The Study Of Effect Of Different Heat Treatment Processes Of Milk On Quality Of Yogurt And Cheese

With the rapid development of China's economy and the continuous improvement of living standards, people pay more and more attention to the nutrition and health of the diet,and yogurt and cheese are liked among the people because of their high nutritional value and health function. The heat treatment process of milk has a direct impact on the quality of yogurt and cheese. Therefore, many experts and scholars have done a lot of research on the heat treatment process of milk.In this study, by measuring the pH, acidity, water holding capacity, texture and apparent viscosity of yogurt, the effects of different heat treatments on the quality of yogurt were studied. By using by microfluidimeter, stability analyzer, scanning electron microscopy and electrophoresis, the reason for the difference of texture and microstructure of yogurt was analyzed. In addition, by measuring the pH value, moisture content, yield texture, and meltability of the cheese, the influence of different heat treatment processes on quality of cheese was studied. By using the microfluidometer, stability analyzer, rheometer,scanning electron microscopy and electrophoresis, the differences in quality of cheese were analyzed.According to the analysis of pH, acidity, water holding capacity, texture and apparent viscosity of yogurt, it was found that with the heat treatment intensity increased, the different heat treatment processes of skim milk did not influence the pH and acidity of yogurt, but influenced the water holding capacity, texture and apparent viscosity. Among 5 different heat treatment processes, the water holding capacity, texture and apparent viscosity of the yogurt made of skim milk heated by 95 ?, 5 min was the best. The study on the reasons of the differences in quality showed that the denaturation rate of whey protein in skim milk heated by 95 ?, 5 min was higher, and the denatured whey protein was involved in the formation of gel network, the degree of crosslinking became larger and the structure became denser, and then improved its quality.According to the analysis of pH, moisture content, yield, texture, and meltability of cheddar cheese, it was found that with the heat treatment intensity increased, the pH and meltability of cheddar cheese decreased, and the water content and measured yield increased. The pH value and meltability of the cheese made of low-fat heated by 65 ?, 30 min were the highest, the pH value was 5.11 and the diameter increase rate was 138.45%.The moisture content and yield of the cheese made of low-fat heated by 85?,1 min were the highest, which were 58.62% and 10.87% respectively. In addition, with the increase of heat treatment intensity, the hardness, elasticity, cohesion and chewiness decreased, and the adhesion increased. The hardness, adhesion, cohesion and chewiness were significantly different (p<0.05) and elasticity was not significant different (p>0.05). The study on the reasons of the differences in quality showed that with the increase of heat treatment intensity, the denaturation rate of whey protein increased, the formed macromolecular polymer was retained in the network structure, which affected the aggregation of casein molecular, inhibited the excretion of whey, increased moisture content, in addition, the denatured whey protein trapped in the cheese increased the yield of cheese.