the
organoleptic quality of apple fruit. The amount and kinds of volatiles are affected
by many factors including culture (Brown et al., 1968; Cunningham et al., 1986;
Dimick and Hoskin, 1983; Paillard, 1981; Smock and Neubert, 1950; Yahia,
1986; Yahia et al., 1991), orchard environment (Brown et al., 1968; Somogyi et
al., 1964; Yahia, 1994; Zerbinni et al., 1980), harvest date (Brown et al., 1966;
Sapers, 1977; Seifabad, 1988; Song, 1994), stage of fruit development and
storage conditions (Song, 1994; Willaert et al., 1983; Yahia, 1986; Yahia et al.,
1991; Yahia, 1991a). Changes in the amount and kinds of volatiles occur during
storage, thereby changing the apple's aroma and ﬂavor. Understanding and
controlling the pattern of volatile changes during storage is an important
challenge for the apple industry.
PROGRESS IN APPLE VOLATILE RESEARCH

Interest in apple volatiles and essences began in this century. Power and
Chestnut (1920) identiﬁed a number of compounds they believed responsible for
aroma. White (1950) enlarged the list of compounds that contribute to apple
aroma. He reported that the volatiles contained eight alcohols, four carbonyls,
and numerous esters. Huelin (1952) identiﬁed several aldehydes and ketones.
In the meantime, he found acetaidehyde as a major constituent. Due to the
application of more powerful analytical tools such as the combined gas

chromatography-mass spectrometry (GC-MS) (Holmes and Morrel, 1957) and

12

the use of more sensitive detectors such as the ﬂame ionization detector (F ID),
detection of volatile compounds at the part per billion (ppb) level became
possible in the early 1960's. Since then, the number of volatile compounds
identiﬁed from apple has increased rapidly (Fig. 1). Flath et al. (1967) identiﬁed
56 compounds, of which, twenty were previously unreported. They found that cis
or trans-2-hexenal and ethyl 2-methyI-butyrate had an apple or apple-like aroma;
the former two were described as having a green apple odor. Koch et al.
(1976), demonstrated the importance of (E)-2-hexena| in the odor of commercial
apple essence. VVrlliams et al. (1980) reported 88 identiﬁed components in
which 55 were not found previously. To date, over 300 organic volatile
compounds have been identiﬁed from apples or apple products (Dimick and
Hoskin, 1983; Maarse, 1991), but only 20-40 volatiles contribute to apple aroma
(Table 1, Fig. 1). Ethyl 2-methyl butanoate, ethyl butanoate, (E)-2-hexenal, (E)-
2-hexenol, hexyl acetate, hexyl butanoate, hexyl hexanoate, hexanol, 1-hexanol,
1-butanol, (Z)-3-hexenal,(Z)-3-hexenol, (E)-hexenyl acetate, -damascenone,
ethyl hexanoate, propyl 2-methyl butanoate, 4-methylallyl benzene, and other
unidentiﬁed volatiles are reported to contribute to typical apple aromas and are
considered to be character impact compounds (Berger, 1991). Aldehydes are
the most abundant group of volatiles in immature apples (Depooter et al., 1987),
but when fruit ripening begins, the major volatiles are esters and aliphatic
alcohols (Flath et al., 1967; Mattheis et al., 1991b; Song, 1994; Song and
Bangerth, 1994). Volatiles, including the above character-impact volatile

compounds of apple do not contribute equally to apple aroma. For example,

13

ethyl 2-methylbutyrate was 30-fold lower than hexanol in commercial apple
juices, but it was 30 times more important to juice aroma than hexanol (Lea and
Ford, 1991). Jepsen (1978) reported that apple juice ﬂavor quality was positively
correlated with ethyl 2-methylbutyrate, (E)-2-hexanal and butanoi, but negatively

correlated with ethanol and ethyl acetate.

14

7% l L 41 l I l A l l J l l j

 

633- —
in
Q) d
E
E
o
>
“—
3 5331 -
m
.o
E
3
Z
433- -

-
vv

 

‘
‘

 

*

463 4<63ﬁ 4173 r 4<'83\h;j 419:7 4<':3 ' 4<';3 4<<3
U

 

Fig. 1. Number of volatiles identiﬁed to be produced by apples since 1920. (from

Yahia, 1994)

15

Table 1. Volatile components isolated from apple (Dimick and Hoskin, 1983; Maarse,

1991; Yahia, 1994). (Asterisk indicates important volatiles to apple ﬂavor)

 

Alcohols:
methanol n-propanol
ethanol isopropanol
l-propanol n-butanol*
2-butanol isobutanol
pentanol 2-methyl butanoi

2-methyl butanoi-1-ol
3-methyl butanoi
3-pentanol
2-methyl-2-pentanol
4-methyl pentanol
(E)-2-hexenol
1-hexen 3-ol
(Z)-3-hexen-1-ol
(E)-2-hexen-1-ol
octanol

3-octanol
2-heptanol
E-thylhexanol
2-phenethanol
6-methyl-5-heptanol
benzyl alcohol

isobareol

16

2-methyI-2-butanol
2-pentanol
4-pentanol
3-methyl pentanol
hexanol *
(E)-3-hexenol
5-hexenol
(E)-hex-2-en-1-ol
heptanol
(Z)-3-octen-1-o|
decanol
2-octanol
2-nonanol
1-nonanol
(Z)-5-octenol
terpinen-4-ol

citronellol

Table 1 (Cont’d)

 

geraniol

(formates):

methyl formate
propyl formate
2-methylbutyl formate
pentyl formate

hexyl formate

(acetates):

methyl acetate

propyl acetate ‘
isobutyl acetate *
pentyl acetate '
3-methylbutyl acetate *
heptyl acetate

benzyl acetate
(E)-hex-3-enyl acetete
trans-2-hexenyl acetate
nonyl acetate

ethyl phenyl acetate

(propionates):

methyl n-propionate
ethyl 2-methylpropionate

propyl propionate *

17

eugenol

ethyl formate
butyl formate
3-methyl butyl formate

l-pentyl formate

ethyl acetate

butyl acetate'

t-butyl acetate
2-methylbutyl acetate *
hexyl acetate *

octyl acetate '
cis-3-hexenyl acetate
n-octyl acetate
2-phenylethyl acetate

decyl acetate

ethyl propionate *
ethyl hydroxypropionate

isobutyl propionate *

Table 1 (Cont’d)

 

2-methylbutyl propionate *

hexyl propionate
(butyrates):

methyl butyrate

propyl butyrate *

butyl butyrate *

pentyl butyrate

hexyl butyrate *

ethyl crotonate
(isobutyrates):

methyl isobutyrate

butyl isobutyrate

pentyl isobutyrate
(2-methyl butyrates):

methyl 2-methyl butyrate

propyl 2-methyl butyrate

isobutyl 2-methyl butyrate

hexyl 2-methyl butyrate *

3-methylbutyl butyrate
(pentanoates):

methyl pentanoate

propyl pentanoate

amyl pentanoate

hexyl pentanoate

3-methyl propionate

Butyl propionate

ethyl butyrate *
isopropyl butyrate
isobutyl butyrate *
isopentyl butyrate "

cinnamyl butryate

ethyl isobutyrate
isobutyl-isobutyrate

hexyl isobutyrate

ethyl 2-methyl butyrate *
butyl 2-methyl butyrate *
pentyl 2-methyl butyrate

2-methylbutyl butyrate

ethyl pentanoate *
butyl pentanoate

isoamyl pentanoate

Table 1 (Cont'd)

 

(isopentanoates):

methyl isopentanoate

isopentyl isopentanoate
(hexanoates):

methyl hexanoate *

propyl hexanoate *

isobutyl hexanoate

2-methylbutyl hexanoate *

hexyl hexanoate *
(hexanoates):

butyl trans-2-hexenoate
(heptanoates):

ethyl heptanoate

butyl heptanoate
(octanoate):

ethyl octanoate

butyl octanoate

pentyl octanoate

hexyl octanoate
(nonanoates):

ethyl nonanoate
(decanoates):

ethyl decanoate

isobutyl decanoate

ethyl isopentanoate

ethyl hexanoate *
butyl hexanoate *
pentyl hexanoate

3-methylbutyl hexanoate *

propyl heptanoate

hexyl heptanoate

propyl octanoate
isobutyl octanoate

isopentyl octanoate

butyl decanoate

pentyl decanoate

Table 1 (Cont’d)

 

isopentyl decanoate

(dodecanoates):

ethyl dodecanoate

hexyl dodecanoate

(other):

diethyl succinate
dimethyl phthalate
diethyl phthalate

2-methylbutyl oxtanoate

Aldehydes:

formaldehyde
propanal
2-oxopropanal
isobutanal
(E)-2-butenal
isopentanal
(E)-2-hexenal *
(E)-3-hexenal
(E)-2-heptenal
nonanal
undecanal

benzaldehyde

Ketones:

2-propanone

3-hydroxybutan-2-one

20

hexyl decanoate

butyl dodecanoate

ethyl-2-phenyl acetate
dipropyl phthalate

butyl (E)-hex-2-enoate

acetaidehyde
2-propenal
butanal
2-methyl butanal
pentanal
hexanal
(Z)-3-hexenal
heptanal
octanal
decanal
dodecanal

phenylacetaldehyde

2-butanone

2,3-butanedione

Table 1 (Cont’d)

 

Ethers:

Acids:

2-pentanone
4-methylpentan-2-one
2-heptanone
4-heptanone
7-methyioctan-4-one

acetophenone

diethyl ether
dibutyl ether
3-methyl butyl ether
methyl phenyl ether

cis-linalool oxide

formic acid
propanoic acid
isobutanoic acid
3-methyl butanoic acid
pentenoic acid
hexanoic acid
heptanoic acid
octanoic acid
nonanoic acid
decanoic acid
undecanoic acid

dodecanoic acid

21

3-pentanone
2-hexanone
3-heptanone

2-octanone
6-methyl-5-hepten-2-one

gamma-undecalactone

methyl propyl ether
2-methyl butyl ether
dihexyl ether
4-methoxyallyl benzene *

(E)-linalool oxide

acetic acid

butanoic acid

2-methyl butanoic acid
pentanoic acid
4-methyl pentanoic acid
(E)-2-hexenoic acid
cis-3-heptenoic acid
cis-octenoic acid
cis-3-nonenoic acid
decenoic acid
undecenoic acid

dodecanoic acid

Table 1 (Cont'd)

 

Bases:

Acetals:

tridecanoic acid
tetradecanoic acid
pentadecanoic acid
hexadecanoic acid
heptadecanoic acid
octadecenoic acid

9, t2-octadecadienoic acid
nonadecanoic acid

eicosanoic acid

ethylamine

isoamylamine

diethyoxymethane
dihexoxymethane
1-ethoxy-1-propoxyethane
1-butoxy-1-ethoxyethane
1-ethoxy-1-octoxyethane
1-butoxy-1-2-methyl butoxy ethane
1 ,1-di-2-methyl butoxy ethane

1 , 1-di-hexoxyethane

1,2-methyl butoxy-1-hexoxy ethane
4-methoxyallyl benzene

furfural

2,4,5-trimethyl-1 ,3-dioxolane

22

tridecenoic acid
tetradecanoic acid
pentadecenoic acid
hexadecenoic acid
heptadecenoic acid
9-octadecenoic acid
9,12,15-0ctadecatrienoic acid
nonadecenoic acid

benzoic acid

butylamine

hexylamine

dibutoxymethane
dihexoxyethane

1 ,1-diisobutoxyethane
1-ethoxy-1-hexoxyethane
1,1-diethoxyethane

1 ,1 —dibutoxyethane
1-butoxy-1-hexoxy ethane
1,1-diethoxy propane
1,1-dipthoxy pentantane
furan

5-hydroxy methylfurfural

Table 1 (Cont’d)

 

Hydrocarbons:
ethane thylene
farnesene benzene
ethyl benzene 1-methylnaphthalene
2-methylnaphthalene damascenone
pinene

 

BIOGENESIS OF APPLE FLAVOR COMPONENTS

Apple ﬂavor is composed of numerous classes of compounds, which
include lipids, carbohydrates, proteins (Maga, 1975; Salunkhe and Do, 1976;
Yahia, 1994) as well as some vitamins and minerals (Salunkhe and Do, 1976).
The origin, formation, and metabolism of aroma volatiles is not completely
understood (Goodenough and Entwistle, 1982; Yahia, 1994). Figure 2
summarizes possible diverse origins and mechanisms of biogenesis of the
volatile compounds (Yahia, 1994).

