Effects of harvest times with polyethylene (PE) film liner, 1-methylcyclopropene (1-MCP) and aminoethoxyvinylglycine (AVG) treatments on fruit quality in‘Sangjudungsi’persimmon during cold storage

The ‘Sangjudungsi’ persimmon fruit (Diospyros kaki Thumb.) was harvested at the commercial orchard in Sangju, Korea. The fruits were harvested at different harvest dates in 2015 and 2016. The fruits in 2015 were harvested at commercial harvest time on 20^th October (mature stage). and the fruits in 2016 were picked up on 10^th October, which was 10 days earlier than 2015. Harvested fruits were immediately transported to laboratory, and all the experiments were carried out at the postharvest laboratory of Horticultural Science, Kyungpook National University, Korea.

The fruit selected were uniform in shape and size, and free from decay and damage. The same treatments were immediately applied to harvested fruits before cold storage. For PE film liner treatment, polyethylene film liner bags (20 μm thick, Taebang Patec Co., Ltd., Seoul, Korea) were used to evaluate fruit storability. For 1-MCP treatment, 1 μL/L of 1-MCP (AgroFresh Co., Seoul, Korea) was used by fumigating the fruit for 18 h in an enclosed container. For AVG treatment, the fruit was dipped in the solution containing 75 mg/L of AVG (Valent BioScience, Libertvilles, IL, USA) for 5 min and dried for 1 h at ambient temperature. All the treatments were stored together at -1℃ in air with 90-95% relative humidity for up to 4 or 5 months of cold storage.

For the measurement of respiration rate and ethylene production, 3 fruits of each treatment were weighted and individually sealed in 1.6 L enclosed container for 1 h. Then, 1 mL of the headspace gas was injected into a gas chromatograph (GC-2010, Shimadzu Co., Tokyo, Japan) with flame ionization detector and activated column. Analyses were run at the oven temperature at 90℃ with the injector and detector temperature, respectively, 100℃ and 200℃ for both ethylene and respiration.

Peel color variables (L*, a*, and b*) were evaluated with a chromameter (CR-200, Minolta Co., Tokyo, Japan) on equatorial and calyx-end regions of the fruits. The measurement was taken 3 readings per region of each fruits (n=15). The flesh firmness was evaluated with a digital penetrometer (Fruit Pressure Tester, FT-327, Alfonsine, Italy). Fruit firmness values were an average of 15 fruit per treatment and 3 times per fruit were taken at the equatorial regions. The juice from each fruit was used to determine the soluble solids content (SSC) of the fruit by a digital refractometer (PR-201α, ATAGO, Tokyo, Japan). The weight loss was measured in 15 individual fruits per treatment monthly throughout the storage period (n=15). The storage disorders such as peel blackening, fruit softening, and rot were assessed visually in individual 15 fruits. A 5-point scale was used to evaluate the severity rate of peel blackening and rot, and scored as 0=0%, 1=1% to 10%, 2=11% to 25%, 3=26% to 50%, 4=51% to 75%, and 5=76% to 100% on the fruit corresponding affected area.

The data for statistical analysis were subjected to two-way ANOVA and mean differences were analyzed using Duncan’s multiple range tests at p=0.05 level. SPSS (IBM SPSS Statistics 23, SPSS Inc., New York, NY, USA) was used for statistical analysis.

The ethylene production between the two different harvested dates was not significantly different in any treatments during cold storage for both 2015 (mature harvested fruit) and 2016 (early harvested fruit). However, earlier ethylene production was observed in mature harvested fruits as compared with early harvested fruits (Fig. 1A, 1B). Respiration rate in early harvested fruit treated with AVG and 1-MCP was significantly higher than PE film liner and control after storage of 4 to 5 months (Fig. 1D), while those were observed in mature harvested fruits treated with only 1-MCP treatment after storage of 3 months (Fig. 1C). In addition, the respiration rate between the harvesting dates was also different because the rate detected in mature harvested fruits was higher than in early harvested fruits, (Fig. 1C, 1D).

Fig. 1. Effects of PE film liner, 1-MCP, and AVG treatments on ethylene production and respiration rate on mature harvested fruit in 2015 (A, C) and early harvested fruit in 2016 (B, D) in ‘Sangjudungsi’ persimmon during cold storage at -1℃. All values are expressed as means±standard error (n=15).

