EFFECTS OF DIFFERENT DRYING METHODS ON THE TOTAL PHENOLICS,
ANTIOXIDANT PROPERTIES, AND FUNCTIONAL PROPERTIES OF APPLE
POMACE
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
By
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
Mohammed Tuwayrish Aldosari

A THESIS
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
Food Science—Master of Science
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
2014

ABSTRACT
ddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
EFFECTS OF DIFFERENT DRYING METHODS ON THE TOTAL PHENOLICS,
ANTIOXIDANT PROPERTIES, AND FUNCTIONAL PROPERTIES OF APPLE
POMACE
ddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
By
ddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
Mohammed Tuwayrish Aldosari
dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd
Apple pomace was dried using three different drying methods: freeze drying at
air temperature of 20ºC, drum drying at drum temperature of 140ºC, and cabinet drying
at air temperatures of 60 ºC, 80 ºC, and 100 ºC. The dried samples were measured
using Hunter Color CIE L*,a*, and b* values. The total color difference (△E) of apple
pomace was affected by the drying temperature and the type of drying method. The
freeze dried pomace was significantly higher in L* value compared to all of the other
samples, whereas cabinet drying at 100°C showed the highest average color a* and b*
values. The dried apple pomace was analyzed for total phenolics and antioxidant
capacity using ORAC, and DPPH. The total phenolics of dried pomace, with the highest
value ( 3.05 mg GAE/g) observed in freeze dried and the lowest (1.85 mg GAE/g). In
the cabinet dried pomace, total phenolics decreased gradually as the process
temperature was increased from 60 °C to 80 °C or 10 0 °C. Freeze dried pomace had
the highest antioxidant activity as exhibited by ORAC and DPPH results, 350.27 and
278.8 µmol TE/g, db, respectively. Drum drying of pomace at 140 °C reduced activity to
158.06 and 216.45 µmol TE/g, db, by ORAC and DPPH assays, respectively. Cabinet
drying of pomace resulted in lower antioxidant values as drying temperature increased
from 60 °C to 80 °C or 100 °C.

ACKNOWLEDGEMENTS
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I cannot express enough thanks to my committee for their continued support and
encouragement: Dr. Kirk Dolan, my advisor; Dr. Leslie Bourquin and Dr. Gale
Strasburg. I offer my sincere appreciation for the learning opportunities provided by my
committee.
My completion of this project could not have been accomplished without the
support of Saudi Arabian FDA for funding M.S. program; Phil Hill from BE Dept. for
refurbishing the drum dryer; Professor Loescher and Jesse Traub for use and training
on the freeze dryer; Sunisa Roidoung for training on the Biotek Plate Reader;
Abdulmajeed Alotaibi from Engineering Department– thank you for allowing me time
away from you to research and write.
Thanks to my parents as well, Mr. Tuawayrish Aldosari and Mrs. Nora Aldosari.
The countless times you kept the children during our hectic schedules will not be
forgotten.
Finally, to my caring, loving, and supportive wife, Dalal Aldosari: my deepest
gratitude. Your encouragement when the times got rough are much appreciated and
duly noted. It was a great comfort and relief to know that you were willing to provide
management of our household activities while I completed my work. My heartfelt thanks.

iii

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................vi
LIST OF FIGURES ........................................................................................................ viii
INTRODUCTION ............................................................................................................. 1
1

LITERATURE REVIEW ............................................................................................ 3
1.1 Apple Pomace .................................................................................................... 3
1.2 Antioxidants........................................................................................................ 4
1.3 Phenolic Components ........................................................................................ 5
1.4 Pomace drying ................................................................................................... 8
1.5 Drying Methods .................................................................................................. 8
1.5.1 Principles of Hot-air Drying ........................................................................ 10
1.5.2 Principles of Freeze Drying........................................................................ 11
1.6 Analysis of Total Phenlics and Antioxidant Capacity ........................................ 12
1.6.1 Total Phenolic Assay ................................................................................. 12
1.6.2 Oxygen Radical Absorbance Capacity (ORAC)......................................... 13
1.6.3 Diphenylpicrylhydrazyl Assay (DPPH) ....................................................... 13

2

MATERIALS AND METHODS ............................................................................... 15
2.1 Apple Powder Preparation ............................................................................... 15
2.2 Sample Preparation ......................................................................................... 15
2.3 Drying Methods ................................................................................................ 15
2.3.1 Drum Drying .............................................................................................. 16
2.3.2 Hot-air Drying ............................................................................................ 16
2.3.3 Freeze Drying ............................................................................................ 16
2.4 Hunter Color CIE .............................................................................................. 17
2.5 Antioxidants Extraction ..................................................................................... 18
2.6 Determination of Total Phenolic Content.......................................................... 19
2.6.1 Preparation of Reagent.............................................................................. 19
2.6.2 The procedure of experiment..................................................................... 19
2.7 Determination of Antioxidant Activity: Oxygen Radical Absorbance Capacity
(ORAC) ...................................................................................................................... 20
2.7.1 Preparation of Reagent.............................................................................. 20
2.7.2 The procedure of experiment..................................................................... 21
2.8 Diphenylpicrylhydrazyl (DPPH) Antioxidant Assay ........................................... 22
2.8.1 Preparation of Reagent.............................................................................. 22
2.8.2 The procedure of experiment..................................................................... 22
2.9 Data Analysis ................................................................................................... 23
iv

3

RESULTS AND DISCUSSION ............................................................................... 24
3.1 Effects of Drying Methods on the Color Properties of Dried Apple Pomace..... 24
3.1.1 Hunter Color CIE ....................................................................................... 24
3.2 Effects of Drying Methods on the Antioxidant Properties of Dried Apple Pomace
29
3.2.1 Total Phenolics .......................................................................................... 29
3.2.2 Antioxidant Capacity assayed by ORAC.................................................... 31
3.2.3 Antioxidant activity by DPPH (diphenylpicrylhydrazyl) assay..................... 32

4

CONCLUSIONS ..................................................................................................... 34
4.1
4.2

Conclusions...................................................................................................... 34
Future Research .............................................................................................. 35

