.q. s ,- "EN” ’4 and” by“: cynquu any? n '1 21:171.; 917.1... .31... ... L... t... v.» s \- 511w LIBRAFHES till “lill‘ilii l l ll. llllll 31 LIBRARY Mlchlgan State Unlvorslty This is to certify that the thesis entitled Modified-Atmosphere Packaging of Raspberry and Strawberry Fruit: Characterizing the Respiratory Response to Reduced 02, Elevated C02, and Changes in Temperature presented by Dennis W. Joles has been accepted towards fulfillment of the requirements for M.S. Horticulture degree in flag/arm Major professor Date HAY/93 / / 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution b“ J...» w w PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE ' DCT 0 5 2007 MSU Is An Affirmative Action/Equal Opportunlty Institution cad Mum”! MODIFIED-ATMOSPHERE PACKAGING OF RASPBERRY AND STRAWBERRY FRUIT: CHARACTERIZING THE RESPIRATORY RESPONSE TO REDUCED 02, ELEVATED C02,4AND CHANGES IN TEMPERATURE BY Dennis W. Joles A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1993 ABSTRACT MODIFIED-ATMOSPHERE PACKAGING OF RASPBERRY AND STRAWBERRY FRUIT: CHARACTERIZING THE RESPIRATORY RESPONSE TO REDUCED 02' ELEVATED C02,.AND CHANGES IN TEMPERATURE BY Dennis W. Joles Modified-atmosphere (MA) packaging has the potential to provide suitable atmospheres to extend the storage life of raspberry and strawberry fruit. To design an effective MA package for raspberry or strawberry the fruit's respiratory response to reduced 02, elevated C02, and temperature should be known. Therefore, experiments were conducted to determine 02 uptake, C02 production, and ethanol content of raspberry and strawberry fruit over a range of 02 levels, CO} levels and temperatures. The lower 02 limit for aerobic respiration was identified from a breakpoint in the fruit's respiratory quotient (RQ) and ethanol content. Mathematical models were developed to characterize the 02 uptake and RQ of these fruit. These models and the lower 02 limit data were used to describe the effect of a change in temperature on package 02 and CO2 levels. A system that responds to package ethanol vapor was developed for sensing the induction of anaerobic respiration. To mom .1 .1 i ACKNOWLEDGMENTS I would like to thank Dr. Arthur Cameron for giving me the support, guidance and opportunities to learn and improve myself. I would like to thank Dr. Eric Grulke and, especially, Dr. Randy Beaudry for their advice and assistance during the course of my research. Thank you also, Dr. Ahmad Shirazi, Dr. Pete Petracek, Dr. P. Chowdary Talasila, Russell Stacy-Ryan, Mark Yelanich, Jane Waldron, and all the basement crew for your help and your time. Thank you Grandpa for teaching me to work hard and for beginning my interest in horticulture. Most of all, thank you Jane for your understanding, cooperation, and love. iv TABLE OF CONTENTS CHAPTER 1 MODIFIED-ATMOSPHERE PACKAGING OF 'HERITAGE' RED RASPBERRY]. Abstract . . . . . . . . . . . . . . . . . . . . . 2 Introduction . . . . . . . . . . . . . . . . . . . 4 Materials and Methods . . . . . . . . . . . . . . 7 Results . . . . . . . . . . . . . . . . . . . . . 13 Discussion . . . . . . . . . . . . . . . . . . . . 15 List of References . . . . . . . . . . . . . . . . 19 CHAPTER 2 MODIFIED-ATMOSPHERE PACKAGING OF STRAWBERRY FRUIT: CHARACTERIZING RESPIRATION AS A FUNCTION OF 02 AND TEMPERATURE . . . . . . . . 44 Abstract . . . . . . . . . . . . . . . . . . . . . 45 Introduction . . . . . . . . . . . . . . . . . . . 47 Materials and Methods . . . . . . . . . . . . . . 50 Results . . . . . . . . . . . . . . . . . . . . . 57 Discussion . . . . . . . . . . . . . . . . . . . . 60 List of References . . . . . . . . . . . . . . . . 64 CHAPTER 3 MODIFIED-ATMOSPHERE PACKAGING OF STRAWBERRY AND RASPBERRY FRUIT: MODELING PACKAGE 02 AND CO2 OVER A RANGE OF TEMPERATURES . . . . . . 89 Abstract . . . . . . . . . . . . . . . . . . . . . 90 Introduction . . . . . . . . . . . . . . . . . . . 91 Model Development . . . . . . . . . . . . . . . . 94 Materials and Methods . . . . . . . . . . . . . . 98 Results and Discussion . . . . . . . . . . . . . . 98 List of References . . . . . . . . . . . . . . . 106 LIST OF TABLES Table CHAPTER 1 Table 1. Activation energies (Eg),° Arrhenius constants (Ar)! and correlation coeff1cients (r'z) for .00521 and .00766 LDPE film. Values were obtained from linear transformations of the equation: P = A exp(- EQ/R T)2 where P is permeability to 02 or C0 (mmole cm cm'2 -'1h -'1kPa ); E8 is the energy 0 activation of 02 or CO permeation (kJ mol1); and R is the gas2 cons ant (. 0083144 kJ mol1K”) (Pauly, 1989). . . . . . . . . . . . . . . . . . Table 2. Whole package 02 and C0 permeabilities (Po A/Ax and Pco A/Ax, respect1vely) for the packages used inc cJthese experiments at 0,10 and 20C. Appropriate values were substituted into Eqs. [2] and [3] to calculate 02 uptake and CO2 production for fruit at 0, 10, or 20C. Table 3. Constants for Michaelis-Menten (Eq [6]) equation describing the relationship between uptake (mmol kg h ), steady- -state 02 partiaf pressure (kPa), and temperature for raspberry fruit sealed in LDPE pouches and stored at various temperatures. The constants of the Michaelis- Menten equation were estimated by non-linear regression analysis. . . . . . . . . . . . . . . . Table 4. Estimated values for Eq. [7], describing the relationship between calculated RQ, steady-state (5 partial pressure (kPa) and temperature for September-harvested raspberry fruit stored at 0, 10, and 20C. . . . . . . . . . . . . . . . . . . . CHAPTER 2 Page 22 23 24 25 Table 1. Target C5 partial pressures and the corresponding package dimensions and fruit weights calculated to obtain these partial pressures. The appropriate package dimensions and fruit weights were calculated using Eq. 1 combined with preliminary strawberry uptake data. The target weights correspond respectively with each target 02. . . . . . . . . vi Table Table Table 2 . Constants forO Eq. 9 describing the relationship between uptake (mmol kg1h1), steady-state 02 partial pressure (kPa) , and temperature for 'Honeoye' and 'Allstar' strawberry fruit (Eq. [9]) and shown in Figures 5 and 6. mois the maximum rate of C) uptake at 0C, Q1O is t e increase in 02 uptake for a 10C increase0 in temperature, kv. is the 02 partial pressure at which the rate of 02 uptake is half the maximum rate, and POZ‘mis a value describing the of the fruit's skin to 02 . These constants were estimated by non-linear regression analysis using SAS 0 O O O O O I O O 0 O O 3. Estimated Wconstants for Eq. [10], describing the relationship between calculated RQ, steady— state 02 partial pressure (kPa) and temperature for 'Honeoye' and 'Allstar' strawberry fruit. The t coefficient in this models is an estimate of aerobic RQ. . . . . . . . . . . . . . . . . . . . CHAPTER 3 Table l. Constants describing the relationship between Table 02 uptake (mmol kg'1h1), steady- -state 02 partial pressure (kPa), and temperature for 2'Allstar' strawberry fruit (estimated in Chapter 2). Rfim°is the maximum rate of 02 uptake at 0C, Q10 is t e 1ncrease in 02 uptake for a 10C increase in temperature, k” 2is the internal 02 partial pressure at which the rate of 02 uptake is half the maximum rate, and P0 “"‘is a value describing the of the fruit's skin to 02. . . . . . . . . 2. Constants describing the relationship between 02 uptake (mmol kg1-'1h ), steady-state 02 partial pressure (kPa), and temperature for 'Heritage' raspberry (estimated in Chapter 1). Kv. is the external (package CIZ) 02 jpartial pressure at which the rate of<32 uptake is half the maximum rate. vii Page 67 68 104 105 LIST OF FIGURES Figure Fig. Fig. Fig. Fig. Fig. Fig. Fig. CHAPTER 1 1. Effect of raspberry fruit weight on steady- state 02 (circles) and CO2 (triangles) partial pressures for' September (open symbols) and October-harvested (closed symbols) raspberry fruit sealed in LDPE packages where A: 300 cm2, Ax = .00521 cm for packages at 10 and 20C, and A = 300 cm2, Ax = .00766 cm for packages stored at 0C. . . 2. Interdependent effects of steady-state O2 partial pressures and storage temperature on the calculated rate of C) uptake for September (0) and October-harvested (E1) raspberry fruit sealed in LDPE packages. See Eq. [6] and Table 3 for the equations and constants describing the curves. . . 3. Interdependent effects of steady-state O2 partial pressures and storage temperature on the calculated rate of CO production for September (0) and October-harvested (D) raspberry fruit sealed in LDPE packages. . . . . . . . . . . . . 4. Effect of steady—state C5 partial pressure and storage temperature on the respiratory quotient of September (0) and October-harvested (U) raspberry fruit sealed in LDPE packages. See Eq. [7] and Table 4 for the equations and constants describing the curves. . . . . . . . . . . . . . . . . . . . 5. Interdependent effects of steady-state 0Z partial pressure and storage temperature on headspace ethanol vapor concentration for September (0) and October-harvested (D) raspberry fruit sealed in LDPE packages. . . . . . . . . . 6. Relationship of headspace ethanol vapor concentration and the respiratory quotient measured for September (0) and October-harvested (D) raspberry fruit sealed in LDPE packages and stored at 0, 10, and 20C. . . . . . . . . . . . . 7. Effect of raspberry fruit weight on steady- state 02 and CO2 partial pressures in sealed packages with (O) and without CaO(v) where A = 400 cm2, Ax = .00521 cm LDPE and held at 20c. . . . . viii Page 26 28 29 33 34 35 37 Figure Fig. Fig. Fig. Fig. Fig. Fig. Fig. fig. 8. Effect of steady-state C5 partial pressures on the rate of O uptake for raspberry fruit sealed packages with (O) and without (v) CaO and matched with a Michaelis-Menten equation. . . . . . . . . 