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Ethylene production was not significantly affected at all treatments at different harvest dates. This result confirmed that very low and similar ethylene production was found at different harvest dates in ‘Rojo Brillante’ persimmon (10). Regarding different harvest dates, the production in respiration rate was different at their respective harvest time. In our study, early harvested fruits produced lower respiration rate than mature harvested fruits. The late harvested ‘Fuyu’ and ‘Hachiya’ persimmons produced more respiration rate than early harvested ones (11). In 2016, 1-MCP treatment produced more respiration rate at 4 and 5 month of storage compared with control and PE film liner treatments. However, in 2015, non-significant results were observed at all treatments. Due to the high accessibility and affinity of 1-MCP to the receptors, the effectiveness of 1-MCP application in persimmon can be varied (6). Application of 3 μL/L 1-MCP treatment in persimmon was suppressed ethylene production compared with control fruits (5). In pears, AVG did not block ethylene production sufficiently at low temperature (12). Respiration and ethylene production rate did not affect by 1-MCP and AVG treatments in different harvest dates may be due to the low concentration of the treatments.

PE film liner treatments maintained more significantly the weight loss during storage in both years compared with others (Fig. 2A, 2B). Whereas, the lowest weight loss was found in early harvested fruit treated with 1-MCP (Fig. 2B), followed by AVG and control (Fig. 2B). In addition, the firmness value of early harvested fruits was higher than that of mature harvested fruits and its decrease was slow in early harvested fruits (Fig. 2C, 2D), while its values of fruits (of 2015 and 2016) treated with AVG and 1-MCP was similar, but which were higher than control at the end of storage (Fig. 2C, 2D). The soluble solids contents (SSC) detected in the fruits (of 2015 and 2016) treated with 1-MCP were unstable at the early storage, and slightly decreased by 1 and 2 months after cold storage (Fig. 2E, 2F).

Fig. 2. Effects of PE film liner, 1-MCP, and AVG treatments on flesh firmness, weight loss, and soluble solids content (SSC) on mature harvested fruit in 2015 (A, C, E) and early harvested fruit in 2016 (B, D, F) in ‘Sangjudungsi’ persimmon during cold storage at -1℃. All values are expressed as means±standard error (n=15).

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Variation of fruit peel color between the two different harvesting dates was significantly different because the color observed in early harvested fruits was brighter L* and b* than in mature harvested fruits. However, a* value in mature harvested fruits was significantly higher than in early harvested fruits (Fig. 3 and 4). On the other hand, variation of the fruit peel color observed in calyx-end region was significant compared to equatorial ones. In the calyx-end region, values of L* and b* in the fruits (of 2015 and 2016) treated 1-MCP were significantly higher than other treatments at the end of storage (Fig. 3A,E and 4A,E). The similar results were also observed in equatorial region of the fruits treated with AVG and 1-MCP (Fig. 3B,D,F and 4B,D,F). Although hunter a* value was observed as non-significant result at all treatments in 2016 (Fig. 3D, 4D), its significant declination was observed in PE film liner treatment, and which was less than those of other treatments in 2015 (Fig. 3C, 4C). In late harvested fruits, variation of the fruit peel color by PE film liner was significantly less than 1-MCP treatment in both regions starting from 3 month after storage to the end of storage (Fig. 3A-F).

Fig. 3. Effects of PE film liner, 1-MCP, and AVG treatments on the color variables (L*, a*, and b*) in calyx-end regions on mature harvested fruit in 2015 (A, C, E) and early harvested fruit in 2016 (B, D, F) in ‘Sangjudungsi’ persimmon during cold storage at -1℃. All values are expressed as means±standard error (n=15).

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Fig. 4. Effects of PE film liner, 1-MCP, and AVG treatments on the color variables (L*, a*, and b*) in equatorial regions on mature harvested fruit in 2015 (A, C, E) and early harvested fruit in 2016 (B, D, F) in ‘Sangjudungsi’ persimmon during cold storage at -1℃. All values are expressed as means±standard error (n=15).

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The flesh firmness is one of the important aspects to consider the quality attributes in persimmon fruits. Increase in cold storage period is directly correlated with decrease in flesh firmness. In ‘Rojo Brillante’ persimmon, the firmness which was lower than 10 N was not acceptable from a commercial point of view (13). In this experiment, the control in mature harvested fruits was found lower than 10 N at the end of storage in 2015. However, in 2016, the firmness value lower than 10 N was not observed at all treatments until the end of storage. According to different harvest dates, the firmness value of early harvested fruits was slowly decreased in this study. The firmness values of ‘Rojo Brillante’ persimmons picked at early harvested date were slowly declined at 1oC, compared with mature harvested fruits (10). 1-MCP and AVG treatments showed their effective results on maintaining decrease in firmness at different harvest dates.

