Quality of Strawberries Automatically Packed in Different Plastic Films

Transcription

1 JOURNAL OF FOOD SCIENCE ENGINEERING/PROCESSING Quality of Strawberries Automatically Packed in Different Plastic Films J. M. García, R. J. Medina and J. M. Olías ABSTRACT The quality of strawberries (Fragaria ananassa Duch. cvs. Oso Grande and Camarosa) non wrapped or packed in cellulose, perforated polypropylene, nonperforated polypropylene (automatically), and polyvinylchloride (manually) during storage at 188C was compared. Nonperforated polypropylene packages of fruit had the highest CO 2 and the lowest O 2 content, and the most desirable quality parameters. However, this type of package had undesirable appearance due to water condensation. Cellulosic films maintained a well balanced internal atmosphere, but were wrinkled. Perforated polypropylene and polyvinylchloride packages exhibited the best appearance, but fruits packed in perforated polypropylene films rapidly deteriorated. Unwrapped fruits had the least desirable quality in both varieties. Key Words: Fragaria ananassa; postharvest; storage; strawberries; packaging INTRODUCTION MANY MARKETS FOR STRAWBERRIES ARE GREAT DISTANCES FROM the production points. Thus, effective handling procedures are required to prevent excessive deterioration. Spanish strawberries are produced primarily in Huelva (southern Spain), but the principal markets for the fresh fruits extend across central Europe. Surface transported strawberries may take 3 or 4 days to arrive at the markets. Strawberries are highly perishable, with a short postharvest life at room temperature, due to their high susceptibility to fungal infections (El-Kazzaz et al., 1983) and to rapid loss of water from their tissues (Aharoni & Barkai-Golan, 1987). To decrease fruit respiration rate and fungal spoilage, forced air precooling at 1 2 C has been used (Olías et al., 1995). To reduce weight loss and maintain fruit quality during storage strawberries are routinely harvested by hand in polystyrene baskets which are subsequently manually wrapped with polyvinyl chloride (PVC) films in the packing houses. However, for ecological reasons the use of PVC is being discouraged. Automating the packaging process would represent a major decrease in production costs. Polypropylene films, an alternative to PVC, have less disposal problems. They are the most applied for automatic packaging of strawberries and may be used in perforated or nonperforated form. Perforated films provide only a mechanical barrier to help minimize damage or further manipulation of the fruits. Nonperforated films enable formation of a modified atmosphere in the package due to their low permeability to O 2 and CO 2, and affect respiration of the berries. This kind of atmosphere can extend the acceptable quality of strawberries, delaying spoilage. However, excessively high levels of CO 2 and/or very low levels of O 2 can induce development of offflavors. Cellulosic films have been introduced in automatic packaging. In addition to the advantage of being natural in origin, their permeability to respiratory gases produces internal modified atmospheres The authors are affiliated with Depto.de Fisiología y Tecnología de Productos Vegetales, Instituto de la Grasa (CSIC) Avda. Padre García Tejero, 4, 41012, Sevilla. Spain. Address inquiries to Dr. Jose M. Garcia. in the strawberry package similar to PVC or polypropylene films. Our objective was to compare fruit quality of strawberries automatically packed using different commercial plastic films with those packed by the manual method. MATERIALS & METHODS STRAWBERRY FRUITS (FRAGARIA ANANASSA DUCH. CVS OSO GRANDE and Camarosa) were harvested and transported the same day to the packing house (San Bartolomé de la Torre, Huelva, Spain). Damaged and nonuniform fruits were removed and selected fruits were randomly placed in polystyrene baskets designed to contain 500g strawberries (25 30 fruits/basket). These were randomly assigned to 5 groups of 60 baskets each. Fruits were refrigerated under forced air precooling at 6 C and, afterwards, three groups of 60 