双温冷激处理对黄瓜品质和生理的影响及传热特性分析

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

为探究果蔬冷激过程中传热特性对保鲜效果的影响,分别对黄瓜进行常规冷激处理(0℃冰水混合物处理42min)及双温冷激处理(0℃冰水混合物处理14min后放到6℃冷水中处理14min,最后返回0℃冰水混合物处理14min)。测定了处理过程中黄瓜组织温度分布及贮藏期间失重率、硬度、过氧化物酶(peroxidase,POD)活性等品质和生理变化,分析了黄瓜贮藏品质与传热特性的内在关系。结果表明:双温冷激处理在延缓细胞膜降解、提高POD活性方面显著优于常规冷激处理(P<0.05),在10℃冷库贮藏15d后,其相对电导率、POD活性分别是常规冷激组的92%及1.24倍;双温冷激黄瓜内部组织温度梯度在处理第29min时的阶跃式升高,以及从处理第29min到处理结束过程中,黄瓜内部组织温度梯度高于常规冷激黄瓜,或许是双温冷激处理黄瓜保鲜效果较好的内在因素。所得结论可为双温冷激处理的应用提供参考。

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.