3 m a 9. T‘? (.351?me i : J.-‘ ~ ”hit" _. -,.u.. a’ fresh u ..» $1.1 " is“ .. n I r, .. V n > \— '. ~. , ~.~'._(.~ 3. 1, g ' a. ‘ ‘ " ' 14%* - ‘ .A' w“; ‘ t. ,f“ “r, éAyL _Z “fin-«fl -_.‘ :g‘dfi , ~51; Fan». t~_\ «u -.~ -T‘.’ "21:3 cit-~21 a .. «um i' 3-335" figpfigm ,_. :‘ Ii I y_ w - _;’‘l m . From Equation 5 and 8, the respiration rate (ml kg‘1 hr'l) is calculated: 12.le2 - acd.V.W'1.[(b+c.t)d'1].[e'(b*“)d] [3] When solving this equation for the same time (t) value, oxygen concentration and corresponding respiration rate can be determined, respectively, from Equation 4 and (8). Typical data are plotted in Figure (3). OXYGEN UPTAKE (ML KG—l HR—l) 59 r l I , . 0.16 0.20 0.00 . 0.04 . 0.08 t 0.12 OXYGEN PARTIAL PRESSURE (otm) Figure 2. Plot of oxygen uptake (ml kg" hr") in closed system versus oxygen partial pressure (atrn). Y = a-(l-e“‘"°‘. Values of constants are 16.2316, 17.0696 and 0.63384 respectively for a, b and c. Table 3. Values for constants of the best fit curve of equation Y . a(1 - e4” ' ’0)c describing oxygen uptake (ml kg’1 hr'l) as a function of oxygen concentration in closed system and in MAP trials at 20' C. Closed systemz MAP trials Fruit mlmber 1 2 Constants a 16.2316 245417 17.5764 b 17.0696 152347 18.7800 0.6334 0.8683 0.67330 r2 1.000 0.999 0.873 2 Fit curve of the difi'erence of subsequent data ( l) and (2) first derivative approach. 61 Fitting the rate of respiration led to a curve with following equation that has the same form as in the first approach and illustrated by Equation (6). Constant values are given in Table 3 (2). After substitution and rearrangement of this new Equation (6) into Eq. (3), weight of fruit can be expressed as follows: PA 03:1 (min-[021“) w - [9] a(1-e’b° [02])“ This relationship first used by Cameron et al. (1989) determines fruit weight according to parameters of the package system as illustrated in Figure 4. Modellsstinlr. The above models were tested using apple fruit sealed in packages of known permeability. The procedure for the determination of optimum fruit weight consisted of empirical packaging trials using various fruit weights. The concentration of oxygen within sealed packages, at steady state, decreases with increasing fruit weight and film thickness (Figure 5) and this relationship was characterized by the following equation: Oxygen uptake (ml lq-t hr-tl . 28 Y - ah-eer’ )e 20 18 1O 0.1 L l L L1 L l L l l L l l L_LI l l _ ' I 0 0.03 0.00 0.00 0.12 0.15 0.10 0.21 Oxygen (atm) F'lgln'e.3.,Plotofthefirstder-ivativeofoxygendepletioncurvein closedsystemversusoxygeneoncentration. Values ofconstantsare 245417.15.2347and0.8686respectivelyfora,bandc. 5 Fruit weight (kg) " -I- an .. 41- so " P . A I DX (ml hr-1 afar-1) + 00 ~3- 100 " .. -9- tan ,. ' I ‘ ifis‘ - :‘E~§~- ‘ > . I 4‘: 3‘- L l l l J l L .- — —-h, -L’ I I ’ 0 0.02 0.04 0.00 0.08 0.1 0.12 0.14 0.10 0.18 0.2 Oxygen (atrn) Figure 4. Predicted weight of apple fruit for a range of film characteristics that would generate desired 02 (atm) in the sealed package at 20'C. [0,] = “0"“) + c I [10] Where; [02] 8 oxygen concentration (%), fw =- fruit weight (kg) and, a, b and c are arbitrary constants. Tabulated values of constants are presented in Table 4. The calculated respiration rates from Equation (3) were plotted vs oxygen gradient and fitted to an equation curve for all 3 films combined as illustrated in Figure 6. The best fit equation was similar to the one obtained in closed system and had the form of Equation (6). Constants values were given in Table 5. After substituting Equation (6) into Equation (3) and rearranging the equation in order to express film characteristic (P-A -DX'1) the relationship yielded to: a(1 - e'b'lml)c -w PADX'I =- ' [11] (lozlstm ' [Ozlpkg) The difl'erence between Equation (9) and (1 1) is rearrangement of different parameters. Equation 1 1 was used to generate data of film characteristics needed for a given fruit weight and desired oxygen concentration at equilibrium. Predicted data are presented in Figure 7. Table 4. .Values for constants of equation (Y .. a. e‘b'x) + c) of oxygen concentrations in the package as a function of fruit weight for different LDPE films at 20 ' C. Constants Film thickness (pm) a b c 25.4 0225034 -0.32677E-02 0.2196E-02 44.4 021763 0533321 0.010094 50.8 0.2648669 -0.79268OE-2 0.11095E-02 Oxygen partial pressure (otm) 0.204 A 44.4 pm (100‘ I g 25.4 urn 9 50.8 urn 0 '100 r200 r300’r400 ‘500r600' 700138001900j Fruit weight (kg) Figure 5. Oxygen concentration in different packages made from difi'erent LDPE films and the best fit curve at steady state for different ‘Empire’ apple fruit weights. at 20 ' C. Respiration rate (ml/kg/hr) 67 . Y "' BIT) ' (1- ‘EXP(-5(ZI' >0) " 5(3) o r I I j? I T T I 0.00 0.03 0.06 0.09 0.12 0.15 ~ 0.18 0.21 Oxygen gradient (atm) Figure 6. Oxygen uptake (ml kglhr“) of 'Empire’ apple fruit fiom packagesasafunctionofoxygenpartialpresslneatZO'Candthe averagedatabestfitcurvefor3films. 0.24 P.A I DX (ml hr-1 atm-l) 200 -0- 0.18 h fruit '3'- 0.00 150 - + 0.00 -a- 4.20 too - 50 "3 - L L L l l l l l I l l L l l 1 l l l 0 0.02 0.04 0.00 0.08 0.1 0.12 0.14 0.10 0.18 0.2 Oxygen (atm) 0 Figure 7. Predicted film characteristics required to establish a desired oxygen concentration for various apple fruit weights in a sealed package at 20 ' C. OXYGEN UPTAKE (ML KG—l HR—l) 20 : B—El PACKAGE SYSTEM . H CLOSED SYSTEM _ : .- '- 2 3 3 3‘5 15.. 5 = = ‘ 12- . " 8~ 2 4.. 0 . r - r . r . r r 0.00 0.04 0.08 0.12 0.16 0.20 OXYGEN PARTIAL PRESSURE (cm) Figure 8. Plot of oxygen uptake (ml kg" hr‘) versus oxygen partial pressure (atrn) for closed system and package system. Y a a'(1-e"’m. Values of constants are given in Figure 2 for closed system and in Table 3 for package system respectively for a, b and c. 70 Table 5. Values for constants of equation (Y = a . (1 - e('b ' x))"' describing respiration rate as a function of oxygen gradient for each film and their average fit curve at 20'C. Constants values Film thickness (pm) a b c 25.4 19.43273 15.64932 0.54026 44.5 15.72387 19.99732 0.798078 50.8 15.18553 58.81798 1.529614 Average curve 17.5764 18.782 0.673 71 DISCUSSION The technique of oxygen depletion in a closed system as described for tomatoes by Cameron et al. (1989) permitted measurements of oxygen concentration without interference of errors or leaks associated with conventional sampling of the headspace. Oxygen depletion curves obtained in this study for apples were closely similar to what was found for tomatoes (Cameron et al. 1989). Results obtained from packaging trials showed similar oxygen uptake values with relatively small differences due to the permeability of each film. The best fit equation curve for MA packaging trials showed a similar pattern to that obtained with the closed system as illustrated in Figure 8. It was assumed in both methods that carbon dioxide has no or little efi'ect on oxygen at steady state and this was supported by other research data shown in Section III of this work. The respiration rate is oxygen concentration dependent; the lowest values were obtained when the oxygen was low in packages with high fruit weight or with film less permeable to oxygen. Better understanding of the effect of oxygen on respiration rate and the minimum 02 concentration in the package to prevent fermentation is needed in packaging research. Data generated from Equation (9) and (11), for fruit weight and film characteristics and presented in Figures 4 and 7, constitute an interesting means to design the package model for apple fruit. For instance, if apples should be stored at 0.06 atrn of oxygen at 20 ' C, Figure 4 shows that fruit weight should be ca. 0.30, 0.60 and 0.90 kg, respectively, for 20, 40 and 60 ml hr'1 atrn‘1 of film permeability constants for 02. For 1.2 kg of apples stored at 0.04 and 0.06 atm of 02, Fig. 7 indicates that film characteristics should be, respectively, 80 and 110 ml 02' hr'latm‘l. For the latter example, if 4 apples were packed in 800 cm2 film, P.DX'1 varies from 10 x 10‘1 and 13.75 x 10‘1 cm, respectively, for 0.04 and 0.06 atrn of 02. This also indicates that there is a wide range of flexibility between the film characteristics and fruit weights that may be choosen to achieve Oxygen flux through (11- (I1.hr-l) N O 20 .4 0 l l .5 00 .ss 0 Oxygen uptake by fruit (n1.hr-l) 0 0.03 0.00 0.00 0.12 0.15 0.18 0.21 Oxygen partial pressure (arm) Figure 9. Plot ofthe rate of oxygen flux and rate of oxygen uptake by the apple fruit as a function ofoxygen partial‘pressure (atrn) in the package, film permeability characteristics (ml hr") and apple fruit weight (kg). Each intersection between oxygen flux (solid line) and oxygen uptake (symbol) indicates the 02 concentration at steady state for the film/“fruit weight combination. 