APPENDIX .................................................................................................................... 36
REFERENCES .............................................................................................................. 48

v

LIST OF TABLES
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Table 1. Gallic acid concentrations for the standard curve ............................................ 19
Table 2. Trolox concentrations used for the standard curve.......................................... 22
Table 3 Moisture percent of apple pomace sample before drying methods .................. 37
Table 4 Moisture percent of drum dried apple sample .................................................. 37
Table5 Moisture percent of freeze dried apple sample.................................................. 37
Table 6 Moisture percent of cabinet dried apple sample at 60 ºC ................................. 37
Table 7 Moisture percent of cabinet dried apple sample at 80 ºC ................................. 37
Table 8 Moisture percent of cabinet dried apple sample at 100 ºC ............................... 38
Table 9 The relative humidity of drum dried apple sample ............................................ 38
Table 10 The relative humidity of cabinet dried apple sample at 60 ºC ......................... 38
Table11 The relative humidity of cabinet dried apple sample at 80 ºC .......................... 38
Table 12 The relative humidity of cabinet dried apple pomace at 100 ºC...................... 38
Table 13 Air velocity of cabinet drying ........................................................................... 39
Table 14 The Hunter Color CIE data of apple pomace before drying methods ............. 39
Table15 Location of blank, Trolox and sample wells .................................................... 39
Table 16 The Hunter Color CIE data of apple pomace after drying methods ................ 40
Table 17 Effects drying methods on the antioxidant in apple pomace before drying ..... 41
Table 18 Effects drying methods on the antioxidant in apple pomace after drying........ 42
Table 19 Effects drying methods on total phenolics in apple pomace before drying ..... 45
Table 20 Effects drying methods on the total phenolics in apple pomace after drying .. 46
Table 21 Effects drying methods on DPPH in apple pomace before drying .................. 46

vi

Table 22 Effects drying methods on DPPH in apple pomace after drying ..................... 47

vii

LIST OF FIGURES
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Figure 1. Apple processing for juice production .............................................................. 4
Figure 2. A quercetin (flavonol); B apigenin (flavone); C naringenin (flavanone); D (+)catechin (flavan-3-ol); E cyaniding (anthocyanidins) ....................................................... 7
Figure 3. Schematic representation of a top loading double drum dryer (GOUDA) ......... 9
Figure 4. Schematic Diagram of a Hot-Air Dryer ........................................................... 11
Figure 5. Scheme of L*a*b* model ................................................................................ 18
Figure 6. Effect of different drying methods on the Hunter color L* values of dried apple
pomace (means sharing the same letters are not significantly different from each other
at p= 0.0023, based on Tukey’s HSD test) .................................................................... 26
Figure 7. Effect of different drying methods on the Hunter color a* values of dried apple
pomace (means sharing the same letters are not significantly different from each other
at p= 0.0071 , based on Tukey’s HSD test) ................................................................... 27
Figure 8. Effect of different drying methods on the Hunter color b* values of dried apple
pomace (means sharing the same letters are not significantly different from each other
at p= 0.1174, based on Tukey’s HSD test). ................................................................... 28
Figure 9. Effect of different drying methods on the color changes (∆E values) of dried
apple pomace (means sharing the same letters are not significantly different from each
other at p= 0.1348, based on Tukey’s HSD test)........................................................... 29
Figure 10. Effect of different drying methods on the total phenolics content of dried
apple pomace (means sharing the same letters are not significantly different from each
other at p= 0.0001, based on Tukey’s HSD test)........................................................... 31
Figure 11. Effect of different drying methods on the ORAC values of dried apple
pomace (means sharing the same letters are not significantly different from each other
at p= 0.0001, based on Tukey’s HSD test) .................................................................... 32
Figure 12. Effect of different drying methods on the antioxidant values of dried apple
pomace using DPPH assay (means sharing the same letters are not significantly
different from each other at p= 0.0001, based on Tukey’s HSD test) ............................ 33

viii

INTRODUCTION

Fruit juices are considered “healthy” drinks. In recent years, consumption and
exporting of juices have increased because of the improvement in processing methods
and transportation (Askar 1998). In 2006-2007 the world produced 46.1 million tons of
apples. The country that produces the most apples is China, which harvests more than
50 % of the world’s apples followed by the USA. The world processes 25-30% of the
fruit into juice (Figure 1) (Bhushan and others 2008). Brazil produces 800,000 tons of
apple pomace each year (Protas 2003).Michigan ranks second in apple production in
USA. Many of the apple-growing farmers have small orchards. According to Michigan
Apple Committee, in 2013, Michigan harvested approximately 1260 million pounds of
apple, and the average of harvest is 828 million pounds of apples per year. Besides
fresh consumption, a large portion of production is used to produce apple juice/ cider.
The remaining residue after juice extraction (skins, flesh, and stems) is considered to be
a waste product, and is called pomace. Apple pomace is nutritionally rich and contains
bioactive compounds, such as antioxidants. To process apple pomace into a valueadded ingredient, moisture must be removed by drying, which can be done using
different drying methods (e.g., freeze drying, cabinet drying, and drum drying). These
methods are different with respect to cost, processing time, heat application, and
production rate.
The objectives of this research were to compare the effects of three different
drying methods (drum drying at one drum temperature at 140 °C, freeze drying at 20 °C,
and cabinet drying at three different temperatures 60 °C, 80 °C and 100 °C) :1) on the

nutritional characteristics of total phenolics and antioxidant activity as assayed by
ORAC and DPPH; and 2) on color values for the quality of apple pomace (Hunter Color
CIE).

2

1
1.1

LITERATURE REVIEW

Apple Pomace
Apple pomace is a by-product that is generated by processing apples into

different apple products such as juice, cider, and wines (Figure 1) (Vendruscolo and
others 2008). Recently, the emphasis on apple pomace has been to utilize it for the
extraction of value-added products, such as antioxidants and dietary fiber (Bhushan
and others 2008). Other uses for apple pomace include extraction of pectin, animal
feed, and more recently fermentation to produce citric acid or alcohol (Hang 1987).
Apple pomace has started to be increasingly used as source of apple fiber and bioactive
compounds (Walter and others 1985), which in turn has been incorporated into cookies,
granola bars, and muffins to add to the overall fiber value (Ingredients 2012); (Carson
and others 1994). Although the addition of apple pomace is good for products
nutritionally, it lowers the overall appearance, texture, and flavor (Beereboom and
Glicksman 1979). Of these issues, only the flavor can be addressed by the addition of
spices, and use of flavors such as vanilla (Belshaw 1978).

3

Figure 1. Apple processing for juice production
1.2

Antioxidants
Antioxidants play an important role in our health; as they may protect us from

serious diseases such as cancer (Borek 1997). An antioxidant is defined as “any
substance, when present at low concentrations compared to those of an oxidizable
substrate, significantly delays or prevents oxidation of that substrate (Halliwell 1989).”
Oxygen is important for life, and is used for energy production in our bodies. However,
1-3% of oxygen we breathe has detrimental effects that make “reactive oxygen species”
(ROS), which include superoxide radical (O2−) and hydrogen peroxide (H2O2). Through
providing contact with metal ions that make free radicals, which are atoms with an
4

unpaired electron created by interaction between oxygen and molecules. Free radicals
attack and damage almost everything in our bodies If O2− and H2O2 combine with
transition metal ions, the resulting free radical species can damage the human body
(Halliwell 1997).
The antioxidants come from different sources, such as enzymes (catalase), large
molecules (albumin), small molecules (polyphenols) and hormones (melatonin) (Prior
and others 2005). Also, fruits and vegetables contain many antioxidants such as vitamin
C + E, found in berries, tomato garlic, ginger, carotenoids and apple pomace (Moure
and others 2001).
The antioxidants are divided into two classes: 1) primary antioxidants that are
called chain-breaking antioxidants, they can interact with lipid radicals which result in
more stable products , and 2) secondary or preventative antioxidants, which retard the
oxidation rate (Antolovich and others 2002). The difference between them is that the
secondary antioxidants postpone the oxidation by interfering with the prooxidant
system, and the secondary antioxidants disable the conversion of free radical species to
a more stable product (Abulude and others 2013) .
1.3