9. Effect of steady-state O2 partial pressures on headspace ethanol vapor concentration for raspberry fruit sealed in packages with (O) and without (v) CaO. . . . . . . . . . . . . . . . . CHAPTER 2 1. Effect of 2changing the ratio of package surface area umnz) to film thickness (cm) and fruit weight on steady-state 02 for 'Honeoye' strawberry stored at temperatures of 25 , 20,15, 10, 5, and 0C. . . . . . . . 2. Effect of 2changing the ratio of package surface area unnz) to film thickness (cm) and fruit weight on steady-state 02 for 'Allstar' strawberry stored at temperatures of 25 , 20,15, 10, 5, and 0C. . . . . . . . 3. Effect of 2changing the ratio of package surface area umnz) to film thickness (cm) and fruit weight on steady-state CO2 for 'Honeoye' strawberry stored at temperatures of 25 , 20,15, 10, 5, and 0C. . . . . . . . . 4. Effect of 2changing the ratio of package surface area umnz) to film thickness (cm) and fruit weight on steady-state CO2 for 'Allstar' strawberry stored at temperatures of 25 , 20,15, 10, 5, and 0C. . . . . . . . . . . . 5. Interdependent effects of steady- -state 02 partial pressures and storage temperature on the calculated rate of 02 uptake for 'Honeoye' strawberry fruit sealed in LDPE packages. See Eq. [9] and Table 2 for the equations and constants describing the curves. . . . . . . . . . 6. Interdependent effects of steady-state O2 partial pressures and storage temperature on the calculated rate of 02 uptake for 'Allstar' strawberry fruit sealed in LDPE packages. See Eq. [9] and Table 2 for the equations and constants describing the curves. . . . . . . . . . . . . . . ix Page 39 41 69 70 72 74 76 78 Figure Fig. Fig. Fig. Fig. Fig. Fig. '7. Effect of steady-state O2 ;partial pressure and. storage temperature on the respiratory quotient of 'Honeoye' strawberry fruit sealed in LDPE packages. See Eq. [10] and Table 3 for the equations and constants describing the curves. . . 8. Effect of steady- -state 02 partial pressure and storage temperature on the respiratory quotient of 'Allstar' strawberry fruit sealed in LDPE packages. See Eq. [10] and Table 3 for the equations and constants describing the curves. . . 9. Interdependent effects of steady-state O2 partial pressure and storage temperature on headspace ethanol vapor concentration for 'Honeoye' strawberry fruit sealed in LDPE packages. . . . . . . . . . 10. Interdependent emffects of steady- -state 02 partial pressure and storage temperature on headspace ethanol vapor concentration for 'Allstar' strawberry fruit sealed in LDPE packages. . . . . . . . . . . . . . . . . . . . . CHAPTER 3 1. Predicted changes in [02 ]ka and [COM] as a function of temperature and 9film permegbility characteristics for 'Allstar' strawberry fruit from Eq. [3] and Eq. [8] with constants from Table 1 and Chapter 2. The dotted line on each graph represents the lower 0 limit for 'Allstar' strawberry fruit as determined by the increase in RQ and ethanol content (Chapter 2). . . . . . . 2. Predicted changes in [02 ]pg and [COM] as a function of temperature and film permegbility characteristics for 'Heritage' raspberry fruit from Eg. [3] and Eq. [8] with constants from constants Table 2 and Chapter 1. The dotted line on each graph represents the lower 0 limit for 'Heritage' raspberry fruit as determ1ned by the increase in RQ and ethanol content (Chapter 1). Page 80 82 84 86 108 109 Figure Fig. Fig. 3. Predicted changes in [OZ]pkg and [C02]pk as a function of temperature and film permeébility characteristics for 'Heritage' raspberry fruit and 'Allstar' strawberry fruit from Eq. [3] and Eq. [8] with the film permeability characteristic being a E8 of 37 and a permeability ratio of 1.0. 4. The change in absorbance at 460 nm over time for a ethanol sensing film at 25C exposed to a ethanol vapor partial pressure of .006 kPa and to 150 vapor. . . . . . . . . . . . . . . . . . . xi Page 111 113 CHAPTER 1 MODIFIED-ATMOSPHERE PACKAGING OF 'HERITAGE' RED RASPBERRY FRUIT: THE RESPIRATORY RESPONSE TO REDUCED OXYGEN, ENHANCED CARBON DIOXIDE AND TEMPERATURE Abstract. Raspberry (Rubu§:idaeus L. 'Heritage') fruit were sealed in low density polyethylene packages and stored at 0, 10, and 20C during the Fall of 1990 and 1991. A range of steady-state O2 and C02 partial pressures were achieved by varying fruit weight in packages of a specific surface area and film thickness. Film permeability to O2 and CO2 was measured and combined with surface area and film thickness to estimate total package permeability. Rates of‘CQ uptake, (KR production and RQ were calculated using steady-state O2 and C02 partial pressures, total package permeability, and fruit weight. The rate of'Ch uptake was found to decrease with a decrease in 02 partial pressure over the range of partial pressure studied. A model was developed for the rate of 02 uptake as a function of 02 partial pressure and temperature, using the Michaelis-Menten equation with me changing exponentially with temperature. Estimated me values approximately doubled with each 10C increase in temperature and the apparent KIn 0%) was estimated to be 5.59 kPa 05 for fruit at 0, 10, and 20C. RQ as a function of 02 partial pressure and temperature was fitted with an exponential equation. Combining the RQ equation with the Michaelis-Menten equation allows CO2 production to be predicted over temperature and the range of'Cb partial pressures generated. We found that headspace ethanol increased at RQs above 1.3 to 1.5. Based on RQ, ethanol production, and taste, we recommend that raspberries be held at 02 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C. Steady-state C02 partial pressures of 3 to 17 kPa generated after 3 days at 20C had little or no effect on 02 uptake and headspace ethanol concentrations. Introduction Raspberries are a very perishable commodity, in part due to high rates of respiration and transpiration, a morphology that predisposes them to crushing, and susceptibility to gray mold fruit rot. Techniques providing even a relatively short extension of shelf life could have a profound effect on fresh-marketing of raspberry fruit. Exposure to COg levels of 20% or greater has been shown to delay gray mold decay of raspberries and extend shelf life (Goulart et al., 1992; Smith, 1958; Winter et al., 1939). Elevated C02 has also been shown to improve firmness of strawberry fruit (Smith, 1992). No research has yet demonstrated a beneficial effect of reduced oxygen for raspberries. Modified-atmosphere (MA) packaging has the potential to provide suitable atmospheres to extend shelf life of raspberry fruit. In an MA package, steady-state package partial pressures of 02 ([02] ) and C02 ([C02] ) are pkg pkg achieved when the rates of 02 uptake and CO2 production by the fruit are equal to the rates of 02 and C02 flux through the film (Beaudry et al., 1992; Cameron et al., 1989). In MA packaging, [C05] cannot be elevated without W9 some reduction in [Oil The extent of the reduction in 02 Pkg' and elevation of C02 depends on the rates of 02 uptake and (K5 production of the fruit and the permeability of the polymer barrier to 02 and C02. Thus, to design an MA it is package for raspberries with elevated [C02L*g, 5 and elevation of C02 depends on the rates of 02 uptake and (X5 production of the fruit and the permeability of the polymer barrier to 02 and C02. Thus, to design an MA package for raspberries with elevated [COZL*9, it is necessary to know the rates of C02 production and 02 uptake as influenced by reduced 02 and elevated C02 partial pressures. Burton (1978) reported that raspberries stored in 2-3% 02 developed off-flavors. When 02 around fruits falls below some critical level, there is a shift from aerobic to anaerobic respiration, with associated ethanol production and eventually off-flavor development (Kader, 1986). The extent of anaerobic metabolism can be measured as an increase in the RQ, since ethanol production involves decarboxylation of pyruvate without uptake of 02° Beaudry et a1. (1992) found that the critical 02 level for blueberries (defined as the partial pressure of’C5 where an increase in RQ was noted) increased with temperature. Thus, it is important to define a critical lower 0% limit for raspberries over a range of possible storage temperatures. Several authors have assumed that elevated [C02]pkg can effect the rate of 02 uptake of fresh produce (Hayakawa et al., 1975; Henig and Gilbert, 1975; Lee et al., 1991; Song et al., 1992), although there is little direct supporting evidence to our knowledge. We addressed this question by generating a range of [02] and [€02]ka levels using MA 9w packages (Beaudry et al., 1992; Cameron, 1990) and adding CaO as a.Cx5 absorber to a similar group of packages. Thus, 6) it was possible to determine 02 uptake as a function of [02]Inks in the presence and absence of generated C02. The objectives of this study were to use the technique described by Beaudry et al. (1992) to investigate the influence of [02] [C05] and temperature on the rates of Pkg' pkg 02 uptake and C02 production and on the 02 partial pressure at the RQ breakpoint for 'Heritage' red raspberry fruit. Another objective of this study was to compare the respiratory behavior of fruits harvested at different times in the season. 