73 recommended conditions of storage of the commodity. Figures 4 and 7 show that increasing fruit weight and film thickness reduces the concentration of oxygen in the package. As the fruit weight in the package increases so also does oxygen depletion rate. Packages more permeable to 02 are required to achieve the desired steady state oxygen partial pressure within sealed packages as product weight increases (Figure 9). The results of this study shows that the empirical and mathematical approach are both applicable in developing packaging guidelines for fruits and vegetables. The flexibility obtained between film characteristics and fruit weight is wide and supports the feasability of developing a package system for some commodities (Cameron et al. 1989). 74 LITERATURECITED . Barmore, CR. 1987. Packing technology for fresh and minimally processed fruits and vegetables. J.Food QuaL 10: 207-217 Boylan-Pett, W. 1986. Modified Atmosphere Packaging for Tomatoes. iii MS. Thesis Michigan State University East Lansing MI. il- . Cameron, A.C., W. Boylan-Pett, and 11. Lee. 1989. Design of Modified Atmosphere Packaging Systems: Modeling oxygen concentrations within sealed Packages of Tomato fruits. J. Food Sci. 54 (6): 1413-1416 & 1421. . 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. . Henig, Y.S. 1975. Storage stability and quality of produce packaged in polymeric films, p. 144-152. In " Postharvest biology and handling of fruits and Vegetables. NF Hard and DR. Salunke (Ed) A.V.I. Westport, CN. . 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. . Kader, AA 1986. Biochemical and physiological basis efiects of controlled and modified atmospheres on fruits and vegetables. Food Technol. 40(5): 99-103. . Kawada, K. 1982. Use of polymeric films to extend postharvest life and improve marketability of fruits and vegetables- Unipack: Individually wrapped storage of tomatoes, oriental persimmons, and grapefruit, p. 87-89. In ”Controlled Atmosphere for the Storage and Transport of Perishable Agricultural Commodities" D.G. Richardson and M. Meheriuk (Ed) Oregan State Univ. School of Agr. Symp. Series. 1. 75 9. Prince, T.A., R.C. Homer and S.W. Gyszley. 1982. Storage of precooled tulip bulbs in controlled atmosphere packages. In "Controlled Atmospheres for the Storage and Transport of Perishable Agricultural Commodities" D.G. Richardson and M. Meheriuk (Ed), p. 77 Timber Press, OR. 10. Smith, S.G., J. Geeson and J. Stow. 1987. Production of modified atmospheres in deciduous fruits by the use of films and coatings. HortScience 22:772-776. 11. Zagory, D. and AA Kader. 1988. Modified Atmosphere Packaging of Fresh Produce. Food Technology 42: (9) 70-74 & 76-77. SECTION III MODIFIED ATMOSPHERE PACKAGING OF ‘EMPIRE’ APPLE FRUIT FROM CONTROLLED ATMOSPHERE STORAGE 76 77 INTRODUCTION Controlled atmosphere (CA) storage of fruits to extend their seasonal availability is well documented in the literature. Except for apples and pears, CA storage is not widely used despite successful studies carried out in many countries around the world for difierent commodities, including bananas (McGlasson and Wills, 1971), cabbage (Geeson gt al., 1977), oranges (Ben-Yehoshua, 1985), tomato (Kidd and West, 1932; Kawada, 1982; Dennis gt al., 1979). Common CA conditions recommended, and widely used for several years, for apple storage were 3% oxygen and 5% carbon dioxide with some variance depending upon cultivar. In the early years of CA storage, these conditions were obtained by allowing fruit respiration to modify the storage atmosphere; in many countries this is still the practice with CA rooms of approximatively 100 - 200 ton capacity. Once the desired level of 02 is reached, the 02 and C02 levels are monitored and scrubbers are used to control C02 and the rooms are ventilated with air to ' maintain the desired 02 concentration. In recent years, 3% Oz : 5% C02 concentrations have been largely abandoned for many cultivars and now there is a world-wide trend to use Ultra Low Oxygen (ULO). 02 concentrations as low as 1% and for some cultivars, lower C02 concentrations even to 1% C02 further prolong the storage period and keeping quality of some apple and pear cultivars. Several researchers, (Chen, 1985; Chen :1 al., 1985; Lange, 1985; Lau, 1985; Lidster 91 al., 1985) reported, independently, good results with oxygen below 2% and C02 kept around 1 to 1.5% in order to prevent anaerobic conditions and C02 injuries. ULO storage conditions are now widely used in most areas without major problems. Dilley (1987) recommended CA storage of Michigan apples at 1.5% Oz and 3% C02. In England, Sharples and Stow (1982) reported that the use of 1.25% 02 and 1% C02 permitted storage of ‘Cox’s Orange Pippin’ apples for up to 9 months rather than 2.5 to 3 months in air. The authors reported that 78 the same conditions were recommended for storage of ‘Idared’ and ‘Jonagold’. Truter and Eksteen (1987) in South Africa, working with 3 apple varieties (‘Golden Delicious’, ‘Starking’ and ‘Granny Smith’), concluded that 1% Oz and 1% C02 gave particularly good results in maintaining quality of apples after 9 months of CA storage. One of the major concerns of postharvest researchers on quality of fruit from CA is the suppression of fruit aroma and flavor (Bangerth, 1984). Despite the ability of the fruit stored at these low 02 atmospheres to attain quality characteristics after exposure to ambient air at 0'C for 2 to 3 weeks (Ian, 1985), fruit firmness declines rapidly after removal from CA (Smith gt 3.1., 1987). Obtaining and maintaining low concentrations of gases in CA rooms is sometimes a difficult and expensive practice for commercial stores. In order to preserve high quality fruit during distribution of fruit to market after CA the fruit must be maintained under refrigeration and moved to market as quickly as possible. Modified atmosphere packaging (MAP) offers a means for quality preservation that may be used as a supplement to or an alternative for refrigeration that may be employed for fruits at harvest or from CA storage. The principle of MAP is to create modified concentrations of oxygen, carbon dioxide and relative humidity within the headspace surrounding the commodity using film plastic. This technique was introduced for bulk transport and transit for the first time in the 1950’s for holding horticultural produce and is still in limited use today. MAP has been the subject of numerous articles and publications in the last decade (Kader, 1986). In theory, MAP in consumer units employing a polymeric film, a steady state concentrations of Oz and C02 will be established inside package units due to fruit respiration and film permeation to 02 and C02. Gas concentration at steady state is an important variable in extending the storage 79 period of fruits by MAP. Commodities may differ with respect to the optimum gas concentrations for maximum shelf life and quality preservation. Several researchers have investigated the use of polymeric films in order to create favorable atmospheric conditions for produce (Henig and Gilbert, 1975; Smith gt al. 1985, 1987; Laurie gt al.,1989; Allen and Allen, 1960; Tolle, 1962; Scott and Tewfik, 1947; Boylan-Pett, 1986) and the list is extensive for several commodities. Anaerobic conditions or very poor quality of the commodity was reported by Scott and Tewfik (1947), due