Effects of exogenous γ-aminobutyric acid treatment on fruit quality and preservation of postharvest Jing’an ponkan

Abstract:【Objective】Citrus has important economic value in China. However, fruit decay and quality  deterioration seriously affect storage life and postharvest value of citrus fruits. γ-aminobutyric acid (GA-BA) is widely present in plants, affects secondary metabolism and improves the antioxidant and stress resistance of plants. Meanwhile, GABA was widely studied for effective storage and preservation of fruits and vegetables. The study aimed to explore the effect of exogenous GABA on fruit quality and an-tioxidant capacity of Jing’an ponkan during storage, so as to provide a theoretical basis for the applica- tion of GABA in postharvest storage and quality regulation of citrus fruit.【Methods】Jing’an ponkan fruits were harvested from a commercial orchard located in Jing’an county, Yichun city, Jiangxi prov- ince, and then the fruits were transported to the laboratory in Jiangxi Agricultural University within 6 h.Only fruits with uniform size and free from any visible injury were selected for further experiments. A total of 600 fruits were randomly divided into two equal groups and used for the following treatments in triplicate. One batch was soaked in 0.5 mmol·L^-1 GABA for 2 min, and another batch was immersed in double distilled water under the same conditions to serve as control. After treatment, the fruits were per-mitted to air drying, single fruit was bagged with a polyethylene bag (18 cm × 14 cm × 5 μm), and then they were stored at ambient temperature (20±1℃, with RH 95%±2%) for 60 days. The fruit quality in-dexes such as weight loss rate, citrus color index (CCI), total soluble solids (TSS), titratable acidity (TA), soluble sugars and organic acids content, the activities of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX), as well as to-tal phenols content, flavonoids content, hydrogen peroxide (H2O2) content and hydroxyl radical scaveng-ing rate were determined at 0 d, 10 d, 20 d, 30 d, 40 d, 50 d, 60 d after storage.【Results】The results showed that exogenous GABA treatment could significantly reduce the fruit weight loss rate, increase the peel lightness (L value), but had no difference in red-green difference (a* value) and yellow-blue dif- ference (b* value) of the peel, and maintain the contents of TSS, TA and total sugar at a high level. The results also showed that sucrose content was the highest in the sugar component of Jing’an ponkan fruit, accounting for 40.18%-46.54% of total sugars content, followed by fructose (25.15%-26.73%) and glucose (21.70%-27.27%), and GABA treatment maintained the contents of sucrose, fructose and glucose at a higher level than those of CK group. At 10, 20, 30 d of storage, the increase of soluble sug-ar contents in GABA group fruits were 6.42, 3.32 and 5.6 mg·g⁻¹ for sucrose, 1.83, 1.63 and 2.39 mg·g⁻¹for fructose, and 3.79, 1.05 and 3.54 mg·g⁻¹ for glucose, respectively. For the acid component of Jing’ an ponkan fruit, the proportion of citric acid content was the highest and showed a downward trend dur-ing the whole storage period, which was consistent with the changing trend of TA and organic acids con-tent. At the 20-40 d of storage, the citric acid content of GABA treated fruits was significantly higher than that of the control fruits, which were 1.62, 1.2 and 1.29 times, respectively, so as to maintain better fruit quality. Simultaneously, GABA treatment also significantly increased the activities of CAT, SOD and POD in mid-storage (30-40 d) and the activity of APX in early-storage (10 d) and late-storage (60 d),and GABA treatment promoted the accumulation of total phenols and flavonoids in the early storage(10 d) and late storage (50-60 d). During the storage period of Jing’an ponkan fruit, the hydroxyl radi-cal scavenging rate with GABA treatment group was higher than that of the control group except 40 d of storage, and the difference was significant at the 10 d. The hydroxyl radical scavenging rate of Jing’an ponkan fruit increased with GABA treatment. In the early storage (30-40 d) of ponkan fruit, GABA treatment could significantly reduce the accumulation of H2O2, but significantly higher than that of the control group at 50 d and 60 d of storage.【Conclusion】The results showed that exogenous GABA treat-ment could reduce the weight loss rate of Jing’an ponkan fruit, improve the peel brightness, maintain high TSS, TA, sugar and acid contents, stimulate CAT, APX, SOD and POD activities, and promote the accumulation of total phenols and flavonoids. The above results suggested that GABA treatment might maintain the postharvest storage quality and preservation effect of ponkan fruit by regulating sugar and acid metabolism, enhancing antioxidant enzyme activity and increasing antioxidant substance content.