Storage on the Quality of Snow Pea Pods (Pisum Sati6um L

Postharvest Biology and Technology 21 (2000) 213–223 www.elsevier.com/locate/postharvbio

Effect of modiﬁed atmosphere packaging (MAP) and controlled atmosphere (CA) storage on the quality of snow pea pods (Pisum sati6um L. var. saccharatum)

Juan A.T. Pariasca a, Takeshi Miyazaki c, Hiroyuki Hisaka c, Hiroki Nakagawa b, Takahide Sato a,b,*

a Graduate School of Science and Technology, Chiba Uni6ersity, 1 Yayoi-cho, Inage, Chiba 263-8522, Japan b Faculty of Horticulture, Chiba Uni6ersity, 648 Matsudo, Chiba 271-8510, Japan c Chiba Prefectural Experimental Agriculture Station, 808 Daizenno, Chiba 266-0066, Japan Received 17 January 2000; accepted 25 July 2000

Abstract

The effects of precooling, modified atmosphere packaging (MAP) and controlled atmosphere (CA) storage on the storability of snow pea pods (Pisum sati6um L. var. saccharatum) at 5°C were determined. Bagging pods with polymethyl pentene polymeric films (PMP) of 25 and 35 mm thickness, in conjunction with precooling, modified the in-bag atmosphere concentration to approximately 5 kPa O2 and 5 kPa CO2, leading to better maintenance of the pod external quality (appearance and color), as well as internal quality (chlorophyll, ascorbic acid, and sugar contents).

Sensory scores were also maintained. Under CA storage at 5°C, gas compositions ranging from 5 to 10 kPa O2 with 5 kPa CO2 were the best storage conditions of those tested, since changes in organic acid, free amino acid and sugar contents, and pod sensory attributes were slight, corroborating the MAP results. The appearance of pods stored under CA conditions was much better than that of air-stored pods (control). Low O2 (2.5 kPa with 5 kPa CO2) and high CO2 (10 kPa with 5 kPa O2) concentrations have a detrimental effect on quality of stored pods since they developed slight off-ﬂavors, but this effect is reversible since it was partially alleviated after ventilation. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Snow pea pods; MAP; CA; Precooling; Storage; Quality

1. Introduction

Western consumers have begun to prefer the edible podded pea (snow pea pods), a special type of pea in which the pods rather than the seeds are * Corresponding author. Tel.: +81-47-3088863; fax: +81- eaten (Splittstoesser, 1978). The demand for snow 47-3088863. pea pods has been increasing steadily in some E-mail address: [email protected] (T. Sato). markets such as the US and Japan.