possibly to insufficient permeability of films for o2 and C02 and thus they advocated perforation of plastic films to overcome low 02 concentration and build-up of C02. Today, most polyethylene bags for apple fruit have perforations. Most of the early work in MAP was based on empirical methods. Some authors recognized the significance of developing predictive equations for desired gases at steady state and developed formulae or equations to optimize the package atmosphere. This methodology was first attempted by Jurin and Karel (1963) and Karel and Go (1964) for bananas. They developed a graphical approach for the model. Henig (1972) developed differential equations that estimated 02 and C02 concentrations within the package unit. However, the optimization was not fully achieved and the model had some limitations. Film permeability characteristics were not included in the computer solution. Hayakawa gt al. (1975), working with tomatoes, generated, from Henig and Gilbert’s 1975 model, a mathematical approach and algebraic formulae that characterized the gas exchange of the tissue. The authors succeeded in developing their model. Other researchers succeeded in developing other , techniques that characterize commodity respiration rate, film characteristics and other parameters to optimize their models (Cameron gt al., 1989; Prince, 1980). Several patents have been issued covering the use of polymeric films to extend the 80 preservation period of perishable fruits and vegetables; most notable among them was the ‘banavac’ patents of the United Fnrit Company (Badran, 1969) The objective of this study was to evaluate the effects of atmospheric modification by MAP on quality retention of ‘Empire’ apple fruit following CA storage and to characterize the efi'ects of films of different permeabilities at various storage temperatures. 81 MATERIALS AND METHODS ‘Empire’ apple fruit were harvested from a commercial orchard in the Grand Rapids, Michigan, area on Sept. 19, 1986. The fruit were preclimacteric with respect to ethylene production. Approximately 20 percent of the apple fruit had internal ethylene concentrations between 0.1 and 02 141.1" with the remainder of the fruits having lower levels. The average flesh firmness at harvest was 84 N, and the starch index was 4. Based on these maturity parameters, the fruit were judged to be of ideal maturity and physiological development for CA storage. These guidelines are based upon previous investigations with ‘Empire’ apple fruit (Fica gt al.,l987) with provision that the fruit are subsequently cooled and placed in CA within 7 days of harvest. The apple fruit were stored under CA at the Michigan State University Clarksville Horticultural Experiment Station. The CA rooms had a capacity of 2,500 bushels (approximately 50 tons). CA conditions of 1.5% 02, 1.8% C02 , greater than 96% RH were achieved within 4 days of harvest by using a Prism Alpha nitrogen generating system from Permea, Inc. (Monsanto Co, St Louis, MO). Storage temperature was 0 ' C. The nitrogen is used to purge the oxygen from CA rooms. This system was also used as a scrubber to purge carbon dioxide from the room to maintain C02 below 2% (Dilley, 1987, 1990) circumventing the need of other C02 scrubber systems. Apple fruits were removed from CA after 4 months, and were kept overnight at 20 ' C after which they were randomly sorted into experimental sub- samples of sound fruit. A sample of 10 fruits was used to determine flesh firmness and another 10 fruits for C02 production at the temperatures employed for the packaging study to determine respiration rate. Four low density polyethylene (LDPE) films of various thicknesses (25.4, 44.4, 50.8 and 76.2 llm corresponding to 1, 1.75, 2 and 3 mil respectively) from 82 Dow Chemical, Midland, Michigan, were tested at 5 different temperatures (0, 5, 10, 15, and 20'C). Bags of 25 x 25 cm with a surface area of 1250 cm2, were made in the laboratory using an impulse heat sealing machine Model 420 from Audion, Holland Four uniform fruits, each with an average weight of 130 .11; 3 g were pm in each bag. Each treatment and control (unsealed bags) were comprised of 6 replications. A 'I‘yvek pouch (5 x 5 cm dimension) containing 5 g 1 0.01g of magnesium oxide was used as a carbon dioxide scrubber and this was placad inside the bags unless otherwise stated. The packages were then stored in controlled temperature chambers where the relative humidity was kept at approximately 90%. W Oxygen and carbon dioxide. The concentrations of 02 and C02 inside the packs were monitored in triplicate at two day intervals until steady-state was established. Steady-state was considered to be reached when the 02 or C02 concentration in the packages stabilized. Gas sampling was done by withdrawing 1 ml samples of gas from the package headspace using plastic syringes equipped with a 25ga 1/2' hypodermic needle. The needle was inserted through a silicone rubber septum fixed to a 1.6 cm x 2 cm piece of polyethylene electrical tape on eachbag. Carbondioxidewasmeasuredwithaninfraredgasanalyzer(ADC model 88300) employing N2 as a carrier gas. In this procedure, the gas sample is injected as a pulse into the N2 carrier gas through a section of latex rubber tubing leading to the IR detector cell. The IR detector signal is recorded as peak height on a strip chart recorder as the C02 now diluted by the carrier gas, passes _. through the detector cell. The nitrogen carrier gas flow rate was adjusted to provide a linear output from the IR detector cell proportional to the C02 in the gas sample or C02 standards injected. Carbon dioxide and 02 in the packages 83 were also determined as needed by gas chromatography. Ethanol evolution. At weekly intervals, 2 one ml samples of gas were withdrawn from the packs as described earlier for 02 and C02, and injected into a Varian GC (Model 3400) equipped with a flame ionization detector. Helium was used as carrier gas. Ethanol standards were prepared to known concentrations (141.14) in the headspace vapor of an ethanol/water solution in a thermostatically controlled water bath. This was employed for calibration of the GC and determination of the ethanol concentration in the packages. The retention time for ethanol was 1.80 min. GC conditions for operation and detection were as follows: column, injection, and detector temperatures 135, 135 and 250'C respectively. The column support was Poropak Q 80/ 100 mesh (2 mm x 60 cm). Flesh firmness. Flesh firmness was determined weekly with 8 uniform fruits (2 package units) with an average diameter of 65 to 70 mm. An Effigi penetrometer with an 1 1 mm diameter tip mounted on a drill press stand was employed. Readings were taken on the pound-force scale. Measurements were made on two opposite sides of each fruit on the pared surface after removing the skin. The two readings were averaged and converted to Newtons (N) prior to data analysis. External and internal disorders. Visual observations for the presence of superficial disorders were made for each fruit before flesh firmness determination. After measuring flesh firmness, the fruits were sectioned equatorially and examined for internal disorders and anomalies. Fnrit volatiles determination. Volatiles produced by the fruits were determined at each assessment period, before being used for flesh firmness analysis and internal disorders assessment. Fruits from two packs with an average total weight of 1 kg, were placed in a 10 L desiccator which was flushed 84 continuously with air at a rate of 50 cc/min at 20'C for 5 hours. Fruit volatiles were collected using a 6 mm x 10 cm glass tube containing Tenax-GC (80/ 100 mesh) from ANSPEC, Ann Arbor, MI, as an adsorber. At the completion of the adsorption period the tubes were stored at -20 ' C until analyzed. Volatiles were extracted from the Tenax adsorbent with isopentane. The solvent (2 ml) was added by micropipette to the adsorption tubes which were fixed to test tubes with a rubber septum. The assembly was centrifuged for 5 min at 1500 x g to collect the isopentane extract. GC analysis was performed on aliquots of the isopentane solution with a Hewlett Packard GC, Model 5850 A, equipped with flame ionization detector. The column was a 0.25 mm x 60 m capillary column coated with Carbowax 20M. The carrier gas was He at 28 ml/min. The temperature was held at 30'C for 1 min then increased to 180'C at 2'C/min. Dataanalysis. Analysisofvariancewasusedtoanalyzetheresultsandmeans were compared by the Student Newman-Keuls test at 5% when apropriate. Analysis were performed with a computer statistical package Costat. 