baskets were automatically wrapped with polypropylene (PP; mm thick, 110 and 450 cm 3 /m 2 day, permeability for O 2 and CO 2, respectively), polypropylene perforated with 8 mm holes in 3% of the total film surface (PPP; mm thick; Plastibag S.A. Puerto de Santa María, Spain) and cellulosic (CL; mm thick; 400 and 1050 cm 3 /m 2 day, permeability for O 2 and CO 2, respectively; La Cellophane Española S.A., Burgos, Spain) films. A fourth group of baskets was manually wrapped using a PVC film (0.035 mm thick; 500 and 1200 cm 3 /m 2 day, permeability for O 2 and CO 2, respectively; Bordem España S.A., Valencia, Spain), constituted a control group. The fifth group of 60 baskets was not wrapped to monitor fruit condition without any package. Subsequently, fruits were cooled to 1 C, and stored for three days, simulating the period of transportation to market. The fruits were then placed at 18 C for a storage period of four days. The experiment was carried out three times, in April, May and June of The data presented are the mean values from these experiments. Sampling was conducted after storage at 1 C and every day during storage at 18 C. Changes in the carbon dioxide and oxygen contents of each package atmosphere were evaluated in three wrapped baskets taken randomly with different baskets from each sampling date. A sample of 5 ml of headspace gas was withdrawn from each basket, using a syringe, which was sealed with a rubber septum. Subsequently, samples of 150 L were injected into a gas chromatograph (model 5890, Hewlett-Packard, Santa Clara, USA) equipped with a thermal conductivity detector and a molecular sieve column, mesh, (Carbosieve SII. Supelco Inc., Bellefonte, USA) of 3m length and 3 mm i.d., using helium as carrier gas. The injector and detector were 250 C and the oven temperatures were 33 and 225 C for O 2 and CO 2 determinations respectively (Pérez et al., 1997). Weight changes of strawberries were measured in five baskets from each packaging method throughout the storage period. The incidence of postharvest decay (fruits with visible mycelial growth) was monitored in three samples of four baskets randomly taken from each packaging group, at each sampling date. Data were expressed as percent of decayed fruit. Healthy fruits (40) from the same samples were randomly taken to analyze changes in skin color in each treatment. Color of each fruit was measured in the equatorial zone, using a Minolta CR200 chromameter (Minolta Camera Co. Osaka, Japan) and employing the L*a*b* color spacing system. The same fruits were used for measuring fruit firmness using a Zwick 3300 densimeter (Zwick Gmbh & Co, Ulm, Germany) with a 5 mm disk (force required to depress the disk 2.4 mm into the fruit). Data were expressed in newtons/ per cm 2 of probe surface. The juices were extract- Volume 63, No. 6, 1998 JOURNAL OF FOOD SCIENCE 1037

2 Quality of Packed Strawberries... ed from 4 groups of 10 of the same fruits, to determine the content of soluble solids, with an Atago DBX-55 refractometer (Atago Company Ltd., Tokyo, Japan), and titratable acidity with a Crison automatic titrator (Crison Instruments A.G., Baar, Switzerland) that measured the volume of 0.1 N NaOH required by 10 ml of juice to reach ph 8.0. Data were expressed as % citric acid (García et al., 1995). We developed a method to compare reproducibly the effect of different packages on fruit quality, assessed by the physical and chemical parameters described above. Different treatments were ranked by accumulating rankings obtained in each one of the following parameters: postharvest decay the treatment with the lowest mean value for fruit decay; weight losses the treatment with the lowest mean value; firmness the treatment with the highest mean value; brightness the treatment with the highest mean value for L* in the skin color of fruits; red skin color, the treatment with the highest mean value for a*; soluble solids the treatment with the highest mean value; and titratable acidity the treatment with the lowest mean value. For each of these seven parameters the five packaging methods ranked from 1 to 