Effects of exogenous melatonin on fruit quality and physiological characteristics during room temperature storage in Yuluxiang pear

Abstract: 【Objective】The objective of this research is to disclose the effects of different concentrations (0, 0.1, 0.5 and 1.0 mmol · L^{- 1} ) of exogenous melatonin (MT) on fruit quality and physiological characteristics of Yuluxiang pear during room temperature (20±1) ℃ storage, so as to explore the optimum concentration of melatonin for Yuluxiang pear storage at room temperature.【Methods】The experiment fruits with uniform shape, size, color and maturity, and without any mechanical injury, disease or pest damage were selected. The fruits were soaked into 0.1, 0.5 and 1.0 mmol·L-1 MT solution, and the fruits soaking into the distilled water was used as control. All of the fruits were air-dried for approximately 40 min and then placed into 0.02 mm thick polyethylene bags. Both groups were stored for 21 days at (20±1) ℃. At 7-day intervals during shelf-life, fruit appearance and internal quality index including fruit weight, skin color (L* , h°), fruit hardness, soluble solids content, titratable acid content and vitamin C content were measured. Respiration rate and ethylene production were measured by gas chromatography for 20 days, the contents of malondialdehyde (MDA), and the activities of peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia- lyase (PAL) were measured with the frozenpeel samples every 7 day.【Results】The result showed that the application of melatonin at 0.1, 0.5 or 1.0 mmol·L­­­ˉ¹ reduced the decay rate and weight loss of fruit. In this study, both untreated and MT treated fruits exhibited gradual decrease in L* value, h* value and vitamin C, and the content of soluble solids and titratable acid increased at the first 7-day, and then fell down the next few days. At day 7, L* value of 1.0 mmol · L­­­ˉ¹ MT treatment was the lowest, but there was no significant (p＞0.05) difference with control. At day 21, h* value of 0.05 mmol·L-1 MT treatment was higher than other groups. MT treatment at 1.0 mmol·L^-1 reduced the decrease of vitamin C. In addition, 1.0 mmol·L­­­ˉ¹MT treatment that significantly (p＜0.05) delayed the fruit firmness deceased at the first 7 days of storage. Nevertheless, MT treatment had no notable impact on soluble solids content. As for fruit titratable acid content, there were significant (p＜0.05) differences among the MT treatments with different concentrations. At day 7, titratable acid content in 0.1 mmol·L^{- 1} MT treated fruits was the highest. At day 14, titratable acid content in control was higher than 0.1, 0.5 and 1.0 mmol·L­­­ˉ¹ MT treatments. At day 21, titratable acid content in 1.0 mmol·L­­­ˉ¹ MT treated fruits was the highest. During the room temperature storage, the activity of POD increased at 14 days of storage, but dropped rapidly at 21 days of storage. PAL activity increased both in control and MT treated fruits at 21 days of storage. Compared to the control, 0.1 and 0.5 mmol·L-1 MT treatment and 1.0 mmol·L­­­ˉ¹ MT treatment showed higher POD and PAL activity at 21 days of storage. At day 7, PPO activity with 0.5 mmol · L­­­ˉ¹ MT treatment was significantly (p＜0.05) higher than that with other treatments. MDA content sharply increased in untreated fruits at 7 days of storage, which adversely decreased in 0.1, 0.5 and 1.0 mmol·L^-1 MT treatment. All the concentrations of MT treatments could inhibit the increase of MDA content, but 1.0 mmol·L-1 was the suitable concentration. MDA content in 1.0 mmol·L-1 MT treated fruits was significantly lower than that in untreated fruits at 14 days of storage. The ethylene release rate of both untreated and treated fruits reached a peak value on the 4th day. Compared to the control and 0.1 mmol·L^-1 MT treatment, 0.5 and 1.0 mmol·L-1 MT treatments decreased the ethylene production of Yuluxiang pear during the whole shelf life.【Conclusion】 Compared with the control, suitable MT treatment can slow down the increase in fruit decay rate and weight loss. 1.0 mmol·L­­­ˉ¹ MT treatment delayed the decrease of vitamin C and fruit firmness at 7 days of storage, and enhanced the activity of POD and PAL during the shelf life, and meanwhile, restrained the flourish of MDA content and ethylene production. It is surely believed that suitable exogenous MT treatment can improve the storage quality of Yuluxiang pear during shelf life at room temperature.