85 RESULTS Production rates of C02 at difierent temperatures after 4 months in CA storgae were given in Figure 1. As expected the rate of production is function of temperature. In the absence of a C02 scrubber, carbon dioxide concentrations at equilibrium increased with temperature from 0 to 20‘C for all film thicknesses employed (Figures 2 and 3). For the 25.4 um films the values ranged from 2.7 to 5.1 % at 0 and 20'C, respectively; while for 76.2 um films the values were 3.4 to 12.7 %, respectively, over the same temperature range. For the 44.4 and 50.8 um films the C02 values followed the same trend but were intermediate in magnitude and in relation to film thickness. Including a C02 scrubber in the package reduced the steady state level of C02 to similar levels for all film thicknesses at a given temperature. Moreover, the C02 levels were low and similar and increased only slightly over the temperature range of 0 to 20°C. The values ranged from 1.8 to 21% C02 at steady state at O'C for packages made of film 25.4 um and 76.2 pm thick, respectively. Even using the 76.2 urn film, the C02 level ranged from 2.1 to only ' 2.9 over a temperature range of o to 20-c; and 29% was the highest co2 value observed among all packages containing a C02 scrubber. This value (2.9 %) is less than one / fourth the level of C02 at steady-state (12.4%) found for the same film without a scrubber when package units were held at 20 ' C. Carbon dioxide levels as high as 12% can damage fruits of many apple cultivars, whereas C02 levels less than 3 % are normally considered safe over a wide temperature range. These data clearly demonstrates the value of including an effective C02 scrubber within the package. The C02 scrubber prevented the accumulation of C02 above 3% over a temperature range of 0 to 20 ' C where fruit respiration may be expected to quadruple. It must be stressed that this interpretation is based 35 002 PRODUCTION (ML kg-1 HR-‘li 30 25 20 i 15 10 e e .. d ‘ .. 5 e e c 2 20 C ’ d ..d d 0 1 a 5 7 ’ 8 10 13 14 TIME (DAYS) Figure 1. Production rates of carbon dioxide for ‘Empire’ apple fruit in semi- closed system at various temperatures. Fruits were held in CA for 4 months. Values followed by the same letter for each time (days) are not significantly difierent at p =- 0.05. 10 Gas concentratlon ('5) Ethanol (win) 9 .. «Xv cos («4qu '0- cos (ouqol + 02 («not x 0 _ ~9- oa (moot -X- Ethanol t-uqO) —e- situation-1400) ‘ ‘0 7 6 5 4 3i ................. g 2t: ------------------- 9 q . Ol 10 9 .- 3 .. 7 L. art— 6 5 4 (a! - _/"X’ I /..—- ’0 ’- 0 9' -1 5" l o 5 10 15 20 Storage temperature ('C) Figure 2. Gas concentrations of oxygen and carbon dioxide ( 96) and ethanol (vpm) at steady state within packages containing ‘Empire’ apple fruit made from 25.4 (A) and 44.4 (B) um LDPE films. Fruits were held at various temperatures for 3 week period following 4 months of CA storage. 88 0 Gas concentration ('5) A Ethanol (vpm) g - "2" ca: {-14qu ~0- co: («4qu 41- oz t-uqol ii 0 _ €- oat-uqO) -><~ Ethanol (~111qu -0- ethanol (ouqo) ‘ 7 0 5 4 3 2 14 100 13 - ' B ,1: 12 _ '3' 1(1‘0 1‘ ' - 120 10 - .- s - - 100 15 Storage temperature ('C) Figure 3. Gas concentrations of oxygen and carbon dioxide (96) and ethanol (vpm) at steady state within packages containing ‘Empire’ apple fruit made from 50.8 (A) and 76.2 (B) pm LDPE films. Fruits were held at various temperatures for 3 week period following 4 months of CA storage. 89 upon steady-state values for C02 and if the neutralizing capacity of the scrubber was exceeded by long periods at warm temperatures, C02 eventually accumulated to steady-state values similar to those observed without a scrubber. Oxygen concentrations at steady-state in packages of ‘Empire’ apple fruit without a C02 scrubber were found to decrease as the temperature was raised from 0 to 20'C for all film thicknesses employed (Figures 2 and 3). For the 25.4 um film the values ranged from 7.6 to 3.1% at 0 and ZO'C, respectively; while for the 76.2 um film the 02 values were 3.1 to 1.1 %, respectively, over the same temperature range. The 02 values for the 44.4 and 50.8 um films were intermediate in magnitude as expected. The presence of a C02 scrubber in the package consistently lowered, albeit insignificantly, the steady-state 02 values reached with packages of all film thickness and over virtually all temperatures in comparison to 02 5 -state values reached without a C02 scrubber. The COz/Oz ratios at steady-state within the packages were found to increase with temperature and with film thickness for packages with or without a C02 scrubber (Figure 4). For the 25.4 um film the ratio values rose from 0.4 to 1.0 at 0 and 20 ‘ C, respectively; while for the 76.2 um film the values were 1.1 to 4.7, respectively, over the same temperature range. For the 44.4 and 50.8 um films the ratios followed the same general trend and were intermediate in magnitude between the thinner and thicker films. The COz/Oz ratios for the packages with C02 scrubber were generally about half as large as for packages without C02 scrubber. An example of the change in 02 and CO2 within sealed packages as a function of time at 20‘C for the 76.2 um film is shown in Figure 4. Ethanol vapor was found to accumulate in the packages with or without a C02 scrubber as the temperature increased above 15 ' C (Figures 2 and 3). This effect was generally less with a 002 scrubber with some notable exceptions with 5 Gee concentration ('5) + 02 (e MgO) ‘0' 02 (- MgOI ‘5' CO, (e MgO) Period (days) Figure 4. Changes in the concentrations of oxygen and carbon dioxide within packages containing ‘Empire’ apple fruit made from 76.2 um LDPE film, with or without MgO and held at 20‘C. 91 the 25.4 um film. Ethanol accumulation increased at a given temperature as film thickness increased from 25.4 to 76.2 um. The highest value recorded was 137 141.1‘1 for the thickest film at the warmest temperature. With the exception of values taken at 20 - c no values for ethanol exceeded 111.14. Flesh firmness. Fnrit firmness data are presented in Tables la to 3a for packages without C02 scrubber and in Tables 1b to 3c for packages with C02 respectively, for 1, 2 and 3 week storage periods. At low temperatures of 0 and 5 ‘ C no difi'erence in values of firmness was observed between unsealed and packaged fruit. However, increasing temperature up to 20 ' C and storage length up to 3 weeks led to significant firmness loss in unsealed packages. Similarly, no difference was found between difl'erent film thicknesses at these temperatures duringthefirsttwoweeksofstorage. Afterthatapple fruitfrompackages made of 25.4 and 44.4 um LDPE films had higher firmness than 50.8 and 76.2 um films. This was also true when fruit were stored at higher temperatures of 10 to 20 ' C. Including C02 adsorbant in the package had no significant effect on firmness retention. External and internal disorders. At each removal period, fruit from difi'erent packs were inspected visually for any symptom of disorders. Some fruit kept at high temperature (20' C) and in the least permeable films had 02 steady state levels near 1% Oz and showed surface bleaching symptomatic of anaerobic injury. However, no internal browning or breakdown of the fruit was observed upon cutting the fruit in half. Eating quality of these fruits was acceptable after exposure to ambient air for 1 hour or more. Fnrit from packages did not shrivel and the weight loss was significantly lower (P g 0.05) for packaged vs fruits in unsealed packages (6.73%). Although the weight loss of fruits was slightly higher for C02 scrubbed packs (1.65%) in comparison to those not scrubbed (1.32%) after a one week period, the pattern remained similar for both scrubbed and not 92 scrubbed packs. Weight loss (%) over the three week storage period was relatively low; 2.19% and 1.96%, respectively, for scrubbed and not scrubbed. Fnrit volatiles in MAP. Fruits which had been packaged eventually produced volatiles similar in type and quantities to those produced by ‘Empire’ apple fruit held under 1.5% and 3% 02 at 20'C in the study conducted earlier. These fruit were from the same CA storage lot held under conditions of 1.5% Oz and 1.8% co2 for 4 months at 0-0 and did not begin to produce volatiles significantlyuntil theyhadbeentransferredtoairatZO'Cfor7days. This indicates that these CA conditions for a period of 4 months delayed ripening. The pattern of volatiles production of fruits kept in air from 1 through 21 days at 20'C is shown in Fig 5a to 5d. It is evident from the progression of the nature, magnitude and complexity of volatile components produced from day 1 through day 21 that the major components that contribute to flavor and aroma developed as the fruit progressed from an unripe to fully ripe then overripe condition. Figures 5a to 5d will serve as the guide for comparing the volatiles produced by the apple fruit packaged in various films. Only the data on volatiles produced by fruit held at 20 ' C is presented. This is considered to be the most strigent comparison and extreme conditions expected to be encountered in 0 handling ‘Empire’ in MAP. It should also be noted that some packages became nearly anaerobic over the 3 week period at 20 ' C so anomalies among volatiles between these and those fruits kept in the strickly aerobic environment might be expected and noteworthy with respect to normal flavor and aroma development. The Figures for volatiles produced by fruit with and without a C02 scrubber are provided as C02 accumulation to levels above 5% may be expected to cause some metabolic effects. The first general impression to be gained from volatiles produced by MAP fruit is that fruit volatiles never reached the complexity nor magnitude of 93 production compared to fruit kept in air over the 3 week period. This can be seen comparing Figure 5d for air vs Figure 6c through Figure 9c for MAP fruit in the various film thicknesses. The fruits kept in air for 3 weeks at 20'C were obviously overripe and quite senescent by this time so many of the volatiles were likely being derived from extensive membrane degradation associated with advanced ripening. However, even after the shorter durations, the air stored fruit showed a more complex pattern of volatiles than fruit from packages as seen in FiguresSbandcvsFigures6aandbthroughFigures9aandbforMAPfruit. ThesecondgeneralefiectobservedwasthatfruitinMApackageswith a C02 scrubber generally exhibited a more complex pattern of volatiles than MAP fruit without a scrubber. This may reflect the retarding effect of C02 accunmlation on ripening development. For fruit held for 21 days in MAP with 76.2 um films without a C02 scrubber, the volatiles pattern (Figure 9c) is quite complex and this may be indicative of a C02 induced metabolic disturbance perhaps linked to fermentation as the 02 level in these packages was near 1% O2 and C02 was over 12%. Table 1a. Flesh firmnessz (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged without a C02 scrubber in LDPE films of various thickness for 1 week. TEMPERATURE OF STORAGE (‘ C) 0 5' 10 15 20 FILM THICKNESS (um) 25.4 735ab 73.88 73.1c 72.7b 73.3a 44.4 72.1a 70.6a 66.9ab 652a 63.7b 50.8 75.3b 74.3a 642a 643a 62.8b 762 73.4ab 72.6a 67.9b 665a 68.2b UNSEALED 71.3a 723a 66.1ab 642a 62.3b Mean 73.1 72.7 67.6 66.6 66.0 0221 0273 02.39 03.03 02.45 LSDonS 2 Data followed by the same letter within columns are not significantly different at p =- 0.05 Y Flesh firmness at removal from CA was 84 N. 95 Table 1b. Flesh firmness‘ (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged with a C02 scrubber in LDPE films of various thickness for 1 week. TEMPERATURE OF STORAGE (- C) o 5 10 15' 20 FILM THICKNESS (urn) 25.4 742ab 74.0a 72.8b 73.0b 715a 44.4 71.6a 71.9a 69.4ab 65.8a 643a 50.8 . 76.4b 753a 68.4ab 63.6a 63.48 76.2 71.4a 71.6a 69.8ab 653a 67.6a UNSEALED 71.3a 72.2a 66.1a 642a 623a MEAN 72.9 73.0 693 66.4 65.8 15110.05 g 03.18 02.98 0431 06.19 07.80 2 Data followed by the same letter within columns are not significantly different at p a 0.05 Y Flesh firmness at removal from CA was 84 N. 96 Table 2a. Flesh firmnessz (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged without a C02 scrubber in LDPE films of various thickness for 2 weeks. TEMPERATURE OF STORAGE (‘ C) 0 5 10 15 20 FILM THICKNESS (um) . 25.4 69.9a 68.7c 66.6b 70.0b 67.9c 44.4 70.18 64.7b 643ab 63.0a 60.38 50.8 69.4a 65.2b 59.4ab 67.8b 61.3a 76.2 68.6a 65.8b 6322b 633a 65.1b UNSEALED 672a 622a 61.5ab 61.8a 59.7a MEAN 69.0 65.3 63.0 65.2 62.8 LSDom 03.06 02.09 03.82 03.69 ~ 01.61 2 Data followed by the same letter within columns are not significantly different at p = 0.05 3' Flesh firmness at removal from CA was 84 N. 97 Table 2b. Flesh firmnessz (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged with a C02 scrubber in LDPE films of various thickness for 2 weeks. TEMPERATURE OF STORAGE (' C) 0 5 10 15' 20 FILM THICIOIESS (14!!!) 25.4 70.2ab 69.7b 68.1c 68.1b 66.58 44.4 71.3b 66.3ab 655bc 62.7a 63.4a 50.8 68.6ab 65.6ab 62.6ab 66.7ab 63.7a 76.2 69.4ab 6528b 59.4a 63.4a 61.38 UNSEALED 672a 622a 61.5ab 61.8a 59.7a MEAN 69.3 66.2 63.3 64.5 63.0 LSDQOS 02.76 04.48 0331 03.71 05.09 2 Data followed by the same letter within columns are not significantly different at p = 0.05 Y Flesh firmness at removal from CA was 84 N. 98 Table 3a. Flesh firmnessz (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged without a C02 scrubber in LDPE films of various thickness for 2 weeks. I TEMPERATURE OF STORAGE (' C) o 5 10 15 20 FILM THICKNESS (um) 25.4 682b 663d 65.1c 626d 602C 44. 4 68.6b 628bc 58.3b 56.8bc 55.6b 50. 8 67.8b 642cd 55.4a 54.3b 57.8c 76.2 643a 60.5ab 55.9a 58.8c 58.3c UNSEALED 635a 58.9a 54.6a 51.98 48.3a MEAN 665 625 57.8 56.9 56.0 LSDOOOS 01.99 0230 0231 0256 02.03 2 Data followed by the same letter within columns are not significantly different at p =- 0.05 y Flesh firmness at removal from CA was 84 N. Table 3b. Flesh firmnessz (N) of ‘Empire’ apple fruity from CA storage after holding at various temperatures and packaged with a C02 scrubber in LDPE films of various thickness for 2 weeks. TEMPERATURE ,_ 0F STORAGE (° I“ _ o 5 10 15 20 FILM THICKNESS (um) 25.4 67.4ab 673c 64.7c 71.7c 60.5c 44.4 695b 63.2b 60.5b 53.8ab 51.6b 50.8 65.9ab 61.6b 56.9a 56.4b 58.4c 76.2 65.7ab 62.3b 532a 523a 60.2c UNSEALED 635a 58.9a 54.6a 51.9a 483a MEAN 66.4 62.6 58.0 552 55.8 LSDw 03.09 0254 03.1 03.11 0237 2 Data followed by the same letter within columns are not Significantly different at p = 0.05 3' Flesh firmness at removal from CA was 84 N. 100 H- o—. "O H as ~c' 233:8 3 a 0,. "flags 2 __ “In a 31 g V 3. (b) n.- %x 10 flan .? it n i L §_m 1616 .0 X 3 - : IIWJ’ 1.8 2 g: ;L; I 2,3.E33 a L1H)“ if?“ ‘1. : Jtfifql iJIIILii-j . Figure 5. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 1 day in air at 20°C. 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-Z-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. 101 '3 1,. (a) .7. $9“ :5 '= s z 3 g 3 Figure 6a.Gas chromatographic profile ofvolatiles produced by‘Empire’ apple fruit from controlled atmosphere storage afier 7 days in package made of 25.4 pm LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-Z-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. tans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. 102 1 m g d to 5'35 " ‘\.’5 1 2. 1 a 3 a. a: 3'3 ‘ 3 N 2" h ‘9 :3" 5 3 3 W (8 .3 g ' § #6 o -0 42,1: IO 7) Figure 6b. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 14 days inpaekage made of 25.4 um LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-Z-methyl butyrate, 4. hexanal, 5 . ethyl hexanoate, 6. trans—B-haen- l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. 