5 according to each established criterion, assigning 1 point, if the treatment exhibited the best value, 2 points if it exhibited the second best and so on. Two packages were considered different if the difference between their accumulated values was statistically significant (P 0.05). If two or more treatments exhibited statistically similar values for a parameter, they were ranked with the same value for that parameter, according to the formula: RESULTS & DISCUSSION THE PERMEABILITY OF FILMS TO RESPIRATION GASES IS THE MAIN factor which determines package atmosphere. After the third day of storage (Fig. 1 and 2), PP packages of both types showed a CO 2 content ( 20%) potentially harmful for fruit quality (Kader and Morris, 1977; Ke et al. 1991; Larsen and Watkins, 1995). Furthermore, at this time the O 2 content of Camarosa packages, became 5% (Fig. 3 and 4). This low O 2 content is not dangerous for fruit marketability, but can contribute to the damaging effects of high CO 2 atmospheres. Anaerobic respiration induces the synthesis of toxic metabolites which can cause multiple undesirable changes in the fruit, including softening or browning and development of off-flavors (Browne et al., 1984; Zagory and Kader, 1988; Kader et al., 1989). CL and PVC packages showed well balanced internal atmospheres, enabling maintenance of fruit quality without the risk of off-flavors. As in the case of PP packages, those containing Camarosa fruits exhibited higher CO 2 contents. In particular, CL packages of Camarosa fruits showed a mean value 40% higher than similar Oso Grande packages. This probably reflects a higher respiration rate for the Camarosa as compared to Oso Grande. As expected, PPP packages exhibited an internal atmosphere similar to air. Robinson et al.(1975)reported that losses of 6% of the initial value of fresh weight in a soft fruit should be considered the limit for marketability. According to this criterion, the unwrapped fruits lost commercial acceptance before the second and fourth days of storage for RV m ( i 1, i n n i )/n where: RV Ranking value; m Number of treatments with a better ranking value; n Number of treatments with the same ranking value. When a treatment was not statistically different for one parameter from any other two treatments which were different from each other (in that parameter), the first treatment was arbitrarily ranked with the same partial value as the member of the statistically similar treatment with the lower ranking for that parameter. At each sampling date, the partial ranking values obtained for each treatment for the different quality parameters were accumulated, with the best treatment being that with the lowest sum of absolute values. Sensory analyses were carried out by the analytical panel of the Instituto de la Grasa, consisting of 12 tasters, ranging in age from 35 to 45 years, with 10 years experience in evaluation of strawberry quality. The external appearance of the different packages, and the quality of the fruits were visually compared using a ranking test. Each panelist ranked 5 packages, representative of each one of the five treatments, according to external appearance. This test was carried out three times (days 0, 1 and 3 of storage) in the open area of a laboratory isolated from any external odor or sound, at ambient temperature (18 22 C) and illuminated by daylight, always at the same time (starting at 10:00 AM). Samples were coded with two characters randomly selected by computer, and presented randomly to each panelist on a white tray. In the test instructions panelists were encouraged to explain the reasons for their ranking. For comparing fruit taste, each panelist ranked 5 strawberries representative of each of the five treatments. This test was done two times (days 1 and 3 of storage) in the same laboratory and under similar environmental conditions as the ranking of package appearance. Fruits were coded with two characters randomly selected by computer, and were presented in random order to each panelist on 5 transparent small plates placed on a white paper. In the test instructions