7 Materials and Methods Plant material On 20 Sept. 1990, 15 Oct. 1990, and 9 Sept. 1991, fruit of 'Heritage' red raspberry were hand-harvested from Gibb's Farm in Onondaga, Mich., and spread three to four berries deep in coolers containing ice. A sheet of plastic film was placed over the ice to prevent direct contact. After transportation to Michigan State University, the fruit were sorted and packaged immediately. Packaging During Sept. 1990, fruit weights of approximately 5, 7.5, 10, 12.5, 15, 17.5, 22.5, 27.5, 37.5, and 50 g were sealed in packages made of low density polyethylene (LDPE) (Dow Chemical, Midland, Mich.) and placed in 0 and 10C. Fruit weights of approximately 5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 30, 37.5, and 45 g were sealed into packages placed at 20C. For fruit at 10 and 20C, surface area was 300 cm2 (10 x 15 cm) and film thickness was .00521 cm (2 mil.). For packages placed at 0C, film thickness was .00766 cm (3 mil.) with the same surface area. In Oct. 1990, fruit weights of approximately 3, 5, 7.5, 10, 12.5, 17.5, 22.5, and 30 g were sealed into packages and placed in 10 and 20C. Surface area and thickness were the same as the September harvest. Five and six replications per target weight were used in the October and September experiments, respectively. To avoid crushing of the fruit, a rigid support was placed inside each package consisting of a cellulose acetate 8 strip (2.5 cm wide, 30 cm long and .0508 cm thick) and a 3- inch x 5-inch note card. The fruit rested on the note card and the cellulose acetate strip encircled the fruit. Every package had a gas sampling septum attached, consisting of a dab of Dupont Silicone II tub/tiling glue on a short strip of electrical tape (Boylan-Pett, 1986). For the 1991 experiment, packages were constructed of 2-mil (.00521 cm) LDPE film with a surface area of 400 cm2 (10 x 20 cm). Target weights were 5.5, 13.5, 18, 28, and 48 g with eight packages at each target weight. A 10 x 12 cm spunbonded polyethylene pouch (Tyvek type 1059B, Dupont, Wilmington, Del.) was constructed containing CaO (98%, Aldrich, Milwaukee, Wis.) as a.CI§ scrubber (1 g CaO per 10 g fruit). A pouch was included in half of the packages at each weight. Film permeability Film permeability was measured for three film samples taken from various locations in the 2-mil and 3-mil rolls, using the system described by Beaudry et a1. (1992). Each sample was individually sealed in a permeability cell and submerged in a water bath. The permeability cell contained two chambers which were separated by the film sample. A gas mixture of O2 and CO2 was directed into one chamber and pure 1% gas into the other (100 ml-min”). The appearance of 02 and CO2 was continuously monitored in the N2 stream, using a sequential arrangement of O2 (Ametek S-3A/II with a calcia- zirconia electrochemical detection cell; Ametek Co., Thermox 9 Instrument Div., Pittsburgh) and CO2 (ADC 225-Mk3 analytical infrared gas analyzer; Analytical Development Co., Hertfordshire, England) analyzers. By altering water bath temperature, permeabilities were measured at 5C intervals between 0 and 30C. Each film sample was measured over the entire temperature range three to five times. The Arrhenius equation was used to describe permeation of gases through polymers and can be expressed as: P- = A,‘ exp (- E8) [1] I where Pi is permeability to 02 or CO2 (mmole°cm-cm’2'h'1'kPa' 1); E8 is the energy of activation of 02 or CO2 permeation (kJ'molq); and R is the gas constant (.0083144 kJ-molq°K”) (Pauly, 1989). Regression analysis was performed on transformed data to estimate values of Ea, the Arrhenius constant Ar and correlation coefficients (Table 1). Appropriate Ea.and AT‘values were substituted into Eq. [1] to calculate PQ-A/Ax and RmfA/AX at 0, 10, and 20C (Table 2). Gas analysis and respiration rate calculations Headspace O2 and CO2 partial pressures were determined by withdrawing two 0.5 ml samples from packages using an insulin-type syringe and injecting into a Nélgas stream (150 to 200 m1-min'1 flow rate) which was connected to the sequential O2 and C02 analyzers described above. Response time was 10 s per sample. To avoid sampling errors, a third sample was taken if any difference was noted between the first two samples. 10 Headspace ethanol concentrations were determined by withdrawing two 0.5-ml samples from the package headspace using a glass syringe (0.5 m1 Gastight #1750; Hamilton Co., Reno, Nev.). Gas analysis was performed on a Carle Series 100 gas chromatograph (Hach Co., Loveland, Colo.) equipped with a Haysep 80/100 porous polymer column (Alltech Assoc. Inc., Deerfield, 111.). Column temperature was 120C and the flow rate of the N2 carrier gas was 100 ml;min". Ethanol analysis of the 1990, September-harvested fruit at 20C showed a large amount variability between replicated packages. To reduce variability in future experiments, the time from sampling to analysis was minimized and needles were checked to ensure that they were not plugged with silicone from the sampling septum. The time to reach steady-state O2 and CO2 levels was estimated by measuring [02] pkg and [C02]pkg over t1me 1n separate packages containing the lowest and highest fruit weights for each storage temperature. When no further change in [OZ]pkg and [C02] was detected in these packages, W9 gas analysis was performed on all the packages at that temperature. Gas analysis was performed after 12 days at 0C, 7 days at 10C, and 3 days at 20C. Respiration rates were calculated using the following formulae: 1302- A T ([OZJatm ‘ [021pkg) [2] Ro2 = W 11 co,‘ A _ T ([C02]pkg I [C02]atm) [3] RC0; _ w where R02 and Rcoz are the rates of 022 uptake and CO2 production (mmol-kg'1-h’1), respectively; P02 and Pcoz are permeability coefficients for O2 and CO2 (mmol°cm1°cm'2hour' 1-kPa'1), respectively; A is film area (cmz); Ax is film thickness (cm); [02]atm and [02] are atmospheric and package Pkg 02 partial pressures (kPa), respectively; [C02] and [C02] pkg atm are package and atmospheric C02 partial pressures (kPa) , respectively; and W is fruit weight (kg) (Beaudry et al., 1992) . The relationship of 02 uptake to [02] and pkg temperature was fitted using the Michaelis-Menten equation: Vmax . [02’]ka Kyz + [02] R02 = [41 Pkg 1% in this equation was substituted for the standard Km notation because this estimate is an apparent K% of the entire fruit which also takes into account skin resistance to gas diffusion. Vim was modeled as a function of T: o . 1o [5] where Romf'ois the maximum rate of 02 uptake at 0C, Q10 is the increase in 02 uptake for every 10C increase in temperature, and T is temperature in C. Substituting Eq. [5] into Eq. [4] yielded: 12 T (mjxfi. Q 10) [02:1ka [6] A nonlinear regression analyéfis 9%fl95timate the values of 1%, a, and b was conducted on SAS (SAS Institute Inc., Cary, NC) using the data set from the September-harvested fruit at 0, 10, and 20C. K1. was originally modeled as a function of temperature but regression analysis revealed that it was constant over the temperatures studied. The RQ was calculated as Rco, divided by R02. The relationship between RQ, steady-state 02,.and temperature was fitted with the model: RQ : q 'Exp( r '7P) +-l [02]pkg [7] Nonlinear regression analysis was conducted on SAS to estimate the values of q and r. No postharvest fungicide treatments were used on these fruit. Data was not taken from packages with obvious holes or moldy fruit. 13 Results Steady-state 02, (:02, and respiration rates Increasing fruit weight in a package decreased steady- state 02 and increased steady-state CO2 at 0, 10, and 20C (Fig. 1). The choice of fruit weights resulted in a range in [02]pkg from under 1 to 10 kPa at 0C and 1 to 12 kPa at 10 and 20C. Steady-state [C01] ranged from 1 to 8 kPa at 0C, pkg 1 to 10 kPa at 10C, and 1 to 13 kPa at 20C. Ky, was found to be 5.59 kPa 02 at 0, 10, and 20C while Vfim approximately doubled with each 10C increase in temperature (Table 3). A decrease in [05] slowed R02 (Fig. mg 2) and Rec, (Fig. 3) at all temperatures. R and R02 of the cm October-harvested fruit were consistently higher than the September-harvested fruit (Figs. 2 and 3), although the difference were not significant. The RQ increased gradually as [05] decreased from 10 M9 to 6 kPa but climbed more rapidly at lower [0?] levels D“ (Fig. 4). October-harvested fruit had a slightly higher RQ value at higher [0?] levels and showed a less definite “a increase in RQ at lower [05] levels. Values for the model mg (Eq. [7]) describing the relationship of R0 with [02]pkg and as a function of temperature are presented in Table 4. R€02 [C51fle' at any of the temperatures and harvests studied, can be calculated by multiplying the equation for R0 (Eq. [7]) by the equation for 02 uptake (Eq. [6]) . Headspace ethanol concentrations and RQ followed a similar trend with [05] at 10 and 20C (Figs. 5 and 6). W9 Headspace ethanol concentrations at 0C were low until [Ozhmg l4 dropped below z3 kPa and then increased sharply. For each harvest and temperature, headspace ethanol was relatively low at RQs below z1.3 and increased at RQs greater than 1.3 to 1.5 (Fig. 6). September-harvested fruit at 20C showed a high amount of variability in their headspace ethanol concentrations (Figs. 5 and 6) which may have been due in part to sampling errors (see Materials and Methods). Packages with and without Cao In packages containing CaO, [C03] was 0.1 kPa or m9 less, while in packages without CaO, [C202]pkg ranged from 3 to 17 kPa (Fig. 7). Rm values were similar for packages with and without CaO (Fig. 8). The Kyls (02 kPa) were 4.09 (SE=i.84) and 4.31 (SE: i.60) for packages with and without CaO, respectively. Vmax values (02 uptake mmol-kg"°h'1) were 3.09 (SE=:.26) and 3.62 (SE=i.22) for packages with and without CaO, respectively. The 95% confidence intervals showed that these coefficients were not significantly different. Headspace ethanol vapor as a function of [021‘3kg was similar for packages with and without CaO (Fig. 9). 