A. Primary volatiles:

The aroma of apple originates primarily from carbohydrates, amino acids,
and lipids (Salunkhe and Do, 1976; Yahia, 1994). Generally speaking, apple
aromas are genetically controlled with genetic differences leading to distinct
differences in ﬂavor between cultivars (Kakiguchi et al., 1986). The primary, or
natural, volatiles of apple fruit are those to be derived from enzymatically

controlled lipid, terpene, amino acid, and phenyl propane metabolism (Schreier,

23

1984). Fatty acids are considered be the most important source of carbon
skeletons needed for primary or natural odor volatiles biosynthesis in apple
(Yahia, 1994). During fruit ripening,

some endogenous fatty acids are converted into esters, ketones. and alcohols
(Tressel and Drawert, 1973; Yamashita et al., 1977). Drawert (1975) and
Paillard (1979) reported that fatty acid metabolism was implicated in the
formation a range of primary volatiles, which include the aliphatic esters, acids,
alcohols, and carbonyls. Yahia (1994) reported that "alcohols were formed from
the B-oxidation of aliphatic acids", for example, butanoi and hexanol were
produced by fatty acids with an even carbon number; propanol and pentanol
however, were formed from those with an odd carbon number. Even though the
pathway of ester synthesis is not fully understood (Goodenough and Entwistle,
1982), it seems clear that the formation of esters in fruit is largely dependent on
the availability of precursor alcohols and acids (Bartley et al., 1985; Knee and

Hatﬁeld, 1981; Song et al., 1996; Yamashita et al., 1977).

24

 
 
    
    

Hydrocarbons—Isoprene units Acetate
Pyruvate 4 %

Organic Short & Medium

acids chain fatty amdsN

_ Esters
Phenolics

 

 

C3 -C5 units Saturated Alcohols
fatty acids
. . Unsaturated
Aromatic Ammo aCIds fatty acids
amino acids
Keto acids tAIdehydes

Fig. 2. Some possible routes for the synthesis of ﬂavor compounds in apple.
(From Yahia, 1994.)

25

The biosynthesis of esters in apple is frequently examined by supplying
fruit tissues with short chain alcohols and/or carboxylic acids (Yahia,1994). For
example, when hexanol was supplied as vapors to whole apple, the alcohol was
incorporated into the “hexyl” portion of hexylacetate (Knee and Hatﬁeld, 1981;
Song et al., 1996). Bartley et al. (1985) reported that when short chain alcohols
(CZ-Ca) and methyl esters of short chain fatty acids (C,-C,,) were supplied as
vapors to whole apples, the alcohols were converted to the corresponding
acetate esters, while the methyl esters of short chain fatty acids were converted
to esters with an alkyl group of C2 or C,.

B. Secondary volatiles:

Secondary volatiles are formed by various uncontrolled enzymatic
reactions during fruit processing or chewing (Schreier, 1984). Therefore, the
secondary volatiles play a important role in the ﬂavor of processed products and
of the fresh fruit after cutting or chewing (Yahia, 1994). Some secondary
volatiles such as aldehydes (hexanal and (E)-2-hexenal) and alcohols (such as
hexanol), were produced quickly after apple crushing and homogenizing
(Drawert et al., 1968; Feys et al., 1980). The production of secondary volatile
compounds from free fatty acids is very common in plant tissues and food
systems when the tissues are crushed and exposed to oxygen (Croft et al.,
1993; Drawert et al., 1973; Erikson, 1975; Galliard et al., 1976;
Hatanaka,1983;). Gardner (1980) reported that the process of secondary
volatile production is catalyzed by lipoxygenases (LOX), which catalyzes the

peroxidation of polyunsaturated fatty acids with a cis, cis, 1, 4-pentadiene

26

structure to form conjugated hydroperoxides. The fatty acid hydroperoxides are
unstable and their breakdown contributes signiﬁcantly to the secondary volatile

development (Crouzet et al., 1984; Galliard et al., 1976, 1977).

FACTORS AFFECTING VOLATILE PRODUCTION OF APPLE

A. Preharvest Factors. Many preharvest factors can affect volatile
production of apple fruits. The genetic differences between cultivars also
contribute to marked aroma differences and generally speaking, almost all fruits
have their own characteristic aroma (Salunkhe and Do, 1976). The kinds and
amount of volatiles and their patterns differ in the different cultivars of apples
(Brown et al., 1968; Cunningham et al., 1986; Dimick and Hoskin, 1983; Paillard,
1981; Smock and Neubert,1950; Yahia, 1986; Yahia et al., 1991a). For
example, ‘Golden Delicious’ and ‘Jonagold’ have higher butyl and hexyl acetate
production than other cultivars (Song, 1994; Yahia, 1994). Butyl pentanoate,
pentyl pentanoate, and isopentyl pentanoate were found in various cultivars, but
were absent from ‘Mclntosh’ and ‘Cortland’ apples (Yahia, 1994).

Fruit maturity at harvest also affects aroma (Song and Bangerth, 1994;
Yahia, 1994). If a fruit is picked prior to full maturity volatile production is
markedly reduced relative to mature fruits and it may never develop its
characteristic ﬂavor (Brown et al., 1966; Brackmann et al., 1993; Lidster et al.,
1983; Paillard, 1981; Song and Bangerth, 1994). Hasen et al. (1992a) reported
that early-picked ‘Jonagold’ fruit not only had a delayed onset of volatile

production, but the production rate was lower compared to late-picked fruits.

27

However, if a fruit is picked too late, it also produces fewer volatiles compared to
optimally harvested fruit and the types of volatiles differ.

Finally, culture and orchard environment are also important factors
affecting aroma. For example, nutrients available in the soil can affect ﬂavor
production in many fruits. ‘Mclntosh’ apples from trees receiving a heavy
nitrogen fertilization treatment produced more volatile compounds than those
from a low nitrogen fertilization treatment (Smock and Neubert, 1950; Somogyi et
al., 1964). According to Brown et al. (1968), volatiles in freshly harvested
‘Golden Delicious’ fruit were increased by phosphorous fertilization. However,
Forsyth and Webster (1971) found higher levels of phosphorous fertilizer
treatment depressed the production of ethyl esters, acetaidehyde, and hexanol

in ‘Mclntosh’ fruit after cold storage.

8. Postharvest Factors:

Effect of temperature. Refrigeration is required for the long-term storage
of apple fruits to minimize loss of external and internal quality. However, long-
terrn storage of apples at 0 to 3°C can cause physiological disorders for some
apple cultivars (VVIIIS and Scott, 1975). Low temperatures affect not only the rate
of metabolism of apple, but also the make-up of the metabolic products. If
apples are susceptible to chilling, several physiological disorders may result,
Including low temperature breakdown, late storage corking and ﬂavor loss. \NIIIS
and Scott (1975) reported that low temperature breakdown is a physiological

disorder that causes a reduction in the level of volatile compounds during apple

28

cold storage. Fruit stored at 10 and 15°C produced more volatiles than those
stored at 3°C (Grever and Doesburg, 1965). When storage temperature
increased from -1°C to 10°C, ‘Jonathan’ fruit showed an increase in the
emission of acetate esters (Wills and McGlasson, 1971). When CA stored
‘Mclntosh' and ‘Cortland’ apples were transferred to 20°C, the production of
some odor-active volatiles was increased signiﬁcantly. However, there was no
signiﬁcant increase when the apples were transferred to 3.3°C (Yahia et al.,
1991). Insufﬁcient aroma in long-term, low-temperature-stored fruits is a
signiﬁcant commercial problem, and this problem seems to have become more
serious with the use of CA storage in conjunction with low temperature storage.
The Optimal temperature for aroma maintenance needs to be identiﬁed for
important apple varieties to minimize the effect of chilling.

Effect of oxygen and carbon dioxide concentration. Controlled-
atmosphere (CA) storage in conjunction with low temperature is highly effective
in maintaining apple quality in terms of preserving texture and slowing ripening
and senescence. However, suppression of aroma by low 02 and high CO2 is
sometimes a problem (Brackman et al., 1993; Guadagni et al., 1971; Knee,
1981; Patterson et al., 1974). Importantly, suppression of fruit ﬂavor can persist
even when apples are removed to normal atmosphere (Hansen et al., 1992b;
Knee and Sharples, 1981; Lidster et al., 1983; Liu 1985; Streif and Bagerth,
1988; Yahia et al., 1990a, 1991). The severity of CA storage suppression of
ﬂavor depends on the atmospheric composition and the duration of storage.

Generally speaking, the lower the 02 concentration, the higher the CO2

29

concentration, and the longer the duration in CA storage, the greater the level of
aroma suppression (Knee et al., 1981; Lidster et al., 1983; Patterson et al., 1974;
Streif et al., 1988; Wills and Scott, 1975; Yahia et al., 1990).

The effect of low 02 storage on aroma production is likely a function of
retarded ripening. Patterson et al. (1974) found that ‘Cox's Orange Pippin’ fruit
gradually lost their capacity to ripen normally when they were stored in 2 kPa
oxygen at 3.5 °C. When “Cox's Orange Pippin’ fruit were stored in air or 5 kPa
carbon dioxide in air, volatiles other than ethylene were produced in greater
amounts than for fruit stored in 2 kPa oxygen. Storage of ‘Mclntosh’ fruit in 1.5
kPa 02 +1.5 kPa CO2 or 1.0 kPa 02 + 1.5 kPa CO2 at 2.8 °C, acetaidehyde,
ethanol, hexanol and ethyl butyrate were suppressed (Lidster et al., 1983). Streif
and Bangerth (1988) reported that decreasing the 02 partial pressure from 21
kPa to 3 kPa has little effect on volatile production, but if the partial pressure of
02 decreases to 1 kPa, volatile production will be signiﬁcantly reduced upon
return of fruit on air. Brackmann et al. (1993) measured volatile production from
‘Golden Delicious' fruit stored 8 months at 1 °C in air and under various
controlled-atmospheres including ultra low oxygen (ULO) storage conditions (1
kPa Oz, 3 kPa C02 levels), their results show that all CA storage treatments
suppress aroma production compared to fruit storage in air. The greatest
reduction was found under ULO (1 kPa Oz) and high CO2 (3 kPa) partial
pressure.

Effect of ethylene. Ethylene, which is recognized as the ripening

hormone, plays an important direct role in regulating the ripening of climacteric

30

fruits (Biale and Young, 1981; Rhodes, 1980; Yang, 1985). Ripening involves
complex changes in metabolism of fruit in which both anabolic and catabolic
processes are involved (Biale, 1975). Speciﬁc events correlated with ripening
include increased respiration, autocatalytic ethylene production, chlorophyll
degradation, carotenoid synthesis, conversion of starch to sugar, aroma volatile
production, and solubilization of pectins and cellulose (Biale and Young, 1981;
Grierson, 1985; Rhodes, 1980;). Reduced ethylene synthesis and/or action is a
factor common to CA, and the suppression of aroma production after long-term
CA storage may be caused by ethylene-related changes in physiology rather
than the alteration in 02 and CO2 partial pressures (Bangerth and Streif, 1987).
Yahia et al. (1991) reported that butanoates, 2-methyl butanoates, pentanoates
and hexanoates were either severely or completely suppressed under low
ethylene CA (LCA) storage. Because of the effect of ethylene concentration,
"LCA storage would result in greater suppression of ﬂavor than conventional CA
storage" (Yahia et al., 1991)

Effect of storage duration. Having a ready supply of apple fruit year-
round is important for meeting consumer needs for apple fruit availability.
However, the fact that apple production is seasonal causes shippers and storage
operators to desire extended apple storability and improve storage quality. The
duration of apple storage has a close relationship with volatile production
(Patterson et al., 1974; erlaert et al., 1993). Streif and Bangerth (1988) found
that the effect of O2 and CO2 partial pressures on aroma production was clearly

dependent on the duration of storage; the longer the storage duration, the

31

greater the suppression of ﬂavor. Guadagni et al. (1971) reported that the rate
of ethyl 2-methylbutyrate production steadily increased after storage for 1-4
months, at 1 °C, and dropped off severely after 4 and 6 months. “Cox’s Orange
Pippin’ fruit volatile ester biosynthesis declined 75% after 5 months storage in 2
kPa 02 with or without 5 kPa COZ(Hatﬁeld and Patterson, 1974). When
‘Mclntosh’ apples were stored 1.5 kPa 02 +1.5 kPa CO2 or 1.0 kPa 02 + 1.5 kPa
CO2 at 2.8 °C for 320 days, some volatiles were completely suppressed even
after the apples were moved into air (Lidster et al., 1983).