tasters were asked to give particular attention to the possible occurrence of off-flavors. Analysis of variance was performed on all data for the physical and chemical quality parameters of the fruit, and the least significant differences at P 0.05 obtained by Duncan s multiple range test were used to establish differences between means. Sensory analyses were analyzed by Friedman s test to evaluate if the ranking obtained had statistical significance. The test of least significant difference was used to determine which treatments in the rankings were significantly (P 0.05) different (Land and Shepherd, 1988). Fig. 1 Changes in CO 2 packages of Oso Grande strawberries during storage at 18 C. Fig. 2 Changes in CO 2 packages of Camarosa strawberries during storage at 18 C JOURNAL OF FOOD SCIENCE Volume 63, No. 6, 1998

3 Table 1 Effect of package and storage time at 18 C on weight loss, decay and firmness of Oso Grande strawberries Package Storage Wt loss Fruit decay Firmness (days) (%) (%) (N/cm 2 ) At harvest Unwrapped day d a 2.4a 23.2b Polyvinylchloride 0.12a 4.8a 26.6a Cellulose 0.58b 5.0a 27.0a Perforated polypropylene 0.96c 4.0a 24.3b Polypropylene 0.02a 3.7a 23.5b Unwrapped day c 11.9a 18.9c Polyvinylchloride 0.33a 7.6a 22.5a Cellulose 1.59b 13.7a 22.5a Perforated polypropylene 1.61b 12.3a 21.7b Polypropylene 0.07a 13.5a 21.6b Unwrapped day d 30.6a 16.0c Polyvinylchloride 0.61b 19.4a 18.2b Cellulose 2.94c 24.0a 20.1a Perforated polypropylene 3.23c 16.4a 19.6a Polypropylene 0.11a 23.3a 19.8a Unwrapped day d 86.5b 10.8c Polyvinylchloride 1.23b 81.4b 18.2a Cellulose 5.27c 72.4b 18.6a Perforated polypropylene 5.25c 73.2b 16.4b Polypropylene 0.24a 33.8a 16.7b Table 2 Effect of package and storage time at 18 C on weight loss, decay and firmness of Camarosa strawberries Package Storage Wt loss Fruit decay Firmness (days) (%) (%) (N/cm 2 ) At harvest Unwrapped day e a 0.0a 18.9a Polyvinylchloride 0.16b 0.0a 19.9a Cellulose 0.67d 0.0a 18.8a Perforated polypropylene 0.33c 0.0a 19.8a Polypropylene 0.04a 0.0a 19.0a Unwrapped day e 1.3a 19.4c Polyvinylchloride 0.24b 0.0a 19.6c Cellulose 0.88d 0.0a 22.9ab Perforated polypropylene 0.38c 0.0a 23.9a Polypropylene 0.05a 0.0a 21.6b Unwrapped day e 4.8a 17.3b Polyvinylchloride 0.61b 4.1a 18.2ab Cellulose 2.10d 1.2a 17.6b Perforated polypropylene 0.86c 5.2a 19.3a Polypropylene 0.14a 2.5a 17.4b Unwrapped day e 84.5b 12.4c Polyvinylchloride 1.45b 92.2b 16.2a Cellulose 4.96d 77.6b 15.9a Perforated polypropylene 1.77c 94.1b 13.8b Polypropylene 0.37a 37.6a 13.7b Oso Grande and Camarosa, respectively (Tables 1 and 2). By the fourth day fruits wrapped with CL and PPP films had reached values very close to the acceptance limit, especially Oso Grande. Picón et al. (1993) had reported high weight losses in refrigerated Chandler and Douglas strawberries manually wrapped with cellophane. Fruits packed in PP films showed the lowest weight losses, even being lower (P 0.05) than the losses of fruits manually packed in PVC, due to the lower water permeability of PP. No differences (P 0.05) were found between the degree of fruit decay in the different packages assayed for both cultivars during the three days storage (Tables 1 and 2). However, on the fourth day fruits wrapped with PP exhibited lower values for decay. The high CO 2 in the internal atmosphere of this package had a fungistatic effect, slowing the marked increase in decay observed in the other packages at a similar storage at 18 C. Researchers have reported incidences of fungal spoilage in berries if they were wrapped with plastic films generating high CO 2 atmospheres during storage at low temperatures (Barkay-Golan et al., 1983; Browne et al., 1984; Picón et al., 1993). Aharoni and Barkai-Golan (1987) reported lower fruit decay in Aliso fruits packed in PVC after 10 days storage at 2 C plus two days storage at 20 C. Chambroy et al. (1993) reported that control of fungal development was not possible at 20 C, regardless of composition of package atmosphere. Our results suggest that an increasing content of CO 2 in the package atmosphere could delay the exponential