103 5 7 1 2 (n .. 3 ‘02 o~ :: a s ; 9 u 0. N u ISII u :— no: .73 fit” tau 0- J4 use at. ‘ ms {IO-SI .J 397 ‘l H I =5 :3 “g .. ' , U1 3 g. i l‘l'halfiL v an N. 38 4:.” L1I‘ (I) a M. 5 n H ' S! E F- a 2 3 a is n ‘ : ~° 0! "HF" °_ 3. H (A ,2 :e h hid-‘13” t. . h . Figure 6c. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 21 days in package made of 25.4um LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-Z-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexenol. 104 . l o .02 :- 23: :5 E w 3 8 q S :3 a I l b ‘3 4 r; '. w ~ I . C” :35“: “:3 #3 41“ ‘9, . :1: All i Figure 7a. Gas chromatographic profile of volatiles produwd by ‘Empire’ apple fruit from controlled atmosphere storage after 7 days in package made of 44.4 um LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 5. ethyl hexanoate, 6. trans-3- hexen-l-ol, 7. l-hexenol and 8. ds-B-hexen-l-ol. 105 1 2 5553252 m n E". s ' a 5 g‘ g g ' 7 8 .JJU U“ MWéWdhLMlHLA-WMJW» 42.9 8 ~13; 1“ n" 0) "l4 “Mum mm Figure 7b. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 14 days in package made of 44.4 pm LDPE film with (A) or without MgO (B) at 20°C. 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. uans-3-heltcn-1-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. C gum 3-—l2 0‘ l5 8‘ 32.85 31 39 “I” 106 7 8 l 2 (A) :5 g) a .7- 3‘3'3‘83 a q 9 5 "its O u' “an“ ~ ”—— 5.... ¢——-—n s: .5 t u 23.13:.) l. %—n 45 Erin: in.“ - s in n i“ )I it so as “II 31 _.3 I5 bl L? 85 J - WU “m «JAM Weir Figure 7c. Gas chromatographic profile of volatiles produced by 'Empire’ apple fruit from controlled atmosphere storage after 21 days in package made of 44.4 um LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen—l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. IS 51 107 (A, t 35': If s E 18 :a 3 6 as 33 4 3 ,, a - a d ‘2 “t a Rafi m :5 .11 Figure 8a.Gas chromatographic profile ofvolatiles produced by‘Empire’ apple fruitfromcontrolled atmosphere storage after 7daysinpaekage made of 50.8 pm LDPE film with (A) or without MgO (B) at 20°C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl 2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. 8." 108 l 2 3 gig 232 . m 3?? 55:7 33 '7 41x77“ 7 “a J. 7 . g 7 .7» M 17!»)..li M 555353 m P a d 3 E i 8 ~ " M 7:7 5:: .7 7: Figure 8b. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 14 days in package made of 50.8 m LDPE film with (A) or without MgO (B) at 20‘C, 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-Z-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-S-hexen-l-ol, 7. l-heltenol and 8. cis-3-hexen-l-ol. JJ‘ 109 *A-——1751 o- LTLS §%:::;;J‘ ’5t10 (I) -ILI ‘5]9 NJ! ISIO 1131 LA. Figure 8c. Gas chromatogxaphic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 21 days in package made of 50.8 um LDPE film with (A) or without MgO (B) at 20°C. 1. ehtyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. C— i I. 1.5 26.0 o 6 JG Eta.“ 110 Q Q. 0"! 7,0 I” n n $.43 N Figure 9a. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage after 7 days in package made of 76.2 um LDPE film with (A) or without MgO (B) at 20°C. 1. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3-hexen-l-ol, 7. l-hexenol and 8. cis-3-hexen-l-ol. L!” .0 N “-53 00 I? 111 27:5 ,3 m 7 E 93 4 «- .5. - ' "33 :3 I: .. 55 53 §§ 7777 22.-1......17 z ' WM’H" ”AWL; C” . at: 3E:Jlbo tart rose 215: 2171 res: :nrs . Jtso “I on Figure 9b. Gas chromatographic profile of volatiles produced by ‘Empire’ apple fruit from controlled atmosphere storage afier 14 daysin package made of 76.2 um LDPE film with (A) or without MgO (B) at 20 “C. l. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-methyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-3—hexen-l-ol, 7. l-hexenol and 8. cis-B-hexen-l-ol. 112 3:77: 7:33: § § '7 77 .33 4:7 i 2* .-.- i 7 " 3 .a ' 1 '- §a 7" ' E: Figure 9c.Gas chromatographic profile ot‘volatilec produced by‘Empire’ apple fruit from controlled annosphere storage after 21 daysin package made of 76.2um LDPE film with (A) or without MgO (B) at 20‘C. l. ethyl acetate, 2. ethyl propionate, 3. ethyl-2-mahyl butyrate, 4. hexanal, 5. ethyl hexanoate, 6. trans-B-hexen-l-ol, 7. l-hexenol and 8. cis-3-hmten-l-ol. f}:— 1- 27 29 ‘th 113 DISCUSSION The gas concentration inside MAP units containing ‘Empire’ apple fruit without a C02 scrubber showed a rapid decline of oxygen and an accumulation of C02 during the first 2 to 3 days of storage. This rate of change was progressively greaterasthetemperamrewasincreasedfromOtOZO‘Candasfilmthickness increased from 25.4 to 76.2 um. The C02 concentration rose to a maximum of 15% with the 76.2 um film at 20°C and then stabilized at a fairly constant lower level over a 3 week period. This behavior is typin and is related to the rate of C02 production in relation to the film permeation rate for C02 (T omkins, 1962). The presence of MgO as a C02 scrubber only slightly altered the pattern of 02 reduction in packages. The explanation for this may lie with the lower levels of C02 obtained in packages with a scrubber. Carbon dioxide, a product of respiration, is known to inhibit respiration via a feed-back mechanism. Comparison of the data of co2 and o2 in Figures 2 and 3 reveals that as the co2 level increased with temperature in packages without a C02 scrubber the 02 level did not generally decrease as much as in packages with a scrubber. A slightly lower respiration rate would reduce the 02 gradient and result in slightly higher 5 -state 02 values in packages without C02 scrubbers with a given film thickness. Another factor that may contribute to this observation may be the slight reduction in void volume in packages with the C02 scrubber. Packages with less void volume would be expected to come to steady-state 02 levels more quickly than packages with larger void volumes. It is unclear however, that high C02 obtained in packages without the adsorbant slows the respiration and thus 02 at steady state remains high. Steady-state concentrations of 02 and C02 in packages were determined by fruit weight and respiration, by film characteristics and by temperature. The levels of 02 and C02 attained are roughly proportional to film thickness and 1 14 temperature of storage and the trend is illustrated in Figure 4. Steady-state was reached fastest in the least permeable film; with equilibrium reached within 3 to 4 days at 20‘C compared to about 10 days at O‘C (data not shown). This behavior is due to film permeability characteristics which are temperature dependent. The effect of temperature was very significant, reflecting both the higher rate of respiration as temperature increased and the temperature efi'ect on film permeation. The combined efiect aflects the establishment of equilibrium conditions within the package units. Steady-state values will difier between packages at different temperatures unless the rate of diffusion through the film barrier is affected by temperature to the same extent as respiration. However this is not the case, the steady-state concentrations at lower temperatures were, respectively, high for oxygen and low for carbon dioxide. The steady state values reached changed as the temperature incremd and, as a result, the level of 02 decreased and C02 increased in the package. ‘ Film permeability considerably afiected the steady-state concentrations of 02 and C02. High C02 concentrations (15%) and very low 02 (less than 1%) were obtained with 76.2 pm thick film at 20‘ C as shown in Fig. 5. However, these conditions tended to stabilize at equilibrium. Similar observations were reported for other commodities: Boylan-Pett (1986) and Geeson gt a], (1985) for tomatoes; Smith gt al. (1987) for apples and Prince (1982) for tulip bulbs. The use of a C02 scrubber in the packages tended to suppress the accumulation of C02. Eventually, however, a burst of C02 occured as the MgO was neutralized. This was true for all treatments but varied in time in temperature and in film thickness. This pattern was correlated to