15 Discussion The effect of elevated C0.2 partial pressure on the respiratory rate of a fruit or vegetable is dependent on the commodity and level of’CI5 used (Kidd, 1916; Kubo et al., 1990; Mangin, 1896; Thornton, 1933). Some general models describing'cg uptake of fresh produce in MA atmospheres have been based in part on the assumption that elevating C02 partial pressure to any level will inhibit.C§ uptake (Hayakawa et al., 1975; Henig and Gilbert., 1975; Lee et al., 1991; Song et al., 1992). Elevated.CI5 has been reported to reduce 02 uptake in some climacteric fruit (Kerbel et al., 1988; Kubo et al., 1990; Young et al., 1962). For raspberries, there was no evidence that CO2 partial pressures of 3 to 17 kPa altered the rate of 02 uptake (Fig. 8). The rate of'Ch uptake by blueberries and grapes have been shown to be unaffected by C02 partial pressures up to 60 kPa (R.M. Beaudry, in press; Kubo et al., 1990) . We found elevated C02 partial pressures of 20 to 30 kPa had little if any effect on Og'uptake by 'Heritage' red raspberries in reduced 02 atmospheres (D.W. Joles, C. Talasila, and A.C. Cameron, unpublished data). Thus, 02 uptake by raspberries in our MA packages could be described as a function of'CE partial pressure and temperature only (Eq. [6] and Table 3). Beaudry et al. (1992) found for blueberries that an anaerobic RQ breakpoint was sharply defined and on this basis was able to identify lower 02 levels as a function of temperature. For raspberries, RQ increased gradually with 16 decreasing 02 which made it difficult to define a clear lower 02 limit based on RQ breakpoint. In addition, RQ of aerobic fruit at 0C was approximately 1.0 whereas at 10 and 20C, aerobic fruit had an RQ of zl.3 (Fig 4). Ethanol production also increased gradually with decreasing Ozaat 10 and 20C with no clear breakpoint (Fig 5). At 0C, ethanol production increased relatively sharply as 05 fell below 3 kPa. In general, ethanol production did not increase substantially until the RQ rose above 1.3 to 1.5 (Fig 6) which approximately corresponded to 0% levels of 3 to 4 kPa at 0C, 5 to 6 kPa at 10C, and 6 to 8 kPa at 20C (Fig. 4). RQ levels above 1.0 without substantial ethanol production may have been due to the utilization of organic acids as the primary respiratory substrate or localized anaerobic respiration combined with partial ethanol metabolism. The correlation between RQ, headspace ethanol, and decreasing 02 observed at 10 and 20C (Figs. 4, 5, and 6) supports the latter explanation, while at 0C the gradual increase in RQ contrasted with the sharp break in ethanol production (Fig. 5) may indicate that organic acid oxidation results in a RQ increase up to a level of z1.3. In informal taste tests, we noted off-flavors when 02 levels fell below z3 kPa at 0C and #5 kPa at 10 and 20C. This approximately correlates with the 02 partial pressure .where RQ exceeded 1.3 to 1.5 at each temperature. We recommend, based on RQ, ethanol production, and taste, that raspberries be held at.C5 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C, in order to avoid anaerobic induction l7 and the possibility of off-flavor development. It should be noted that raspberries are very sensitive to reduced oxygen levels. For instance, the anaerobic induction point for blueberries at 0C was found to be 0.5 kPa (Beaudry et al., 1992) whereas for raspberries at 0C, it was not less than 3 kPa. I In packages with and without a.CI5 scrubber, headspace ethanol concentrations as a function of'C5 partial pressures were very similar (Fig. 9) which indicates that anaerobic induction was not influenced by the elevated CO: levels generated in these packages. Its been reported that an atmosphere of z20 kPa CO2 retards molds and extends shelf life of raspberry fruit (Goulart et al., 1992; Smith, 1958; Winter et al., 1939). Mold development was retarded for at least a day in packages with CO2 partial pressures above 15 kPa (data not shown). However, using LDPE, 02 levels at these C02 partial pressures were anaerobic (Figs. 1 and 7). All polymer films have a higher permeability to C02 than to O2 (Pauly, 1989). Thus, by using polymer films, beneficial (£5 levels (#20 kPa) cannot be reached without the induction of anaerobic respiration. C5 diffuses approximately 25% faster than CO2 in air which infers that the permeability of a perforation to 0% is 1.3 times higher than the permeability to C02. If a package were designed by selection of an appropriately sized perforation to maintain 10 kPa 02,,and if RQ was zl.3, then 18.5 kPa CO2 could be generated at steady-state. However, permeation through a hole changes relatively little 18 with temperature, while 02 uptake by raspberry fruit approximately doubles with a 10C increase in temperature (Eq. [6] and Table 3). Thus, anaerobic conditions could develop if perforated packages experience an increase in temperature. These are factors which will need to be incorporated into an effective MA package system designed for raspberries. 19 List of References Beaudry, R.M., A.C. Cameron, A. Shirazi, and D.L. Dostal- Lange. 1992. Modified atmosphere packaging of blueberry fruit: Effect of temperature on package 02 and C02. .J. Amer. Soc. Hort. Sci. 117:436-441. Boylan-Pett, W. 1986. Design and function of a modified atmosphere package for tomato fruit. MS Thesis, Michigan State Univ., East Lansing. Burton, W.G. 1978. Biochemical and physiological effects of modified atmospheres and their role in quality maintenance, p. 97. In: H.O. Hultin and M. Milner (eds.). Post-harvest biology and biotechnology. Food and Nutrition Press, Westport, Conn. Cameron, A.C., W. Boylan-Pett, and J. Lee. 1989. Design of modified atmosphere packaging systems: Modeling oxygen concentrations within sealed packages of tomato fruits. J. Food Sci. 54:1413-1416, 1421. Cameron, A.C. 1990. Modified atmosphere packaging: A novel approach for optimizing package oxygen and carbon dioxide. Proc. 5th Int'l. CA Conf., Wenatchee, Wash., 14-16 June. Goulart, B.L., P.E. Hammer, K.B. Evensen, W. Janisiewcz, and F. Takeda. 1992. Pyrrolnitrin, Captan + Benomyl, and high CO2 enhance raspberry shelf life at 0 or 18C. J. Amer. Soc. Hort. Sci. 117:265-270. Hayakawa, K., Y.S. Henig, and S.G. Gilbert. 1975. Formulae for predicting gas exchange of fresh produce in polymeric film package. J. Food Sci. 40:186-191. Henig Y.S. and S.G. Gilbert. 1975. Computer analysis of the variables affecting respiration and quality of produce packaged in polymeric films. J. Food Sci. 40:1033-1036. Kader, A.A. 1986. Biochemical and physiological basis for effects of controlled and modified-atmospheres on fruits and vegetables. Food Technol. 40(5):99-104 Kerbel, B.L., A.A. Kader, and R.J. Romani. 1988. Effects of elevated.Cm5 concentrations on glycolysis in intact 'Bartlett' pear fruit. Plant Physiol. 86:1205-1209. Kidd, F. 1916. The controlling influence of carbon dioxide. Part III. The retarding effect of carbon dioxide on respiration. Proc. Royal Soc. (London) 89:136-156. 20 Kubo Y., A. Inaba, and R. Nakamura. 1990. Respiration and egg production in various harvested crops held in cof- enriched atmospheres. J. Amer. Soc. Hort. Sci. 115:975-978 Lee, D.S., P.E. Haggar, J. Lee, and K.L. Yam. 1991. Model for fresh produce respiration in modified atmospheres based on principles of enzyme kinetics. J. Food Sci. 56(6):1580-1585. Mangin, L. 1896. Sur la vegetation dans une atmosphere viciee par 1 a respiration. Compt. Rend. Acad. Sci. (Paris) 122:747-749. Mason, D.T. 1974. Measurement of fruit ripeness and its relation to mechanical harvesting of the red raspberry (Rubus idaeus L.). Hort. Res. 14:21-27. Pauly, S. 1989. Permeability and diffusion data, p. 435- 449. In: Polymer handbook IV. 3rd ed. Wiley, New York. Robbins, J., T.M. Sjulin, and M. Patterson. 1989. Postharvest storage characteristics and respiration rates in five cultivars of red raspberry. HortScience 24:980-982. SAS Insitute. 1989. SAS/STAT user's guide. Version 6. Vol. 2. 4th ed. Cary, N.C. Sjulin, T.M. and J. Robbins. 1987. Effects of maturity, harvest date, and storage time on post-harvest quality of red raspberry fruit. J. Amer. Soc. Hort. Sci. 112:481-487. Smith, R.B. 1992. Controlled atmosphere storage of 'Redcoat' strawberry fruit. J. Amer. Soc. Hort. Sci. 117:260- 264. Smith, W.H. 1958. The harvesting, precooling, transport, and storage of strawberries and raspberries. Food Invest. Board Misc. Paper 1058. Song, Y., H.K. Kim, and K.L. Yam. 1992. Respiration rate of blueberry in modified atmosphere at various temperatures. J. Amer. Soc. Hort. Sci. 117:925-929. Thornton, N.C. 1933. Carbon dioxide storage III. The influence of carbon dioxide on the oxygen uptake by fruits and vegetables. Contrib. Boyce Thompson Inst. 5:371-402. Winter, J.D., R.H. Landon, and W.H. Alderman. 1939. Use of carbon dioxide to retard the development of decay in 21 strawberries and raspberries. Proc. Amer. Soc. Hort. Sci. 37:583-587. 22 Table 1. Activation energies (Ea ), Arrhenius constants (A.), and correlation coefficients (r 2) for .00521 and .00766 LDPE film. Values were obtained from linear transformations of the equation: P = Ar ' exp(- Ea-/R T) where2 P is permeability to 02 or C02 (mmole cm cm2 h kPa ); Eia is the energy of activation of 02 or CO2 permeation (kJ mol 1); and R is the gas constant 2(. 