Phenolic Components
Phenolic compounds are free radical scavenging molecules present in fruits and

vegetables, and include phenolic acids, flavonoids, coumarins (Larson 1988). There are
some studies showing that phenolic compounds from plants are more efficient than
vitamins E or C in our bodies as antioxidants (Rice-Evans and others 1997). Therefore,
phenolic compounds may have an important role in protecting our health (Rice-Evans

5

and others 1997). Recently, many research studies have focused on the importance of
phytochemical components such as phenolic acids, phenylpropanoids and flavonoids
because they have an active role in antioxidant activity (Rice-Evans and others 1997).
Phenols are divided into different groups. The first group is simple phenols that
contain an aromatic ring with one or more -OH groups (Schwannecke 2009). Phenolic
acids in the form of substituted derivatives of hydroxybenzoic and hydroxycinnamic
acids are the predominant phenolic acids in fruits. These derivatives differ in patterns of
hydroxylations and methoxylations of their aromatic rings (Lule and Xia 2012). The
second group, phenol carboxylic acids, include simple phenols, that bear a carboxyl
group. The third group of compounds, phenyl propane, have an aromatic ring that has 3
carbon atoms. The fourth group, flavan derivatives, is a flavan skeleton that consists of
3 rings. A and B are an aromatic ring and the ring in the center contains oxygen (figure
2) (Hess 1975).

6

Figure 2. A quercetin (flavonol); B apigenin (flavone); C naringenin (flavanone); D
(+)-catechin (flavan-3-ol); E cyaniding (anthocyanidins)

7

1.4

Pomace drying
The drying of pomace has been done by other groups. Yan and Kerr (2012) dried

apple pomace by vacuum-belt drying at 80 ºC, 95 ºC and 110 ºC, they measured total
phenolics content, anthocyanins, dietary fiber content and color properties. Also, Sogi
and others (2013) dried mango peel and kernel by different drying methods (freeze
drying at , hot air drying, vacuum and infrared drying), they measured total phenolics,
antioxidant activity, and functional properties. However, in this study, the drum drying
method has been added. This drying method has favorable characteristics for
commercial production, such as low cost, rapid drying time, and large throughput.
1.5

Drying Methods
There are many drying methods that are commonly used for fruits, such as spray

drying, hot air drying, drum drying, freeze drying, and microwave-vacuum drying. Fresh
fruits have a short shelf life because they have a high moisture content and high sugar
content, allowing microorganisms to grow.. Thus, drying will help extend the shelf life of
fruits through reducing water activity. In industry, much attention is paid to the quality of
products. As mentioned, the fruits have valuable components of vitamins, minerals,
fiber, etc. Thus, these components can be preserved through drying processing.
Polyphenolic compounds in fruits are sensitive to high temperature. For example, drum
drying exposes the product to temperature from 95 to 100 C (Hsu and others 2003) or
as high as 130°C. Due to sublimation, freeze drying does not damage the structure or
quality properties of product (Mejia-Meza 2008). Principles of Drum Drying
Drum drying is one of the most common methods used worldwide for drying the
food in pureed form. This method is appropriate for pureed foods or foods that become
8

pureed after treatment such as milk, mashed potato and fruit pulps (Falagas 1985).
There are many products coming from the drum drying method, such as breakfast
cereals, yeast and fruit puree (Moore and Dekker. 1995). Compared to other drying
methods; drum drying has the best efficiency in terms of high rate of production and
low labor requirements (Moore and Dekker. 1995).

Figure 3. Schematic representation of a top loading double drum dryer (GOUDA)
A drum dryer usually consists of two drums that have the same diameter that are
oriented close to each other (Figure 3) (Matsumoto and others 2000). These drums are
heated by steam that goes inside the drums to make the surfaces hot. These drums
rotate in opposite directions. The product is continuously poured in the crevice between
the drums to create a pool of product that is squeezed to the thickness of the space

9

between the drums, and begins to dry on the drum surfaces. Two fixed knives touch the
surfaces of drums to continuously scrape and remove the dried product to a container
below the drums. The important factors that affect the product are: steam pressure
inside the drums, the clearance or gap between the drums, rotational speed, pool level
between the drums and chemical and physical characteristics of sample being fed
(Gavrielidou and others 2002).
1.5.1 Principles of Hot-air Drying
The hot-air drying method is used to remove water from fruit. The purpose of this
drying method is to decrease the moisture content in the fruit, to avoid growth of
microorganisms and reduce the activity of enzymes, so that the products can be stored
for a long time (Schwannecke 2009) ; (Feng and others 2002). Hot-air drying removes
most of the water from the product by evaporation (Fellows 2000). In hot-air drying,
removing the first 33% of moisture uses about 66% of the total time of drying. Also, the
components of the product may not be stable under thermal processing, possibly
damaging the structure of the crust of vegetables (Zhao 2000). In China, because of
the low cost, hot-air drying is used for over 90% of dried vegetables. However, the
quality of these dried products is poor (Zhang 1999).

10

Figure 4. Schematic Diagram of a Hot-Air Dryer
Trays containing the product are exposed to hot air, which passes along the
surface of the product (Figure 4) (Tang and Yang 2003). Trays have the ability to hold a
depth of 2-6 cm of product per tray (Tang and Yang 2003).The passage of hot air in an
enclosed cabin from above and below the product will increase the effectiveness of
drying. There are influential factors on the rate of drying efficiency, such as the air
speed and heaters (Mejia-Meza 2008). Low relative humidity maintains hot air drying
efficiency, through the integration of fresh air and hot air in the enclosed cabin, which
are connected with the product to remove moisture (Mejia-Meza 2008).
1.5.2 Principles of Freeze Drying
The main purpose of freeze drying is to preserve fruits for an extended time,
especially for fruits that are sensitive to normal or high temperature. This drying method
is expensive and takes a relatively long time of 12 to 24 hours (Mejia-Meza 2008). The
principle of the freeze drying method is based on two phases. The first one is to freeze
the fruit and the second one is to remove the moisture via sublimation of the ice from
11

the fruit that is frozen (Oetjen 2004). Packaging materials are excellent barriers to
prevent the oxidation if the dried fruit is frozen. If dried fruit is not frozen the dried fruit
can easily be rehydrated, which may cause the oxidation. (Oetjen 2004).
The drying cabinet provides vacuum and refrigeration, and contains a heating
shelf and trays. Heating temperature in the drying cabinet is 20 ºC and in the
condenser cabinet from −30 ºC to -60 ºC (Mejia-Meza 2008). In this method we have
two phases: The first phase is the freezing of fruits quickly at atmospheric pressure and
at low temperature of −20 ºC. The second phase is the reduction of the pressure to
below the triple point of water, when moisture will leave the fruit as sublimated vapor,
which will minimize damage to the fruit structure (Fellows 2000) that occurs with other
drying methods.
1.6

Analysis of Total Phenlics and Antioxidant Capacity

1.6.1 Total Phenolic Assay
There are many methods to determine total phenolics such as traditional
methods that depend on absorbed radiation measurement in the ultraviolet region
(Somers and Ziemelis 1972). Folin–Ciocalteu’s reagent has been used to determine
total phenolics since 1965, and was developed by Singleton and Rossi (Singleton and
Rossi 1965). Gallic acid is a popular reagent to estimate total phenolics as molar
equivalents (Arnous and others 2001). Also, gallic acid and 3,4,5-trihydroxybenzoic acid
( C7H6O5) are commonly used to determine total phenolics in fruits and vegetables
(Protas 2003).

