Effects of different treatments on green color retention and internal quality of Kuerlexiangli pear fruit during shelf life

【Objective】Kuerlexiangli pear, cultivated in the Xinjiang Uygur Autonomous Region of China, is renowned for its superior appearance, flavor, and aroma. Widely regarded as the“Prince of Fruits”, Kuerlexiangli pear has gained significant popularity among consumers domestically and internationally. Kuerlexiangli pear is typically harvested within a concentrated season, yet marketed yearround. It is estimated that approximately 60% of the fruit must be placed in cold storage to enable this off- season supply. However, once removed from cold storage, pear fruit is prone to problems such as peel yellowing and rapid quality deterioration during shelf life, which significantly impacts their market value and competitiveness. Therefore, this study investigated the effects of GA3, MT, 40 ℃ heat shock and 1-MCP treatments on the shelf-life green color retention and internal quality of Kuerlexiangli pear fruit, with the objective of providing technical references for delaying fruit peel yellowing and quality deterioration of Kuerlexiangli pear fruit.【Methods】Kuerlexiangli pear fruits were treated with 50 mg·L- 1 GA3, 25 μmol·L-1 MT, 75 μmol·L-1 MT, 40 ℃ hot water or 1 μL·L-1 1-MCP respectively, and then the fruits were stored for 14 days at 26 ℃ and 80% relative humidity in darkness. During shelf storage, samples were collected at 0 (before treatment), 1, 3, 7, 10 and 14 days after treatment for the determination of fruit peel color (L*, a*, b*), chlorophyll content, fruit firmness, total soluble solids (TSS) content, sugar and acid content, respiratory intensity and ethylene release rate. Meanwhile, the most effective treatment groups for green color retention of Kuerlexiangli pear fruits were selected to analyze the relative expression levels of chlorophyll degradation-related genes.【Results】All treatments (50 mg·L-1 GA3, 25 μmol·L-1 MT, 75 μmol·L-1 MT, 40 ℃ heat shock and 1 μL·L-1 1-MCP treatments) effectively delayed peel yellowing of Kuerlexiangli pear fruit during shelf storage. Among them, MT treatments (at both concentrations) were the most effective and delayed the peel-yellowing process by approximately 7 days, whereas GA3, 40 ℃ heat shock and 1-MCP treatments delayed it by only about 3 days. During the later stage of shelf storage, all treatments significantly suppressed the increase of L* and a* values of fruit peel, reduced peel greasiness, and effectively maintained the green color. GA3 and MT treatments also significantly inhibited the increase of the b* values. Both heat shock and 1-MCP treatments resulted in lower b* values, which showed no significant difference compared with the control. After 7 days of shelf storage, the chlorophyll a and the total chlorophyll contents in all treatment groups were higher than those in the control. By day 14, the chlorophyll content of the fruit peel, in descending order, was: the 25 μmol·L-1 MT group, the 75 μmol·L-1 MT group, the 40 ℃ heat shock group, the 50 mg·L-1 GA3 group, the 1 μL·L-1 1-MCP group, and finally the control group. Notably, both MT treatments significantly inhibited the degradation of chlorophyll a and total chlorophyll. Gene expression analysis showed that both MT groups and the 40 ℃ heat shock group significantly suppressed the relative expression levels of chlorophyll degradation-related genes (PsNYC1, PsPAO, PsPAO1, PsPPH1 and PsSGR1) relative to the control. Regarding fruit quality, fruit firmness was markedly reduced by the 40 ℃ heat shock treatment but remained statistically unchanged in the other treatment groups. Furthermore, no significant difference in TSS content was observed among any of the treatments. By day 14, all treatments significantly reduced the content of malic acid and citric acid in the fruit flesh. Although both MT treatments significantly reduced fructose content, they had no significant effect on sucrose or glucose levels. No significant changes in sucrose, glucose or fructose content were observed in the remaining treatment groups. These results indicated that all treatments improved the internal quality of the fruit to a certain extent. In addition, all treatments significantly reduced the respiratory intensity and ethylene release rate during shelf storage. However, by day 14, only the 1-MCP treatment maintained a significantly lower ethylene release rate compared with the control, with no significant differences observed in the other groups.【Conclusion】GA3, MT, heat shock and 1-MCP effectively delayed peel yellowing and maintained the internal fruit quality of Kuerlexiangli pear fruit during shelf storage. Notably, the 25 μmol·L-1 MT treatment showed the strongest effect on green color retention of Kuerlexiangli pear fruit.