Effect of packaging materials. Since modiﬁed-atmosphere packing
(MAP) has the potential to provide low Ozlhigh CO2 regimes similar to those of
CA storage (Beaudry et al., 1992), it is a much researched technique for fruit and
vegetable storage. However, loss or change of ﬂavors by packing material
during storage are potential problems (Matsui et al., 1994). The ﬂavor proﬁle of
apple in MAP can be affected not only by the O2 and 002 partial pressure in the
packaging and storage temperature, but also by the interaction of ﬂavor
compounds with polymer (Debeaufort and Voilley, 1994; Mason et al., 1992;
Matsui et al., 1994; Nielsen and Giacin, 1994; Osajima and Matsui, 1993;). Loss
of ﬂavor constituents or changes their proﬁle may due to their sorption into
packaging material or permeation through the package to the environment
(Nielsen and Giacin, 1994) or due to picking up ﬂavor directly from the packaging
or indirectly by permeation from the environment through the package to the
food (Mason et al., 1992). Low-density polyethylene (LDPE) is commonly used

polymer for MAP of fresh and lightly processed produce and some of its

32

properties such as the perrneabilities of O2 and 002 (Beaudry et al., 1992;
Beaudry and Dude, 1994) and water vapor (Debeaufort and Voilley, 1994) are
well studied. However, only a few studies on LDPE ﬁlm permeability to organic
volatiles such as those produced by apple fruit have been published (Delassus
et al., 1988; Fukamachi et al., 1994).

The loss of ﬂavor by sorption into packaging material or permeation
through the package to the environment commonly occurs in the packaged
products. The permeation process for permeant is described by following
equaﬁon:

P=DxS
Where: P is permeability coefﬁcient, which expresses the permeant transport
rate at steady-state and where P=P0 exp(-Ep /RT). 0 is the diffusion coefﬁcient,
which describes how fast the permeant molecules move in the ﬁlm where D=Do
exp(-ED/RT). S is the solubility coefﬁcient, which is a measure of the amount of
a permeant that will be absorbed by polymer where S=So exp(-HS /R77.
E, = activation energy for permeation; E0 = activation energy for diffusion; H5 is
the heat of solution.

Present studies show that the structure of both permeant and polymeric
packaging material, measurement condition (such as relative humidity,
temperature, etc), permeant concentration and co-permeants are the major

factors affecting volatile permeation.

METHODS OF VOLATILE COLLECTION, ISOLATION, AND ANALYSIS

33

There are many methods available for isolation, collection, and extraction
of volatiles from food, including solvent extraction, distillation, and headspace
(including equilibrium headspace and dynamic headspace) sampling
(Bemelmans, 1978; Sugisawa, 1981).

Distillation and extraction. Distillation is the most widely used technique
to isolate volatiles from apple and other fruits (Stevens et al., 1966; Flath et al.,
1967, 1969). Since there is water present in the distillate, to use this technique,
further solvent extraction is required (Heath and Reineccius, 1986). Extraction
methods are used either to isolate volatiles directly from food or to recover them
from diluted aqueous distillates. These extraction methods are based on the
favorable distribution coefﬁcient of the volatiles between solvent and food or the
distillate (Seifabad, 1988). The ﬁrst report on the distillation—extraction technique
was made by Likens and Nickerson (1964). Since then, the modiﬁed and
improved original Likens-Nickerson apparatus allows distillation and extraction
simultaneously. Since the concentration of volatiles may not be high enough for
GO analysis, it is sometimes necessary to concentrate the distillate which
obtained from distillation-extraction techniques (Seifabad, 1988). Concentration
is usually achieved by volatilizing the solvent with raised temperatures or purging
with a gentle stream of nitrogen (Nursten and Woolfe, 1971; Seifabad, 1988;
Shamaila, et al., 1992). The disadvantages of this method are moderately long
isolation time and potential artifact formation (Alberola et al., 1978) and low
percent recovery (Maarse, 1971 ). Land (1984) reported that the artifacts, which

formed due to heat during distillation-extraction, are eliminated when this

34

apparati are operated under reduced pressure condition. Vacuum distillation
procedure is commonly used to collect full ﬂavor volatiles from fruits and fruit
juices (Alberola et al., 1978; Kakiuchi et al., 1986; Seifabad, 1988).

Headspace analysis: Headspace sampling involves taking the sample
from vapor phase above the product. This technique offers the possibility of
volatile collection without sample destruction or artifact formation (Land, 1975;
Olfsdottir, 1985). Headspace sampling can be performed in static hermetic
environments or dynamic (ﬂow-through) environments.

Compared with other headspace analysis methods, static headspace
analysis is the simplest and fastest for studying the aroma properties and quality
of food materials (Weurman, 1961; Martin, 1969; Guadagni et al., 1971;
Yamashita et al., 1977; McNally and Grob, 1985). However, aroma volatiles are
often present at very low concentration. Using this method, gas chromatography
(GC) does not provide the sensitivity needed for trace analysis of volatiles
(Reineccious, 1983).

In order to increase the concentration of sample, the dynamic headspace
(purge and trap) analysis technique is widely used. In this method, volatile
compounds are removed from headspace by purging the atmosphere around the
product and trapping the volatiles onto a porous polymer (Hirvi and Honkanen,
1982; Shamaila et al., 1992; Song and Bangerth, 1994). The volatile
compounds are either desorbed from the polymeric material by heating (Dirinck
et al., 1981; Mattheis et al., 1991a, 1991b) or removed by various solvent

extraction techniques (Clark and Cronin, 1975; Guadagni et al., 1971;

35

Olafsdottir, 1985; Shamaila, et al., 1992; Song and Bangerth, 1994).

Charcoal was widely used as a porous trap during 1950's and 1960's
because of its high adsorption capacity and absence of involvement in artifact
formation (Heinze et al., 1953; Turk et al., 1951; Tang and Jennings, 1967).
Tenax-GC (2,6-diphenylparaphenylene oxide polymerhas) emerged as a widely-
used porous polymer in 1970’s (Jennings et al., 1972; Zlakis et al., 1973).
Tenax-GC has a very low afﬁnity for low molecular weight alcohols and water
(Jennings et al., 1972; Kuo et al., 1977), but also avoids the production of
artifacts characteristic of other porous polymers under certain operating
conditions (Seifabad, 1988). Jennings and Filsoof (1977) found that Tenax-GC
was a suitable porous polymer for the collection of volatiles from the headspace
of samples by comparing its performance with other various porous polymers.
Tenax-GC and the recently available Tenax-TA (MacLeod and Ames, 1986) are
widely used and considered to be the most effective and broadly suitable
sorbants today (Dirinck et al., 1981; Mattheis et al., 1991a, 1991b; Olafsdottir,
1985; Shamaila et al., 1992; Song and Bangerth, 1994).

The dynamic headspace analysis technique not only has high recovery
rate and less variation, but also provides an inexpensive alternative to other
methods for routine analysis of many intermediate molecular weight aroma
volatiles in beverage and food (Olafsdottir, 1985). Therefore, dynamic
headspace is one of the most suitable methods for volatile analysis for fruit and
vegetables. However, compared with equilibrium headspace and direct

headspace sampling techniques, the dynamic headspace is more complex, time

36

consuming and costly technique. There is a need for the creation of new simple,
fast and accurate methods.

A relatively new sampling methodology, solid-phase extraction, is
exposing a sorption surface in the headspace to collect and concentrate volatiles
by virtue of its sorption characteristics. Unlike direct headspace and purge-and-
trap sampling techniques, solid phase extraction does not require any volume of
gas to be removed from the headspace.

Solid phase micro extraction (SPME) is a special form of solid phase
extraction that uses a solid phase on an extendable ﬁber that is housed in a
hollow needle. Approximately 2 to 12 min are required for absorption (Song et
al., 1997). After absorption, the needle is inserted into the injection port of a GC.

Desorption requires 30 seconds to 1 minute or more, which would lead
unacceptable peak broadening. Thus cryofocussing of the desorbed compounds
is required and the use of a capillary column is often necessary. Solid phase
extraction does not require the removal of a volume of gas as in purge-and-trap,
but still requires desorption and an additional concentration step.

The above methods are widely used for isolation, collection and extraction
volatile compounds from apples. Since each technique has its advantages and
limitations, it is difﬁcult to say which one is suitable if the purpose of the analyses
are not clearly designated deﬁned. For example, the headspace methods are
commonly used in aroma volatile studies because of volatile collection without
sample destruction and artifact formation. However, the methods are not

suitable for higher boiling point volatile compounds. More than one techniques

37

should probably be used when the purpose is to evaluate the complete ﬂavor
proﬁle of apple fruits. Importantly, using different analysis techniques may yield
quantitatively and qualitatively differing results (Kakiinshi et al., 1986), which will
require additional work to reconcile the apparent inconsistencies to compare
data from different analysis methods. What kind analysis techniques should be
used must depend on the purpose, the food matrix, and the volatile compounds

to be analyzed.

38

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of apples. Il. Quality parameters of ‘Golden Delicious’ apples from

orchards at different altitudes. Freddo 34:101-115.

Zlakis, A., H. A. Lichtenstein and A. Tishbee. 1973. Solid adsorbent. J.
Chromatogr.

49

CHAPTER III:

OVERCOMING GAS SAMPLING PROBLEMS: ANALYSIS OF VOLATILES
USING CAPILLARY COLUMN NEEDLES

50

ABSTRACT

In an attempt to develop a simple, rapid sampling method, segments of
capillary gas chromatography (GC) columns were installed in gas-tight
syringes and used as needles for volatile analysis. Results were compared
to a standard stainless steel needle. Volatiles tested included hexyl acetate,
ethyl 2-methylbutyrate, 6-methyl-5-hepten-2-one and butanoi. GC response
increased as the number of times the syringe was pumped (syringe pump
number) increased. As pump number continued to increase, the rate of
increase in the GC response diminished until saturation occurred. The pump
number required to achieve response saturation was determined for each
volatile and each needle type. The use of a capillary needle resulted in an
increase in GC response in the range of 3- to 15-fold relative to a stainless
steel needle. Injection volume affected GC response in a needle- and volatile-
dependent manner. When injection volume was regressed against GC
response, it did not extrapolate through the origin for any of the needle
types. The GC response for capillary column needles increased as
temperature decreased. The capillary column needle may be a useful tool for
rapid and simple analysis of volatiles that readily partition into the column
coating. This sample collection technique allowed the use of a packed-

column GC system under isothermal conditions for volatile measurements.

51

INTRODUCTION

Analysis of aroma-related volatiles requires extraction and, often,
concentration of the volatiles prior to detection. Extraction techniques include
use of solvents, distillation, and headspace sampling. For the analysis of odor-
active volatile compounds of apple fruit, headspace sampling is considered the
most suitable and widely used since it should measure the concentration of
those compounds in the vapor phase that are directly responsible for the odor of
the product (Maarse, 1991). Headspace sampling is accomplished without
sample destruction or the formation of artifact volatiles resulting from heat, tissue
maceration, etc. (Land, 1975; Olfsdottir, 1985). Headspace analysis also
permits detection of odor-active compounds closer to the concentrations and
ratios perceived by human nose if compared with other analysis techniques
(Bemelmans, 1978).

Techniques for headspace sampling include direct headspace (static
headspace), purge-and-trap (dynamic headspace), and solid phase extraction.
Direct headspace sampling is the taking of a gas volume directly from the vapor
phase above the food. Purge-and-trap sampling involves purging the headspace
into a device that absorbs the volatiles to concentrate volatile compounds from
the headspace. Solid-phase extraction sampling involves exposing an
absorptive substance in the headspace to collect and concentrate volatiles by
virtue of its sorption characteristics. Unlike direct headspace and purge-and-trap
sampling techniques, solid phase extraction does not remove any signiﬁcant

volume of gas from the headspace.

52

Compared with other headspace sampling techniques, direct sampling is
the simplest and fastest (Guadagni et al., 1971; Martin, 1969; McNally and
Grob,1985; Weurman, 1961; Yamashita et al., 1977). However, aroma volatiles
are often present at very low concentrations and gas chromatography (GC) using
a ﬂame ionization detector (FID) often does not have sufﬁcient sensitivity for
detection of aroma volatiles present in trace amounts (Reineccious, 1983).

In purge-and-trap analysis, volatile compounds are desorbed from the
trapping material by heating (Dirinck et al., 1981; Mattheis et al., 1991a, 1991b)
or by various solvent extraction techniques (Clark and Cronin, 1975; Guadsgni et
al., 1971; Olafsdottir, 1985; Shamaila, et al., 1992; Song and Bangerth, 1994).
Purge-and-trap techniques require complex and costly equipment employing a
variety of adsorption, desorption and cryofocussing devices (Bertsch et al.,
1975.; Buckholz et al., 1980; Farvvell et al., 1979; Murray, 1977; Olafsdottir et al.,
1985). Tenax-GC (2,6-diphenyI-p-phenylene oxide polymer) and Tenax-TA (2,6-
diphenyi-p-phenylene oxide chemistry) have been widely used for the absorption
and adsorption of a variety of aroma volatiles from foods in purge- and-trap
analysis (Dirinck et al., 1981; Mattheis et al., 1991a, 1991b; Olafsdottir, 1985;
Shamaila et al., 1992; Song and Bangerth, 1994; Song, 1994). Although purge-
and-trap headspace sampling is one of the most suitable methods for the
analysis of apple volatiles, it is complicated, and both time and labor intensive.

