Effects of Different Storage Temperatures on Physico-Chemical Characteristics and Flavor Changes of Ultra Pasteurized Milk

In this experiment,fresh milk was homogenized and then heat-treated at 120 ℃ for 15 s,followed by aseptic filling. Preservation experiments were performed at storage temperatures of 4,25,and 37 ℃ for 45 days to analyze the physical-chemical and flavor changes of the products during storage. The results showed that the protease activity of bacteria and lipase activity of the ultra pasteurized milk changed not significantly under the storage condition of 4 ℃,and the protease activity increased sharply after 25 days at 37 ℃ storage conditions,and reached the maximum value of 3.2 U/mL on the 45th day. The lipase activity at the storage temperature of 37 ℃ all increased sharply after the 10th day of storage,and the vitality was maintained at about 6.25 and 6.75 U/mL,respectively. In addition,during storage,the pH decreased,the particle size increased,and the Zeta potential first decreased and then increased. As the storage temperature increased,the rate of change accelerated,and there were significant differences between samples at different storage temperatures. Regarding color and luster,the ultra-pasteurized milk under 4 ℃ preservation only had significant changes in L^* value,and the other two temperatures had significant changes in L^*,a^*,and b^* values. The results of electronic nose and electronic tongue showed that there was no significant difference in the odor and taste of ultra pasteurized milk during storage at 4 ℃,but the odor and taste were significantly different at 25 and 37 ℃. The results showed that the shelf life of ultra pasteurized milk could reach 45 days at a storage temperature of 4 ℃,while the shelf life of ultra pasteurized milk couldn’t reach 45 days at 25 and 37 ℃.