Effect of two-temperature cold shock treatment on quality and physiology of cucumber and its heat transfer characteristic

Abstract: Cold shock treatment, as a safe, effective physical pretreatment method, had gained growing interest. Part of this interest relates to the growing pressure from consumers to reduce the quantities of postharvest chemicals used for keeping fresh. To investigate the effects of heat transfer characteristics on fruits and vegetables during storage, the concept of two-temperature cold shock treatment was introduced to obtain the different heat transfer characteristics during the process of cold shock treatment. Cucumbers were treated with a common cold shock treatment (42 min at mixture of ice and water) and a two-temperature cold shock treatment (14 min at mixture of ice and water, followed by 14 min at 6℃cold water. and 14 min at mixture of ice and water again), respectively. The temperature distribution of cucumber was measured. The storage quality such as weight loss rate, firmness, and peroxidase (POD) activity were evaluated. Then the internal relationships between the cucumber preservation quality and heat transfer characteristics were analyzed. The results indicated that the two cold shock treatment methods performed better than the comparative group in reducing weight loss rate, restraining soft tissues and color variation, maintaining the membrane integrity, and increasing POD activity. The two-temperature cold shock treatment was significantly superior to the common cold shock treatment in delaying degradation of cell membrane and increasing POD activity (P<0.05), after 15 d storage at 10℃, the membrane permeability, POD activity of the two-temperature cold shock treatment were 92% and 1.24 times of the common cold shock treatment, respectively. The temperature gradient appeared a step increase in the 29th minute of the two-temperature cold shock treatment, and compared to the common cold shock treatment, it maintained a relatively higher value from the 29th minute to the end. These could be the internal reasons for the better preservation quality of cucumber with two-temperature cold shock treatment. The interrelated conclusions can offer a reference for the application and implementation of the two-temperature cold shock treatment in postharvest cucumber.