Effect Of Low Temperature Steam Treatments On Inactivation Of Microbe And Quality Of Fresh-cut Vegetables

The effect of low temperature steam treatments with50-70℃on inactivation of microbe of fresh-cut vegetables was studied, and it revealed the variation of vegetables’quality index during the steam treatments. Meanwhile, the changes in color and texture of fresh-cut vegetables after steam treatments during storage were also explored.1. The effect of steam treatments on inactivation of microbe was studied. The results showed that low temperature steam treatments could reduce microbial residues on the surface of fresh-cut carrot slices effectively, and the processing temperature and time had significant effect on the influence of inactivating microbe (p<0.05). E. coli, S. cerevisiae and Botrytis cinerea inoculated on the surface of fresh-cut carrot slices were sensitive to the steam with60℃, steam with temperature below60℃had poorer inactivating effect, while higher temperature could inactivate these microbe rapidly. Under the same steam treamtments, the mortality rate of the three genus was:S. cerevisiae> Botrytis cinerea> E. coli.2. The effect of steam treatments on nutritional quality of fresh-cut carrot slices was investigated. The results showed that low temperature steam treatments with50℃-70℃was more conducive to retain the nutrients, while moderate temperature steam(80-100℃) and the traditional boiling water blanching had much more harmful effect on the carrot slices’nutrition. Vitamin C was the most vulnerable nutrient but protein was much more stable. Moisture, total phenols and total soluble sugar were less sensitive when treated by low temperature steam, but when the temperature was higher than70℃, they would decreased rapidly and significantly.3. The effect of steam treatments on pigments and color of fresh-cut vegetables was investigated, and the changes in color of samples after low temperature steam treatments during storage were also explored. The results showed that the correlation between color change and pigments loss of vegetables during steam treatments were significant, and low temperature steam treatments showed some positive effects of preserving green color of vegetables. Steam treatment with50℃had little inhibitory effect on the activities of polyphenol oxidase(PPO) and peroxidase(POD) in fresh-cut potatoes, but steam treatment with60℃and70℃could inhibit the activities of PPO and POD significantly(p<0.05). Fresh-cut potatoes under60℃,30min and70℃,6min treatments could inhibit the browning during storage.4. The effect of steam treatments on hardness of fresh-cut potatoes was studied. It showed that low temperature steam treatments could activate pectin methylesteras in potatoes, thus the samples’hardness was improved. When fresh-cut potatoes were processed with no pre-treatment (100℃) and with a pre-treatment (blanching at steam with60℃and70℃followed by processing at100℃),the latter showed better texture, and the hardness under pre-treatment at60℃was firmer than those at70℃. The changes in hardness of fresh-cut potatoes during storage was not significant, it showed that samples under steam treatments with60℃and70℃could maintain their texture during storage as these treatments improved the initial hardness of fresh-cut potatoes.