12

1.6.2 Oxygen Radical Absorbance Capacity (ORAC)
ORAC assays are used to determine the activity of antioxidants and their
relationship with total carotenoid content, total phenolics and ascorbic acid in fruit
(Thaipong and others 2006). This assay is based on the inhibition of the peroxyl-radical
induced oxidation, which is initiated by heat-induced or thermal decomposition of
azocompounds [e.g., 2,2’-azobis(2-amidino-propane) dihydrochloride or AAPH]
(Ganske and Dell 2006) (Glazer 1990). On the basis of this technique, the ORAC assay
utilizes a biological relevant radical source thus uniquely combining both the inhibition
time and the degree of inhibition into one quantity (Ou and others 2001). Some
modifications have been made to the ORAC assay, which include the use of fluorescein
as the probe (Ou and others 2001).
Advantages of the ORAC assay include: the free radicals are used from the
biological perspective; and the ORAC method is a good comparison tool between
different results from different laboratories and it combines reaction time and reaction
degree of antioxidants, . Disadvantages: It requires expensive equipment, it is possible
to get data with large variability, it is sensitive to pH, and it is time-consuming (Frankel
and Meyer 2000).
1.6.3 Diphenylpicrylhydrazyl Assay (DPPH)
(DPPH) is a stable free radical (diphenylpicrylhydrazyl) that is used to determine
antioxidant activity (Gil and others 2002). DPPH is a common method to estimate the
antioxidant activity (Sharma and Bhat 2009). DPPH measures the efficiency of
antioxidants at room temperature to avoid the deterioration of molecules from the heat,
but structural conformation of the antioxidant plays an important role in mechanical
13

interaction between DPPH and antioxidants (Bondet and others 1997). Compounds
can be divided into two groups based on reaction with DPPH: (1) there is a minority that
react very rapidly with DPPH (2) there is a the majority of compounds that react slowly
with DPPH and they have a complicated mechanism (Bondet and others 1997). Also,
there is a combination of factors that affect absorption of DPPH such as pH, oxygen and
light (Ozcelik and others 2003).

14

2
2.1

MATERIALS AND METHODS

Apple Powder Preparation
Raw apple pomace (Rome,Spy, Ida red, Jonathan, Joagold, empire and York)

was obtained from Peterson Farms (3104 West Baseline Road, Shelby, MI 49455. The
raw material was grounded by coffee grinder (Cuisinart, Model DCG-20, East Windsor,
NJ) at room temperature 25 ºC. Dried samples (15 g each) were loaded into the
pulverizer. Samples were prepared for antioxidant extraction, by crushing the sample,
placing in dark bags and keeping in the freezer. Samples were taken from four locations
of the batch. Moisture content was measured by moisture analysis ( Santorius
Corporation, Bohemia, NY, 11716), 1.5 – 3 grams were loaded on the analyzer. Drying
measurements took approximately 30 minutes for each sample ( Raw and dried
sample).
2.2

Sample Preparation
The pomace was kept in a freezer at – 9 ºC in dark bags to avoid losses of

antioxidants by light; each bag contained approximately 45g. The sample was thawed at
room temperature of 25 ºC before drying.
2.3

Drying Methods
Three drying methods were used; drum drying, hot air drying, and freeze drying.

The reason for drying was to remove moisture from apple pomace while saving valuable
quality components, such as antioxidants and phenolic compounds, the levels of the
components were compared using chemical assays.

15

2.3.1 Drum Drying
Samples of 1.6 Kg of apple pomace were mixed with water (1:2) to pour the
slurry onto a drum dryer (American Drum Dryers, Overton Machine Company,
Dowagiac, Michigan USA). The experiment was conducted three times. Drum drying
was run continuously for 15 minutes at a drum surface temperature of 140 °C. The
temperature of the drum was estimated using an infra-red thermometer (Model 9645,
CEN-Tech Company). The sample slurry was dried by pouring it on to the hot surface
of the drums, then by using knives to continuously scrape off the sample from the drum
so that the dried product was collected in stainless steel trays.
2.3.2 Hot-air Drying
The sample was dried at different air temperatures at 60 °C, 80 °C , or 100 °C.
The drying time was 25, 20 and 15 minutes respectively. The perforated tray was
loaded with approximately 150g for each temperature. The velocity of air was 15.2 m/s
measured with a hot-wire anemometer (Model number 407001, Extech Instruments
Corporation, the address is 9 Townsend West Nashua, NH 03063 U.S.A). The relative
humidity was 30.7%, 35.3% and 39% respectively. After drying, the content of moisture
in apple pomace was 3.0%, 3.0% and 3.2% respectively.
2.3.3 Freeze Drying
The freeze drying machine that used to dry apple pomace was Virtis Genesis
(25L Genesis SQ Super XL-70, 2010). The freeze dryer had a sample chamber, seven
shelves, a vacuum pump and a refrigerated condenser chamber. The shelf temperature
was lowered to−30 °C, and the sample was placed ont o shelves with the chamber
closed. The condenser was lowered to –60 ºC and the vacuum pump was turned on
16

until it pulled a near complete vacuum, approximately 50 mTorr. Then, the shelf heater
was turned on to warm up the samples to around 20 ºC. Samples were dried for 3 days
under these conditions, until the dryer had a stable reading of around 10 mTorr
pressure inside the freeze dryer. The samples were removed and kept frozen in dark
colored polyethylene bags at −20 °C.
2.4

Hunter Color CIE
Raw apple pomace’s color depends on the kind of apple. This color plays an

important role in food additives, in making the food attractive. Apple pomace color is
affected by drying method. The color is sensitive to heat, oxygen, enzymes. For
example, in the drum dryer, the high temperature will affect the color because the
temperature of drums is around 135 ºC to 140 ºC . Color was measured before and
after the treatment. The change of color indicates that the product loses part of its
quality through degradation of some important components of apple pomace.