proliferation of fungi during storage of strawberries at 18 C. The use of plastic film to wrap strawberry packages delayed loss of firmness in fruits of both cultivars during storage (Tables 1 and 2). This was more evident in Oso Grande, where differences were significant (P 0.05) after the first day. Among wrapped fruits, no clear differences in fruit firmness were associated with film type. The effect of high CO 2 atmospheres in maintaining or increasing initial firmness of strawberries stored at low temperatures was confirmed in studies using atmospheric control (El-Kazzaz et al., 1983; Smith, 1992; Larsen and Watkins, 1995) or films which produced modified atmospheres with cultivars Douglas and Chandler (Shamaila et al., 1992; Lanzarotta et al., 1993; Picón et al., 1993). However, this effect was Fig. 3 Changes in O 2 packages of Oso Grande strawberries during storage at 18 C. Fig. 4 Changes in O 2 packages of Camarosa strawberries during storage at 18 C. Volume 63, No. 6, 1998 JOURNAL OF FOOD SCIENCE 1039

4 Quality of Packed Strawberries... not observed in our results. Fruit wrapped in PP films, which maintained the highest CO 2 content in the package atmospheres, did not show the highest values for fruit firmness. Perhaps this effect was not so evident for our cultivars Oso Grande and Camarosa. Fruit color is crucial in purchase decisions, especially if the product is wrapped and cannot be touched or smelled. No clear differences were found in skin brightness, expressed by the L* value of the skin color, between fruits of either cultivar however packed (Tables 3 and 4). But unwrapped fruit showed the lowest mean values. Red skin color, estimated by the a* value, was greater in wrapped than unwrapped fruit (Tables 3 and 4). This was true especially for fruits packed in PP or PVC films, which exhibited higher a* values (P 0.05) than unwrapped fruits during the entire storage. Our results confirmed results of Picón et al. (1993) with Douglas fruits covered by perforated cellophane sheets or polyethylene bags after 11 days storage at 2 C. They reported no differences using Chandler strawberries, showing the distinct influence of cultivars. Two important components of strawberry taste, sweetness and acidity, may be instrumentally measured. Soluble solids content of Oso Grande fruits from all packages decreased during storage at 18 C, showing lower values (P 0.05) for this parameter than unwrapped strawberries (Table 3). In contrast, only PP wrapped Camarosa showed a similar decrease in soluble solids during this period (Table 4). Picon et al. (1993) had reported a decrease in soluble solids during storage at 2 C of packed Douglas and Chandler fruits. The titratable acidity of non-wrapped Camarosa fruits was higher (P 0.05) than that of fruits wrapped in plastic films during 18 C storage and the fruits packed in PP film showed the lowest values (Table 4). The acidity of unwrapped Oso Grande was high, but it was exceeded by the values in the PPP wrapped fruits (Table 3). Our results suggest that a high level of O 2 in the package atmosphere induced higher titratable acidity. Picón et al. (1993) also reported the lowest acidity in fruits packed in polyethylene bags, which contained the lowest O 2 concentrations, with Douglas and Chandler. However, Li and Kader (1989) and Ke et al. (1991) reported no differences in acidity between Selva fruits stored at 2 C or 0 and 5 C, respectively, in air or under different controlled atmospheres. The sum of the ranking values from each sampling date, as described for the seven quality parameters gave a reproducible index of changes in fruit quality for each treatment in both cultivars during 18 C storage (Fig. 5 and 6). Unwrapped fruits showed, in general, the highest ranking values, that is the lowest quality. In contrast, the PP, PVC and CL wrapped fruits showed the best mean values. Thus, two films used in automatic packaging resulted in similar or better fruit quality (by physical and chemical parameters) than the PVC used in manual packaging. Sums of ranking values for the external appearance of the different