Most studies conducted on peas have dealt compositions on pod quality was then deter- with the green shell seed crop, which is grown mined in order to improve their storability. almost exclusively for processing. Very little information is available on the optimum storage conditions of snow pea pods. Kader (1992) 2. Materials and methods stated that the pea is a highly perishable immature commodity that can be cooled 2.1. Plant material and stored at temperatures near 0°C to extend 6 its shelf life, has an extremely high respiration Samples of snow pea pods (Pisum sati um L. rate and is classified as a non-climacteric com- var. saccharatum cv. Ichihara wase) were obtained from the Sodegaura packing house, in modity. To retain the best quality, edible-pod- Chiba Prefecture, Japan. ded peas are harvested before physiological maturity is reached (Basterrechea and Hicks, 2.2. Experiment I: Effects of precooling and 1991). Shortly after harvest, loss of sweetness MAP on the quality of snow pea pods stored at and crispness, as well as degreening and the de- 5°C velopment of mealiness, may degrade the quality. Samples free of visual defects were divided Low temperature storage when combined with into two portions. One portion was precooled controlled atmospheres (CA) or modified atmo- using a vacuum cooling system, wherein the in- sphere packaging (MAP), results in reduced res- ternal pod temperature was reduced to approxi- piration and ethylene production rates, retarded mately 4°C. The remaining portion was not softening, and a slowing down of compositional precooled. changes associated with ripening and senescence Subsequently, all samples (precooled and non- (Wills et al., 1981; Zagory and Kader, 1989; precooled) were rapidly weighed to 10092g O’Beirne, 1991). and placed in bags composed of different poly- Previous experiments combining low tempera- meric films: 25 mm polymethyl pentene (PMP-1) ture storage and CA have revealed that an at- and 35 mm (PMP-2), 25 mm low-density polyethylene (LDPE), and 25mm oriented mosphere of 5 kPa CO2 at 5°C maintained the color and flavor of unshelled peas (Tomkins, polypropylene (OPP); non-sealed LDPE (LD- PEns) with folding was used as control. The 1957). Also, increasing the CO2 concentration to 2.6 or 4.7 kPa, combined with 21 or 2.4 kPa sealed package size was 13.5 cm×19.5 cm 2 O , at 1°C maintained the appearance, as well (263.3 cm ). Afterwards, all bags except LD- 2 PEns were heat-sealed, and stored at 5°C. as chlorophyll, soluble sugar and protein con- −12 tents of stored snow peas (Ontai et al., 1992). Oxygen permeances were 79.4×10 mol·s−1·m−2·Pa−1 for PMP-1, 56.0×10−12 for Another related study reported by KPAES PMP-2, 31.3×10−12 for LDPE and 6.5×10−12 (1983) showed that storing snow pea pods at for OPP. The permeance data were provided by either 0 or 5°C did not cause any substantial the manufacturer and converted into S.I. units difference in their appearance or taste during according to Banks et al. (1995). the first week of storage. This study has been conducted to evaluate the 2.3. Experiment II: Effects of CA compositions effects of MAP and CA on the maintenance of on the quality of snow pea pods stored for 3 quality of snow pea pods stored at 5°C. The weeks at 5°C effects of gas concentrations achieved by using different plastic film materials (MAP) in con- Precooled samples of 10092 g were weighed junction with precooling on pod quality were and placed in a humidified flow-through system evaluated first, and the effect of different CA of a 20 L air tight chamber with gas inlet and J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 215 outlet ports, at 5°C. Three replicates of each 2.4.3. Internal quality sample were used. The CA compositions studied were (a) 2.5, 5 and 10 kPa O with 5 kPa CO , and control (air-stored 2.4.3.1. Total chlorophyll. Chlorophyll content was 2 2 analyzed as described by Hisaka (1992), with mod- pods); and (b) 0, 5 and 10 kPa CO2 with 5 kPa O2, and control. These gas compositions were adjusted ifications. Five grams of a sample were homogenized with 20 ml of 90% acetone and 0.1 g of using a flowmeter for the combination of air, CO2 and nitrogen (balance) with a total flow rate of 200 MgCO3 in a mortar. The homogenate was trans- ml min−1. The gas compositions were monitored ferred into a 50 ml volumetric flask which was then using a gas chromatograph (GC) at both inlet and filled with 80% acetone and centrifuged, and the outlet ports. supernatant was filtered through paper No. 2 Samples were taken after 7, 14 and 21 days of (Toyo Ltd., Japan). The filtrate was measured storage (CA pods). Some were transferred to air using a spectrophotometer (model UV2100, Shi- after CA storage (ventilated pods) and held for 2 madzu, Japan) at A 663 and A 645 nm. There were days at 20°C. All samples were stored at −80°C three replicates. until the analyses were carried out. 2.4.3.2. Ascorbic acid. Ten grams of pod tissue 2.4. Assessment and measurement were ground thoroughly in a mortar with 40 ml of

