Effects of Carbon Dioxide Treatment and Modified Atmosphere Packaging on the Quality of Long Distance Transporting “ Maehyang ” Strawberry

This study was conducted to investigate the effects of carbon dioxide (CO2) and modified atmosphere (MA) packaging on the quality of strawberry during long distance transportation. “Maehyang” strawberries (Fragaria x ananassa Duch.) with red color on 70% of the fruit surface were harvested in Gyeongnam province, Korea. The samples were placed in gas-tight chamber with 30% CO2 concentration for 3 hours at 3 ̊C. Strawberry samples were then packaged with modified atmosphere-modified humidity (MA/MH) packaging film. Samples treated with CO2 alone and combined CO2 with MA packaging were stored for one day at 1 ̊C, transported for 10 days at 1 ̊C, and distributed for 3 days at 4 ̊C. Carbon dioxide alone or combination with MA packaging was effective in maintaining quality of “Maehyang” strawberries. Carbon dioxide treatment significantly increased firmness and reduced softening index and decay rate during 14 day transportation and distribution. Samples treated with CO2 + MA had higher overall score with low softening index and weight loss after 14 days of transportation and low temperature distribution compared to CO2 treatment only. The results indicated that a short term application of CO2 or combination treatment of CO2 and MA could be good postharvest handling for maintaining freshness of “Maehyang” strawberries during long distance vessel export.


Introduction
Strawberry is highly perishable fruit and requires careful handling in order to maintain quality after harvest.Strawberry is considered as winter fruit in Korea because con-sumption of the fruit is high in winter season.Though the domestic market of strawberry has been increased in Korea, the strawberry industry tries to expand the export market.Total strawberry export has been increasing and the trend is expected to remain strong, mainly due to the increased shipments to South East Asian countries such as Singapore and Hong Kong of China [1].However, strawberry has a limited shelf-life due to rapid softening and decay during postharvest handling such as transportation, storage and marketing.The main characteristics related to the market quality of strawberry fruits are texture (firmness), flavor and decay rate.Generally, fungal decay is caused to loss of quality on strawberry for storage time [2].It is therefore important to apply an appropriate postharvest treatment to delay respiration, prevent physical damage, dryness and to restrict fungal decay in order to extend shelf-life.Postharvest treatment such as precooling [3], storage at low temperature [4], carbon dioxide [2] [5] [6] and chlorine dioxide [7] can be used for this purpose.For example, Lee H.J. et al. reported that a short term application of CO 2 during cooling has a benefit for keeping freshness of strawberries during export and local marketing [5].Harker F.R. et al. reported that mechanism for CO 2 -induced firmness enhancement in strawberry is due to changes in the pH of the apoplast.Such changes in pH may promote the precipitation of soluble pectins and thus enhance cell-to-cell bonding in strawberry fruit [6].
Controlled atmosphere or modified atmosphere (CA or MA) has been used successfully on maintaining the quality of strawberries.Modified atmosphere packaging can be considered as a self-contained form of controlled atmosphere designed to maintain the internal gas composition of the packaging during transportation and storage.A modified atmosphere extends the shelf-life of the fruits, whereas the sealed container protects them from exposure to diseases and other environmental contaminants [8].Controlling the relative humidity and storage temperature were important factors for keeping the freshness of fruits.
To increase the export of fruit, such as strawberries, it is necessary to develop the postharvest management of fruit during retail marketing after transportation.Compared to air transportation, vessel export is cheaper and can move higher volumes, but it takes 3 -10 days longer to transport goods.Vessel export would seem unsuitable for strawberries, a fruit that can over ripen easily and become soft or rot [7].In this study, to extend the shelf-life of strawberry, we examined the CO 2 treatment alone and combined CO 2 with MA.We investigate the quality of "Maehyang" strawberry during different storage conditions in the retail marketing after vessel export.

Plant Materials and Treatment
Fresh "Maehyang" strawberry fruits were grown and harvested from commercial greenhouses in Jinju, Gyeongsangnam-do, Korea.Strawberry fruits were harvested in the early morning and immediately precooled in storage room at 1˚C for 2 hour.Fruits of uniform medium size with red color on 70% of the fruit surface were used for this study.Postharvest treatment was 30% concentration of carbon dioxide gas with 3 hour and using strawberry modified atmosphere packaging film (Xtend, Stepac, Israel).

