Study On Regulating Effect And Mechanism Of Ascorbic Acid On Postharvest Persimmon Fruit Softness

Ascorbic acid (AsA), as a natural preservative, has been proven that it can keep postharvest apricot, apple, longan and cherry tomato fruit fresh. But in persimmon, we still don’t know what effect AsA will have. In this study, early maturity ’Ninxin’Persimmon and late maturity’Gongcheng’Persimmon which are major cultivar in Guangxi were chosen for experimental material, in order to study regulating effect and mechanism of AsA on postharvest persimmon fruit softness. The study aims at exploring the relationship between exogenous AsA treatment and AsA content in persimmon fruit, antioxidation system function, ethylene synthesis and cell wall degradation, and then clarifying the physiological mechanism which AsA regulates fruit softness. This will lay the foundation for developing new fresh-keeping technology of persimmon fruit. The main findings are as follows:1. Taking early maturity ’Niuxin’Persimmon with routine CO2 astringency removal treatment as testing material, after treating fruit sepal with five percent AsA solution, changes of physiologic and biochemical indexes related to persimmon fruit softening, cell wall degradation, and antioxidant system were studied. The results showed that AsA treatment maximizes’Niuxin’Persimmon freshness. Exogenous AsA treatment produced higher firmness and lower total chromatism than either a blank or a control similarly treated with deionized water. From seventh (7th) to fifteenth (15th) of days after treatment, AsA treatment delayed fruit protopectin decreasing rate and soluble pectin increasing rate, and treated fruit showed lower activity of cell wall degrading enzyme polygalacturonase (PG) and cellulase (Cx) than both of blank and control. During the storage period, the exogenous AsA treatment impeded the decrease of AsA in persimmon fruit, as well as better controlled peroxidase (POD) activity and malondialdehyde (MDA) accumulation, the function of fruit antioxidant system was well protected. Additionally, the AsA treatment also enhanced reducing sugar content to a certain extent. Finally, the supplement post-harvest AsA treatment extends persimmon shelf-life after de-astringency and improves fruit commodity quality.2. Taking late maturity’Gongcheng’Persimmon with ethephon pretreatment as testing material, after soaking fruit one hour with AsA solution, changes of physiologic and biochemical indexes related to persimmon fruit softening, ethylene synthesis, cell wall degradation, and antioxidant system were studied. The results showed that AsA treatment maximizes’Gongcheng’ Persimmon freshness. Exogenous AsA treatment produced higher firmness and lower softness and total chromatism than either a blank or a control similarly treated with deionized water. During the whole storage period, AsA treatment reduced ethylene production and delayed fruit protopectin decreasing rate and soluble pectin increasing rate, and treated fruit showed lower activity of cell wall degrading enzyme PG and Cx than both of blank and control. At the same time, the exogenous AsA treatment impeded the decrease of AsAin persimmon fruit, as well as better controlled POD activity and MDA accumulation, slowed down the reduction of ascorbate peroxidase (APX) and catalase (CAT) activity, the function of fruit antioxidant system was well protected. Additionally, the AsA treatment also enhanced total soluble solid content to a certain extent. Finally, the supplement post-harvest AsA treatment slowed down persimmon softness after ethephon stimulating and improves fruit commodity quality. The 240 mmol/L AsA treatment showed the best effect on inhibitting’Gongcheng’ persimmon fruit soft among 30 mmol/L,120 mmol/L and 240 mmol/L AsA treatment.3. The correlation analysis results showed that firmness was significant positive correlated with protopectin content (r= 0.995**) and AsA content in persimmonfruit (r= 0.881*), moreover, AsA content in persimmon fruit was significant positive correlated with protopectin content (r= 0.893*), and significant negative correlated with PG activity (r=-0.873*) in the process of early maturity ’Niuxin’persimmon softness. Thus a close relationship among persimmon fruit softness and cell wall degradation andAsA content in persimmon fruit was indicated. In the process of late maturity’Gongcheng’ persimmon softness, firmness was significant positive correlated with protopectin content (r= 0.823*), besides, protopectin content was significant positive correlated with AsA content in persimmon fruit (r= 0.900**). This also proved that there is a close relationship among persimmon fruit softness and cell wall degradation and AsA content in persimmon fruit.In conclusion, exogenous AsA treatment could maximize persimmon freshness, concurrently, cell wall degradation was the dominant factor which caused to persimmon fruit softness during the post-harvest storage period, and AsA in persimmon fruit was closely related to cell wall degradation. On the one hand, AsA in persimmon fruit could inhibit cell wall degrading enzymes activity from increasing, and then slowed down cell wall degrading; On the other hand, AsA in persimmon fruit, as a non-enzymatic antioxidant, could enhance the resistance ability of fruit antioxidation system. In addition, exogenous AsA treatment could regulate cell wall degrading by controlling endogenous ethylene synthesis, and then affect fruit softness.