17

Figure 5. Scheme of L*a*b* model
There are different models to measure the color, such as the L*a*b* model,
where RGB represents red, green and blue, and CMYK means cyan, magenta, yellow
and black (Yam
Yam and Papadakis 2004
2004). In this work, the Hunter color parameters and
L*a*b* model (Minolta Color Reader CR
CR-10, Ramsey, NJ) was used for color evaluation.
evaluation
where, L* means lightness component that has specific range from 0 to 100, a* means
the component from green to red and b* means the component from blue to yellow
(Figure 5) (Okubo
Okubo and others 1998
1998) (Yam and Papadakis 2004).
2.5

Antioxidants Extraction
For extraction of phenolics and antioxidants, the method of Sogi and others

(2014) was followed. Briefly, dried pomace samples (2.5 g) were placed into separate
tubes and 20mL of 80% methanol solution was added. The tubes were covered with
aluminum foil. Then, they were put in a sha
shaker for one hour at 200 g.

18

The samples were centrifuged for 10 min at 11,180 g . The supernatant was
poured off into separate tubes. Then, 10 mL of 80% methanol was added into the
residue, placed back in the centrifuge for an additional 10 min at 10,000 g and the
supernatant was poured off again into a separate tube. This step was done twice and
approximately 40 mL of product was obtained.
2.6

Determination of Total Phenolic Content

2.6.1 Preparation of Reagent
The total phenolic compounds test contains two reagents. Saturated sodium
carbonate 7.5%; 7.5 g of anhydrous sodium carbonate was weighed and dissolved in
92.5 mL water. Gallic Acid (0−500 mg/L) was prepared in two steps (1) stock solution:
0.1 g of Gallic acid was weighed and dissolved in 10 ml ethanol to obtain 10 mg/ml, (2)
working solution (100 mg/L): 200 µL of stock solution was weighed and ethanol was
added to make the volume 20 ml to get 100 mg/L. The standard curve was made on
these concentrations, as shown in Table 3.
Table 1. Gallic acid concentrations for the standard curve
Working solution (ml)
0
1
2
3
4
5

Ethanol (ml)
5
4
3
2
1
0

Gallic acid (mg/L)
0
20
40
60
80
100

2.6.2 The procedure of experiment
A volume of 0.5 mL of apple pomace extract was taken (1 part apple pomace
extract: 10 part water) and added to 0.5 m Folin-Ciocalteu reagent (1+9 water) in a test
19

tube that was mixed thoroughly, and the solutions were incubated for 3 minutes. After
incubation, 1 ml of saturated sodium carbonate (7.5%) was added followed by 1 ml of
distilled water. The solution was then incubated for 2 hours in the dark at room
temperature. A spectrophotometer was used at 750 nm and the absorbance was
compared to 0.5 ml of gallic acid (0−100 mg/L) standard curve.
2.7

Determination of Antioxidant Activity: Oxygen Radical Absorbance

Capacity (ORAC)
There are many ways to determine antioxidant level. ORAC assays are used to
determine the activity of antioxidants and their relationship with total carotenoids
contents, total phenolics and ascorbic acid in fruit (Thaipong and others 2006).
2.7.1 Preparation of Reagent
Preparation of stock solutions: Three stock solutions were prepared, which were
sodium phosphate buffer (pH 7.4), using 11.741 g of dibasic sodium phosphate
Na2HPO4 and 4.306 g of monobasic monohydrate sodium phosphate 1M NaH2PO4 that
was mixed and stirred in 900-1000mL of distilled water, pH was adjusted to 7.4 by 1M
NaOH and 1M HCl. Trolox (6-hydroxy -2,5,7,8-tetramethylchroman-2-carboxylic acid),
from hydrophilic group (Zulueta and others 2009), Trolox stock 2.0 mM was prepared
from 0.025g Trolox and 50 ml sodium phosphate buffer (pH 7.4) that were mixed and
stirred in glass flask, which were then wrapped in foil and stored in the refrigerator. The
final stock solution fluorescein was prepared from 0.1g Fluorescein and 100 ml sodium
phosphate buffer (pH 7.4), which was wrapped in foil and placed in refrigerator. These
stock solutions were stored for no more than three months due to their stability.

20

Dilutions of the three stock solutions were prepared on the day of the experiment.
Fluorescein dilution was prepared by adding 10 ml of sodium phosphate buffer (pH 7.4)
10 µL of Fluorescein stock into test tube, then by vortexing the solution. Trolox was
diluted to several different concentrations, 100µM (10mL sodium phosphate + 529 µL
Trolox), 50 µM (10 mL sodium phosphate + 264 µL Trolox), 25 µM (10 mL sodium
phosphate + 132 µL Trolox), 12.5 µM (10mL sodium phosphate + 66 µL Trolox) and
6.25 µM (10 mL sodium phosphate + 33 µL Trolox). Apple pomace dilution was
prepared by adding 10 mL of sodium phosphate buffer (pH 7.4) and 100 µL of sample
extraction into test tubes then mixing by vortex. Finally, AAPH (2,2′-azobis (2amidinopropane) dihydrochloride) was prepared by adding 0.414g AAPH and 10 ml of
sodium phosphate buffer into a test tube, then mixing thoroughly by vortex (Sogi and
others 2014).
2.7.2 The procedure of experiment
Fluorometer Operation: The Biotek Plate Reader was equilibrated to 37 °C. The
wells were loaded as shown in Appendix Table 13: Blank wells were loaded with 25µL
sodium phosphate buffer (pH 7.4). Trolox wells were loaded with 25µL of Trolox
dilutions. Sample wells were loaded with 25µL of sample dilutions and 150µL diluted
fluorescein solution was added to all experimental wells. Plates were placed in the
fluorometer. After 30 minutes, 25µL of AAPH was added to all experimental wells and
the plate was put again in the fluorometer for 3 hours to get the result.

21

2.8

Diphenylpicrylhydrazyl (DPPH) Antioxidant Assay
DPPH analysis: DPPH is stable free radical diphenylpicrylhydrazyl that was used

to determine the antioxidants (Gil and others 2002). DPPH analysis is common method
to measure antioxidant activity (Sharma and Bhat 2009).
2.8.1 Preparation of Reagent
The DPPH test uses 2.0 mM Trolox. Thus, the standard curve was made from
Trolox concentrations listed in Table 2.
Table 2. Trolox concentrations used for the standard curve
Trolox 2.0 mM (ml)

Ethanol (ml)

Trolox concentration (µM)

0

4

0

0.1

3.9

50

0.2

3.8

100

0.3

3.7

150

0.4

3.6

200

0.5

3.5

250

DPPH+ was prepared from 10 ml of DPPH stock and 50 ml of Ethanol. distilled
water was used to obtain 100% Transmittance at 515 nm to get absorbance of
0.7±0.01.
2.8.2 The procedure of experiment
A volume of 3 mL DPPH+ was taken with 0.6 mL of apple pomace extract (1
apple pomace extract: 10 water) and placed into a test tube. It was incubated for 20
minutes in the dark and measured at 515 nm. An absorbance reading was obtained and
compared to the Trolox standard curve (0−250 µM).

