Effects of temperature and PE bags packaging on the postharvest fruit quality in Wanjin kiwifruit

Abstract: 【Objective】Wanjin is a new kiwifruit cultivar selected by Anhui Agricultural University and Wanxi Kiwifruit Research Institute via seedling selection. The purpose of this study is to explore the postharvest storage characteristics of the new variety Wanjin, and to clarify the suitable storage tempera-ture and the thickness of packaging film bag.【Methods】This experiment was divided into two parts: de-termining the appropriate storage temperature of Wanjin and screening out the appropriate thickness of film bag packaging. First, some fruits were randomly divided into 4 treatments, and they were stored at (0±0.5) ℃, (1±0.5) ℃ and (2±0.5) ℃ cold storage (RH 90%±5%) and room temperature (CK1). Regu-lar samples were taken to determine fruit firmness, soluble solids content, respiration rate, ethylene re-lease rate, electrolyte leakage and MDA content, and chilling injury symptoms were observed by calcu-lating chilling injury index. A series of indicators were counted, such as weight loss rate, rotting rate and chilling injury rate for each treatment when the fruits were taken out of storage, so as to make the fruits suitable for storage temperature screening. The results showed that (1±0.5) ℃ was the suitable  storage temperature for Wanjin. The second part of the experiment was as follows. In order to further optimize the storage conditions, the fruits were sealed and packaged in polyethylene film bags(40 cm×60 cm) of different thicknesses (0.01, 0.03 and 0.05 mm) and stored under the storage condition of (1±0.5) ℃. And the unpackaged fruits were used as control (CK2). Regular samples were taken to deter-mine the relevant indicators, and suitable film bag thickness for Wanjin was selected.【Results】When the fruits were stored at room temperature for 25 d, the firmness dropped to 1.52 kg · cm- 2.Compared with the room temperature control (CK1), the effective storage periods of the fruits were prolonged to 65 d, 65 d and 55 d, respectively, after fruits were stored at (0±0.5) ℃, (1±0.5) ℃ and (2±0.5) ℃, and the respiration rate and ethylene production rate of the fruits were delayed for 15 d, respectively. The chilling injury rate of fruits stored at (0±0.5) ℃ was significantly higher than that stored at (1±0.5) ℃ and (2±0.5) ℃. But there was no significant difference between (1±0.5) ℃ and (2±0.5) ℃ treatments.There was no significant difference in the rotting rate among the three refrigerated fruits. The second part of the test results was as follows. In storage from 10 d to 90 d, CO2 concentrations in 0.01 mm, 0.03 mm and 0.05 mm PE film bags were stable at 2.02%-2.59%, 3.19%-3.67% and 4.43%-5.46%, respec-tively. The O2 concentration was maintained at 16.62%-17.51%, 15.03%-16.18% and 13.37%-14.53%, respectively. When fruits were stored for 90 d, the firmness of fruits packaged by 0.05 mm, 0.03 mm and 0.01 mm PE film bags were 4.0, 2.3 and 1.3 times more than that of the control (CK2), respectively.The fruits of the control were shipped out of the warehouse at 90 d. The SSC of fruits packaged by PE film bags was lower than that of the control, among which the SSC was the highest with the 0.01 mm treatment, followed by 0.03 mm treatment, and the lowest with the 0.05 mm treatment. The respiration rate and ethylene production rate of fruits treated with CK2 and 0.01 mm PE film bags appeared at 30 d of storage, and the occurrence rate of fruits treated with 0.03 mm and 0.05 mm was delayed for 10 d, and the peak value was significantly reduced. After 70 days of storage, chilling injury occurred with 0.01 mm treatment. When the fruits were shipped out of the warehouse, the chilling injury rate of the CK2 and the 0.01 mm treatment was significantly higher than that of the 0.03 mm treatment, and the lat- ter was only 3%. The relative conductivity and MDA content in fruits with the PE package treatment groups were always lower than those with the control (CK2), in which the 0.05 mm treatment kept the lowest level. The weight loss rate of the control was the highest when the fruits were taken out of stor-age. The rotting rate of the fruits treated with 0.05 mm PE film bags was up to 72.33% at 180th d, which was significantly higher than that of the control (CK2) and the treatments with 0.01 mm and 0.03 mm PE film bags.【Conclusion】The storage conditions of (1±0.5) ℃ plus 0.03 mm PE film bag treat- ment (CO2: 3.19%-3.67%+O2: 15.03%-16.18%) had the best effect on maintaining the fruit quality of Wanjin kiwifruit, prolonging the effective storage period and inhibiting the occurrence of chilling injury.