Storage, Transportation and Retail Marketing Conditions
"Maehyang" samples treated with 30% concentration of CO 2 alone and combined CO 2 with MA packaging were stored for one day at 1˚C, transported for 10 days at 1˚C by vessel container, and distribution condition; cold storage for 3 days at 4˚C, retail market (10˚C -15˚C) and room temperature.

Quality Evaluations
Quality evaluations included weight loss, firmness, total soluble solid (TSS) and sensory analysis.
Weight loss was evaluated by measuring the weight of eight randomly chosen boxes.
Fruits were weighed using a digital balance scale (HH320, OHAUS, NJ, USA) just before treatment in South Korea, again upon their arrival in Singapore and retail marketing duration.
All texture measurements were undertaken potable firmness testing machine (FHM-5, Takemura, Japan) and 10 individual fruit per treatment were selected for each of them.
Total soluble solids (TSS) were measured according to the AOAC procedures [9].On each evaluation day, 5 fruit from each replicate was wrapped with 2 layer of cotton cloth and squeezed with a hand pressed juice maker.TSS of the resultant juice was measured in terms of brix using a refractometer (PAL-1, Atago Co. Ltd, Tokyo, Japan).
The sensory analysis of strawberry sample was carried out by expert panel.The member of the panel were trained to recognize and overall visual quality of strawberry sample prior to the test.These sensory qualities were evaluated by using 9-point scale ( 9= excellent, 7 = good, 5 = moderate, 3 = poor, and 1 = unusable).A score of 6 was considered as the limit of marketability.To incidence of decay was analyzed by eye and then quantified as a percentage by counting the number of decayed fruits divided by the total number of fruits in a single plastic box, and multiplying by 100.There were 20 -24 strawberries in each plastic box weighing approximately 280 g.Softening score of individual fruit in a box was carried out on 5-scale (0 = 0% surface softened, 1 = up to 10% surface softened, 2 = 10 to 25% surface softened, 3 = 25 to 50% surface softened, and 4 = >50% surface softened) [2].

Statistical Analysis
The experiment was conducted with three replications per treatment.Statistical analyses of the data were carried out using SAS software (SAS Institute, Cary, NC, USA).The level of significance was calculated from the F value of ANOVA.Mean comparison was achieved by Duncan's multiple range test.

Weight Loss
Weight loss during storage due to transpiration was observed for all treatments.Com-bination of CO 2 and MA treatments showed significantly lower values than the control and CO 2 treatment.Modified atmosphere such as box in bag, it maintained moisture and freshness.By Robinson et al., losses of 6% of the initial value of fresh weight of a soft fruit should be considered the limit for marketability [10].In this study, after 14 days of storage, control had loss 2% and CO 2 treatment had loss 3% due to stress of gas injection in acrylic chamber.However treated with combination of CO 2 and MA was shown that loss of fresh weight was 1% in 14 days of storage at under 4˚C.Comparing all treatments, combination of CO 2 and MA treatments had a significant effect on weight loss, presenting the lowest values (Figure 1).

Firmness
One of the main factors used to determine fruit quality and postharvest shelf life is the amount of loss of firmness during the storage of soft fruit such as strawberries [11].By Manning [12], fruit softening is attributed to the degradation of cell wall components, mainly pectin, due to the action of specific enzymes such as polygalacturonase.The firmness of strawberries increased as the 30% concentration of carbon dioxide treatment within 3 hour.After vessel export at 1˚C, firmness was maintained higher than control in all storage condition (Figure 2).Although increases in fruit firmness were reported in other studies by the application of high level of carbon dioxide [5] [6], in addition to the firmness enhancement observed when strawberry fruit are held at low temperatures [13].The firmness of strawberries after vessel export remained higher than harvest firmness values throughout the 15 day period of continuous cold storage at under 4˚C.By F.R. Harker et al., strawberries from all treatments softened rapidly and no residual effect of CO 2 -enhanced firming was detectable within 3 days at 20˚C (data not shown) [6].However, "Maehyang" strawberries treated with CO 2 and CO 2 + MA maintained firmness until 3 days at room temperature (over 26˚C), unlike that of

Total Soluble Solids
Total soluble solids are a critical factor for determining fruit quality and consumer acceptability.Sugars are the main soluble metabolites, and include glucose, fructose and sucrose comprising 99% of total sugar content [14].The TSS of cv."Maehyang" strawberries at harvest was 10.88˚ Brix and all treatments showed increases in the values during the storage time (Table 1).TSS was remained with low temperature storage, whereas TSS of "Maehyang" strawberries stored in retail market at 10˚C -15˚C were shown 9.72˚ Brix at the end of marketing (after harvest 14 days).