While solid phase extraction does not require the removal of a volume of
gas as in purge-and-trap, but still requires desorption and an additional

concentration step such as cryofocussing. A relatively new approach, solid

53

phase micro extraction (SPME) uses a solid phase on an extendable ﬁber that is
housed in a hollow needle. SPME has the potential to reduce the time
investment in sampling and providing a linear response to concentrations of
many volatile compounds (Gardner et al., 1995; Song et al., 1997). However,
this simple and fast sampling approach must work in combination with rapid
separation and detection equipment.

In many cases, research requires the analysis of individual or a few major
volatiles whose concentration is not extremely low, yet too low for direct
headspace sampling. It would be useful to ﬁnd a simple, rapid method for
standard packed-column GC’s where sample preparation is at a minimum. This
would be valuable for monitoring applications.

The purpose of this investigation was to develop a simple and fast method
for analysis of volatiles produced in relatively high amounts by apple fruit using
an isothermal packed-column GC. Needles used had absorptive linings to
concentrate volatiles while attached to standard low-volume (50 to 100 uL) gas-
tight glass syringes. Thus, their use combined aspects of direct headspace,
purge-and-trap, and solid phase sampling techniques. Factors that could affect
linearity, variation and the magnitude of GC response such as the number of
times the syringe plunger was pumped (syringe pump number), injection volume,
needle type, sampling temperature, compound polarity and boiling point were

investigated.

54

MATERIALS AND METHODS

Needle preparation: Steel-jacketed (steel) and glass (glass) capillary
column needles were created for comparison to standard unlined stainless-steel
(stainless) needles. Steel and glass capillary needles were made by cutting
steel and glass capillary columns. The steel capillary column lining (0.28 mm id;
1.0 pm ﬁlm thickness) was crossbonded 5% diphenyl and 95%
polydimethylsiloxane. The glass capillary column (0.32 mm id; 1.0 pm ﬁlm
thickness) was bonded with 100% polydimethylsiloxane. After cutting to the
appropriate length, the column segments were installed in gas-tight syringe
(1710 RN syringe, Hamilton Co., Reno, Nevada) and used as needles for volatile
analysis. A standard 3.8-cm long, 26-gauge stainless steel needle was used as
control.

Preparation of volatile standard: Volatile standards were generated by
evaporating authenticated pure liquids of the volatiles of interest into a specially-
designed 4.3-L glass jar having a ground glass stopper ﬁtted with a Mininert
valves (Supelco lnc., Supelco Park, Bellefonte, Penn.) The liquids were allowed
to completely volatilize. The concentrations of volatiles were calculated based
on their molecular weight, density, purity, and the volume of standard jars. The
concentrations were 16, 16.5, 18.5, and 30.5 uL.L" for ethyl 2-methylbutyrate
(C7H,,Oz), hexyl acetate (CBHsz), 6-methyl-5-hepten-2-one (C8H,,O), and
butanoi (C4H,OO), respectively. These concentrations were <2% of saturation for

each compound at room temperature, so reduced temperatures should not have

55

affected the amount of material in the headspace of container.

Volatile analysis: Volatile samples were directly injected into a GC
(Carle AGE Series 400, Hach Company, Loveland, Colo.) equipped with a ﬂame
ionization detector. The column (3mm O.D., 3.3 m long) was packed with 10%
DEGS-PS, 80/100 mesh Supelcoport. The column was maintained isothermally
at 140°C. Puriﬁed helium (99.9%) was used as carrier gas. The ﬂow rate for the
helium, air, and hydrogen were 60 mL-min“, 200 mL-min", and 20 mL-min'1
respectively. In order to desorb the volatiles, the needle was held in the GC
injector for 3 seconds prior to injection, then held for an additional 2 seconds
before removal.

Effect of syringe pumping: The effect of the number of times a syringe
was pumped (syringe pump number) on GC/FID response was studied by
varying syringe pump number from 1 to 40. This was done for each volatile
(hexyl acetate, 6-methyI-5-hepten-2-one, and butanoi) and the three needle
types. Injection volume was 50 pL. The ﬁrst replication was taken starting with 1
rep and then increasing incrementally to forty pumps. The next replication was
done in reverse order (40 pumps to 1 pump), and so on for 15 replications.

Needle Length: The effect of needle length on GC response was studied
by using ﬁve different length of needles (2.5, 3.5, 4.5, 5.5, and 6.5 cm). After
cutting, the needles were installed in the gas-tight syringe. The injection volume
was 50 uL, and syringe pump number was 20.

Injection volume: The effect of injection volume on GC response was

determined by using 10, 20, 30, 40, 50, 60, 70, and 80 uL injection volumes.

56

The syringe pump number was 20 and three volatile compounds (hexyl acetate,
ethyl 2-methylbutyrate, butanoi) and three needle types (capillary steel, capillary
glass and standard stainless steel) were used.

Environment temperature and volatile partial pressure: The effect of
temperature and concentration on GC response was determined by using two
sample collection temperatures (0°C and 25°C) and three partial pressures of the
volatile compound (1.77, 3.53, and 5.31 Pa). At each temperature and
concentration, more than 10 measurements were made; a capillary steel needle

syringe was used and the syringe pump number was 20.

RESULTS AND DISCUSSION

Effect of syringe pump number and needle type on GC response:
When syringe pump number was increased from 1 to 10, the GC response
increased for all tested volatile and needle types although the pumps number
required to reach saturation differed for each volatile/needle combination (Table
1, Fig. 2, 3, 4). The maximal GC response for hexyl acetate using standard
stainless steel, capillary glass, and capillary steel needles required
approximately 10, 20, and 30 pumps of the syringe plunger, respectively (Fig. 2).
6-Methyl-5-hepten-2-one required 20 pumps for capillary glass needle and 10
pumps for standard steel and capillary steel needles (Fig. 3). For butanoi
measurement however, the required syringe pump number was 5 to 10 for all

needle types (Fig. 4). The data indicate that needles with highly non-polar

57

sorptive linings had a signiﬁcant absorption potential for lager more lipophilic
molecules such as hehyl acetate and 6-methyl-5-hepten-2-one but not for polar
and highly volatile molecules such as butanoi.

Maximal GC response was dependent on the chemical nature of the
volatiles. Once the needle was saturated with hexyl acetate, use of capillary
glass and capillary steel needles resulted in 7- and 14-fold increases in signal
response relative to the stainless steel needle. For 6-methyl-5-hepten-2-one,
capillary glass and capillary steel needles yielded a 2.5- and 3.5-fold
enhancement in signal relative to the stainless steel needle. For butanoi,
however, needle type had no effect on GC response.

The interaction between needle coating, volatile chemistry, and GC
response probably reﬂects the sorption potential of the different needle coating
materials for the different volatiles. Since the needle coating materials were
highly non-polar, polar, highly volatile molecules such as butanoi would not be
expected to be retained appreciably. One would assume, therefore, that if a
needle coating was composed of more polar materials, better retention of polar
compounds could have been achieved and GC response would have been
improved.

Effect of injection volume on GC response: The injection volume
directly affects the amount of material delivered to the GC
and therefore markedly inﬂuences GC response. Generally speaking, increasing
injection volume should increase GC response linearly for almost all uncoated

commercial steel needles. One would also expect that if the relationship is

58

linear, GC response should be near zero when the injection volume is zero.
While this can not be tested directly, ﬁtting a line to data for a range of injection
volumes permits extrapolation. A non-zero Y-axis intercept should be indicative
of needle effects, for example, as when some of the volatile material adheres to
the inner walls of the needle.

When injection volume increased from 10 to 80 pL, butanoi showed a
linear increase for all three needle types (Fig. 5). For the capillary steel needle,
ethyl 2-methylbutyrate and butanoi increased linearly with injection volume (Fig.
6). Interestingly, GC response did not vary signiﬁcantly with injection volume for
hexyl acetate. Importantly, the three compounds differed markedly in their zero-
extrapolated injection volume, indicating marked differences in needle retention
of volatiles. This ﬁnding is consistent with the effect of needle type on GC
response noted earlier. Evidently, the capillary steel needle had very high
adsorption potential for hexyl acetate. The lack of a typical injection-volume/GC
response relationship for hexyl acetate on the capillary steel needle may be
evidence for losing some of the volatile material to the cooler portion of the
needle that resides in the syringe barrel during injection or adsorption to the
glass syringe barrel itself. Butanol had only minor needle retention (Figs. 5 and
6); the volatile material in the needle may be only lightly adsorbed and/or may
represent the material in the needle volume, rather than adsorbed to the needle
lining. One would calculate that roughly 50% of the needle volume would be
expressed just by heating to 250°C. The needle volume in this case was

approximately 10 uL. The increase in response to 5-10 uL additional volume can

59

be calculated from the data in Figs. 5 and 6. The zero extrapolation is many fold
higher than the contribution expected by the needle volume. Therefore, a
signiﬁcant contribution to GC response is evidently made by adsorption. The
response to injection volume tended to be non-linear below 40 uL (Figs. 5 and
6). This may be the result of the requirement for a minimal volume of gas to
sweep the volatile molecules from the needle into the GC.

Effect of needle length on GC response: If the needle is responsible
for retention of a signiﬁcant portion of the volatile molecules, then needle length
should affect GC response. The increase of the needle length not only
increases the adsorption potential of needle but also the volume of injection.
Since needles had inside diameters for capillary steel and capillary glass were
0.28 and 0.32 mm, the effect of length on volume was approximately only 9.85
and12.86 uL, respectively, when needle length was increased from 250 to 650
mm. In addition, because the concentration of tested volatile was as low as 16
ppm, the effect of needle length-related volume on GC response should be
minimal relative to sorption effects. Therefore, the effect of needle length on GC
response should be primarily from the increase of absorption potential when
needle length is increased.

When the length of capillary glass, and capillary steel needles was
increased from 250 to 650 mm (a 2.3-fold increase), GC response for 6-methyl-
5-hepten-2-one increased 2.25- and 2.14-fold, respectively. However, there was
no increase for standard stainless steel (Fig. 7). Compared with the stainless

steel needle, capillary glass and capillary steel needles had a greater increase in

60

GC response due to their higher sorption potential.

Effect of injection volume and needle length on GC response
variation: Injection volumes inﬂuenced the coefﬁcient of variation (CV) of
60 response. Increasing injection volume from 10 to 50 uL, reduced CV 2.5-,
3.7-, and 6.7-fold when standard stainless steel, capillary glass, and capillary
steel needles were used, respectively (Fig. 8).
As needle length increased, a decline in the CV of response was also found for
lined capillary needles, but not for the stainless steel needles. For example,
when capillary glass and capillary steel needles were used in the measurement
of 6-methyI-5-hepten-2-one, the CV declined 3.7- and 4.9-fold, respectively,
when needle length was increased from 2.5 to 6.5 cm (Fig. 9), achieving a low of
1 to 1.5 %.

Effect of environmental temperature on GC response: It is well-known
that temperature affects the sorption process. When the sample was taken in a
lower temperature environment (0°C), the needle absorbed more molecules than
when the sample was taken at higher temperature (25°C), thereby increasing GC
response (Fig. 10). With the technique used here, the process of sorption is
used to collect volatiles in syringe needles. Factors that could affect volatile
absorption and desorption from the needle coating should therefore be well

controlled to achieve consistent and accurate results.

61

CONCLUSIONS

Our study suggests needles lined with sorptive material have a number of
attributes that may be helpful for volatile analysis. Using a capillary column
needle resulted in an increase in SC response of nearly 15-fold relative to a
standard stainless steel needle for lipophilic materials. Plunger pump number
was an important factor affecting GC response. Up to 35 plunger pumps were
required to achieve equilibrium with the sample headspace. This factor, more
than any other, determined rapidity of obtaining a sample. It took roughly one
minute to obtain a gas sample, when the plunger pump number was 40.
Injection volume and needle length affected GC response in a needle- and
volatile-dependent manner. The GC response for capillary column needles
decreased when sample temperature increased. Thus, use of lined needles
requires placement of the standard in the same temperature regime as the
sample. Because capillary GC column needle can work with both ﬂow through
and low volume sealed system such as modiﬁed atmosphere packaging (MAP),
it permits volatile measurement for packaged products under its storage
environment. Therefore, sorptive needles may be a useful tool for determining
the dynamic relationship between ﬂavor volatile synthesis and package
atmosphere for packaged produce.

Since capillary GC column needles improved GC response for volatiles
that readily partition into the column coating, by changing the lining material of
column needle coating, needles conferring better GC response and a broader

range of applicability could, in theory, be constructed. The use of this sample

62

collection technique allows use of a simple GC system such as packed-column
and isothermal heating, instead of the more complex, time-consuming, and

expensive capillary GC system.

63

Literature Cited

Bemelmans, J. M. 1978. Review of Isolation and Concentration Techniques. In
"Progress in Flavour Research” D. G. Land and H. E. Nursten (ed) P 79-98.