0083144 kJ mol ) (Pauly, 1989). Film thickness (GNU Ea Ar r2 .00521 P02 38.11 .1312 .945 Pm2 35.55 .2183 .957 .00766 P 36.85 .0700 .968 Pco2 35.34 .1771 .971 23 Table 2. Whole package 02 and C0 permeabilities (Po'A/Ax and PCO°A/Ax, respectively) or the packages uséd in these experiments at 0, 10 and 20C. Appropriate values were substituted into Eqs. [2] and [3] to calculate O uptake and C02 production for fruit at 0, 10, or 20C. Temp P02'A/ Ax Pco,.A/ Ax Pcoz/ P02 (C) (mm61~h4-kpa4) o 2.443 x 10* 1.200 x 10'3 4.91 10 6.967 x 10* 3.444 x 10‘3 4.94 20 12.11 x 10* 5.769 x 10'3 4.76 24 Table 3. Constants for Michaelis-Menten (Eq [6]) equation describing the relationship between 02 uptake (mmol kg' °"h ), steady-state 02 partial pressure (kPa) , and temperature for raspberry fruit sealed in LDPE pouches and stored at various temperatures. The constants of the Michaelis-Menten equation were estimated by non- linear regression analysis. max.0 19, SE 1102 SE (210 SE 5.59 1.40 .872 .20 H- .04 1.92 H- 25 Table 4. Estimated values for Eq. [7], describing the relationship between calculated RQ, steady-state 02 partial pressure (kPa) and temperature for September- harvested raspberry fruit stored at 0, 10, and 20C. q x r % 1.43 1.09 .053 1.002 26 Fig. 1. Effect of raspberry fruit weight on steady-state 02 (circles) and C02 (triangles) partial pressures for September (open symbols) and October-harvested (closed symbols) raspberry fruit sealed in LDPE packages where A= 300 cm2, Ax = .00521 cm for packages at 10 and 20C, and A = 300 cm2,.Ax = .00766 cm for packages stored at 0C. 27 N O 3 V I S [1 16-200 g .16 g; V12_~§ W V g 8 0° V 5% Vvvgv j $§€v (f) ‘- o 4» 9 § 0 '5'; .&%é%em 0 Q — 10C O 16 t 12~ g §7 O w [1 8_ v; (0 ' 4 O - g 16- OC 1 12~ v g VV % 8‘ 8 v g7 v 9 _ 0% g 8 £9” 4—4 4— U) "97 $0 6 3 O . . . . . .4. . 6 0 110 20 30 4O 50 l 60 Fruit Weight (g) 28 Fig. 2. Interdependent effects of steady-state C5 partial pressures and storage temperature on the calculated rate of’Cb uptake for September (0) and October- harvested (D) raspberry fruit sealed in LDPE packages. See Eq. [6] and Table 3 for the equations and constants describing the curves. O2 Uptake (mmolkg‘1h“1) 4.0 3.0 - 2.0 ~ 1.0- 0.0 1.5- 1.0- 0.5 - 0.0 0.8 - 0.6 P .4: 0.2 ; 0.0 1 29 l l l l 2 4 6 811011214 Steady—state 02 (kPa) 30 Fig. 3. Interdependent effects of steady-state:C5 partial pressures and storage temperature on the calculated rate of'CT) production for September (0) and October- harvested (U) raspberry fruit sealed in LDPE packages. CO2 Production (mmol kg“ h“) 6.0 4.5 - 3.0 1.5 l 0.0 i 2.4 ~ 0 ’ u : '\ ‘0‘ . :3. 0' .I. \. 0.0 0.6 ~ 0.4 ~ 0.2? 0.0 31 06‘ 0 i 4 6 611011214 Steady—state 02 (kPa) Fig. 32 4. Effect of steady-state C5 partial pressure and storage temperature on the respiratory quotient of September (0) and October-harvested (U) raspberry fruit sealed in LDPE packages. See Eq. [7] and Table 4 for the equations and constants describing the curves. Respiratory Quotient ..._.\ 33 [QM-PU”! l {\DCN-PO l l l l l 4 2 4 6 8 10 12 Steody—stote 02 (kPa) i4 34 Fig. 5. Interdependent effects of steady-state C5 partial pressure and storage temperature on headspace ethanol vapor concentration for September (0) and October- harvested (D) raspberry fruit sealed in LDPE packages. 35 500 400 __ (33 O gogept i 300- O D Oct - SE A 200 ~ gm 0 ‘— CJCtit] ' 100 - o :9 D i 00996598? 9g. a a 31 0 ~ 1 . -mi \_./ O . . . s— 126 - p 106 o 00 o_ 100 ~ O D > 75 — Q] [[1] 5 50 @389089 5 25- gjficggm GED _C O . . 0%. @®DCEBOLQ CE 4 , r . . 6O ' 0 DC 0 2 4 6 10 12 14 Steady—state 02 (kPa) 36 Fig. 6. Relationship of headspace ethanol vapor concentration and the respiratory quotient measured for September (0) and October-harvested (D) raspberry fruit sealed in LDPE packages and stored at 0, 10, and 20C. Ethanol Vapor (MIL—1) 500 400 - 300 ~ 200 - 100 ~ 125~ 100- 75- 50- 25- 60- 37 Respiratory Quotient o 0 Sept 0 U 001 mg 0 (x9 DD 0 OO 043% 9 0 O 0 469 . . i “', f , 0: 10C 000 O o 5? 0C 1 2 3 4 38 Fig. 7. Effect of raspberry fruit weight on steady-state O2 and.Cr> partial pressures in sealed packages with (O) and without CaO(v) where A = 400 cmz, Ax = .00521 cm LDPE and held at 20C. 39 2v n." s- f . . r 1 av v n.“ @v. 0 . . O 1 4 OC iv o o .59 01L Cw 86 a o 96. “mm . . - WWW. o v v a v8 0 6 2 00 A. O 6 2 00 A. O 2 1.. .l 3%; .oo Baumixeoflm 8%: No 8661685. 20 30 40 50 60 10 Fruit Weight (g) 40 Fig. 8. Effect of steady-state C5 partial pressures on the rate of<3 uptake for raspberry fruit sealed packages with (O) and without (v) CaO and matched with a Michaelis-Menten equation. 8%: .o Boomixeoflm we or m m .6 m 41 — — q _ «$w. \sw.’ .\ ‘ x \s. NOV 0 D 0.5. O 55.7 D . p o % t D . 08 565.12, 6 08 £5) 0 — _ _ — _ (.94 JM IOUJUJ) 9>101an0 42 Fig. 9. Effect of steady-state C5 partial pressures on headspace ethanol vapor concentration for raspberry fruit sealed in packages with (O) and without (v) CaO. 43 8%: No Boomlxeofim 1:. Ne or m m tn N D 064 0 _ u a _ o 60%» o o . 6. R50 Op 0 D o I %0 DO - o e W. . 08 59:5 6 am. 08 £5 0 ooh OON 00m 00¢ 00m 000 (1—1 .| 77’) JodoA lououg CHAPTER 2 MODIFIED-ATMOSPHERE PACKAGING OF STRAWBERRY FRUIT: CHARACTERIZING RESPIRATION AS A FUNCTION OF 02 AND TEMPERATURE 44 45 Abstract. Fruit of two strawberry cultivars (Fragaria x ananassa D. 'Honeoye' and 'Allstar') were sealed in low density polyethylene packages and stored at 0, 5, 10, 15, 20, and 25C. A range of steady-state 02 (.2 to 16 kPa) and (X5 partial pressures (30 to 2 kPa) were achieved by varying package surface area, package thickness and fruit weight. Package surface area and thickness were combined with measured permeability coefficients to determine total package permeability. Total package permeability was then used with steady-state 02 and C02 partial pressures and fruit weight to calculate the rates of C5 uptake, CO2 production, and respiratory quotient (RQ). A decrease in 02 partial pressure to zs kPa did not noticeably reduce the 02 uptake of these fruit. A detailed mathematical model was developed to characterize 02 uptake as a function of 02 partial pressure and temperature. This model combined the Michaelis-Menten equation for describing C5 uptake as a function of internal C5 and skin permeability to 02. 'Honeoye' and 'Allstar' fruit had similar C5 uptake rates although 'Honeoye' C5 uptake was reduced at slightly higher (5 levels and had a lower estimated value for skin permeability to 02. The Q10 for 02 uptake was estimated to be z2.4 and the apparent Km Hg) was estimated to be z.35 kPa 02 for both cultivars. RQ as a function of 02 and 1 temperature was fitted with an exponential equation. 46 Combining this RQ model with the model for'C5 uptake allows estimation of CO2 production as a function of 02 and temperature. Based on an increase in R0 and ethanol content, we estimated the lower 05 limits for safe storage to be approximately 0.4 at CC, 0.5 at BC, 0.7 at 10C, .9 at 15C, 1.2 at 20C, and 2.0 at 25C for both cultivars. These estimates are similar to previously reported values. 47 Introduction It has been well documented that elevated CO2 levels (10 to 20%) extends strawberry shelf life (Thornton, 1931; Winter et al., 1940: Anderson and Hardenburg, 1959: Couey and Wells, 1970: Woodward and Topping, 1972: Ben-Yehoshua et al., 1975: El-Goorani and Sommer, 1981; Kader et al., 1989; Smith, 1992). It has also been reported that combining low 02 levels (1 to 2%) with elevated CO2 levels (15 to 20%) may help extend strawberry shelf life (Li and Kader, 1989). Modified-atmosphere (MA) packaging has the potential to provide beneficial elevated CO2 and low 02 atmospheres. In fact, recently a California-based company has announced the development of a commercial MA package which utilizes specially microperforated films (Anonymous, Packer, 1990). They claim the use of their package nearly doubles strawberry shelf life although some distributors have noted that mold decay in these packages is still a problem (Anonymous, Packer, 1990). In an MA package, steady-state package partial pressures of O2 ([02]pkg) and C02 ([C02] ) are achieved when pm the rates of 02 uptake and C02 production by the fruit are equal to the rates of O2 and CO2 flux through the film or perforation(s) at that temperature (Beaudry et al., 1992: Cameron et al., 1989). Thus, to design an MA package for strawberries which has beneficial [02] and [€02]ka levels M9 at a desired storage temperature, the fruit's rate of 02 uptake and C02 production at those 02 and C02 levels and temperature must be known. Once these rates are known, the 48 strategy is to select a film which permits a gas flux equal to these rates. Couey et a1. (1966) reported that off-flavors were present in strawberries treated with 05 levels of .25% or below at 3C. This was confirmed by Ke et al. (1991) who also showed that off-flavors were positively correlated ethanol content. Exposure of fruit tissue to 05 levels below their lower tolerance limit induces anaerobic respiration which leads to ethanol production and eventually to off-flavor development (Kader et al., 1989). For raspberries, it was found that at a lower 02 limit, an increase in ethanol content corresponded with an increase in the fruit's respiratory quotient (Joles et al., 1993). For blueberries, its been reported that the lower 05 limit for aerobic respiration increased noticeably with temperature (Beaudry et al., 1992). Thus, to avoid off-flavor development in MA packages when temperature increases, the lower 02 limit must be identified over a range of possible storage temperatures for strawberries. In an MA package, problems with off-flavor development could also arise from variation in 05 uptake rate from fruit-to-fruit or from cultivar—to-cultivar. Robbins et al. (1989) found a 39% difference between the C02 production rate of some red raspberry cultivars in air. So to determine whether a given MA package designed for one strawberry cultivar will be effective for others, any cultivar differences in respiratory response to reduced 02 and changes in temperature must be identified. 49 The first objective of this investigation was to use the techniques described by Beaudry et al. (1992) and Joles et al. (1993) to study the effect of reduced.C5 and changes in temperature on the 02 uptake, C0.2 production, and ethanol production of 'Honeoye' and 'Allstar' strawberry cultivars. The second objective was to use this information to characterize and compare the respiration of these cultivars and identify their lower 02 limits. 