0.9MH3PO4. The mixture was poured into a 100 2.4.1. Atmosphere composition in the head space ml volumetric flask which was then filled with of bags distilled water and filtered through paper No. 2 A 1 ml gas sample was drawn into a syringe, (Toyo Ltd., Japan). The ascorbic acid content of through a piece of rubber stuck to the bags, and the sample was measured by injecting 5 mlofthe injected into a GC (Shimadzu, Japan) equipped filtrate into a food analyzer (model NH-FO41, with a thermal conductivity detector (TCD), and Ajinoki, Japan) that was previously corrected with molecular sieve 5A (60–80 mesh), resistor (shi- a standard of 50 mg ascorbic acid/100 ml distilled malite) Q (100–180 mesh) and activated charcoal water. Two readings were obtained from each (60–80 mesh) columns (Shimadzu). Helium was sample, and the average was used for calculations used as the carrier gas at a flow rate of 25 ml (Miyazaki, 1985). min−1. The injector and column temperatures were 100 and 80°C, respectively. Standard calibration curves for O2,CO2 and N2 were obtained and 2.4.3.3. Organic acids. Five grams of a frozen used for calculations. The O2 content was cor- tissue sample were homogenized and transferred rected for argon. into a 100 ml volumetric flask that was then filled with distilled water. Subsequently, it was cen- 2.4.2. External quality trifuged and filtered through paper No. 2 (Toyo Color was measured using a hand-held col- Ltd., Japan), and the filtrate passed through a 0.45 orimeter (model CR-200, Minolta, Japan). Numer- mm membrane filter and injected into a LC-3A ical values of L*, a* and b* were recorded and HPLC (Shimadzu, Japan) equipped with a UV converted to hue angle (H 0 =tan−1 b*/a*) and detector and a SCR101H column (Shimadzu, chroma (chroma=(a*2 +b*2)1/2) (Francis, 1980). Japan). The column temperature was 60°C, the Appearance, a subjective index, was modified wavelength was 210 nm, and the mobile phase from KPAES (1983): (1) free from defects and was distilled water/phosphoric acid, pH 2.2, firm; (2) minor defects appearing and slightly with a flow rate of 1 ml min−1. Standards wilted pods; (3) obvious minor defects and wilted were chromatographed for quantification and de- pods; (4) saleable (brown calyx, discolored pods, termination of retention times and were also co- obvious defects on pods and completely wilted chromatographed with the sample for pods). identification. 216 J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223

2.4.3.4. Total sugars and free amino acids. Sugar dard kit (type H, Wako, Japan). Asparagine and content was analyzed as described by Iwatsubo et glutamine standards were also used. al. (1992) with some modifications. Five grams of tissue were homogenized with 100 ml of 80% 2.4.4. Sensory analysis ethanol and immersed in water at 80°C for 30 At each sampling time, some pods were boiled min, then cooled and supplemented with 80% for 2 min, and evaluated by a panel of five ethanol in a 200 ml volumetric flask. Subse- untrained persons, based on the following grades quently, the homogenate was filtered through pa- modified from Miyazaki (1985). Off-flavor: (1) per No. 2 (Toyo Ltd., Japan), and the ethanol in none (no off-flavor can be detected); (2) slight; (3) an aliquot of 50 ml of the filtrate was evaporated strong; (4) severe (extremely strong off-flavor can off in a rotary vacuum evaporator. The concen- be detected). Palatability: (1) good (liked or pre- trated sample was transferred to a 25 ml volumet- ferred taste); (2) fair; (3) poor; (4) inedible ric flask which was then filled with distilled water, (severely disliked taste). and filtered through a 0.45 mm membrane filter. This filtrate was used to measure the sugar and 2.4.5. Statistical analysis free amino acid contents. Data were organized in a completely random- To determine the amount of total sugar, 20 ml ized block design (CRBD) with a split-plot ar- of the filtrate was injected into an HPLC (model rangement, with three repetitions, in which each LC-3A, Shimadzu, Japan) equipped with a refrac- repetition was considered as a block. The analysis tive-index (RI) detector and a SCR101N column of variance (ANOVA) of the main effects, and (Shimadzu, Japan), under the following condi- mean separations were obtained using Systat tions: column temperature of 50°C, mobile phase statistical software (version 8.0, SPSS Inc., USA). of distilled water, and flow rate of 1 ml min−1. Data transformations were carried out according Standard calibration curves for glucose, fructose to the requirements (Little and Hill, 1978). and sucrose were obtained and used to estimate the sample contents. The sum of the above three sugars was considered as the amount of total 3. Results sugar. For the determination of free amino acids, the 3.1. Experiment I: Effects of precooling and above filtrate was diluted with 0.05 M boric acid– MAP on the quality of snow pea pods stored at NaOH buffer, pH 8.0, at a ratio of 1:20. An 5°C aliquot of 30 ml of the dilution was mixed with 10 ml of 50 mM 4-fluoro-7-nitrobenzofurazan/aceto- All treatments resulted in the same pattern of nitrile (for fluorescence detection), incubated at O2 and CO2 concentrations within the bags. 60°C for 90 s, and injected into an automated Within 2 weeks of storage, all treatments resulted

