蔬菜真空预冷中降低失水率的方法研究

Study of Methods to Reduce Water Loss Rate for Vegetables in Vacuum Cooling

由于蔬菜在真空冷却过程中温度的降低是通过水分蒸发实现,因此真空预冷中蔬菜失水问题不可避免。叶菜类蔬菜真空冷却效果明显,而根类蔬菜由于存在表皮保护,内部组织致密等特点,真空冷却效果并不明显。以生菜、卷心菜和胡萝卜为研究对象,分别对其进行直接预冷、喷水预冷和表面包覆吸水膜预冷实验研究。结果表明:吸水膜包覆的果蔬,可以显著提高降温速率,缩短预冷时间,降低失水率。生菜吸水膜包覆从初温25℃降低到5℃需要的时间比直接预冷少43%,失水率降低76.3%。卷心菜吸水膜包覆从初温27℃降低到5℃需要的时间比直接预冷少48%,失水率降低76.7%。胡萝卜吸水膜包覆从初温24℃降低到8℃需要的时间比直接预冷时间少37.5%,失水率降低91%。所以采用吸水膜包覆是提高降温速率,降低失水率的一种行之有效的方法。

Water loss is inevitable during vacuum cooling because the temperature is decreased through the loss of water in vegetables. The cooling effect of leafy vegetables in vacuum cooling is evident, but that of root vegetables is not obvious because their tissue is com- pact. Iceberg lettuce, cabbage and carrot were studied by using three type vacuum cooling methods i. e. , direct vacuum cooling, spray water vacuum cooling and water absorbent film package vacuum cooling. The results show that vegetables packaged with water absorbent film have the fastest temperature decreasing rate, the shortest cooling time and the lowest water loss rate. When the temperature of iceberg lettuce in water absorbent film package vacuum cooling is decreased from 25℃ to 5℃, the time taken is 43% less than direct vacuum cooling, and the water loss rate reduces 76.3%. When the temperature of cabbage in water absorbent film package vacuum cooling is de- creased from 27℃ to 5℃, the time taken is 48% less than direct vacuum cooling, and the water loss rate reduces 76.7%. When the temperature of carrot in water absorbent film package vacuum cooling is decreased from 24℃ to 8℃ , the time taken is 37.5% less than direct vacuum cooling, and the water loss rate reduces 91%. So water absorbent film package vacuum cooling is an effective method to im- prove temperature decrease rate and reduce water loss.