packages for both cultivars judged by the sensory panel, showed as a general trend that PPP and PVC were, the packages with best appearance (Fig. 7 and 8). PP packages showed considerable water condensation on the internal surface of the film. This makes visual assessment of the product difficult and high moisture level may be perceived as related to a high degree of decay. CL packages showed an unattractive wrinkled appearance, which made the fruit look old. Packages without covering film allowed rapid deterioration of the fruit appearance due to high weight loss. No differences were reported in the taste of strawberries from the packages assayed on the first and third day of storage (data not shown). By the fourth day of 18 C storage the fruit of both cultivars packed in PP films had developed an off-flavor and would be unmarketable (data not shown). This confirmed reports of Shamaila et al.(1992), that the sensory attributes became less desirable in packed Chandler fruits during storage at 1 C in a microatmosphere with low O 2 ( 3%) and high CO 2 ( 20%) levels. Wrapped fruits showed, in general, better physical, chemical and sensory properties than unwrapped fruit. In contrast, the selection of the most appropriate film for automatic packaging of the strawberries, was not clear. The three films had different advantages and disadvan- Table 3 Effect of package and storage time at 18 C on skin brightness, color, soluble solids and titratable acidity of Oso Grande strawberries Red Soluble Titratable Brightness color solids acidity Package Storage (L*) (a*) ( Brix) (%Citric acid) At harvest Unwrapped day a a 26.20b 9.38a 1.21a Polyvinylchloride 31.90b 28.40a 8.72b 1.22a Cellulose 32.80a 28.30a 9.08ab 1.22a Perforated polypropylene 33.00a 27.80a 9.02ab 1.22a Polypropylene 34.30a 28.40a 8.62b 1.21a Unwrapped day b 26.20c 9.00a 1.20c Polyvinylchloride 35.20a 28.80a 8.28c 1.11a Cellulose 34.50ab 27.20b 8.68b 1.16b Perforated polypropylene 33.80b 27.50b 8.30c 1.19c Polypropylene 32.70b 28.60a 9.12a 1.10a Unwrapped day b 25.70c 8.95a 1.23b Polyvinylchloride 34.90a 28.50a 8.15c 1.18a Cellulose 33.40b 27.20b 8.58b 1.15a Perforated polypropylene 33.80ab 27.50b 8.60b 1.30c Polypropylene 34.80a 28.70a 8.30c 1.14a Unwrapped day b 25.70b 8.62a 1.28b Polyvinylchloride 31.90b 28.10a 7.22c 1.18a Cellulose 32.00b 25.90b 7.72b 1.17a Perforated polypropylene 32.50b 25.80b 7.72b 1.35c Polypropylene 34.60a 28.50a 7.58b 1.29b aoverall means are shown, and those with different letters within the same shelf life time are Table 4 Effect of package and storage time at 18 C on skin brightness, color, soluble solids and titratable acidity of Camarosa strawberries Red Soluble Titratable Shelf Brightness color solids acidity Package life (L*) (a*) ( Brix) (%Citric acid) At harvest Unwrapped day b a 28.15b 8.00ab 0.97b Polyvinylchloride 37.42a 30.82a 7.55b 0.95b Cellulose 34.98b 28.18b 7.68b 0.94b Perforated polypropylene 36.92b 30.00a 7.42b 0.94b Polypropylene 33.48b 29.62a 8.18a 0.86a Unwrapped day c 26.55b 7.20c 0.98c Polyvinylchloride 37.88a 28.55a 7.68b 0.92b Cellulose 36.65b 29.25a 7.62b 0.87b Perforated polypropylene 38.60a 29.10a 8.10a 0.94b Polypropylene 36.10b 29.68a 8.10a 0.87a Unwrapped day a 26.72b 7.58a 0.99c Polyvinylchloride 37.32a 28.75a 6.92b 0.93b Cellulose 35.05a 26.98b 7.85a 0.86a Perforated polypropylene 35.75a 28.68a 7.62a 0.90ab Polypropylene 36.25a 29.22a 7.58a 0.87a Unwrapped day b 25.90b 7.68a 1.20d Polyvinylchloride 35.00bc 28.50a 7.30a 1.04b Cellulose 36.55a 27.90a 6.98b 1.12c Perforated polypropylene 34.62bc 27.72a 7.45a 1.10c Polypropylene 33.72c 27.25a 7.35a 0.83a tages for fruit packaging. CL films enabled formation of a well balanced modified internal atmosphere, but had limitations: of excessive water permeability and wrinkled appearance. PPP films should only be recommended when a very short storage is required (maximum 2 days), and afterwards the fruits packed in this film showed rapid deterioration. PP was best to maintain fruit quality, but there is a major risk of off-flavor development. Furthermore these films resulted in an undesirable appearance due to water condensation JOURNAL OF FOOD SCIENCE Volume 63, No. 6, 1998