50 Materials and Methods Plant material On June 21, 22, and 24 of 1993 'Honeoye' strawberry fruit were hand-harvested from Bird's Farm in Haslett, Mich. 'Allstar' strawberry fruit were hand-harvested on June 29, July 2 and 7 from the same location. 'The harvested fruit were placed into eight-quart flats and transported in an air-conditioned vehicle to Michigan State University. After transportation, fruit with obvious decay or damage were culled. Fruit to be stored at 0 and 5C were harvested on the earliest date while fruit harvested on the last day were stored at 20 and 25C. 'Allstar' fruit to be stored at 25, 20, and 15C were packaged immediately while fruit to stored at 10, 5, and 0C were kept overnight at 0C and packaged the next morning. Package design Packages were designed to generate a range of steady- state 05 levels at temperatures of 0, 5, 10, 15, 20, and 25C. Using unpublished C5 uptake data for 'Allstar' strawberries collected by R.M. Beaudry (unpublished data), a nonlinear regression model (Joles et al., 1993) was developed which estimated strawberry C5 uptake over a range of 05 levels and temperatures. This model was then substituted for R02 in: W: Ax Poz' ([021atm ‘ [021pk9) [1] A R02 51 where W is fruit weight (kg); R02 is the rate of C5 uptake (mmol-kg‘1'h'1); P02 is permeability coefficient for 02 of low 1 density polyethylene (mmol°cm°3\ 0.0 0.5 1.0 1.5 0.0 0.2 0.4 0.6 0.8 Q) 0 15C 0C .1.) (f) 20% _ . % I géw %&b O O % . 93531 . . 1©®L .901 00 05 11) L5 00 ()1 02 (x3 04 PCOZ'A'AX'—1‘W_1 (mmol'kg“'h“'kP0“) 75 Fig. 4. Effect of changing the ratio of package surface area (cm?) to film thickness (cm) and fruit weight on steady-state CO2 for 'Allstar' strawberry stored at temperatures of 25 , 20, 15, 10, 5, and 0C. 76 'Allstor' 30 . . . e 250 5 10C 200 .0 o 8 0 0 10% “9@ A $0 88% [E 0 108990. 0. .0 . 6%. 92>. - —\< 0 1 2 3 0.0 0.2 0.4 0.6 0.8 . a E C) 5 200 5c 0 203 . O 8 0) 80 g 6 1O 0 - m §8>©®<0 M8 0 I 0 ‘ . . . - .0. ‘ . -90 1 - g 0.0 0.5 1.0 1.5 0.0 0.2 0.4 0.6 0.8 00) 15> 150 OC 4" 20% g m 0 D o . 10%@ .%g (80 @o 0 . .8). 3ch 1 . . o§ . o 4090. 0.0 0.5 1.0 1.5 0.0 0.1 0.2 0.3 0.4 [3002-,A\-A><‘1-\/\/‘1 (mmol'kg“'h“'kP0“) 77 Fig. 5. Interdependent effects of steady-state O2 partial pressures and storage temperature on the calculated rate of 02 uptake for 'Honeoye' strawberry fruit sealed in LDPE packages. See Eq. [9] and Table 2 for the equations and constants describing the curves. OZlthoke (Hwnvalkg‘1h—fi) 78 'Honeoye' . 09 (16» 0L3» (10 04-1 [12» 1 (10 . (13 . J 93; 02» 08- (90 0 %,1 04. 101 1 15C 1 0L) 1 * 0.0i 0 5 10 15 20 0 5 10 15 20 Steady—side 02 (kPo) 79 Fig. 6. Interdependent effects of steady-state C5 partial pressures and storage temperature on the calculated rate of'C5 uptake for 'Allstar' strawberry fruit sealed in LDPE packages. See Eq. [9] and Table 2 for the equations and constants describing the curves. '02 Uptoke (1’1”1r1’1olkg“1 h“) 80 'Allstar' 0.9 0.6A In .,' ‘1 O 3 ’ . 4‘ I v 1 19c 0 00 ‘ ‘ 0.0 A 5 10 15 20 0 6 10 15 20 Steody—stote 02 (kPa) 81 Fig. 7. Effect of steady-state C5 partial pressure and storage temperature on the respiratory quotient of 'Honeoye' strawberry fruit sealed in LDPE packages. See Eq. [10] and Table 3 for the equations and constants describing the curves. Resphotoby(luofient 82 ON—P-OUCDO ON-POUCDON-PODOO 0 'Honeoye' 250 q. 100‘ Q? 006) &@%@ AQQLO . V U U“ 200 090 15C 0C (an A AA {'L U v ”U (00 006096?“ 0% 5 10 15 0 5 10 15 Steady—stote 02 (R130) 20 83 Fig. 8. Effect of steady-state C5 partial pressure and storage temperature on the respiratory quotient of 'Allstar' strawberry fruit sealed in LDPE packages. See Eq. [10] and Table 3 for the equations and constants describing the curves. Respiratory Quotient 84 'Allstor' 250 .; 1 100‘ ON-P-OUOJO ON-P-OUCIJON-PCDCI) Steody—stote 02 (kPo) 85 Fig. 9. Interdependent effects of steady—state O2 partial pressure and storage temperature on headspace ethanol vapor concentration for 'Honeoye' strawberry fruit sealed in LDPE packages. Ethonol\kmxw'(kPo) 0.8 0.6 ~ 0.4 ~ 0.2 - 0.0 0.3 - 0.2 ~ 0.1~ 0.0 0.3 - 0.2 ~ 0.0 86 Steody~5t0te 02 (kPo) 'Honeoye' 1 fl ‘ ' 0.24 (I) ' 1 . 25C 8 100 g ‘ 0.18 "'8 '1 O o O (112 “o g 8 g (105 ~§ _‘ O 00 O - gm>OG9Q%M@© . 0.00L §§%,o 890 8 q 0 (110— 1 8 0 6 O (105» '% 1 0 o©m9 8% ~ (1001-d99bo>cm@ 6” 1 O ' I . 1 r 1 . . . . r 1 fi 5 150 00 ~ (105 - - O 0 g 1 0.04 1.0 O ‘ 8 .00 _ 009 (102 E? . O®®%@@) %. O.OO_@@303&QQ 1 0 5 10 15 :1) 0 5 1c> 15 20 87 Fig. 10. Interdependent effects of steady—state C5 partial pressure and storage temperature on headspace ethanol vapor concentration for 'Allstar' strawberry fruit sealed in LDPE packages. Ethanol Vopor (R130) 0.8 0.6 ~ 0.4 - 0.2 - 0.0 . 0.3 - 0.2 ~ 0.1- 0.0 0.5 - 0.2 - 0.1 0.0 ~ " 'Allstar' f 250 01') 0130 EEO (HBO - 15 20 SteOdy—stote 0.24 0.18 - 0.12 - 0.06 ~ 0.00 - 0.15 ~ 0.10 ~ 0.05 - 0.00 - 0.06 ~ 0.04 - 0.02 - 0.00 100 0 g 16%mlokomoool . 50. 6 8 O 0 O 0 5062300010 0% 1 O 00 o . 9 O 0 8 PWW O 51015 20 0 02 (1030) CHAPTER 3 MODIFIED-ATMOSPHERE PACKAGING OF STRAWBERRY AND RASPBERRY FRUIT: MODELING PACKAGE 02 AND CO2 OVER A RANGE OF TEMPERATURES 89 90 Abstract. By combining 02 uptake, RQ, and lower 02 limit data previously collected for strawberry and raspberry fruit with activation energies for a low density polyethylene film and a perforation, models were developed to characterize the effect of temperature on package 02 and CO2 partial pressure. Based on these models it was shown that l) LDPE film cannot provide beneficial cxg package levels and; 2) perforated films can provide beneficial C05 levels because of their CO2 to O2 permeability ratio but, because of their relatively low activation energy to gas diffusion an increase in temperature can cause package Oz‘bo fall below the lower 02 limit. An optimum film for modified-atmosphere packaging of strawberry and raspberry fruit would have a C02 to 02 permeability ratio like that of a perforation but an activation energy like that of a polymer film. A system for sensing low partial pressures of ethanol is also described and its potential use in modified-atmosphere packaging discussed. 91 Introduction Mold decay, bruising, and water loss are the main factors which limit strawberry and raspberry fruit shelf life (Smith, 1958). Reducing storage temperature to below 5C reduces mold decay and transpiration. Elevated C02 atmospheres (10 to 20 kPa) can have a fungistatic effect on the decay pathogens of strawberries and raspberries (Couey and Wells, 1970; El-Kazzaz et al., 1983; Harris and Harvey, 1973; Harvey, 1982; Sommer et al., 1973; Woodward and Topping, 1972; Goulart et al., 1992; Smith, 1958; Winter et al., 1939). Elevated.CI§ has also been shown to increase firmness of strawberries (Smith and Skog, 1992; Smith, 1992) which could reduce bruising. As has already been pointed out (Kader et al., 1989; Beaudry et al., 1992; Joles et al., 1993), modified-atmosphere (MA) packaging has the potential to provide an elevated.Cr5 and a high humidity environment. In an MA package, (Kb package level ([coz] ) cannot be We elevated without a reduction in 02 package level ([OZkag) . The extent [Oz]pkg must be reduced to obtain a beneficial [C05] level (10 to 20 kPa) depends upon the packaging W9 films's ratio of Coztx>(5 permeability. Recently, a California company has developed an MA package for strawberries that is based on the use of perforated films (Anonymous, Packer, 1993). 'Perforations or holes were used because they provide a ratio of COztx>C§ permeability under 1.0. Nonperforated polymer films such as low density polyethylene (LDPE) are 4 to 5 times more permeable to CO2 than to 02. 92 In a commercial application of MA packaging there is a good chance that somewhere in the marketing and transportation chain these packages will encounter an increase in storage temperature. When an MA package encounters an increase in temperature, there is a distinct risk that [05] could fall below the safe lower limit “9 (Cameron et al., 1993a; Cameron et al, 1993b). It has been shown for strawberry and raspberry fruit that when Ob falls below the lower limit anaerobic respiration is induced, fruit ethanol content increases, and off-flavors develop (Chapters 2 and 1; Ke et al., 1991; Couey et al., 1966). The decrease in [05] with increasing temperature stems mg from an increase in 02 uptake rate by the fruit which is larger than the increase in 02 flux through the packaging film with temperature. The extent to which [02]pkg will change with temperature, and consequently the risk of inducing anaerobic respiration will depend upon the packaging film's activation energy (Ea) to 02 permeation and on the fruit's change in 02 uptake rate with temperature. For strawberry and raspberry this risk is compounded by the fact that their lower Ozljmdt.also increases with temperature (Chapters 2 and 1). For strawberry and raspberry fruit, the change in 02 uptake and C02 production with temperature and 02, the change in lower 02 limit with temperature, and the E3 of LDPE to O2 and CO2 permeation have been characterized (Chapters 2 and 1). The first objective of this study was to use this information to model the effect of temperature 93 on [02] and [C02]pkg for strawberry and raspberry fruit in 9“ order to identify when anaerobic [02]pkg or if beneficial [cog] levels are reached in MA packages made with LDPE or 9“ perforations. When induction of anaerobic respiration occurs there is usually a lag phase before the development of off-flavors (Kader et al., 1989; Re et al., 1991). As fruit go anaerobic, they begin to produce ethanol. If the ethanol produced by a fruit could be sensed and used to increase package permeability, then.