Gilson HPLC system (Gilson Med. Elect., USA) in lower O2 contents (Fig. 1). Oxygen in PMP equipped with a ﬂuorometer detector (model M- bags decreased to around 8 kPa, but in OPP bags 121, Gilson) and an ODS-A column (YMC Co., rapidly decreased to nearly 1 kPa. After 2 weeks,

Japan). The column temperature was 30°C and the O2 content was near a steady-state level for all the mobile phase was composed of buffer A (0.2 treatments. Oxygen in PMP bags reached around

MH3PO4:acetonitrile, 10:2) and buffer B (0.1 M 5–6 kPa, while in LDPE bags 2 kPa and in OPP K2HPO4·3H2O, 0.1 M H2KPO4:methanol: aceto- bags 3 kPa (Fig. 1A). Non-precooled treatments nitrile, 4:3.9:2.1), with a flow rate of 1.2 ml resulted in higher O2 contents (Fig. 1B). −1 min , under gradient conditions in which the The CO2 contents in PMP-1, PMP-2 and LDPE A:B ratio was 100:0 for the first 20 min, 80:20 bags increased to around 5 kPa by the second from 21 to 30 min, and 0:100 from 31 to 40 min. week, and maintained approximately the same The concentrations of amino acids were level thereafter (Fig. 1C-D). OPP bags, on the −1 quantified using a 2.5 nM ml amino acid stan- other hand, had CO2 contents significantly higher J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 217 at around 29 kPa after 1 week, which then de- pods did not show any significant variation creased steadily thereafter. among the sugar components. The gas concentration within the package sig- Precooled PMP-bagged pods showed better ac- nificantly affected the external quality of stored ceptability than the others (Table 1). OPP- and pods (Table 1). Pod lightness (L*) did not vary, LDPE-bagged pods developed strong off-flavors but OPP-bagged pods had increased yellowing and non-sealed pods reached an extremely wilted (hue angle reduced), and non-precooled OPP pods condition, and both were graded inedible. were less intensely green (chroma reduced). Ap- pearance was better maintained in precooled 3.2. Experiment II: Effects of CA compositions pods, wherein PMP pods were the best, and OPP- on the quality of snow pea pods stored for 3 and LDPEns-bagged pods the worst, having weeks at 5°C reached a completely saleable condition. MAP had a dramatic effect on the chlorophyll contents of stored pods (Table 1). The reduction 3.2.1. Effects of 2.5, 5 and 10 kPa O2 combined for LDPEns- and OPP-bagged pods was higher with 5 kPa CO2 on stored pod quality than for PMP- and LDPE-bagged pods. With Treatments with low O2 combined with 5 kPa regard to the ascorbic acid content, precooled CO2 resulted in increased malic acid contents pods had higher contents than the non-precooled (Table 2). When CA-stored pods were ventilated ones, whereas PMP- and LDPE-bagged pods for 2 days at 20°C, the malic acid content did not maintained higher contents than LDPEns- and vary, although the fumaric acid content of pods OPP-bagged pods. increased and citric acid decreased after MAP had significant effects on the pod sugar ventilation. content. PMP-bagged pods had the highest con- The tested CA compositions were found to tent among the treatments (Table 1). OPP-bagged increase the total sugar content as well as the pods, on the other hand, exhibited a significant sucrose component, although, sucrose content reduction. PMP- and LDPE-bagged pods had a was reduced through ventilation. Glucose and twofold-increase in sucrose contents, while those fructose contents, on the other hand, were unaf- fected either by low O treatments or by ventila- of OPP-bagged pods decreased. LDPEns-bagged 2 tion (Table 2). The tested CA compositions also increased the alanine content of pods (Table 3). When pods were ventilated, however, alanine and gamma- amino butyrate (GABA) contents were reduced while asparagine, serine, aspartate and glutamate contents were increased.

Sensory scores were also affected by low O2 concentration. Better acceptability was observed

for control, 5 and 10 kPa O2 treatments than for the 2.5 kPa O2 treatment which resulted in the development of off-ﬂavor. However, pod acceptability improved after ventilation (Table 3).