22

2.9

Data Analysis
All data were analyzed using JMP 9.0 software (SAS Institute, Inc., Cary, North

Carolina, USA). One-way analysis of variance (ANOVA) was used to analyze the data
on the effects of drying techniques on the physical and antioxidant properties of dried
mango pomace. The significant difference comparisons were made by Tukey’s HSD
test and the statistical significance was defined as p ≤ 0.05.

23

3
3.1

RESULTS AND DISCUSSION

Effects of Drying Methods on the Color Properties of Dried Apple Pomace

3.1.1 Hunter Color CIE
Apple pomace’s color was examined by Hunter Color CIE L* a* b* system. Color
Reader CR-10 was used to analyze all samples. The mean L*, a*, b* variables for raw
apple pomace were 33.8, 13.73 and 29.2 respectively. The mean values for apple
pomace after freeze drying methods, drum drying method and cabinet drying methods
are shown in Figures 6, 7, 8 and 9.
The freeze dried pomace sample showed the highest average level in whiteness
(L*), whereas the drum dried sample showed the lowest L* value (Figure 6). As
expected, higher temperature used in drum drying affected the Hunter color L* values
negatively. The drying methods used had significant impact on (L*) (p= 0.0023). On the
other hand, increasing temperature from 60 °C to 10 0 °C in the cabinet dryer did not
affect the L* values significantly (Figure 6). There is limited literature on apple pomace
drying using the same methods used in the present study. However, Yan and Kerr
(2013) also reported lower whiteness values in vacuum-belt dried apple pomace when
the temperature was increased from 80° C to 110 °C (Yan and Kerr 2013).
The cabinet drying at 100°C was shown to impart the highest redness or color a*
values, and freeze drying showed the lowest redness or color a* values (Figure 7).
Similar to the Hunter color L*, a* values did not change significantly when cabinet drying
temperatur was increased from 60 °C to 100 °C. The cabinet drying at 100°C showed
the highest average level in yellowness or b* value, and the drum drying sample

24

showed the lowest average level in yellowness b* value (Figure 8); however, the
differences were not significant statistically among all samples (p=0.1174).
The total color difference (△E) values did not show any significant difference
(p=0.1348) when the apple pomace was dried using different drying methods (Figure 9).
This showed that although there were differences in individual color parameter L* and
a*, these did not impact the overall color, as determined by △E. The study by Yan and
Kerr (2013) reported similar results to my result on Hunter color L*, a*, or b* of dried
apple pomace, the apple pomace was dried by freeze drying and vacuum-belt drying at
80C, 95C and 110C. freeze dried sample was the highest average level in whiteness
(L*), whereas the vacuum-belt dried sample at 110C was the lowest L* value(Yan and
Kerr 2013).

25

60
a
a,b

Hunter Color L* Value

50

c

b,c

Drum drying
(140 °C)

Cabinet drying
(60 °C)

b,c

40

30

20

10

0
Freeze drying
(20 °C)

Cabinet
drying(80 °C)

Cabinet
drying(100 °C)

Figure 6. Effect of different drying methods on the Hunter color L* values of dried
apple pomace (means sharing the same letters are not significantly different from
each other at p= 0.0023, based on Tukey’s HSD test)

26

18
a

a,b

Hunter Color a* Value

15

a,b

b
b

12

9

6

3

0
Freeze drying
(20 °C)

Drum drying
(140 °C)

Cabinet drying
Cabinet
(60 °C)
drying(80 °C)

Cabinet
drying(100 °C)

Figure 7. Effect of different drying methods on the Hunter color a* values of dried
apple pomace (means sharing the same letters are not significantly different from
each other at p= 0.0071 , based on Tukey’s HSD test)

27

35
a

a
a

Hunter Color b* Value

30

a

a

25
20
15
10
5
0
Freeze drying
(20 °C)

Drum drying
(140 °C)

Cabinet drying
Cabinet
(60 °C)
drying(80 °C)

Cabinet
drying(100 °C)

Figure 8. Effect of different drying methods on the Hunter color b* values of dried
apple pomace (means sharing the same letters are not significantly different from
each other at p= 0.1174, based on Tukey’s HSD test).

28

30

a
a

a

a

25

Color △E

a
20

15

10

5

0
Freeze drying
(20 °C)

Drum drying
(140 °C)

Cabinet drying
Cabinet
(60 °C)
drying(80 °C)

Cabinet
drying(100 °C)

Figure 9. Effect of different drying methods on the color changes (∆E values) of
dried apple pomace (means sharing the same letters are not significantly different
from each other at p= 0.1348, based on Tukey’s HSD test)
3.2

Effects of Drying Methods on the Antioxidant Properties of Dried Apple
Pomace

3.2.1 Total Phenolics
The mean of total phenolics in apple pomace was measured by
spectrophotometer and expressed in milligrams of gallic acid equivalents (GAE) per
gram of apple pomace. The mean of total phenolic in raw apple pomace was 3.56 ±
0.18 mg GAE/ g apple pomace. Total phenolic of apple pomace average for all samples
are shown and Figure 10. The highest value of total phenolics was noticed in freeze
drying samples and the lower value was noticed in the drum dryer at 140 °C. The total
antioxidant activity of dried apple pomace was significantly affected by temperature and
drying methods (p=0.0001).
29

Phenolic compounds are heat-sensitive and, even cabinet drying at the lowest
temperature (60 °C) resulted in significant decreas e as compared to freeze drying
method. Yan and Kerr (2013) also reported that higher temperature used during
vacuum belt drying of pomace negatively impacted total phenolic content (Yan and Kerr
2013). The results of the present study are also similar to those reported by Sogi and
others (2013) for mango peel and kernel drying, they have used four different drying
methods; freeze drying -20C, hot air drying at 60C, vacuum drying at 60C and infra-red.
The highest value of total phenolic was noticed in freeze drying samples and hot air
drying at 60C was lower the freeze dried sample (Sogi and others 2013). The heat
treatment decreases the total phenolic content due to the cleaving of esterified bond
and glycosylated bond (Xu and others 2007).

30

Total Phenolics (mg GAE/g, db)

5

4
a
3
b

c

c

c

2

1

0
Freeze-dried (20 Drum-dried (140 Cabinet-dried
°C)
°C)
(60 °C)

Cabinet-dried
(80 °C)

Cabinet-dried
(100 °C)

Figure 10. Effect of different drying methods on the total phenolics content of
dried apple pomace (means sharing the same letters are not significantly different
from each other at p= 0.0001, based on Tukey’s HSD test)
3.2.2 Antioxidant Capacity assayed by ORAC
The antioxidant properties of dried apple pomace were compared using ORAC
and DPPH assays. The mean ORAC in raw apple pomace was 1136.2 ± 480 µmol
TE/gsample db. The mean ORAC values of dried apple pomace using different drying
methods are shown in Table 6. The highest mean ORAC value of 350.275 µmol TE/g
(dry basis) was observed in freeze dried apple pomace and the lowest in the drum dryer
at 140 °C sample (Figure 11). The highest content o bserved in freeze dried samples
might be due to lack of any heat used in other methods. The freeze drying method
showed significantly higher (p=0.0001) ORAC values as compared to the other drying
methods used. These results are similar with those reported by Sogi and other (2013),

31

who dried mango peel and kernel using freeze, cabinet (60 °C) and infra-red and
vacuum drying. They reported the highest value of ORAC was in freeze dried sample
and hot air dried sample was lower freeze dried sample (Sogi and others 2013).