Sensory Quality
Sensory quality is related to the characteristics of the food and how consumers perceive them [15].With increasing storage time, deterioration starts with decay, fermentation and bruising [16].Visual quality of "Maehyang" strawberries after vessel transportation was evaluated.Carbon dioxide alone and combination of CO 2 and MA treatment were effective in delaying dark red coloration on fruit surface.Softening index of "Maehyang" strawberries was the highest in the control group at 11 days of storage (<4˚C) (Figure 3).After 15 days of storage (<4˚C), control showed higher score than those of CO 2 and combined CO 2 with MA treated strawberry.However, in low temperature storage under 4˚C, it restrained to occur softening on the surface of strawberry.Comparing all treatments, CO 2 and combination of CO 2 and MA treatments had a significant effect (p < 0.05) on softening index, presenting lower   produce.In particularly, strawberries are highly susceptible to microbial infection and have a short shelf-life caused by Botrytis cinerea [17].Fruit decay was not shown by cold temperature storage (<4˚C) for up to 15 days after harvest.However, the decay rate was the highest in the control group at 3 days room temperature storage cold sto- rage following 10 days transportation (Figure 4).High carbon dioxide levels may have inhibited decay by Nielsen and Leufven [18].At the point of 2 days in room temperature, it occurred fungal decay on control and CO 2 + MA.And after 3 days in room temperature, all treatments were shown that fungal decay on surface.In summary, worth notice is that we did not detect any decay at all when strawberry were sent immediately after vessel export and retail marketing, but only after storage at room temperature (simulation in wholesale market) high levels of fungal decay were shown after 2 days of storage on control and CO 2 + MA, and after 3 days, all treatments were shown high percentage of fungal decay on fruit surface.

Conclusion
Maintaining the quality of highly perishable fruits, such as strawberries, associated with the cold, retail market, local chain systems after long term transporting, is a difficult subject.Atmosphere containing 30% CO 2 was effective in reducing decay rate and fruit softening and maintaining bright red color of "Mayhyang" strawberries during long term transportation and distribution.Samples treated with combination of 30% CO 2 and MA had higher overall score with low softening index and weight loss after 14 days of transportation and low temperature distribution.Thus, CO 2 treatment alone or combination of CO 2 and MA could be a practical postharvest technology to extend shelf-life of "Maehyang" strawberry.Therefore, "Maehyang" strawberry can be exported through vessel transportation.

Figure 1 .
Figure 1.Changes in weight loss of "Maehyang" strawberries treated with CO 2 alone or combination of CO 2 and MA packaging after 10 days of transportation.Vertical lines represent S.E.

Figure 2 .
Figure 2. Changes in firmness of "Maehyang" strawberries treated with CO 2 alone or combination of CO 2 and MA packaging after 10 days of transportation during storage days at 4˚C. 0 means at harvest before treatment.0' means after treatment of CO 2 for 3hr before storage.Vertical lines represent S.E.Different letters indicate significant differences at p ≤ 0.05.

Figure 3 .Figure 4 .
Figure 3. Softening index of "Maehyang" strawberries treated with CO 2 alone or combination of CO 2 and MA packaging after 10 days of transportation during storage days at 4˚C. 0 means at harvest before treatment.0' means after treatment of CO 2 for 3 hr before storage.Vertical lines represent S.E.Softening index was scored using five-point scale based on the degree of softening area of the fruit surface where 0 = normal (0% surface softened), 1 = trace (up to 10% surface softened), 2 = slight (10 to 25% surface softened), 3 = moderate (25% -50% surface softened), and 4 = severe (>50% surface softened).

Table 1 .
Changes in total soluble solids of "Maehyang" strawberry treated with carbon dioxide or MAP at different storage conditions after vessel export.harvest before treatment.0' means after treatment of CO 2 for 3 hr before storage.Data are means ± S.E.