PE film liner treatment was significantly delayed increase in weight loss and the same results were observed at different harvest dates, compared with other treatments. Storage with polyethylene bags reduced the weight loss in ‘Manila’ mango, compared with control or 1-MCP treatments alone (14). Increased weight loss was significantly suppressed when ‘Tonewase’ persimmon stored with polyethylene bags (15), and in apples (16). Application of 150 mg/L AVG to ‘Monroe’ peach did not reduce weight loss at 0℃ (17).

In this study, early harvested fruits had lower SSC, compared with mature harvested fruits. The SSC in different harvest dates was similar and found only little changes during cold storage (10). The unstable SSC was observed in 1-MCP treatment at early storage period in different harvest dates. Overall, non-significant was observed at all treatments during storage. Non-significant results in SSC were observed by AVG in ‘Tsugaru’ apple (9), and by 1-MCP in ‘Red Clapp’s’ pears (18) and in tomato (19). Lower SSC in fruit was associated with lower sucrose concentrations (20).

The differences on fruit peel color variables (L*, a*, and b*) between different harvest dates were observed at their harvest different time. Mature harvested fruits were strongly related to a* value and higher than early harvested fruits. Color index of a* value belonging to late harvest was found higher value at harvest than that belonging to early harvest (10). Peel color changes in ‘Sangjudungsi’ persimmons were significantly noticed in calyx-end regions than in equatorial ones (3), and the similar results were found in this study. 1-MCP treatment delayed skin color change in avocado (21) and inhibited anthocyanin increases in strawberry (22). Only 600 mg/L increased the L* value among three concentrations in ‘Red Chief’ apples (23). In this study, 1-MCP delayed decrease in peel color variables in calyx-end regions at both different harvest dates, compared with control and PE film liner treatments.

With increasing storage period, the incidence of storage physiological disorders was visually distinct. The incidence of peel blackening was distinctly noticed in control fruit (of 2015) after storage of 1 and 4 months (Fig. 5A), while fruit softening was observed in PE film liner treatment (Fig. 5C), In addition, the symptoms of decay were also observed in PE film liner treatment after storage of 3 months (Fig. 5E). However, no decay symptom was observed in the fruits (of 2016) treated with AVG treatment during storage, although PE film liner caused peel blackening at the end of cold storage (Fig. 5B), and softening after storage of 4 and 5 months (Fig. 5D). Incidence rate of softening and decay by control and PE film liner treatments were significantly higher (Fig. 5D), but those incidences were not observed in 1-MCP and AVG treatments throughout the storage period (Fig. 5F). The longer storage periods resulted in higher incidences of physiological disorders. Development of peel blackening was not highly occurred when the fruits were packed in 50 μm PE film bags (24). Peel blackening in 2016 was detected only in PE film liner treatment which may be packed with thin PE film bags. 1-MCP treatment significantly delayed fruit softening in this study, and the similar result was also found in ‘Tonewase’ and ‘Saijo’ persimmons (6). Higher amounts of decay fruits were observed highly in PE film liner treatment at 3 month in 2015 and at 4 month in 2016, compared with other treatments. No decay was observed in AVG treatment at different harvest dates and slightly found in 1-MCP treatment at 3 month in 2015. Decay incidence by 1-MCP treatment was detected after 90 days during air storage at 1℃ (25). However, decay incidence in early harvested fruits was higher than in late harvested ones at ‘Hachiya’ and ‘Fuyu’ persimmons (11), and the similar results were found in this study.

Fig. 5. Effects of PE film liner, 1-MCP, and AVG treatments on storage disorders in peel blackening, softening and decay incidence on mature harvested fruit in 2015 (A, C, E) and early harvested fruit in 2016 (B, D, F) in ‘Sangjudungsi’ persimmon during cold storage at -1℃. A 5 point scale to the detected in severity rate of peel blackening and decay incidence as (0=0%, 1=1% to 10%, 2=11% to 25%, 3=26% to 50%, 4=51% to 75%, and 5=76% to 100%) and softening was scored as percentage (%) on the peel area of the corresponding symptoms. All values are expressed as means±standard error (n=15).

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In the results, 1-MCP treatments delayed slowly decrease in flesh firmness, maintained in degradation of peel color variables and inhibited in occurring higher physiological disorders at both different harvest dates. On the other hands, PE film liner treatment was significantly decreased in flesh firmness, increased in disorders and declined results in peel color variables, compared with other treatments. Early harvested persimmons had better fruit quality attributes, decreased slowly in color variables and firmness, and delayed in storage disorders than mature harvested fruits.

Therefore, the results indicated that the importance of fruit maturity was closely related to different harvest dates and this study would provide a useful tool for postharvest handling and storability of ‘Sangjudungsi’ persimmon fruits during cold storage.