Bertsch, W., E. Anderson, and G. Holzer. 1975. Trace analysis of organic
volatiles in water by gas chromatography-mass spectrometry with glass capillary
columns. J. Chromat. 112: 701

Buckholz, L. L. J., D. A. Withycombe, and H. Daun. 1980. Application and
characteristics of polymer adsorption method used to analyze ﬂavor volatiles
from peanuts. J. Agric. Food Chem. 28: 760.

Clark, R. G. and D. A. Cronin. 1975. A new technique for trapping and sensory
evaluation of ﬂavor volatiles. J. Sci. Food agri. 26: 1009.

Dirinck, P. J., H. L. De Pooter, G. A. Willeart and N. M. Schamp. 1981. Flavor
quality of cultivated strawberries: The role of the sulfur compounds. J. Agric.
Food Chem. 29: 319.

Gardner, 8. D., Johnson, J. A., Artaev, V. B., Sparkman, O. 0., Holland, J. F.
1995. Rapid sampling for rapid analysis: A new method fo VOCs in drinking
water. Proceedings of the 43th ASMS conference on Mass Spectrometry and
allied topics, Atlanta, GA, May 21-26, 1995

Farwell, S. O., S. J. Gluck, W. L. Bamesberger, T. M. Schutte, and D. F. Adams.
1979. Determination of sulfur-containing gases by a deactivated cryogenic
enrichment and capillary gas chromatographic system. Anal. Chem. 51: 609-615

Guadagni, D. G., J. L. Bomben and J. 8. Hudson. 1971. Factors inﬂuencing the
development of aroma in apple peels. J. Sci. Food Agric. 22: 110-115.

Hirvi, T. and E. Honkanen. 1982. The volatiles of two new strawberry cultivars,
"Annelie" and "Alaska Pioneer,” obtained by backcrossing of cultivated
strawberries with wild strawberries, Fragaria vesca, Rugen and Fragaria
virginana. Z. Lebensm. Unters. Forsch. 175: 113-116.

Land, O. G. 1975. Techniques for assessing odor: uses and limitations. Proc.
Int. Symp. Aroma Research. Pudoc., Wageningen, The Netherlands.

Maarse, H. 1991. Volatile compounds in foods and beverages. Marcel, New
York.

Martin, J. M. 1969. Gas chromatographic qualitative and semiqualitative
analysis of apple aroma by means of retention indexes. J. Anal. Chem. Acta. 48:

64

Mattheis, J. P., D. A. Buchanan, and J. K. Fellman. 1991a. Change in apple fruit
volatiles after storage in atmospheres inducing anaerobic metabolism. J. Agri.
Food Chem. 39: 1602-1605.

Mattheis, J. P., J. K. Fellman, P. Chen, and M. Patterson. 1991b. Changes in
headspace volatiles during physiological development of bisbee delicious apple
fruit. J. Agric. Food Chem. 39: 1902-1906

McNalIy, M. E. and R. L. Grob. 1985. Current application of static and dynamic
headspace analysis. A review. Part II: non environmental applications. J. Amer.
Lab. Feb: 106.

Murray, K. E. 1977. Concentration of headspace, airborne and aqueous
volatiles in chromosorb 105 for examination by gas chromatography and gas
chromatography-mass spectrometry. J. Chromat. 135: 49.

Olafsdottir, G., J. A. Steinke and RC. Lindsay. 1985. Quantitative performance
of a simple Tenax-GC adsorption method for use in the analysis of aroma
volatiles. J. Food Sci. 50: 1431-1436

Reineccious, G. 1983. Determination of ﬂavor components. Presented at 43th
Annual Meeting Inst. of Food Technologists, New Orleans, LA.

Seifabad, T. C. 1988. Effect of harvest date and ethylene concentration in
controlled atmosphere storage on the quality of empire apple. Ph. D. thesis
Department of Food Science, Michigan State University.

Shamaila, M., W. D. Powrie and B. J. Skura. 1992. Analysis of volatile
compounds from strawberry fruit stored under modiﬁed atmosphere packaging
(MAP). J. Food Sci. 57: 1173-1176.

Song, Jun, 8. D. Gardner, J. F. Holland, and R. M. Beaudry. 1997. Rapid
analysis of volatile ﬂavor compounds in apple fruit using SPME and GC/time-of
ﬂight mass spectrometry. J. Agric. Food Chem. 45: 1801-1807.

Song, Jun and F. Bangerth. 1994. The production and changes of volatile
compounds from apple fruits of maturities. Acta Hort. 368: 150-159.

Song, Jun 1994. Einﬂuls verschiedenber erntezeitpunkte auf die fruchtreife
under besonderer beriicksichtigung der Aromabildung bei apfeln, tomaten und
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Weurman, C. 1961 Gas-liquid chromatographic studies on the enzymatic
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65

Yamashita, I., Y. Nemoto and S. Yoshikawa. 1977. Studies on ﬂavor
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66

Table 1. The effect of pump number, needle type, and volatile compound on GC

 

 

 

response.
Needle type
Volatiles Syringe Cap. Steel Needle Cap. Glass Needle Standard Steel
Pump Needle
number
GC response

Hexyl acetate 1 585 a" 52 a 200 a
10 3302 b I 1089 b 329 ab
20 4659 C 2240 C 373 ab
30 5324 d 2304 C 368 ab
40 5568 d 2304 C 388 ab

6-methyI-5-hepten-2-one 1 316 a 30 a 1 50 a
10 1443 b 576 a 393 b
20 1472 b 976 C 406 b
30 1440 b 1014 C 408 b
40 1440 b 1000 C 408 b

Butanol 1 329 a 31 1 a 291 a
10 490 ab 475 ab 473 ab
20 498 ab 495 ab 479 ab
30 498 ab 500 ab 492 ab
40 505 ab 504 ab 494 ab

 

* n= 10 to 20; In a column of each syringe plunger pump number, means of GC
response followed by different letter are signiﬁcantly different at 5% level.

67

Figure 1. Standard Jar: The jar was specially-designed glass chamber with a
volume of 4-L, ﬁtted with a Mininert value. The standard concentration
was generated by evaporating sub-micro liter amount of the liquid of each
of the volatile compounds of interest.

68

 

69

Figure 2. GC response as a function of number of times a syringe plunger is
pumped for 50 pL injections of hexyl acetate (1.673 Pa) from glass, gas-
tight syringes ﬁtted with a stainless steel needle and needles made from
capillary column (glass and steel) segments. Arrows denote estimated
saturation point. Bars represent SE of more than 10 randomized
replicates. Each data point represent mean of 10 to 20 injections of a
single standard.

70

GC response

 

 

 

 

 

 
 
    
  

 

6000— 1 ' T 1 ‘ ‘ ‘ L 1 I
q ‘ -e_— Capillary steel—
-Q- Capillary glass
5000' ‘ —§— Standard Steel ‘
4000-
4 7:? ::::
3000i
.i
2000..
1000-
I
LA ,';;;;.;;;;;;:_;;:_;.;;;.;.;:_:_;;.;;:.;;;;;;;_a
0-1 . . , , , , I j ‘ ﬂ I
0 10 20 3o 40

Pump number

71

 

 

Figure 3. GC response as a function of number of times a syringe plunger is
pumped for 50 pL injections of 6-methyl-5-hepten-2-one (1.847 Pa) from
glass, gas-tight syringes ﬁtted with a stainless steel needle and needles
made from capillary column (glass and steel) segments. Arrows denote
estimated saturation point. Bars represent SE of more than 10
randomized replicates. Each data point represent mean of 10 to 20
injections of a single standard.

72

GC Response

 

  

 

 

 

 

F—E‘E— Capillary Steel j
; {O} Capillary Glass |
i {a}:— Steel Needle

l

 

 

 

20
Pump number

73

 

Figure 4. GC response as a function of number of times a syringe plunger is
pumped for 50 uL injections of butanoi (3.051 Pa) from glass, gas-tight
syringes ﬁtted with a stainless steel needle and needles made from
capillary column (glass and steel) segments. Arrows denote estimated
saturation point. Bars represent SE of more than 10 randomized
replicates. Each data point represent mean of 10 to 20 injections of a
single standard.

74

GC Response

 

 

m—Q— Capillary Steel ,
, {Q— Capillary glass I
[ -?§— standard Steel ~

 

 

 

 

 

Tm1'0 . ﬁ1'5' ' ' ‘2'0' ' ' '2'57' 30 35
Pump number

75

1 I I r I l I U I I’ I

I

40

Figure 5. GC response to injection volume of butanoi using a gas-tight syringes
ﬁtted with a stainless steel needle and needles made from capillary
column (glass and steel) segments. Note the ﬁtted line dose not
extrapolate through the origin. Dotted line segment represents
extrapolation to zero injection volume (reﬂects contribution of needle
volume, material adhering to the interior of the needle and effect of
pressure of carrier gas). Syringe pump number: 20; Needle length: 5.7
cm; Temperature: 22°C.

76

GC response

1 l l l l l l l l l 1 l l

 

- Y = 285.358 + 4.82228X
. EMS = 172.187
; R2 = 0.985

?' easing—sage: _
:Q Capillary glass ‘
,2}; Steel needle

._ .._ _ .__ ___. .__,_,-._

 

Y = 186.493 + 6.31744X
EMS = 444.349
R2 = 0.977

  
 
 
 
 
 
  

Y = 90.068 4' 6.07678X
EMS = 207.837
R‘2 = 0.988

 

I l j T I l

0' ' '10: ' '2'0' ' 30 40' ' '5'0' ' 60W 70' ' '8'0' ' '90

Injection volume (uL)

77

 

Figure 6. GC response to injection volume of hexyl acetate, ethyl 2-
methylbutyrate, and butanoi using a gas-tight syringes ﬁtted with a needle
made from steel capillary column segments. Note the ﬁtted line dose not
extrapolate through the origin.

78

_..__.__. # _.

2400i___-#+—%
“ Y = 2346.46 + 1.0581X

 

 

 

1 EMS = 367.007 f, __- _, ___ _
2000‘; R2 = 0-531 ’ Q Hexylacetate .
g j . _: Ethyl-2-methyl butyrate ’ Q
c 1 600 if Butanol ~
8 - ;
fl) _‘ ‘ ;
i Y = 955.729 + 5.31881X '3
Q ~ ..... EMS = 272.505 ;
(9 800 j R2 = 0.986

 
 
 

4004 Y = 281.746 + 4.84286X +-
r—""~ ' , EMS = 346.837 2
l R2 = 0.979
012..

 

0 70 207.30. 40 50 60 270 780 7 90
Injection volume (uL)

79

 

Figure 7. Effect of needle length on GC response to 50 pL injections of 6-
methyl-5-hepten-2-one from glass, gas-tight syringes ﬁtted with a
stainless steel needle and needles made from capillary column (glass and
steel) segments.

80

GC Response

L

L l J l l I l I 1 l l

 

A
00 N
O O
9 <9

:6
.9:
é

Steel Capillary
Glass Capillary
Steel needle

 

400 :

 

Y=374.1*X-144.4
r2=0.98

     
  
   

r2=0.995

Y=404.605+9.4675*X
r2: 0.870

Y=238*X-146.5 :

 

 

I l I I V l I f I l l

4 5 6

Needle length (cm)

81

I WIBEA’. A}! Himlw

Figure 8. Coefﬁcient of variation for injection volume of butanoi using a gas-tight
syringes ﬁtted with a stainless steel needle and needles made from
capillary column (glass and steel) segments.

82

Coefﬁciation of variation (%)

.b
O

(30
O

20

10

0

 

 

 

 

 

 

 

A i 1_I 1 L i I . i . I 1 l i J i I . i 1 I I 1 r I
O O Capillary Glass ~
‘ A Standard Steel
1 i
A O
A . Y = 18.4989 - 0.21231x
_, 5 EMS = 1.1876 _
K R2 = 0.964
A A
Y = 5.349 - 0.1319X + 00009631sz -
I I r I 1 r r I I ‘l r I r I r 1 I I I I I f f T I r I I
10 20 30 40 50 60 70 80

Injection volume (pL)

83

 

Figure 9. Effect of needle length on Coefﬁcient of variation to 50 uL injections of
6-methyl-5-hepten-2-one from glass, gas-tight syringes ﬁtted with needles
made from capillary column (glass and steel) segments.

84

 

Coefﬁciation of variation (%)

_x
.b.

I l 1 1 l l l 1 l l l 1 l

 

_.L
N
I i

.4
O
l .

 

 

-e— Capillary Steel
+ Capillary Glass

Y =6.616 +1.974X-0.2575X2 , -A— Standard Steel , .

 

 

W (.3

\

  
 
 

Y = 7.297 - 0.3311x - 0.09736x2

Y = 6.471 - 0.5937x - 0.03214x2

 
 

I

 

 

3'1'4'1's'ﬂéj
Needle length (cm)

85

.‘ -3: _" .nﬂ"

Figure 10. Effect of temperature and concentration of hexyl acetate vapors on
GC response to 50 1.1L injections from glass, gas-tight syringes ﬁtted with a
needle made from steel capillary column segments (length: 5.7 cm).