3.2.2. Effects of 5 kPa O2 combined with 0, 5 and 10 kPa CO2 on stored pod quality Fig. 1. O and CO concentrations in bags of precooled (A, C) 2 2 Elevated CO concentrations decreased the fu- and non-precooled (B, D) snow pea pods stored for a twenty- 2 eight-day period at 5°C. Gas samples were taken and analyzed maric acid contents of pods (Table 2). Ventilation as described in Section 2. Data points are the means of three of CA pods increased the fumaric acid but de- replicates. LSDs (5%) of main effects are presented. creased the malic acid contents. 218 J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 1.8 c 1.9 b * 1.9 c 3.0 b Palatability 4.0 a 4.0 a Sensory scores 100 g fw) / 2.7 c ea pods stored at 5°C for twenty-eight-day period 100 g fw) / (g 100 g fw) / n.s. n.s. n.s. n.s. * Glucose(g Fructose Off-ﬂavor 100 g fw) (g 0.05. / B n.s. Sucrose(g Total P 100 g fw) / 3.5 a 1.3 a 2.7 a 0.25 a 4.2 a 1.0 b 3.2 a 0.9 a 2.7 a 0.27 a 3.8 a 1.5 a 2.9 b 0.9 a 2.4 a 0.23 a 3.5 a 1.5 a 2.4 * n.s. n.s. n.s. n.s. n.s. ** 1.8 c 0.3 c 2.1 a 0.25 a 3.0 b 0.5 b 2.6 a 0.24 a 3.3 b – – Ascorbic acid Sugars 3.6 a3.6 a 1.3 a 1.1 a 2.8 a 2.5 a 0.28 a 0.25 a 4.3 a 3.8 ab 1.0 b 1.3 b 100 g fw) (mg / 12.4 a 11.7 a n.s. 11.3 ab 12.6 a (mg 0.001. Samples were taken and analyzed as described in Section 2. B P 1.2 c * 0.01, *** B 37.7 a P 0.05, ** ** * n.s. * n.s. n.s. 119.1 a 115.4 b 32.7 b 3.7 a 10.7 b 119.1 a 37.2 a Hue B P b a a 51.9 a 118.6 a 36.9 a 2.4 b 12.1 a n.s. * *** ** n.s. n.s. * ** ** n.s. 51.9 a 52.1 a Color51.3 a Appearance 119.3 a Chlorophyll 37.3 a 1.4 c 12.3 a L* Chroma

) B c ( non-significant, * ) = A ( B Means in each column followed by the same letter are not statistically significant by Tukey’s test, * Data are the means of three replicates. n.s. a b c × PMP-1 51.2 Precooled Non-precooled 51.9 aSignificance 118.3 a 36.0 b 2.6 a A** B n.s. n.s. * A OPP LDPE 2.6 b LDPEnsPrecooling 52.8 a 119.4 a 37.5 a 3.7 a PMP-2 Table 1 Effect of precooling and MAP on the variation of color, appearance scores, chlorophyll, ascorbic acid and sugar contents, and sensory scores of snow p MAP J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 219 100 g fw) / ** (g 3.7 a 100 g fw) / ** * Fructose 0.18 a 100 g fw) / 0.05. n.s. n.s. n.s. 3.0 an.s. 0.29 a n.s. 4.60 a 2.5 an.s. n.s. 0.20 a 3.3 b n.s. n.s. 2.9 a 0.30 a 4.33 ab (g 3.0 a 0.27 a 3.84 b 2.8 a 0.15 b 3.5 a 2.5 a 0.14 b 3.2 b 3.0 a 0.31 a 4.63 a 2.5 a 0.18 a 3.6 a 2.5 a B P 100 g fw) (g / * 0.6 b ** 1.1 a 0.6 b (g 0.6 b 1.3 a 0.9 a 100 g fw) / ** * n.s. n.s. * 2.5 b3.0 a 1.3 a 1.0 b 3.0 a 0.30 a 4.33 b 1.7 b 0.9 a 2.6 a 0.13 b 3.7 a ** ** n.s. * ** 2.9 a 3.3 a 1.2 a 3.0 a 0.32 a 4.51 a 2.4 ab (mg 100 g fw) / 0.001. Samples were taken and analyzed as described in Section 2. n.s. 395.7 a Succinic 459.1 a B P 0.01, *** 100 g fw) / B P 869.8 a 750.5 b883.5 a 359.4 a 2.5 a 0.6 b 817.9 ab 834.6 b 2.8 a 992.6 a n.s. n.s. * n.s. n.s. * n.s. * * Malic Sucrose Glucose Total (mg 1049.6 a 300.9 a 3.2 a 1106.1 a 345.7 a 1.7 b 1.0 a 0.05, ** B P b a a 100 g fw) (mg / 2 2 97.1 b 63.4 a 61.5 a 97.6 a 63.7 a 64.6 a 60.5 a 1062.6 a 350.6 a 61.2 a * n.s. 104.5 a n.s. n.s. n.s. n.s. n.s. n.s. Organic acids Sugars Citric Fumaric (mg CO ) and CO c B 2 d