[C>2]pkg would increase and off- flavors could be avoided. The second objective was to introduce a concept and a technique which may help avoid the development of off-flavors in MA packages by sensing and responding to the ethanol produced by anaerobic fruit. 94 Model Development Total C5 uptake of strawberry and raspberry fruit at steady state conditions can be described by: P0.A —:K— ([OZJatm ‘ [02]pkg) [1] R02 = W (Chapters 2 and l) where R02 is the rate of 02 uptake (mmol°kg'1-h’1); P02 is the packaging film's permeability coefficient for O2 (mmol-cm- cm'z-h'1-kPa'1); A is film area (cmz); Ax is film thickness (cm); [02]ng and [02] are atm package and atmospheric O2 partial pressures (kPa) , respectively (Chapters 2 and 1; Cameron, 1990; Beaudry et al., 1992) . R02 as a function of [02] was also described pkg by the Michaelis-Menten equation: 1213:): . [(32]ka [2] R02 - K.,, + [02] Pkg where Rom: is the maximum rate of 02 uptake at that temperature; K7! is an apparent Km of the entire fruit which incorporates any resistance of the fruit's skin to 02 diffusion and thus includes any differences between 02 diffusion and 02 uptake as function of temperature (Chapters 2 and 1) . Combining Eq. [1] and [2] yielded: 95 which was solved for [02L*9: Ax (KI/1 + WPOARST - [02]pkg)2 + 4K9: [021mm _ 2 _ AX max W— + KI " O ( P02131202 /2 [ 2]atm) [3] 2 (Cameron et al., 1993a). For strawberry and raspberry mu.T % ) has been defined: 1%: as function of temperature (R | —. ( max,T _ max,0 . 1 R0. R0. 010 where Romj'ois the maximum rate of Oz uptake at 0C, Q10 is the C) ’ (41 increase in 02 uptake for every 10C increase in temperature, and T is temperature in C (Chapters 2 and 1). In a previous study, an apparent Km 0%) for strawberry fruit was estimated which didn't incorporate skin permeability and was based on fruit internal.C§ partial pressure. Because Eq. [3] uses an apparent Km which describes a [Oz]pkg partial pressure, the k“ (an internal C5 partial pressure) reported for strawberries needed to be converted to a.[C>2]pkg partial pressure. This was accomplished using a variation of Fick's Law: sin 5 R02 = P0: ' ([021pkg ’ [021int) [ ] where P3? is a value describing the ratio of a strawberry fruit's O2 permeability and surface area to its skin thickness and weight (Chapter 2) (mmol-kgq-h4°kPa4); [02] int 96 is an internal O2 partial pressure (kPa) . K11. at any temperature is by definition an O2 partial pressure at which R02 is half of R02 . Thus, R02 divided by 2 is rate of strawberry fruit 02 uptake at Kw Substituting the estimated values for P321", km and the function defined IQ: with temperature (REMl ) (Chapter 2) into Eq.[5] yielded an equation that calculated 8% with temperature (Kg): K}, = + k.,, (61 For raspberry fruit the 3% did not change significantly over the temperatures studied (Chapter 1). The constants which were estimated (Chapter 2) to describe 'Allstar' strawberry 02 uptake (R330 Q10, k7,, and P0?) are given in Table 1 and the constants estimated (Chapter 1) for 'Heritage' raspberry 02 uptake (Kw Romy and Q10) are given in Table 2. Film permeability was assumed to change with temperature as defined by the Arrhenius equation: E _ . _ a 7 P,- — Al. exp ( R . (T+273)) [ ] where Pi is permeability to 02 or CO2 (mmole°cm-cm'2°h'1-kPa' 1); AF is the Arrhenius constant for 02 or CO2 permeation; Ea is the energy of activation of 02 or C02 permeation (kJ'mol' 1); and R is the gas constant (.0083144 kJ'mol'1'K’1). The Ar and Ea values for LDPE reported in Chapter 1 were used (Ars of .07 and .177 for 02 and C02 permeation, respectively; Eas of 36.85 and 35.34 for O2 and CO2 permeability, 97 respectively). For perforations it was assumed permeability changed in a manner consistent with the Arrhenius equation but with an Easflmdlar to that of free diffusion (£5 kJ mol' 1) (Nobel, 1983) and an Ar for CO2 permeation equal to that of'Cb permeation (i.e. permeability ratio equal to 1.0). By substituting the equations for a change in permeability with temperature (Eq. [7], the estimated K” values (Eq. [6] or Table 2), and the function defined for I§?Ifor strawberry and raspberry fruit (Eq. [4]) into Eq. [3] allowed [02] ‘to be calculated for strawberry and. pkg raspberry fruit over a range of temperatures. (£5 production at any temperature and 02 level can be calculated by multiplying the RQ by the R02 at that temperature and 02. Thus, [C02] (as a function of pkg temperature and 02 can calculated: Ax Pco2 T [COZkag = (R02 ' RQT ‘ W A) + [(30.2]...t.n [8] where R32 and RQT are the equations estimated for strawberry and raspberry'C5 uptake and RQ as a function of temperature and O2 partial pressure (Chapters 2 and 1); P is film or cg perforation permeability to CO2 (mmol- cm- cm'z' h°1° kPa") . [02%,k9 and [C02] was calculated for strawberry and D“ raspberry fruit only over the temperature range (0 to 25C and 0 to 20C) where 02 uptake and RQ have been measured by previous studies (Chapters 2 and 1). 98 Materials and Methods Ethanol sensor The ethanol sensor was based on the enzyme alcohol oxidase which catalyzes the reaction: Ethanol-+C5 Alcohole1dase> I502+-Acetaldehyde To obtain a color change, the production of H55 was coupled to another enzyme reaction. The color change reaction was catalyzed by the enzyme peroxidase which used H55 to oxidize o-dianisidine and produce a color change in o-diansisidine from white to dark brown. The enzymes and the o-dianisidine were all imbedded into a polyvinyl-alcohol (PVA) film. As o-dianisidine is oxidized the absorbance at 460 nm increases which can be seen visually and quantified spectrophotometrically. The procedure for preparing the ethanol sensor was to first wash the plasticizer (glycerol) out of the plasticized PVA by simply rinsing it in a water bath for 2 hours. The PVA was then dried. One gram of PVA was dissolved in z9 ml £50 by heating in a microwave. The viscous dissolved sclution was then brought to a pH of 7.5 by adding a 50 mM NaPol. buffer in .1 ml aliquots until the pH was reached. pH measurement was accomplished using indicator strips (Baxter, McGaw Park, IL). Ten mg (4 units) of alcohol oxidase 99 (Sigma, St. Louis, Mo), 2 mg (100 units) peroxidase (Sigma, St. Louis, MO) and 50 mg o-dianisidine (water insoluble) (Sigma, St. Louis, MO) was added to the viscous solution. The viscous solution was then spread over a glass plate (#100 cm? area) using electrical tape to provide a border. The gel on the plate was then dried overnight under N2. To analyze the reaction, a 1.cm@ piece of the film was cut and put in a high humidity jar for 1 hour. It was then suspended on the inside of a spectrophotometry cuvette in the place at which the beam passes through the cuvette. A small dab of vacuum grease was used to suspend the film. Ethanol solutions were added to the bottom of the cuvette, making sure it did not touch the film. The cuvette was sealed and placed in the spectrophotometer where absorbance at 460 nm was measured at 25C. 100 Results and Discussion The lower 02.1imit of strawberry and raspberry fruit (dotted line in Figs. 1 and 2) has been reported to increase with temperature (Chapters 2 and 1). An MA package, using a LDPE film, designed to have a [Oz]pkg above the lower 02 limit would only generate [C02]pkg levels of 3 to 8 kPa (top of Figs. 1 and 2) for strawberry and raspberry fruit. [C02].3kg levels of below 10 kPa generally do not reduce mold decay (Couey and Wells, 1970; El-Kazzaz et al., 1983; Harris and Harvey, 1973; Harvey, 1982; Sommer et al., 1973) and are less effective in increasing firmness of strawberry fruit (Smith, 1992). LDPE is 4 to 5 times more permeable to COz‘than to 02. This means C02 production by a fruit would have to be 4 to 5 times greater than 02 uptake to raise [C02] above 10 kPa. m9 A difference between CO2 production and 02 uptake of this magnitude only occurs when fruit are very anaerobic and the risk of off-flavor development is very high. Thus, an LDPE alone cannot be an effective packaging film for strawberry and raspberry fruit. If an LDPE was combined with a in- package CO2 generating system like that the one developed for meats (Benedict et al., 1975), then beneficial [C02]F3kg levels could perhaps be generated. The differential between CO2 and O2 permeability for a perforation is under 1.0 (Cameron et al., 1993a). The RQ (ratio of C02 production to 02 uptake) for strawberry and raspberry fruit was found to be over 1.0. Combining the permeability ratio of a perforation with the RQ of the fruit 101 allows beneficial [cog] levels (above 10 kPa) to be M9 generated at safe [02]pkg levels at optimum low temperatures (middle of Figs. 1 and 2). However, in a perforated (package, it is predicted that safe [02] levels are not pm maintained when temperatures increase to above 15C for strawberry (middle of Fig. 1) and above 7C for raspberry _(middle of Fig. 2). An LDPE package was predicted to maintain safe [OZJF3kg levels over the same temperature range (top of Figs. 1 and 2) because its activation energy for'CQ permeation is z7 times higher than that for a perforation (36.85 compared to z5.0 kJ'molq) (Chapter 1; Nobel, 1983; Cameron et al., 1993a). A perforated package can be designed to compensate for its low activation energy by having very high initial [02]pkg levels at low temperatures but, if this is done, beneficial [C05] levels are not generated at the m9 temperatures that are optimum for storage (bottom of Figs. 1 and 2). A very effective MA package for strawberry and raspberry fruit would be one that had a permeability ratio similar to that of a perforation but had an E8 like that of LDPE. Figure 3 shows that in a package with these characteristics [C05] could be maintained at beneficial W9 levels while [02]pkg remained at a safe levels as temperature increased. Unfortunately a packaging film with these characteristics is not currently available. So, other ways to avoid the risk of inducing anaerobic respiration in an MA package must be devised. 