86

1 (“M 'I 05“"qu

GC Response

1 I l L l L l J l l 1 1 I J l L 1 I l l

 

 
  
 

-_ o Y = -1279.78 + 1304.95x
9. 0 C EMS = 33397.6
. R2 = 0.997

 

Y = 466.92 + 425.472X
EMS = 27.7843
R2 = 1.000

   

 

 

I
I F I r I v I 1 I r I I r l I r r I I r

1 2 3 4 5
Concentration (Pa)

87

 

 

CHAPTER IV:

EVALUATION OF A PACKAGE SYSTEM FOR THE MEASUREMENT OF
AROMA VOLATILE SYNTHESIS

88

EVALUATION OF A PACKAGE SYSTEM FOR THE MEASUREMENT OF
AROMA VOLATILE SYNTHESIS

Abstract: Polymer ﬁlm packages have been used to measure respiration, but
their use to measure aroma volatile production has not been demonstrated.
Apple (Malus domestica Borkh. cv. Golden Delicious) fruit were placed in
packages, in glass containers, and in packages within glass containers to
determine the feasibility of using the gradient of aroma volatiles across the ﬁlm to
calculate the rate of production by the product. The ﬂux of C02, 02, ethylene,
hexyl acetate, butyl acetate, 2-methylbutyl acetate, and a-farnesene was
determined as affected by temperature and 02 level. At the same 02
concentration, non-packaged fruit evolved greater amounts of the esters and a—
farnesene than packaged fruit. The ﬂux of a-farnesene, hexyl acetate and 2-
methylbutyl acetate was approximately 27-, 1.7-, and 1.4-fold higher,
respectively, for fruit in a glass container without packages than for fruit in
packages within glass containers. The packaging material is suspected of
absorbing a-farnesene and the esters, thereby altering the aroma proﬁle of
packaged produce relative to a ﬂow-through system. When storage temperature

increased from 0°C to 22°C the production rate of hexyl acetate and 2-

 

methylbutyl acetate increased 11- and 17-fold, respectively. At 0 C, as 02 Li
decreased in concentration from 10% to 5% (v/v), hexyl acetate and butyl
acetate declined signiﬁcantly; however, 2-methylbutyl acetate production was not

affected. This can be taken to indicate the production of the branched-chain

89

alcohols such as 2-methyl butanol is not as 02 concentration-dependent as

straight-chain alcohols such as hexanol and butanol.

90

INTRODUCTION

Modiﬁed-atmosphere packaging (MAP) "has the potential to provide low
Ozlhigh CO2 regimes similar to those of controlled-atmosphere (CA) storage"
(Beaudry et al., 1992), and is widely used to store fresh and lightly-processed
fruits and vegetables. However, the optimal atmospheric environment is difﬁcult
to maintain during MAP storage since many plant and environmental factors
affect O2 and CO2 concentrations. In addition, loss or changes in ﬂavors during
MAP storage is one of the primary concerns in providing high quality food
(Matsui et al., 1994). The aroma proﬁle of packaged products can be affected by
the interaction of aroma compounds with the packaging ﬁlm (Debeaufort and
Voilley, 1994; Matsui et al., 1994; Mason et al., 1992; Nielsen and Giacin, 1994;
Osajima and Matsui, 1993). Changes in the aroma proﬁle may due to sorption
into packaging material or permeation through the package to the environment
(Delassus, 1986; Nielsen and Giacin, 1994) or due to sorption of odor-active
volatiles from the packing or the environment into the package (Mason et al., p
1992). In addition to ﬁlm effects, the package may alter the aroma proﬁle

through its effect on package 02 and CO2 levels and, subsequently, on aroma

 

biosynthesis.

Low-density polyethylene (LDPE) is a commonly used polymer for MAP of
fresh and lightly-processed produce. Some of its properties such as the
pemneabilities to O2 and 002 (Beaudry et al., 1992; Cameron et al., 1993;

Lakakul et al., 1994) and water vapor (Debeaufort and Voilley, 1994) are well

91

studied. However, few studies of the permeability of LDPE ﬁlm to aroma
volatiles have been reported (Delassus et al., 1988; Fukamachi et al., 1994).

Loss of ﬂavor can occur by sorption into or permeation through the
packaging ﬁlm to the environment. The permeation process is described by
following equation when sorption is Fickian in nature:

P=DxS

Where P is permeability coefﬁcient which expresses the permeant transport rate
as a function of ﬁlm thickness, ﬁlm area, temperature and driving force. D is the
diffusion coefﬁcient it describes how fast the permeant molecules move in the
ﬁlm. 8 is the solubility (or sorption) coefﬁcient, which is a measure of the amount
of a permeant that will be absorbed by polymer. The steady state permeability is
useful quantity for describing the rate of mass transfer through a polymer ﬁlm at
steady state. Based on F ick’s Law the steady state permeability can be
described by following equation:

AMx _ POAOApx
At _ l

 

Were: AM" is the total amount of permeant x (mol) which permeates through a
At

 

polymer ﬁlm with a cross-sectional area A (m2) a thickness L (m), and a partial
pressure gradient of Ap, (Pa) during time t(s). Present studies show that the
structure of both permeant and polymeric packaging material, measurement
conditions (such as relative humidity, temperature etc.), permeant concentration

and co-permeants are the major factors affecting volatile permeation.

92

Aroma volatile synthesis by fresh produce during ripening (Song and
Bangerth 1994; Seifabad, 1988) and following CA storage (Brackmann et al.,
1993; Mattheis et al., 1991a; Song and Bangerth, 1994; WIIIaert et al., 1983) has
been much studied. Since apple volatiles are produced in minute quantities,
especially under conditions of apple storage such as low 02, high C02, and low
temperature, investigators typically remove the fruit from the storage
environment and warm them to room temperature for aroma biosynthesis
measurements. Thus, little is known regarding the dynamic changes of volatile
production during storage under modiﬁed atmospheres. The purpose of these
studies was to test whether a simple packaging system could be used for
measuring aroma volatile production by plant organs under storage conditions.
Our hypothesis was that the aroma volatiles would attain steady-state in the
package (in much the same way that Ozand CO2 reach steady-state) such that
the ﬂux of volatiles from the package was essentially the same as the ﬂux from

the fruit.

MATERIALS AND METHODS
In order to measure the rate of flux of aroma compounds from package,
packages were enclosed in ventilated glass chambers. The rate of ﬂux of
volatiles from the packages was compared to that from fruit in glass chambers
with no packages. The behavior of volatiles in the packages in chambers was

further compared to fruit held in packages without chambers.

93

Fruit storage: Apples (CV. Golden Delicious) were harvested from the
Michigan State University Clarksville Horticultural Experiment Station on 2,
October 1995. Fruit were held 2 days at 0°C prior to use. Two experiments
were conducted: one at 0°C and a second at 22°C. At 0°C, fruit were given four
treatments (each with 4 replications): 1) apples were placed in a 2 L glass
container ventilated with air, 2) apples were placed in a glass container
ventilated with a modiﬁed atmosphere, 3) apples were ﬁrst placed in a low
density polyethylene (LDPE) bag which was then placed in a ventilated glass
container (Beaudry et al., 1992) (Fig. 1), and 4) fruit were placed in packages
alone. The three target 02 levels (4-5, 7-8, and 10-11 kPa) in the package
headspace were achieved by sealing different weights (110-240 g) of apple fruit
in LDPE packages with area of 0.02 m2 and ﬁlm thickness of 0.00508 cm (2 mil).
At 22°C, fruit were given three treatments (with 5 replications for each
treatment): 1) packaged, 2) packaged and placed in a glass container (package-
in-a-jar), and 3) unpackaged and placed in a glass container. The packaged
treatments involved sealing the fruit in a 2 mil (.00508 cm) thick LDPE package
with an area of 0.06-0.07 m . At 0 and 20°C, glass containers were ventilated
with a low air ﬂow (6-7 mL-min“). Packages without containers were placed a
storage shelf exposed to ambient atmosphere. For package-in-a-jar and jar only
treatments, air or a modiﬁed atmosphere ﬂow was slowly passed through the
glass containers such that the 02 level in the package was similar to that in glass
containers with no package. The storage duration for 0°C and 22°C was 90 and

35 days, respectively.

94

Preparation of standard: A standard of known concentration was
generated for hexyl acetate, butyl acetate, 6-methyl~5-hepten-2-one, ethyl 2-
methylbutyrate, hexanal, butanol, and 2-methylbutyl acetate by evaporating sub-
microliter amounts of the liquid of each compounds into a specially-designed 4.3-
L glass chamber, ﬁtted with a Mininert (Supelco) valve (Fig. 2). The
concentrations of volatiles were calculated based on their molecular weight,
density, purity, and the volume of standard jars. During measurement, the
temperature of standard jars was carefully controlled.

The perrneabilities of LDPE film: using a specially built permeation cell
(Fig. 3) tested The permeability of LDPE to single aroma compounds. The cell
was composed of two hemispheric glass chambers, each ﬁtted with inlet and
outlet ports. The donor and receiver chambers were divided by the ﬁlm to be
studied. The LDPE ﬁlm thickness was 0.00508 cm (2—mil) and the area was 7.55
cmz. On the donor side, the volatile of interest was metered into a humidiﬁed air
stream free of aroma volatiles. The volatile partial pressure on the donor side
was maintained in the range of 1 to 9 Pa (approximately 10 to 90 ppm). On the
receiver side, humidiﬁed air stream free of aroma volatiles was metered at 1.5-
1.6 mL min". The total pressure in both chambers of the cell was maintained
near atmospheric pressure (approx. 105 Pa). Receiver- and donor-side volatile
concentrations were measured more than 10 times for each of two permeation
cells. The analysis method was the same as described previously for volatile
analysis. The standard jar was maintained at the same temperature as the

permeability cell. Permeability was measured at 0, 5, 10, 15, 20, 25, and 30 C

95

 

 

 

 

:1°C by changing the room temperature. In order to assure that the system was
at steady-state, the measurement was made 8 to 12 hours after the desired
temperature was obtained. The ﬁlm samples were changed with each

temperature change. The steady state permeability was calculated by following

 

equaﬁon:

 

P= Q'L
A o t 0 A p
Were Q is the total amount of permeant which has passed through a
polymer ﬁlm with an area A during time t. L is thickness of the ﬁlm, and Ap is
partial pressure gradient of the permeant. The permeability is expressed in
mol-m°m’2-s‘-Pa“.

Measurement of aroma production: The partial pressure gradient
across the ﬁlm of the package (P,in - Pf“) was measured and, using Fick's Law,
permeability of LDPE to ethylene and major apple aroma volatiles was
determined. Using these permeability measurements, the rate of production of
aroma volatiles was also calculated for apple fruit enclosed in a package, but

lacking the jar. Controls were apple fruit enclosed in a jar only and in a package

 

only. For atmospheres were examined air, 10% 02, 7 to 8% O2 and 4% Oz.
Aroma volatile sampling and analysis: A steel capillary column

segment (0.28 mm id; 1.0 pm phase thickness, 5% diphenyl and 95% dimethyl

polysiloxane) was installed in a gas tight syringe (1710 RN, 100 uL syringe) and

used as a needle for volatile analysis. Volatiles were pulled into the syringe

96

barrel by pumping the syringe plunger 30 times while the needle was in the
headspace of the sample. Volatiles were absorbed by the needle coating.
The sampling protocol was validated as previously described (Chapter III).
Gas samples were directly injected into the GC (Carle AGE series 400, Hach,
Loveland, Colorado). In order to desorb the volatiles absorbed by the needle,
the needle was held in the GC injection port maintained at 220°C for 3 seconds
prior to injection. The GC was equipped with a ﬂame ionization detector, and a
3.3 m long, 3mm ID packed column (10% DEGS-PS, 80/100 mesh Supelcoport)
was used for volatile analysis. The column was maintained isothermally at
140°C. Puriﬁed helium (99.9%) was used as a carrier gas. The ﬂow rates for
the helium, air, and hydrogen were 60 mL-min“, 200 mL-min", and 20 mL-min“,

respectively.

RESULTS AND DISCUSSION

Permeability of LDPE ﬁlm to using permeation cell. With the exception of
butanol, the permeability of LDPE ﬁlm to all the tested volatiles increased with
temperatures (Fig. 4). The permeability ranking at 20°C was hexyl acetate > 6-
methyI-5-hepten-2-one >butyl acetate >ethyl 2-methylbutyrate >hexanal
>butanol. Interestingly, determination of the permeability using this technique
does not require the use of a standard if the response of the detection system is
linear with concentration. This is because the standard would be used to
determine both the rate of ﬂux as well as the gradient.