5 kPa ( O non-significant, * = and 2 ) B n.s. B Means in each column followed by then.s. same letter are not statistically significant by Tukey’s test, * Data are the means of three replicates. 5 397.0 a Transferred to air at 20°C for 2 days. O B 5 94.4 a 3.2 a / Ventilation / ( a b c d 5 98.3 a 917.9 a 434.7 a 0 5 1.8 b 10 × ] × / / / / (b) 5 kPa A B n.s. Non-ventilatedSignificance A 842.4 a 412.6 a n.s. n.s. ** Ventilated Ventilated 1270.8 a 327.2 a B A Non-ventilatedA 316.1 a n.s. Significance 2.5 5 Table 2 Effect of different CA compositions on the variation of organic acid and sugar contents of snow pea pods stored for a twenty-one-day period at 5°C CA (A) CA (A) Control 98.4 Control 289.3 a (a) 5 10 [9 5 5 Ventilation 220 J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 2.7 a 1.8 b 1.6 b Palata-bility 1.6 b 1.7 a ** n.s. 1.8 b Sensory scores 1.5 b 100 g fw) / g m n.s. ** * ( 100 g fw) at 5°C / g m ine; Val, valine. n.s. Pro 100 g fw) / g m GABA Val ( 100 g fw) / g m 927 a 5.5 b 252 a 540 a 1.8 a 2.0 a Ala Off-flavor ( 872 a 6.8 a 248 a 552 a 2.3 a 2.5 a 0.05. B 100 g fw) ( / P g m n.s. * * n.s. n.s. n.s. n.s. n.s. * n.s. 466 a 1242 a 4.8 a 601 a 724 a 2.0 a 436 a 1072 b 5.3 b 528 a 677 a 433 a 1052 ab 5.7 a 540 a 675 a 1.7 ab 1.6 b 408 a 844 b 4.3 a 459 a410 a 645 a 520 b392 a 1.4432 b a 4.6 b 639 b 290 a 6.0 a 498 a 264 a 1.4 b 551 a 1.6 b 402 a 911 a 5.5 ab 261 a 628 a 1.5 b 1.7 b n.s. ** * n.s. n.s. * n.s. n.s. n.s. * n.s. * 384 a 828 a 6.1 a 232 a 503 a 1.6 b 451 a ( Amino acids 100 g fw) / g 971 a 863 a 733 a 674 a m * 1023 a 517 a n.s. n.s. 100 g fw) / g m n.s. 672 a 1030 a 435 a 1152 a 6.3 a 510 a 665 a 1.7 ab 1.7 b 508 b 689 b 421 a 1290 a 9.0 a 505 a 667 a 1.8 a 2.0 a n.s. ** * n.s. * ** n.s. n.s. * n.s. 741 ab ( 0.001. Samples were taken and analyzed as described in Section 2. 100 g fw) / B g m P ** 1986 a 1766 a Ser 2087 a 1982 a * n.s. ( 0.01, *** B P 100 g fw) ( / g m n.s. n.s. n.s. * ** * n.s. 388 a 1855 a 658 a 903 a 591 a 505 a 1837 a 682 a 981 a 450 a 521 a Gln Asp 585 a 1903 b 644 b 536 b 412 b 365 b 2233 a511 a 849 a * 862 a 1723 b 649 b 875 a 0.05, ** B P b a a 2 2 100 g fw) ( / g CO m n.s. n.s. n.s. ** n.s. n.s. n.s. * * ** n.s. 4330 a 3239 b 4143 a 4056 a 4490 Asn Glu Thr 4265 b 5614 a 5366 a n.s. * 4680 a (