400

a

350

b

ORAC (µmol TE/g, db)

300
250

b,c

200

b,c

c

150
100
50
0

Freeze drying
(20 °C)

Drum drying
(140 °C)

Cabinet drying
(60 °C)

Cabinet
drying(80 °C)

Cabinet
drying(100 °C)

Figure 11. Effect of different drying methods on the ORAC values of dried apple
pomace (means sharing the same letters are not significantly different from each
other at p= 0.0001, based on Tukey’s HSD test)
3.2.3 Antioxidant activity by DPPH (diphenylpicrylhydrazyl) assay
The DPPH assay was the second method used to assess effect of drying
methods on antioxidant levels of dried apple pomace. The mean of DPPH in raw apple
pomace was 294.839 ± 6.132 µM TE/ g (dry basis). Total phenolic of apple pomace
average for all samples are shown in Table 7 and Figure 12. The highest mean of total
DPPH was observed in freeze drying sample and the lower in the drum dryer at 140° C.
Successively lower DPPH values were observed in cabinet dried apple pomace, as the
32

temperature was increased from 60 °C to 80 °C and 1 00 °C. The DPPH of dried apple
pomace was significantly affected by temperature and drying methods (p=0.0001). Sogi
and others also reported similar results where freeze dried mango peel and kernels
retained the highest DPPH values, as compared to cabinet drying (Sogi and others
2013).

300

a
b

DPPH (µmol TE/g, db)

250

c

d

e
200

150

100

50

0

Freeze-dried
(20 °C)

Drum-dried Cabinet-dried Cabinet-dried Cabinet-dried
(140 °C)
(60 °C)
(80 °C)
(100 °C)

Figure 12. Effect of different drying methods on the antioxidant values of dried
apple pomace using DPPH assay (means sharing the same letters are not
significantly different from each other at p= 0.0001, based on Tukey’s HSD test)
Trolox was used as standard curve for ORAC and DPPH assays. There are
some differences between these assays. The ORAC assay is sensitive, more expensive
and requires more time. However, it measures the degradation throughout the
experiment. The DPPH assay is quicker than the ORAC assay, but it measures the
degradation only at one time, rather than throughout the experiment.
33

4 CONCLUSIONS
4.1

Conclusions
The apple pomace color was affected by the type of drying method and

temperature. Hunter Color CIE variables were used to measure affect on L*, a*, and b*
values to assess differences among drying methods. The freeze dried sample was the
highest in L* values. Cabinet drying at 100 °C was shown to result the highest average
a* and b* values. The freeze dried sample showed the lowest average level in a* value,
which was slightly different with drum drying sample.
The total antioxidant activity of dried apple pomace was significantly affected by
the three different drying methods; freeze drying, drum drying, and cabinet drying.
However, cabinet drying air temperatures of 60 ºC, 80 ºC, or 100 ºC did not significantly
influence on total antioxidant in apple pomace. Type of drying method was shown to
have a significant effect on total antioxidant of dried sample of apple pomace.
The total phenolics of dried apple pomace samples did change significantly; the
freeze dried sample contained the highest levels of total phenolics, and the lowest
levels of the total phenolics were observed in the drum dried sample.
The DPPH of dried apple pomace samples did show significant differences; the
highest average of total phenolic was absorbed in the freeze dried sample, and the
lowest average of the total phenolics was observed in the drum-dried sample. The
results of this study demonstrated that freeze drying was the best method to process
apple pomace for value-added ingredient use. The next best method was cabinet drying
at lower temperatures, and finally drum drying.
34

Although drum drying showed the most detrimental effect on color, phenolics, and
antioxidants, its significantly lower cost and faster speed of drying may offset the
negative nutritional effects. For example, drum-dried apple pomace could be used as a
low-percentage ingredient or blended with premium-dried apple pomace to meet both
cost and nutritional requirements.
4.2

Future Research

1. Investigate other drying methods such as vacuum drying or infrared drying, which
use different drying temperatures.
2. Study various packaging options for shelf life, which include microbial analysis
and sensory analysis.
3. Do analysis of vitamins and minerals and dietary fiber of the pomace.

35

APPENDIX

36

Table 3 Moisture percent of apple pomace sample before drying methods
Raw apple pomace
Sample

Percent Moisture
%

1

76.2

2

76.4

3

75.6

Average Percent Moisture %

76.06 ± 0.4163

Table 4 Moisture percent of drum dried apple sample
drum dried apple
sample

Percent Moisture
%

1

3.03

2

3.12

3

2.88

Average Percent Moisture
%
3.01 ± 0.1212

Table 5 Moisture percent of freeze dried apple sample
Drum dried apple
sample

Percent Moisture
%

1

5.06

2

4.86

3

5.21

Average Percent Moisture
%
5.04 ± 0.1755

Table 6 Moisture percent of cabinet dried apple sample at 60 ºC
Drum dried apple
sample

Percent Moisture
%

1

3.14

2

3.17

3

3.19

Average Percent Moisture
%
3.16 ± 0.0251

Table 7 Moisture percent of cabinet dried apple sample at 80 ºC
Drum dried apple
sample

Percent Moisture %

1

3.02

2

3.04

3

3.07

Average Percent Moisture %

3.04 ± 0.0251

37

Table 8 Moisture percent of cabinet dried apple sample at 100 ºC
Drum dried apple sample

Percent Moisture %

1

3.01

2

2.96

3

2.95

Average Percent Moisture %

2.97 ± 0.0321

Table 9 The relative humidity of drum dried apple sample
Samples

Relative humidity %

1

45.2

2

47.2

3

42.3

Average Percent Moisture %

45.2 ± 2.4637

Table 10 The relative humidity of cabinet dried apple sample at 60 ºC
Samples

Relative humidity %

1

31

2

31

3

30

Average Percent Moisture %

30.66 ± 0.5773

Table11 The relative humidity of cabinet dried apple sample at 80 ºC
Samples

Relative humidity %

1

35

2

36

3

35

Average Percent Moisture %

35.33 ± 0.5773

Table 12 The relative humidity of cabinet dried apple pomace at 100 ºC
Samples

Relative humidity %

1

39

2

40

3

38

Average Percent Moisture %

39.00 ± 1.00

38

Table 13 Air velocity of cabinet drying
Samples

Air velocity m/s

1

15.8

2

14.8

3

15.1

Average Air velocity m/s

15.23 ± 0.5131

Table 14 The Hunter Color CIE data of apple pomace before drying methods
L*
Sample
1