temperature and may be explained by the saturation of the chemical adsorbant as reported earlier (Boylan-Pett, 1986). Tomkins (1966) found that the level of C02 in the packages did not significantly afi'ect the 02 assimilation. However, in this 1 15 study, the 02 equilibrium value was generally lower in packages with a C02 scrubber which kept C02 at lower steady state values. This is consistent with high C02 levels suppressing 02 uptake by the fruit. The C02 absorbant tended to also limit water condensation in the packages. This was also seen in preliminary experiments (datanotshown)using ngvsS gofMgO perpackagewith 0.5 kg of fruits wherein this was associated with a higher weight loss of fruit. However, the adsorption isotherm of the MgO scrubber was not determined nor was the actual humidity within the packages, although some packages showed water condensation on the inner surface of the film. Ethanol vapor accumulated inside packages dependent upon temperatures and this was independent of the presence of a C02 scrubber. Ethanol accumulation in the bags was positively correlated to film thickness. Increasing both temperature and film thickness resulted in the greatest ethanol accumulation (Figures 2 and 3). As the concentration of 02 at equilibrium was considered to be above the extinction point for alcoholic fermentation yet ethanol accumulated, it is speculated that apple fruit while in CA may produce ethanol and was released at warm temperature also C02 content inside the packages may have had a direct effect on ethanol production. It is generally recognized that high levels of C02 can induce fermentation of plant tissu. Ethanol levels were higher at high C02 levels in packages at similar 02 levels. Ethanol levels were generally lower with the MgO C02 scrubber in the package and this is consistent with this interpretation. Oxygen values at equih'brium at 15 and 20 ‘ C may have been below the extinction point of alcoholic fermentation for some tissues of the fruit before reaching steady state and this would allow ethanol production. Correlation coeficients of ethanol concentration vs 02 level were very significant and varied from (r- 0.57 to r a 0.93). The coeficients were calculated for each film at different temperatures with or without the use of magnesium oxide (data not 1 16 presented). Ethanol accumulation in the package is symptomatic of alcoholic fermentation by the fruit tissue. Cases where ethanol accumulated to high levels were associated with low 02 levels and/ or high C02 levels. High levels of C02 can induce fermentation even at relatively adequate 02 levels (above the extinction point) which normally would not support alcohol formation. This may explain the lower ethanol levels found in packages with a C02 scrubber at equal or nearly equal 02 levels at similar temperatures. The accumulation of C02 in the package is partly a consequence of fi'uit respiration from aerobic processes at 02 levels above the extinction point of fermentation. And at 02 levels below the extinction point of fermentation, C02 would be derived increasingly from alcoholic fermentation as 02 is depleted in the tissue. The actual extinction point of fermentation for the fruit as a whole entity is not a single fixed value but rather a term that should be considered at a subcellular level; namely at the mitochondrial level where the C02 is converted to water in oxidative phosphorylation. Cytochrome oxidase. the terminal electron acceptor in respiration has a very high afinity for 02 and is considered to be saturated at 02 levels much lower than 1%. Thus, fruit cells near the surface of fi'uits in 1% 02 may still be rcspiring aerobically while those deep within the fruit flesh may become deprived of 02 by gas diffusion limitation in relation to oxygen demand and progressive depletion of 02 consequentially results in anaerobic respiration or fermentation (Lougheed, 1987). The results of this study showed also that good retention of flesh firmness, reduced weight loss, good external appearance, and good organoleptic quality of fruits was maintained by modified atmosphere packaging. Greater beneficial ‘ effects of MAP were found at the higher storage temperatures of 15 and 20 ‘ C than at the lower temperatures of 0 and 5 ‘C. At 20°C fruits in the least 117 permeable film tended to retain firmness during the first week, but subsequently firmness decreased with increasing period of storage to levels similar to those of the other films. Fruits that had been packaged produced volatiles similar in type and relative quantity to those produced from fruits held under the continuous flow CA system studied in Section I. These fruits were from CA storage at 1.5% with 1.8% C02 for 4 montln at 0°C and did not begin to produce volatiles significantly unfiltheyhadbeentransferredtoairatZO‘Cfor7days. Thisindicatesthat these CA conditions delayed ripening development for a period of 4 months. Modified atmosphere packaging of these apples, in the different thicknesses of LDPE films, altered the rate of volatile production subsequent to returning the fruit to air. Moreover, this was found to be influenced by the temperature. Fruits ' from all packaging treatments tested showed a delay in flavor and aroma development compared to apples kept in air and this may be attributed to atmospheric conditions developed inside packages that reduced respiration rate and ripening. Fruits kept in air showed a significant increase in volatile components after 7 days compared to that of fruits from the other treatments. A maximum volatile production by fruit in air was attained after 14 days and continued to increase up to 21 days. However, fruit packaged in difi'erent film thicknesses had their maximum production of volatiles at 21 days. The lag in time observed, again may be attributed to the ripening delay by modification of atmospheric conditions surrounding the fruit. Volatile components, of which several are known to contribute to the characteristic flavor and aroma of Empire, apples were directly related to fruit ripening development stage (Chiraghi, 1988). At the time of harvest fruit were mature but unripe and thus lacked in aroma. After 4 months exposure to the controlled atmosphere conditions employed in these studies, the fruit remained 118 unripe. Following subsequent storage in air for one week, volatiles which are associated with ripening began to be produced in significant amounts; whereas, for those from fruits kept under MAP conditions for 7 to 14 days the rate of volatiles production was slower than that for non packaged fruits subsequent to transferring the fruit to air. Eventually the MAP fruits produced volatiles similar in type and relative magnitude to those produced sooner by fruits transferred immediately to air after CA storage. Difierences observed in the pattern of volatiles produced by MAP and air-stored fruits may be attributed to the low oxygen and relatively high C02 established in the packages which delayed the normal ripening response. C02 scrubbing did not afi'ect the pattern of volatiles. Moreover, fruits in MAP ‘with 76.2 um films without a C02 scrubber and held for 3 weeks at 20 ° C showed an abnormal profile than fruit keep in air. This may be associated with low 02 and relatively high C02 reached in these packages. This was not seen for other fruits in MAP with 76.2 um films at lower temperature or in MAP of other films at all temperatures. Accumulation of C02 and reduction of 02 in the atmosphere surrounding fruits achieved by MAP of fruits from CA storage reduced fruit respiration, ‘ ethylene action and thus ripening. These results indicate that the beneficial effects of MAP on keeping quality of apples may be realized even at relatively high temperatures of 15 to 20° C. ' 119 LITERATURE CITED Allen, A.S., and Allen, N. 1950. Tomato film findings. Mod. Pack. 23(6):IB-126. Bangerth, F., G. Bufler and, H. Halder-Doll, 1984. Experiments prevent ethylene biosynthesis and/ or action and effects of exogenous ethylene on ripening and storage of apple fruitan "Ethylene: Biochemical, Physiological, and Applied Aspects,” Y.Fuchs and E. Chalutz (ed), 9291. Martinus Nijhofi/Dr. Junk, The Hague. Ben-Yehoshua, s. 1985. Individual seal packaging of fruit and vegetables in plastic film. A new postharvest technique. HortScience 20 : 32-37 Boylan-Pett, w. 1986. Modified Atmosphere Packaging of tomato fruit. MS Thesis, Mich State Univ. East Lansing, MI, us». Badran, A.M. 1969. Controlled atmosphere storage of green bananas. US. Patent 3,450,542. Cameron, A.C,, Boylan-Pett, W., and 1.1.. Lee. 1989. Design of Modified Atmosphere packaging systems; modeling oxygen concentrations within sealed packages of tomato fruits. J. Food Sci. 54 (6):1413-1416. Chen, PM. 1985 . _ Some advantages and disadvantages of low oxygen storage of red Delicious apples. Postharvest Pomology Newsletter 3: 10- 13. Chen, P.M., Olsen, KL, and M. Meheriuk. 