and CO ) (B) B 2 d

5 kPa ( c O non-significant, * = and 2 B B n.s. * Means in each column followed by then.s. same letter are not statistically significant by Tukey’s test, * Asn, asparagine; Gln, glutamine;Data Ser, are serine; the Asp, means aspartate; of Glu, three glutamate; replicates. Thr, threonine; Ala, alanine; GABA, gamma-amino butyrate; Pro, prol 5 757 a Transferred to 20°C for 2 days. O 5 638 a / / 8 a b c d 5 3696 a 519 a 1741 a 0 5 5057 a 554 ab 1727 b 10 × × / / / / AB n.s. A (b) 5 kPa 2.5 5 Significance VentilatedNon-ventilated 1762 b 10 Ventilation Table 3 Effect of different CA compositions on the variation of free amino acid contents and sensory scores of snow pea pods stored for a twenty-one-day period CA (A) CA (A) Ventilated Control ControlNon-ventilated 6093 a 669 b 810 a 5 Significance A* A B n.s. * 5 5 Ventilation (a) J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 221

Total sugar content was also affected by the The degradation of ascorbic acid was also

CO2 concentration (Table 2). Sucrose and fruc- avoided by MAP, precooling and low-tempera- tose contents were signiﬁcantly higher with 5 and ture storage. According to Zagory and Kader

10 kPa CO2 treatments than with other treat- (1989), degradation of ascorbic acid is associated ments. There were no signiﬁcant variations in with wilting in some green leafy vegetables after glucose content. Ventilation resulted in lower su- harvesting. However, the optimum low O2 content crose and fructose contents compared with unven- can prevent ascorbic acid losses, presumably tilated treatment. Glucose content, however, through prevention of oxidation. remained at the same level after ventilation. On the other hand, greater accumulation of

The CO2 combined with 5 kPa O2 treatments CO2 and reduction in O2 (29 and 1 kPa, respec- signiﬁcantly reduced the contents of some free tively) resulted from bagging pods with OPP ﬁlm, amino acids, such as serine and aspartate, but which has the lowest permeance (Fig. 1). This gas increased glutamine, alanine and GABA contents concentration within the OPP bag led to anaero- (Table 3). Glutamine content did not vary after bic respiration, causing a severe deterioration of ventilation, while serine, aspartate, asparagine, the overall appearance of stored pods, and a glutamate and GABA content increased and ala- greater degradation of chlorophyll, ascorbic acid nine content decreased. and sugar contents.

Also, high CO2 concentrations had a detrimen- In the case of LDPEns-bagged pods, the overall tal effect on pod sensory attributes. A develop- pod appearance severely deteriorated due to ex- ment of slight off-ﬂavor which led to decrease in cessive weight loss of more than 6% (Hardenburg the acceptability was observed with the 10 kPa et al., 1986) causing a reduction in the ascorbic

CO2 treatment. However, such an effect dimin- acid content (Zagory and Kader, 1989). The in- ished slightly after ventilation (Table 3). crease in PMP- and LDPE-bagged pod sugar contents during storage may be explained by the accumulation of sucrose. 4. Discussion In terms of the sensory attributes of pods, PMP-bagged pods showed better acceptability

A gas concentration of around 5 kPa O2 and 5 due to a better taste and an absence of off-flavor. kPa CO2 at a storage temperature of 5°C resulted Our results also showed that the precooling effect from bagging snow pea pods with a PMP poly- on the maintenance of pod quality was not signifi- meric plastic film (having the highest gas perme- cant, as expected, because the delay in cooling the ance) (Fig. 1). PMP resulted in the 4.6 kPa CO2 non-precooled pods was short. concentration recommended by Ontai et al. (1992) Weight losses were minimal for all the CA for storing snow pea pods either at 10 or 1°C, but treatments, due to the humidified flow-through not the O2 content which was higher than the system used. The overall appearance, however, recommended 2.4 kPa O2. was better maintained for pods under all CA This level of gas concentration within a PMP compositions than for control pods. package had a significant effect on the external Malic acid accumulation was enhanced by low quality of stored snow pea pods, either by inhibit- O2 treatment, but was not affected by high CO2. ing shriveling or by better maintenance of pod On the contrary, as a result of keeping lettuce in color and appearance (Table 1). Likewise, the air enriched with 5–20 kPa CO2 at 0°C, Ke et al. maintenance of pod internal quality components (1993) found that malate content decreased. was also achieved. The degradation of chlorophyll Malate accumulation is further favored by the and sugar content was reduced, corroborating the changes in energy during the conversion of malate results of Ontai et al. (1992). Weichman (1986) in the tricarboxylic acid cycle (TCA) (Ke et al., and Zagory and Kader (1989) have noted that 1993). Numerous studies support the finding that high CO2 and/or low O2 concentrations reduce low O2 and/or high CO2 atmosphere can retard the breakdown of chlorophyll to pheophytin. decomposition of organic acids in plant tissue. 222 J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223