The increase in permeability from 0 to 30°C for hexanal,

97

 

 

ethyl 2-methylbutyrate, butyl acetate, hexyl acetate, 6-methyl-5-hepten-2-one,
and butanol were 10.21, 8.36, 2.63, 2.59, 1.64, and 0.59, respectively. In this
study, the LDPE ﬁlm was tested above its glass transition temperature (T9) of -
100°C. T9 is the temperature of which the polymer goes from a crystalline state
to an amorphous state. The fact that measurements were made well above Tg,
accounts for the observed temperature sensitivity of permeability to the volatiles
examined. The different properties of the tested volatiles (such as size, shape,
and polarities) could directly or indirectly affect their solubility and diffusivity in
LDPE resulting in different permeability values.

LDPE permeability under actual storage conditions. Using the packaged
fruit in a ventilated glass container, the permeability of the packaging ﬁlm to
some volatiles including ethylene was calculated using the package headspace
and container headspace partial pressures and the measured rate of ﬂux (Figs. 5
and 6). The permeability to hexyl acetate, 2-methylbutyl acetate, and 0t-
farnesene was, respectively, 288, 130, and 172 times higher than to ethylene.
Since many volatile compounds are simultaneously migrating through the ﬁlm
during the actual MAP storage, there is a possibility that signiﬁcant matrix effects

can result. In some instances, the permeant can change driving force and the

 

permeation properties of packaging ﬁlm by the interaction between permeant
and polymer (eg. via swelling of the polymer). Thereby the permeant may
increase or decrease the permeability of the package to other co-permeants. At

0°C, for instance, the permeability of the MAP ﬁlm to hexyl acetate and butyl

98

acetate measured by package-in-a-jar system were lower than for the
permeation cell declined while ethyl 2-methylbutyrate was increased (Fig. 7).
The effect of co-permeants on the permeability of packaging ﬁlm can also differ
with temperature. The package permeability to ethyl 2-methylbutyrate increased
4.4- and 0.4-fold respectively when the permeability was measured with co-
perrneants at 0°C and 22°C relative to measurements made with no co-
permeants. Under real storage conditions, the permeability of LDPE ﬁlm to
some volatile may never reach steady-state (Fig. 5) since the dynamic change
in both the amount and the kinds of co-permeants and other unknown organic
compounds in the package.

MAP storage of apple. The O2 and CO2 partial pressures reached
steady-state in approximately 5 to 18 days following sealing of the fruit in the
package (Figs. 8, 9 and 10). The peak ethylene production declined with
decreased package O2 and increased CO2 concentration (Fig. 11). The ethylene
production rate of apple fruit was also dependent on the storage temperature.
Increased storage temperature caused an increase in the rate of respiration

(data not shown) and ethylene production (Fig. 12). The maximum ethylene

Itma‘ ll

production rate was approximately 2.5-fold higher at 22°C than at 0°C. The rate

 

”Ilia

of increase to achieve the maximum rate also occurred sooner for the fruit held
at 22°C.

The effect of O2 and CO2 partial pressures on volatile production rates
during MAP storage of apple. At 0 °C, package atmospheric composition

affected the production of aroma compounds (Fig. 13). The production of hexyl

99

acetate appeared to be the most sensitive. The production rate of hexyl acetate
for the package with 7-8 kPa O2 and 3 kPa CO2 was 1/2 that of the package with
10-11 kPa O2 and 2-2.5 kPa C02. The production of butyl acetate and 2-
methylbutyl acetate did not appear to differ between these packages. The
production rate of hexyl acetate and butyl acetate for the package with 4-5 kPa
O2 and 3-4 kPa CO2 was reduced. The results suggest that relative to packages
with higher 02 and lower CO2 levels the production rate of straight-chain volatile
compounds such as hexyl acetate and butyl acetate were more sensitive to
reduced 02 levels and elevated CO2 levels than branch-chain volatile
compounds such as 2-methylbutyl acetate. This differential sensitivity is
consistent with known differences in the biosynthetic pathways for straight and
branched-chain volatiles (Tressl and Drawert, 1973). The precursors of straight-
chain alcohols for ester synthesis were thought to be derived from the oxidation
of fatty acid through the B—oxidation pathway (Yahia, 1994; Gerhardt, 1983).
Branched-chain esters however, were thought to be formed by the
transamination and subsequent oxidative decarboxylation of the amino acid
(Yahia, 1994; Tressl and Drawert, 1973).

Compared with 0°C, room temperature storage caused a higher volatile
accumulation in the package (compare Figs. 14 and 15 with Figs. 8 and 9). The
data for a-farnesene content for packages stored at 0°C are lacking due to the
low amount of material present in packages at that temperature, however, -

farnesene accumulated to signiﬁcant amounts at 22°C (Fig. 16). The mean

100

production rate of 2-methylbutyl acetate and hexyl acetate were 6.49 X 10'8 and
5.45 X 10‘8 mol-kg"-h", respectively, when apples were stored at 22°C.
However, under the same atmospheric composition (10 kPa O2 and 2 kPa C02),
the mean of production rate of these compounds was 3.58 X 10‘9 and 4.44 X 10'9
mol-kg"- h", respectively when storage temperature was 0°C. The difference in
production with temperature reﬂects an increase in the production rate of hexyl
acetate and 2-methylbutyl acetate of 11- and 17-fold, respectively, as storage
temperature was increased 22°C.

Effect of package ﬁlm on volatile proﬁle. When apple fruit were sealed in
a glass container, the production of volatiles from the container was higher than
for apples in packages in containers (Fig. 17). The ﬂux of a-famesene, hexyl
acetate and 2-methylbutyl acetate was 266-, 1.7-, and 1.4-fold higher,
respectively, for fruit in glass container than for those in package in a container.
The sorption of a-farnesene and the other volatiles into LDPE ﬁlm is evidently
considerable such that a signiﬁcant portion of the volatiles are not released even
after several weeks. The result is that package presence alters the aroma proﬁle
of packaged produce relative to the more inertjar only system. Understanding
the dynamic relationship between the composition of the package atmosphere,
the volatile synthesis, and sorption or permeation of packaging ﬁlm is important
for quality improvement of packaged produce. Since packaging ﬁlm can
selectively absorb certain ﬂavor constituents from food, changing the ﬁlm type

would likely alter the volatile proﬁle. The relationship between volatile synthesis,

101

 

package atmosphere, and permeation or sorption of packaging ﬁlm is dynamic,
complex and of potential importance in perceived quality of packaged fruit.

Using a package-in-a-jar system we are able to simultaneously measure
the volatile concentration and the permeability of the packaging ﬁlm to those
volatiles. The proﬁle changes of C02, 02, and volatile concentration, volatile
production rate and permeability of LDPE ﬁlm during storage suggest a
permeation-based respirometry system was not suitable for the calculation of the
ﬂux of organic molecules. However, it may be a useful methodology for
evaluating the effects of package atmosphere and other treatments for packaged

produce.

102

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Modiﬁed-atmosphere packaging of blueberry fruit: Effect of temperature
on packaging oxygen and carbon dioxide. J. Amer. Soc. Hortic. Sci. 117

Brackmann, A., J. Streif and F. Bangerth. 1993. Relationship between reduced
aroma production and lipid metabolism of apples after long-term controlled-
atmosphere storage. J. Amer. Soc. Hort. Sci. 118
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Cameron, A. C., B. D. Patterson, P. C. Talasila, and D. W. Joles. 1993.
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Lidster, P. D., H. J. Lightfoot, and K. B. Mcrae. 1983. Production and
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104

 

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105

 

Figure 1. Package-in-a-jar system. Apples (110-240 g) were sealed in a 2-mil
(0.00508 cm) thick LDPE package with an area of 0.06-0.07 m’.
Packages were placed in a 2-L glass jar ventilated at 6-7 mL/min with
air. The package and jar headspaces were sampled for aroma volatile
analysis. The permeability of packaging ﬁlm was calculated by the
gradient of aroma volatiles across the ﬁlm, the rate of production by
product was simultaneously calculated based on the ﬂux of volatile
compounds.

106

 

 

 

 

gas inlet

 

 

  

IIIIIIII llllllllllllllllllllIllIIIIIIIIIIIIIIIIIII—|

 

0‘2!

 

107

N

gas exit

 

 

Figure 2. The standard jar was a specially-designed, 4-L Erlenmeyer ﬂask
having a ground-glass stopper ﬁtted with a Mininert valve. Volatile
concentrations were generated by evaporating sub-microliter amounts
of the liquid of each of the volatile compounds of interest.

108

Figure 3. Glass permeation cell used for measurement of steady-state
permeability of plastic ﬁlm to single volatile permeants.

110

 

.32.!

 

 

i Metered air inlets x L i

//

/
/

 

 

 

 

 

ﬂjF-ﬁ —§-'_=-
(I

 
         

\

 

 

Vapor generator

 

 

 

 

 

ll

 

.3;

r
Sam lin chambers ,
1% .. 5:/

H Receiver
“‘1'

 

 

lri

 

 

 

r:—

I . .
‘y Exrtlines v

111

Figure 4. Effect of temperature on the permeability of LDPE ﬁlm to Hexyl
acetate, 6-methyl-5-hepten-2-one, butyl acetate, Ethyl 2-
methylbutyrate, hexanal, and butanol. Test ﬁlm area was 7.55 cm2
and thickness was 0.00508 cm (2-mil). Four replicates were
performed and 10 measurements were made for each permeation cell.

 

 

112

4 l l l l l l lLl [J 1 l I l l l l l 1 L411 1 l l l I. l l

 

, -é— Hexyl acetate

J —_Q'— 6-methyl-5-hepten-2-one
45-13 , —§— Butyl acetate

—i:— Ethyl-2-methyl butyrate
-§- Hexanal

—§- Butanol

 

Permeability (mol-m-m'Z-s“-Pa“)

 

 

 

 

 

0 ﬁ" I I ﬁ' I‘l'lﬁjitib' I I

'2'0" '25' ' ' '30'
Temperature (°C)

113

Figure 5. Effect of storage duration on the ‘apparent’ permeability of LDPE ﬁlm
to volatiles during MAP storage of apple at 22°C as measured by the
package-in-a-jar system. Each symbol represents 5 replications :t SE

114

 

I I I l I I

l I I I l I L I I I

 

3E-13-

1E-13-

 

Apparent Permeability (mol-m-m‘a-s"-Pa“)

 

—§— hexyl acetate
--:5— (wt-farnesene

—E— 2-methylbutyl acetate

 

 

4

 

.- ....,....,.4..,
1h 20 25 30

Storage duration (days)

115

T I U

‘I
35

I T I

 

 

Figure 6. Permeability of LDPE to ethylene during MAP storage at 22°C as
measured by the package-in-a-jar system. Each symbol represents 5
replications t SE

116

 

 

 

Permeability (mol-m-m'Z-s"-Pa“)

 

I I I I I l I I I I I I I I

I I I I I I

 

 

6'"'é""1b""1§""2'o'

Storage duration (days)

117

N
01

 

Figure 7. Permeability of LDPE to selected volatiles as measured by the
permeation cell and package-in-a-jar systems.

118

 

Permeability (mol-m-m'z-s"-Pa“)

 

 

. a ..
.- «lag:
" 1111
oh}, '3‘

00° 0°c 22°c 22°c
Hexyl acetate

  

_ measured by permeation cell
E measured by package-jar system

 
      

 

0° 0°c 22°022°c 0°c 0°c
Ethyl 2-methylbutyrate Butyl acetate

119

 

 

Concentration (ppm)

02 (kPa)

JLALAIAAIAIAIIILLLAJ

ILLAA

I

All.

lAlAllLA-AIAIII

 

:6— Ethylene

 

 

'vv—vv'vuv'
—L

.5
0

0|

VVVVIII'V

0

 

LllLL‘l I. Illllll I I

 

0.03-

0.02-

 

. 19:-
-§- Butyl acetate
3:-

2-methylbutyl acetate

Hexyl acetate

 
 

 

 

f' i—rvﬁr

' 7107 72'0' ' ' '3'0' ' ' '4'0' 7' 30' ' ' '6'0' ' ' '7’0' ' ' 007' 90 1
Storage duration (days)

121

 

co, (kPa)

1
\I
O

160

' I ' I
-b 01
O O

75
o
Ethylene (Pa)

 

 

Figure 8. Effect of storage duration on 02, CO2, ethylene and volatile partial
pressures in packages that maintained approximately 10 kPa 02
during MAP storage of apple at 0°C. Each symbol represents 5
replications 1: SE.