5 Fig. 5 Changes in sums of ranking values for seven quality parameters of different packages of Oso Grande strawberries during storage at 18 C. (Vertical bars represent least significant differences at p#0.05.) Fig. 7 Changes in sums of ranking values for visual appearance of different packages of Oso Grande strawberries during storage at 18 C. (Vertical bar represents least significant difference at p#0.05.) Fig. 6 Changes in sums of ranking values for seven quality parameters of different packages of Camarosa strawberries during storage at 18 C. (Vertical bars represent least significant differences at p#0.05.) Fig. 8 Changes in sums of ranking values for visual appearance of different packages of Camarosa strawberries during storage at 18 C. (Vertical bar represent least significant difference at p#0.05.) REFERENCES Aharoni, Y. and Barkai-Golan, R Preharvest fungicide sprays and polyvinyl wraps to control Botrytis rot and prolong the postharvest storage life of strawberries. J.Hort Sci., 62: Barkai-Golan, R., Aharoni, Y., Karadavid, R., and Kopel, A Suppression of Botrytis rot in strawberries packaged in polyethylene or vinyl wraps. Hassadeh. 64: Browne, K.M., Geeson, J.D., and Dennis, C The effects of harvest date and CO 2 - enriched storage atmospheres on the storage and shelf life of strawberries. J. Hort. Sci. 59: El-Kazzaz, M.K., Sommer, N.F., and Fortlage, R.J Effect of different atmospheres on postharvest decay and quality of fresh strawberries. Phytopatology 73: García, J.M., Aguilera, C., and Albi, M.A Postharvest treatment on Spanish strawberry (Fragaria x ananassa Cv. Tudla). J. Agric. Food Chem. 43: Kader, A.A. and Morris, L.L Relative tolerance of fruits and vegetables to elevated CO 2 levels. In Controlled Atmospheres for the Storage and Transport of Perishable Agricultural Commodities., D.H.(Ed.). Michigan State Univ. Hort. Rpt. 28: Kader, A.A., Zagory, D., and Kerbel, E.L Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. Nutr. 28: Ke, D., Goldstein, L., O Mahony, M., and Kader, A.A Effects of short-term exposure to low O 2 and high CO 2 atmospheres on quality attributes of strawberries. J. Food Sci. 56: Land, D.G. and Shepherd, R Scaling and Ranking methods. Ch. 6 in Sensory analysis of food, J.R. Piggott (Ed.). p nd ed. Elsevier Science Publishers LTD., London, UK. Lanzarotta, L., Massantini, R., and Mencarelli, F Postharvest physiology of strawberries wrapped in plastic film. Industrie Alimentari 32: Larsen, M. and Watkins, C.B Firmness and concentration of acetaldehyde, ethyl acetate and ethanol in strawberries stored in controlled atmospheres. Postharvest Biol. Technol. 5: Li, C. and Kader, A.A Residual effects of controlled atmospheres on postharvest physiology and quality. J.Amer Soc. Hort. Sci. 114: Olías, J.M., Sanz, C., and Pérez, A.G Acondicionamiento Post-recolección del fresón de Huelva para consumo en fresco. Caja Rural de Huelva. Huelva, Spain. Pérez, A.G., Sanz, C., Olías, R., and Olías, J.M Effect of methyl jasmonate on in vitro strawberry ripening. J. Agric. Food Chem. 45: Picón, A., Martínez-Jávega, J.M., Cuquerella, J., Del Río, M.A., and Navarro, P Effects of precooling, packaging film, modified atmosphere and ethylene absorber on the quality of refrigerated Chandler and Douglas strawberries. Food Chemistry 48: Robinson, J.E., Browne, K.M., and Burton, W.G Storage characteristics of some vegetables and fruit. Ann. Appl. Biol. 81: 399. Smith, R.B Controlled atmosphere storage of Red Coat strawberry fruit. J. Amer. Soc. Hort. Sci. 117: Shamaila, M., Powrie, W.D., and Skura, B.J Sensory evaluation of strawberry fruit stored under modified atmosphere packaging by quantitative descriptive analysis. J. Food Sci. 57: Zagory, D. and Kader, A.A Modified atmosphere packaging of fresh produce. Food Technol. 42: Ms received 11/24/97; revised 3/16/98; accepted 6/5/98. Thanks to M.C. Martínez for technical assistance. We express our sincere gratitude to CICYT for supporting research project ALI Volume 63, No. 6, 1998 JOURNAL OF FOOD SCIENCE 1041