102 One concept for avoiding the risk is based on the fact that there is usually a lag phase between induction of anaerobic respiration and the development of off-flavors (Kader et al., 1989; Re et al., 1991). When fruit go anaerobic, they begin to produce ethanol. If the ethanol produced by a fruit could be sensed and used to increase package permeability, then [0?] would increase and off- W9 flavors could be avoided. We are developing a sensing system that will change colors in response to very low partial pressures of ethanol. This system uses an enzyme called alcohol oxidase which is imbedded in a film of polyvinyl-alcohol. This enzyme catalyzes the oxidation of ethanol to acetaldehyde and produces hydrogen peroxide in the process. Currently to sense ethanol vapor and obtain a color change, we are coupling the alcohol oxidase catalyzed reaction to another enzyme reaction. This reaction utilizes the hydrogen peroxide produced by alcohol oxidase to oxidize a compound that changes in absorbance and color as its oxidized. Figure 4 shows the change in absorbance over time which occurs when the ethanol sensor is exposed to an ethanol partial pressure of .006 kPa or to water. There is a lag phase in this reaction that lasts z30 minutes but after 50 minutes there is a significant difference in absorbance at 460 nm. After 90 minutes a noticeable change in color was seen (absorbance of z.10). Because some of the chemicals used in our current color change reaction are suspected carcinogens this system is not 103 suitable to be used in commercial MA packaging applications. However, we have shown that our ethanol sensor can produce hydrogen peroxide at very low ethanol partial pressures (Fig. 4). Hydrogen peroxide is a very reactive chemical, so it seems feasible that it could be active enough in small quantities to cause a change in 0‘2 permeability perhaps, via a free radical reaction or by triggering a electronic detector. We have not yet developed a system to accomplish this but feel its development would be a major breakthrough for MA technology. Another approach for maintaining safe [0?] levels 9“ with an increase in temperature is to have the package respond to the temperature of the storage environment. This approach was proposed by Patterson and Cameron (1992). Their system is based on the opening of holes in a package when temperature increases beyond a threshold. The holes are originally blocked by hydrocarbons with a specific melting temperature. When the melting temperature of the hydrocarbon is exceeded the hole is opened and consequently (5 permeability increased. Because current packaging films do not have the characteristics (i.e. favorable permeability ratio and E8) levels for to obtain beneficial [C05] and safe [02] pkg pkg strawberry and raspberry fruit over a range of possible storage temperatures, some type of sense-and-respond technique should be developed to supplement perforation- based MA packaging. 104 Table 1. Constants describing the relationship between 02 uptake (mmol-kg'l'h' 1), steady-state O2 partial pressure (kPa), and temperature for ’Allstar’ strawberry fruit (estimated in Chapter 2). R8? is the maximum rate of 02 uptake at 0C, 010 is the increase in 02 upfake for a 10C increase in temperature, k5,, is the internal 02 partialwpressure at which the rate of 02 . ‘ . Ski . . . uptake [5 half the maxrmum rate, and P0, 18 a value descrlbmg the of the fruit’s skin to 02. ' max.0 skin R02 SE Q10 SE ky2 SE PO2 SE + .259 :02 2.48 _.08 .368 22.11 1.11 $.15 105 Table 2. Constants describing the relationship between 02 uptake (mmol -’kg 1 h' 1), steady- -state 02 partial pressure (kPa), and temperature for ’Heritage’ raspberry (estimated 1n Chapter 1). Ky2 15 the external (package 02) 02 partial pressure at which the rate of 02 uptake is half the maximum rate. ,0 Ky: SE R81“ SE Q10 SE 5.59 i .40 .872 i .04 1.92 t .20 106 List of References Anonymous. 1990. FreshHold extends breathable packaging to fresh strawberries. Packer, August 11, XCVII(32):5A. Beaudry, R.M., A.C. Cameron, A. Shirazi, and D.L. Dostal- Lange. 1992. Modified atmosphere packaging of blueberry fruit: Effect of temperature on package 02 and C02. .J. Amer. Soc. Hort. Sci. 117:436-441. Benedict, R.C., B.D. Strange, S. Palumbo, and C.E. Swift. 1975. Use of in-package controlled atmospheres for extending the shelf life of meat products. J. Agric. Food Chem. 23(6):1208-1212 Cameron, A.C. 1990. Modified atmosphere packaging: A novel approach for optimizing package oxygen and carbon dioxide. Proc. 5th Int'l. CA Conf., Wenatchee, Wash., 14-16 June. Cameron, A.C., R.M. Beaudry, N.H. Banks, and M.V. Yelanich. 1993a. Modified-atmosphere packaging of blueberry fruit: Modeling respiration and package oxygen partial pressure at different temperatures. Accepted to J. Amer. Soc. Hort. Sci. Cameron, A.C., B.D. Patterson, P.C. Talasila, and D.W. Joles. 1993b. Modeling the risk in modified-atmosphere packaging: A case for sense-and-respond packaging. Proc. Intl. CA Conf. In Press. Couey, H.M., Follstad M.N. and M. Uota. 1966. Low oxygen atmospheres for control of postharvest decay of fresh strawberries. Phytopathology 56:1339. Couey, H.M. and J.M. Wells. 1970. Low oxygen or high carbon dioxide atmospheres to control of postharvest decay of fresh strawberries. Phytopathology 60:47. El-Kazzaz, M.K., N.F. Sommer, and R.J. Fortage. 1983. Effects of different atmospheres on postharvest decay of strawberries. Phytopathology 73:282. Goulart, B.L., P.E. Hammer, K.B. Evensen, W. Janisiewcz, and F. Takeda. 1992. Pyrrolnitrin, Captan + Benomyl, and high C02 enhance raspberry shelf life at 0 or 18C. J. Amer. Soc. Hort. Sci. 117:265-270. Harris, C.M. and J.M. Harvey. 1973. Quality and decay of California strawberries stored in C02 enriched atmospheres. Plant Dis. Reptr. 57:44. Harvey, J.M. 1982. (Kb atmospheres for truck shipment. In Controlled atmospheres for storage and transport of 107 perishable agricultural commodities, D.G. Richardson and M. Meheriuk (Ed.) p 359. Timber Press, Beaverton. Joles, D.W., A.C. Cameron, A. Shirazi, P.D. Petracek, and R.M. Beaudry. 1993. Modified-atmosphere packaging of 'Heritage' red raspberry fruit: The respiratory response to reduced oxygen, enhanced carbon dioxide, and temperature. Accepted J. Amer. Soc. Hort. Sci. June 1993. Kader, A.A., D. Zagory, E.L. Kerbel. 1989. Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. Nutrition 28:1—30 Ke, D., L. Goldstein, M. O'Mahony, and A.A. Kader. 1991. Effects of short-term exposure to loW'021and high C02 atmospheres on quality attributes of strawberries. J. Food Sci. 56(1):50-54. Nobel, P.S., 1983. Biophysical plant physiology and ecology. W.H. Freeman, New York, pg. 608. Patterson, B.D. and A.C. Cameron. 1992. Modified atmosphere packaging. International Patent No. PCT/AU90/00267. Smith, W.H. 1958. The harvesting, precooling, transport, and storage of strawberries and raspberries. Food Invest. Board Misc. Paper 1058. Smith, R.B. 1992. Controlled atmosphere storage of ‘Redcoat' strawberry fruit. J. Amer. Soc. Hort. Sci. 117:260- 264. Smith, R.B. and L.J. Skog. 1992. Postharvest carbon dioxide treatment enhances firmness of several cultivars of strawberry. HortScience 27(5):420-421. Sommer, N.F., R.J. Fortlage, F.G., Mitchell, and E.C. Maxie. 1973. Reduction of postharvest loss of strawberry fruit from grey mold. J. Amer. Soc. Hort. Sci. 98:285. Winter, J.D., R.H. Landon, and W.H. Alderman. 1939. Use of carbon dioxide to retard the development of decay in strawberries and raspberries. Proc. Amer. Soc. Hort. Sci. 37:583-587. Woodward, J.R., and A.J. Topping. 1972. The influence of controlled atmospheres on the respiration rates and storage behavior of strawberry fruits. J. Hort. Sci. 47:547-533. Fig. 108 1. Predicted changes in [02]]; and [C02]pk as a function of temperature and ffim permeability characteristics for 'Allstar' strawberry fruit from Eq. [3] and Eq. [8] with constants from Table 1 and Chapter 2. The dotted line on each graph represents the lower C) limit for 'Allstar' strawberry fruit as determined by the increase in RQ and ethanol content (Chapter 2). Steady—stateGas Partial Pressure (kPa) _\ GNP-03000 109 'Al lsta r' Strawberry _ [002]... Lower 02 limit Temperature (C) 110 Fig. 2. Predicted changes in [0213 and [C02]Rk as a function of temperature and {Tim permeabiiity characteristics for 'Heritage' raspberry fruit from Eq. [3] and Eq. [8] with constants from constants Table 2 and Chapter 1. The dotted line on each graph represents the lower 02 limit for 'Heritage' raspberry fruit as determined by the increase in R0 and ethanol content (Chapter 1). 111 'Heritage' Raspberry LDPE [0.]... /, l‘ / Fig. 112 3. Predicted changes in [02]k and [C02]pk as a function of temperature and £33m permeabiiity characteristics for 'Heritage' raspberry fruit and 'Allstar' strawberry fruit from Eq. [3] and Eq. [8] with the film permeability characteristic being a Eatof 37 and a permeability ratio of 1.0. 113 [€02]... 114 Fig. 4. The change in absorbance at 460 nm over time for a ethanol sensing film at 25C exposed to a ethanol vapor partial pressure of .006 kPa and to H20 vapor. 115 @2539 Defiance: mm 0 0.40 _ _ _ _ _ _ _ _ q _ a _ BID .00m $3039 expov 41 1 DID Imo - m n 0.61 1 O 6 4 - 1 m I e 0.0m1 m a - a .m w OPT .. b 0.00 was. E _ _ _ _ _ _ _ .. _ _ _ O No so 00 mo 400 AND A36 A339 :5 HICHIGRN STRTE UNIV. 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