120

 

Figure 9. Effect of storage duration on 02, C02, ethylene and volatile partial
pressures in packages that maintained approximately 8 kPa O2 during
MAP storage of apple at 0°C. Each symbol represents 5 replications :I:
SE

122

 

Production (mol-kg“-h")

 

 

 

 

 

 

 

l+l 1:1 til

 

'1b'

-methylbutyl acetate
utyI acetate

Hexyl acetate

 

' U V I U ' ‘ ' I V I

20 3'0 '4'0' 1"5'0' ' ' '6'0' "'7'0" ' 18'0' ' ' '9'0' '

Storage duration (days)

123

 

Ethylene ( a)

 

Figure 10. Effect of storage duration on 02, C02, ethylene and volatile partial
pressures in packages that maintained approximately 4 kPa 02 during
MAP storage of apple at 0°C. Each symbol represents 5 replications
1: SE.

124

 

02 (kPa)

Concentration (ppm)

  

 

     
    

 

 

 

 

 

 

20‘ L I A L . L4 1 LLL L l A A. L; I n A . L I I I L . I L-‘ I I . . .4 . ~20
c T >
164, -9— Ethylene :16};
12: :12;
8': +: 02 :8 ON
4. _4 0
0=- - - - . - 0
0.05 L-A. .. LI 1; - 1;-..14...LLJ_LL._L41 l
1 -§- 2-methylbutyl acetate .
0 04- -§- Butyl acetate P
' -§— Hexyl acetate
0.039 ..
0.02- . .
I
I :9
0.01- 1". r t
,/ ,;
i 5
0.00 ' ' I V f' 'T ' Vi ' T ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' I—I ' f' ' 1 ' r ' ' I ' ' ' '
0 10 20 30 40 50 60 70 80 90 100

Storage duration (days)

125

 

I ' I I l ' I
P 01 O) ‘I
O O O O

'rbw
-L
o o o

 

, .
O

Ethylene (Pa)

 

Figure 11. The effect of O2 partial pressure and storage duration on ethylene
production rate during MAP storage of apple fruit at 0°C. Each
symbol represents 5 replications t SE

126

Ethylene Production (mol-kg"-h“)

IIIlllIlIILJlIILJllIIIIIIIIIIIIIIIIIILI

 

8E-13

7E-13-
.,
6E-13-

I

5E-13-l
4E-13~

3E-13-

2E-13-w

q

1E-13-

q

 

0

%}10%o, a
4E7e%q
{g4s%q

  

1. Zioj I '3'0' 1 '4'0I T lgoi I IéIOI I Iiol I I
Storage duration (days)

127

80

III

I

90

rI

1

 

 

Figure 12. Effect of storage temperature and storage duration on ethylene
production rate of apple fruit during MAP storage (10% 02). Each
symbol represents 5 replications :I: SE

128

 

l 1

 

2.0E-12-

 

1:
'0)
x. I
3 1.5E-12-
g 'l
C .
.9 .
g 1.0E-12-
'0 ..
o I
L—
Q .
g 1
2 5.0E-13
>1
.5
NJ

>
III

I

 

IllelJIIlIILlIlIlIIIIIlIlIllllIIllII
—§—22°C .
| " —e—:: 0°C -
F
J-
L
h
- ‘ :5 _
65 it .
F
a I-
III'III'IfI III

 

 

IIITrIT'III
8

'10' ' '2'0 30 40 5'0 6'0' ' ’7’0 0 90 100
Storage time (days)

129

 

Figure 13. Changes in hexyl acetate, butyl acetate, and 2-methylbutyl acetate
production rate during MAP storage of apple under different package
atmosphere and storage duration. Storage temperature was 0°C.
Each symbol represents 5 replications :1: SE

130

Production rate (mol-kg“-h“)

 

 

 

 

 

 

 

 

 

I 4 j I I l l n I 1 1 n I l l l I l l n I l l j I n I l I . 1+1 1 n 4 l A L;
1E-08 -§- 1o-11% 02 and 2-2.5%COZ Hexyl acetate 9 E
-§- 7-8% 02 and 3% CO2 :
8509 -’g— 4-5 9a 02 and 3.5% CO2 r
65-09 g; :-
4E-09 " e; E
2E-09 _____._. a: _-
O , , , , .........,........
I I l A 1 1+. 3 I I n 1 I n l J_l L 1 I4 1 L l I n n I
1E-08 Butyl acetate _.
E
0 V T Vﬁ t I I .
r ' 100

' ' '1br'ﬁ2'o' 30 '4'0'

‘ .50: ' '6'0' j 70. t 3,0. . ‘

Storage time (days)

131

90

 

 

 

Figure 14. Concentration of 2-methylbutyl acetate in the headspace of
packages containing apple fruit, which were further enclosed in jars, in
the headspace of those same jars and in the headspace of jars
containing apple fruit not enclosed in packages. The storage
temperature was 22°C. Each symbol represents 5 replications :I: SE

132

 

Concentration (pL-U)

I I I I I I I I I I I I I I I I I L I I I I I I I I I I

 

 

{—— Jar headspace (no package)

—§— Package headspace (package in jar)
{Q- Jar headspace (package in jar)

43:— Package headspace (package alone)

 

 

wwwww

I I I l I I I l I I I I I I I I I r I l I I I I I

 

.r.1é..r.1b....1k....2.0..j.2,5.

Storage duration (days)

133

 

 

Figure 15. Concentration of hexyl acetate in the headspace of packages
containing apple fruit, which were further enclosed in jars, in the
headspace of those same jars and in the headspace of jars containing
apple fruit not enclosed in packages. The storage temperature was
22°C. Each symbol represents 5 replications t SE

134

 

Concentration (ML-L")

1.8

IIIIIIIIIIIIIIIIIIIIIIIII—LIIIIIIILIILIL

 

1.6-

1.44

I

1.2-

1.0-

0.8-

1

0.6-

d

0.4-

0.2~

 

0.0

i
l)

I.
' . 3 U’ ‘
‘.

—§— Jar headspace (no package)

{Q‘— Package headspace (package in jar)
-§— Jar headspace (package in jar)

{i— Package headspace (package alone)

  

\

 

"M
f

 

 

5161 .ﬁ.1b.r. .210..-.2.5....3.0..-.35ra..

Storage duration (days)

135

 

Figure 16. Concentration of a-farnesene in the headspace of packages
containing apple fruit, which were further enclosed in jars, in the
headspace of those same jars and in the headspace of jars containing
apple fruit not enclosed in packages. The storage temperature was
22°C. Each symbol represents 5 replications :t SE

136

IIIIIIIIIIIIIIILIIIIIIIIIIIIIJIIIILIIII

 

ens-l
-:'
.J
Q I
‘5
:2-
cu
f:
c
a) ..
o
C
O
01‘

 

—§- Jar headspace (no package)

-§— Package headspace (package in jar)
—§- Jar headspace (package in jar)

-i— Package headspace (package alone)

1

 

 

 

 

 

Av! >-=-"—""""““‘ a
;b 1b 1 l l

20 25 30 35
Storage duration (days)

137

 

4

0|

Figure 17. The ﬂux of volatiles released from the package-in-a-jar and jar only
system during MAP storage of apple. The 02 level in the package was
similar to that in glass jars with no package. Storage temperature was
22°C. Each symbol represents 5 replications :t SE.

138

Flux (moi-s")

LIIIIIIIII LIIIIIII

IIIIIIIIIIIJIIIIIIII

 

 

eeeeee

 

 

2-methylbutyl acetate (no package)
Hexyl acetate (no package)
a-farnesene (no package)
2-methylbutyl acetate (package in jar)
Hexyl acetate (package in jar)
a-tamesene (package in jar)

 

/
' ’ . ‘nuoﬂ. .....................................................................
'Ui. ........ I: ........ :1 "NEW? MB ............ .g
A ............................

out A nnnnnnnnnnnnn

I I I1bl I rI1b rj I I2l0I I I I2l5I I I I3IOI I I I315I I I I4

Storage duration (days)

139

I

I I I I [I I I I rI I I I I IfI I l I I

 

O

CHAPTER V:

SUMMARY AND CONCLUSIONS

140

 

The ﬁrst purpose of these studies was to develop a simple and fast
volatile sampling (collection and concentration) method for the analysis of major
apple volatiles. The new volatile collection methodology and a specially
designed package-in-a-jar system were used to simultaneously measure volatile
production, concentration, and the permeability of package to those volatiles.
The effects of packaging ﬁlm to volatile proﬁle during storage were also
investigated.

Capillary 60 column segments were installed in gas tight syringes and
used as needles for volatile analysis. Using capillary column needles resulted in
an increase in GC response in the range of 2- to 15-fold relative to a standard
stainless steel needle having no internal coating. The number of times the
syringe plunger was pumped (pump number) was the factor that most inﬂuenced
GC response. To achieve response in certain range, the saturation for a
particular needle/volatile combination, a pump number of 40 was required.
Large non-polar molecules such as hexyl acetate required higher pump number
to reach equilibrium than smaller, more polar molecules like butanol. Like
syringe pumping number, injection volume and needle length affected GC
response in a needle and volatile dependent manner. As injection volume was
increased from 10 to 80uL, GC response to butanoi and ethyl-2-methylbutyrate
increased linearly. GC response to hexyl acetate experienced little increase in
response to increasing injection volume in the range of 10 to BOpL. The results
indicated that the minimal volume of 50 uL of sample or other gas (such as N2 or

air) was needed for pushing the adsorbed and/or absorbed volatile from needle

141

 

to the column when a capillary needle was used. When the length of capillary
glass, and capillary steel needles was increased from 2.5 to 6.5 cm, GC
response increased 225% and 214%, respectively. When the length of capillary
glass, and capillary steel needles was increased from 2.5 to 6.5 cm, GC
response increased 225% and 214%, respectively. The GC response for
capillary column needles decreased when the sampling temperature was
increased.

Since capillary GC column needle will work with both ﬂow through and low
volume sealed system such as modiﬁed atmosphere packaging (MAP), it permits
volatile production to be measured for products in the package under its storage
environment. Therefore, capillary GC column needle may be a useful tool for
determining the dynamic relationship between ﬂavor volatile synthesis and
package atmosphere for packaged produce. In addition, by changing the
column needle coating, one may create needles that are more speciﬁcally
matched to the volatiles of interest, leading to enhanced analytical sensitivity.

The effect of polymers used in packaging on the aroma of the packaged
product has been little explored. Using a package-in-a-jar system we are able to
simultaneously measure volatile production by plant organ (Malus domestica
Borkh. cv. Golden Delicious) and the permeability of the packaging ﬁlm to those
volatiles. In this system, apple fruit were placed into a glass container or sealed
in a low density polyethylene (LDPE) package and subsequently placed into a
glass container or were placed into a package alone. Air or a modiﬁed

atmosphere was slowly passed through the glass containers such that the O2

142

level was similar to that in the packages in containers. The package and jar
headspaces were sampled using direct gas sampling and capillary column
needles. Odor-active volatiles were analyzed by gas chromatography. The
effect of temperature, atmosphere and ﬁlm presence to some major volatile
compounds was determined. The package permeability to hexyl acetate, 2-
methylbutyl acetate, and -famesene was, respectively, 287-, 130-, and 172- fold
higher than those to ethylene.

The 02, C02, and ethylene proﬁle changes during MAP storage were
easily measured in a package-in-jar system with capillary needles. When
atmospheric composition changes from 10% 02 + 2% CO2 to 5% 02 + 5% C02,
ethylene production was reduced signiﬁcantly. However, when 02 concentration
decrease from 10% to 8% and CO2 concentration increase from 3% to 5%, the
rise in ethylene production rate was delayed slightly.

The package-in-jar system can be used to estimate production rate under
actual storage environment. At 0°C, as 02 decreased in concentration from 10%
to 5% (v/v), hexyl acetate and butyl acetate production declined signiﬁcantly; 2-
methylbutyl acetate production however, was not affected by this range of
atmospheric composition. This can be taken to indicate the production of 2-

methyl butanol (a branched alcohol derived from amino acids) for 2-methylbutyl

acetate formation is not as 02 concentration dependent as straight-chain alcohol.

Compared with 0°C, there was a higher volatile concentration and
production rate for fruit held at room temperature. Under the same atmospheric

composition, when storage temperature increased from 0°C to 22°C the

143

production rate of hexyl acetate and 2-methylbutyl acetate increased 11.27- and
17.1 5-fold, respectively.

At the same 02 partial pressure, non-packaged fruit evolved greater
amounts of all volatiles than packaged fruit. The ﬂux of -farnesene, hexyl
acetate and 2-methylbutyl acetate was 266-, 1.7-, and 1.4-fold higher,

respectively, for fruit in a glass container. The reduced production found for

packaged apples was probably due to loss of volatiles to the packaging material.

The sorption of -farnesene and some other volatiles into LDPE ﬁlm apparently

alters the aroma proﬁle of packaged produce relative to a ﬂow-through system.
The package-in-a-jar measurement system and capillary GC column

needle may be a useful methodology for determining the dynamic relationship

between ﬂavor volatile synthesis and package atmosphere for packaged produce.

144

GAN STATE UN

HICHI IV. LIBRARIES
lllll llllllllllllllll llllll llll lllllllllllllllllllllllllllllllll
3129301 700570

7