Effects of Different Temperature Changing Rates during Precooling on Reducing Mechanical Damage of Peach Fruit after Harvest

Peach fruit is rich in nutrition, easy to digest and absorb, and loved by consumers. However, peach fruits are prone to mechanical damage after harvesting, decay and quality loss, limiting their commercial value. This study investigated the effect of different precooling rates on the reduction of mechanical damage in peaches after harvest. 'Hujingmilu' peach fruits were subjected to precooling treatments (rapid precooling for 3 h and slow precooling for 16 h, reducing the core temperature of the fruit from 27 ˚C to 9 ˚C), with the control (Control check, CK) being without precooling. Afterwards, the fruits were subjected to compression damage (A texture analyzer with a probe diameter of 100 mm, a test depth of 10 mm and an extrusion speed of 1.5 mm/s was used to simulate the compression process). Overall, the precooling treatment, especially the rapid precooling treatment of 3 h, reduced bruise index, decay rate and weight loss rate, delayed the decline of fruit firmness during storage and accelerated the rise of phenylalanine ammonia lyase activity in the late storage period. In particular, the bruise index and decay rate of the fruits subjected to rapid precooling (3 h) were reduced by 11.7% and 8.3%, respectively, compared to the control treatment. Furthermore, the precooling treatments, regardless of time (3 h or 16 h), minimised increase in respiration rate, ethylene production, malondialdehyde content and polyphenol oxidase activity in the peach fruit with compression damage. The polyphenol oxidase activities in rapid precooled and the slow precooled fruits were 75.7% and 72.1%, respectively of the control at 21 d of storage. In addition, the precooling treatments also delayed the increase in total phenolic content, with rapid and slow precooling having 85.1% and 92.1%, respectively of phenolic content contained in the control treatment at 7 d of storage. In conclusion, rapid precooling of postharvest peach fruit prior to compression damage can reduce quality deterioration and decay of the peach fruit, and therefore, could improve the marketability of the fruit.