However, since the mechanism remains unclear, (1970), where alanine content increased in apricot the results are varied and sometimes contradictory and peaches. Glutamate content decreased and (Weichman, 1986; Zagory and Kader, 1989; Ke et GABA content increased in tomato (Saijo et al., al., 1993). 1989) and lettuce (Ke et al., 1993) under similar Total sugar content was affected by the CA conditions. This indicates that amino acids in composition as well as the sucrose component, pods can likewise be differentially affected by CA corroborating our results obtained under MAP composition as occurs with organic acids. Accord- conditions (Table 1 and Table 2). Low O2 treating to Wills et al. (1981), a decrease in free amino ment could induce an accumulation of sucrose in acids reflects an increase in protein synthesis, pods, although no differences that might suggest while an increase reflects a breakdown of enzymes an effect due to either low O2 or 5 kPa CO2 were and decrease in metabolic activity. found among the different treatments. On the CA compositions as low as 2.5 kPa O2 and as other hand, when high CO2 treatments were eval- high as 10 kPa CO2 reduced pod acceptability. uated, pods stored under 5 and 10 kPa CO2 had However, this detrimental effect was alleviated significantly higher sucrose contents than those in after ventilation, indicating a reversible process

0 kPa CO2 and in control conditions. Further- (Table 3). The taste of pods could be affected not more, when pods were ventilated, the sucrose only by the changes in types and amounts of content diminished, indicating that increasing the carbohydrates, organic acids, amino acids, lipids

CO2 concentration led to an accumulation of and phenolics (Pesis, 1995), but also by the varia- sucrose. Ontai et al. (1992) revealed that snow pea tions in their proportions. pods stored under the previously mentioned con- The favorable effect achieved by the PMP gas ditions exhibited an increase in their total sugar concentration, which was further corroborated by content, but no information was provided regard- the CA results, indicated that the 2.4 kPa O2 ing the component variations. Furthermore, recommended by Ontai et al. (1992), did not Miller and Brooks (1932) showed that treating result in a better maintenance of pod quality at peas with high CO2 increased sugar levels. The 5°C. increase in sucrose in our results was clearly an Based on our results, it can be suggested that effect of high CO2, since increased amounts of the deterioration of appearance, shriveling, and sucrose were observed under MAP and CA condi- reduction in the ascorbic acid and sugar contents, tions, but not in air-stored pods, at storage tem- are the primary factors limiting the storage of peratures of both 5 and 20°C (data not shown). snow pea pods. Polymethyl pentene films (PMP) This is corroborated by the results of Weichman attained a suitable gas composition, which length- (1986), in which sucrose accumulation was ob- ened the storage life to about 4 weeks at 5°C. served as a result of a CO2 concentration much Furthermore, our study has also revealed that an higher than the optimal one, for horseradish, atmosphere composition ranging from 5 to 10 brussels sprouts and carrots. kPa O2 and approximately 5 kPa CO2 is optimal The major free amino acids found in snow pea for maintaining pod quality. Storing pods under pods were asparagine, serine, alanine and aspar- CA compositions other than in the above-men- tate, which accounted for 60% of the total con- tioned range, may lead to the development of tent. Another 25% was accounted for by off-flavors and a reduction in pod acceptability. glutamine, glutamate, threonine, proline and va- However, such effects are partially reversible by line. Free amino acid contents were affected by ventilation. both low O2 with 5 kPa CO2 and high CO2 with 5 kPa O2 concentrations. Furthermore, results after ventilation showed that the tested CA com- Acknowledgements positions suppressed or enhanced pod amino acid contents (Table 3). Similar results with high CO2 We thank M. Katagiri of Tohcello Co., Ltd. for concentrations have been found by Wankier et al. supplying PMP films. J.A.T. Pariasca et al. / Posthar6est Biology and Technology 21 (2001) 213–223 223

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