30.1

Sample
2

31.8

Sample
3

39.5

Average
L*

Average
a*

a*
13.0

33.8 ±
5.00

Average
b*

b*
24.8

13.73 ±
0.94

14.8
13.4

30.3

△E*

Average
△E

7.44
29.2 ±
3.96

32.5

3.40

3.96 ±
3.22

1.06

Table 15 Location of blank, Trolox and sample wells
1

2

3

4

5

6

7

8

9

10

11

BLK

STD1

STD3

STD5

SPL1

SPL2

SPL3

SPL4

SPL5

SPL6

0

50

12.5

100

100

100

100

100

100

STD1

STD3

STD5

SPL1

SPL2

SPL3

SPL4

SPL5

SPL6

0

50

12.5

100

100

100

100

100

100

STD1

STD3

STD5

SPL1

SPL2

SPL3

SPL4

SPL5

SPL6

0

50

12.5

100

100

100

100

100

100

STD2

STD4

STD6

SPL1

SPL2

SPL3

SPL4

SPL5

SPL6

100

25

6.25

50

50

50

50

50

50

STD2

STD4

STD6

SPL1

SPL2

SPL3

SPL4

SPL5

SPL6

100

25

6.25

50

50

50

50

50

50

A

B

C

D

E

F

BLK

BLK

BLK

BLK

39

12

Table 15 (cont’d)
G

BLK

STD2
100

STD4
25

STD6
6.25

SPL1
50

SPL2
50

SPL3
50

SPL4
50

SPL5
50

SPL6
50

H

Table 16 The Hunter Color CIE data of apple pomace after drying methods
Drying
Method

Temperature ºC

Freeze
Dried

20

L*
52.6
51
53.9

Average
L*
52.5 ±
1.4525

a*
14.2
11.3
11.6

Average
a*
12.36 ±
1.59

b*
30.9
28.6
30.5

Average
b*
30 ±
1.22

△E*

28.77

Average
△E
25.03 ±
3.32

23.9
22.42

Drum
Dried

140

38.8
47
39.9

41.9 ±
4.45

12.4
12.5
12.5

12.45 ±
0.05

26.4
29.7
26.7

27.6 ±
1.82

15.98

16.9 ±
4.11

21.4
13.33

Cabinet
Dried

60

43.7
45
45.4

44.7 ±
0.88

14.8
14.3
15.6

14.9 ±
0.65

28.6
27.5
28.4

28.16 ±
0.58

20.77

18.45 ±
2.25

18.32
16.26

80

47.8
49.9
48.1

48.6 ±
1.13

14.7
12.9
12.5

13.36 ±
1.17

30
25.8
26

27.26 ±
2.36

24.6

20.38 ±
4.72

21.26
15.28

100

44.1
42.4
46.7

44.4 ±
2.16

15.1
15.7
15.5

15.43 ±
0.30

30.8
28.9
31.5

30.4 ±
1.34

22.74
17.66
19.59

40

19.99 ±
2.56

Table 17 Effects drying methods on the antioxidant in apple pomace before
drying
ORAC (µmol TE/g apple pomace)

Average ORAC (µmol TE/g apple Pomace)

1059.2
1488.7
1498.2
2060.5
1706.2
790.6
700.4
949.2
817.3
1511.4
1869.1
707.2
321.5
913.8
666.3
1089.7
1166.7
1059.2
1488.7
1498.2
2060.5

1136.2 ± 480

41

Table 18 Effects drying methods on the antioxidant in apple pomace after drying
Average ORAC (µmol
Drying Method

Freeze Dried

Air Temperature
(°C)

ORAC (µmol TE/g apple Pomace)

378.8
425.8
388.8
305.9
263.6
190.1
363.2
373.4
370.3
336.5
292.6
211.2
406.1
463.5
413.8
324.1
318.2
145.2
405.1
453.4
420.5
360.4
378.8

20

42

TE/g apple Pomace)

350.275 ± 21

Table 18 (cont’d)

Drum Dried

Cabinet Dried

152.7
159.2
154.8
168.4
143.1
115.7
126.8
139.2
153.8
160.4
164.7
125.1
210.1
285.9
280.7
154.0
136.6
102.3
224.7
256.1
296.3
292.4
299.4
278.6
201.5
222.6
238.1
291.1

140

60

43

158.066 ± 26.9

244.450 ± 48.9

Table 18 (cont’d)

Cabinet Dried

329.5
272.5
162.0
15.3
349.2
311.9
242.3
179.2
338.2
352.3
313.7
302.9
133.9
148.5
148.3
243.4
237.2
198.7
167.8
161.0
179.5
282.3
301.5
253.2
158.0
172.6
149.2
264.8
303.8
250.1
93.7
134.8
125.4
245.7
251.3
238.8

80

44

195.700 ± 21

Table 18 (cont’d)
135.2
202.1
210.7
228.1
239.1
203.7
140.3
188.4
240.8
221.3
248.6
212.2
162.2
221.3
222.8
0.0
257.9
194.5
158.3
198.3
227.6
189.1
180.8
161.7

100

Cabinet Dried

187.775 ± 14.5

Table 19 Effects drying methods on total phenolics in apple pomace before
drying
Total Phenolics

Average Total Phenolics

(mg GAE/g apple pomace)

(mg GAE/g apple pomace)

3.65
3.42
3.37
3.77

3.56 ± 0.18

45

Table 20 Effects drying methods on the total phenolics in apple pomace after
drying
Air
Drying Method

Total Phenolics

Average Total Phenolic

(mg GAE/g apple pomace)

(mg GAE/g apple pomace)

Temperature
(°C)

Freeze Dried

20

2.84
2.99
3.18
3.17

3.05 ± 0.16

Drum Dried

140

1.70
2.10
1.90
1.72

1.85 ± 0.18

Cabinet Dried

60

2.58
2.55
2.40
2.51

2.51 ± 0.07

80

2.20
1.95
1.99
2.41

2.14 ± 0.20

100

2.01
2.09
2.18
2.07

2.09 ± 0.07

Table 21 Effects drying methods on DPPH in apple pomace before drying
DPPH µmol TE/g

Average DPPH µmol TE/g

286.502
297.618
294.442
300.793

294.839 ± 6.132

46

Table 22 Effects drying methods on DPPH in apple pomace after drying
Air Temperature
Drying Method

DPPH µmol TE/g

Average DPPH µmol TE/g

(°C)
Freeze Dried

Drum Dried

Cabinet Dried

20

140

60

80

100

278.326
279.526
277.125
280.327
214.891
219.593
217.634
213.716
245.459
244.674
245.851
243.104
237.700
237.308
236.132
236.916
229.303
227.344
230.086
232.436

47

278.826 ± 1.400

216.459 ± 2.657

244.772 ± 1.214

237.013 ± 0.669

229.792 ± 2.106

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