1985. Efi'ect of low oxygen atmosphere on storage scald and quality preservation of "Delicious” apples. J. Amer. Soc. Hort. Sci. 110: 16-20. Dennis, G, K. M. Browne and F. Adamicki. 1979. Controlled atmosphere storage of tomatoes. Acta Hort. 93:75-83 Dilley, DR. 1987 . New Developments in Scrubbing Technology for Controlled Atmosphere storage. The Great Lakes Fruit Growers News. May, 1987. Dilley, DR. 1988. Recommended storage conditions for Michigan apples. Postharvest Laboratory Mich. State University, East Lansing, MI. USA. 120 Dilley, DR. 1990. Application of air separator technology for controlled atmosphere storage of apples. Ed. J. Fellman. Proceedings of the 5th controlled atmosphere storage Research Conference. Wenatchee, WA, June 14-15 vol. 1:409-418. Geeson, J.D., K. M. Browne, K. Sheppard and J.K. Guaraldi. 1985. Modified Atmosphere packaging to extend the shelf life of tomatoes. J. Food Technol. 202339-349 Hayakawa, K., Y.S. Henig, and S.G. Gilbert. 1974. Formulae for predictin gas exchange offresh produce in polymeric film package. J. Food Sci. 40:186-191. Henig, Y.S. 1972. Computer analysis of the variable afiecting respiration and quality of produce packaged in polymeric films. PhD Thesis Rutgers University, New Brunswick, NJ. U.S.A. 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. Jurin, V., and M. Karel. 1963. Studies on control of respiration of McIntosh apples by packaging methods. Food Tech. 17(6):104-108. Kader, AA. 1986. Biochemical and physiological basis for efi'ects of controlled and modified atmosphere on fruits and vegetables. Food Tech. 40(5):99- 104. Karel, M., and J. Go. 1964. control of respiratory gases. Mod. Pack. 37(6):123- 127,190,192. ' Kidd, and West, C. 1932. Gas storage of tomatoes. Gt. Brit. Dept. Sci. Indus. Res. Food Invest. Bd. Rept. 209-211. Lange, E. 1985. Recent advances in low 02 and low ethylene for apples in Poland. Proceeding of the 4th National Controlled Atmosphere Research Conference. pp. 295-307. Lau, 0.1. 1983. Efi'ects of storage procedures and low oxygen and carbon ' dioxide atmospheres on storage quality of "Spartan” apples. J. Amer. Soc. Hort. Sci. 108(6):953-957. Ian, 01.. 1985. Storage responses of four apples cultivars to low 02 atmospheres. Proceeding of the fourth National Controlled Atmosphere 121 Research Conference, pp. 43-56 Laurie, G.H. and BE. Mackey. 1989. Permeability of flexible polymer films used to wrap citrus fruits to the fumigants ethylene dibromide and methyl bromide. J. Amer. Hort. Sci. 114(1):86-90 Lidster, P.D., k.b. McRae and EM. Johnson. 1985. Retention of apple quality in low-oxygen storage followed by standard controlled atmosphere regimes. J. Amer. Soc. Hort. Sci. 110:755-759. little, GR. and B1. Tugwell. 1985. Storage construction for effective ultra-low oxygen storage in Australia. Proceeding the fourth National CA Research Conference, 281-289. Lougheed EC. 1987. Interactions of oxygen, carbon dioxide, temperature and ethylene that may induce injuries in vegetables. HortSci. 22:791-794. McGlasson, W.B., and R.B.H. Wills. 1971 Efiects of oxygen and carbon dioxide on respiration, storage life and organic acids of green bananas. Aust. J. Biol. Sci. 24: 1103. Prince, TA. 1980. Design and function of a modified atmosphere package for precooled tulip bulbs. PhD Dissertation, Mich. State Univ, East Lansing, MI. ' Scott, LE, and S. Tewfik. 1947. Atmospheric changes occurring in film-wrapped packages of vegetables and fruits. Proc. Amer. Soc. Hort. Sci. 49: 130. Sharples, R0. and J .R. Stow. 1982. Recommended conditions for the storage of apples and pears. Report of the East Malling Research Station for 1981, 199-202. Smith, S.M.; D.S. Johnson, J. Chesworth, J. Mori. 1985. Short term storage of Discovery apples. J .Hort. Sci. 60, 207-214 Smith, S., J. Geeson and J. Stow. 1987. Production of modified atmospheres in deciduous fruits by the use of films and coating. HortScience 22:772. Tolle, WE. 1962. Film permeability requirements for storage of apples. USDA Tech. Bull. 1257. ' Truter, 6.1., and GJ. Eksteen. 1987. Storage potential of apples under controlled atmosphere storage at ultra-low oxygen concentrations. Sagtevrugteber. (South Africa) pp. 141-145. GENERAL CONCLUSION 122 123 The results from the dynamic atmosphere storage studies conducted at the relatively high temperature of 20 ° C, which is often experienced in marketing of several horticultural comodities, indicated that apple fruit of both ‘Empire’ and ‘McIntosh’ varieties held at this temperature and low oxygen concentrations retained flesh firmness better and had reduced weight loss than fruit held in air over the 3 week period test. Fruit held at 3% 02 developed typical profiles of volatiles known to contribute to aroma as in the air. However, although 1.5% 02 for prolonged periods up to 3 weeks retained better flesh firmness, fruit exhlbited a profile of volatiles symptomatic of the onset of fermentation and these conditions should be avoided for long exposure periods. The low oxygen concentrations employed were similar to those found in MAP suggested that MAP may offer a beneficial effect on maintaining quality of apple fruit after removal from controlled atmosphere storage. A predictive technique to achieve establishment of desired conditions of oxygen in sealed package was developed. The oxygen depletion method and MAP trials yielded similar equations of prediction of weight and film characteristics. Although more refinement may be needed for this technique, similarity of results between empirical and mathematical approachs was encouraging and shows their applicability as guidelines in the area of modified atmosphere packaging research for apple fruit. MAP trials in different LDPE films showed that fruits kept in films made of 25.4 um LDPE ripened more rapidly than those in thicker films (i.e, 76.2 um). This is due probably to the permeability of the film and thus to the relatively high steady state concentration of oxygen that resulted in these package units. The efiect was more noticeable at high temperatures of 15 and 20° C than at 5 and 10° C. Low oxygen and high carbon dioxide tended to delay fruit ripening and 124 deterioration. Fruits packaged with 76.2 um LDPE films and held at 20° C for up to 3 weeks accumulated ethanol and exhlbited a volatiles profile symptomatic of fermentation. This was correlated with low oxygen and high carbon dioxide levels within the package. Fruits in films with intermediate permeability to 02 retained more flesh firmness and weight than fruits kept in air and developed the capacity to produce typical types and relative quantities of volatiles but with a lag time estimated of about 1 week. This indicates that MAP of apple fruit following CA storage may extend the poststorage preservation period by at least 1 week relative to storage in ambient air. It must stressed however, that at removal from controlled atmosphere, apple fruit used in these studies showed very limited ripening development during storage. Holding fruit from CA storage or otherwise where ripening has been allowed to advance and subjecting them to low 02 i.e 1.5% level at 20°C should not be undertaken. "7'17 11711111711111.1111?