Study On Microwave Sterilization Process Of Milk And Machine Design

Milk is a high nutritional food, named as"the king of food", which contains rich valuable ingredients for body health. However, high nutrition in milk is easy to breed the microorganism to destory its quality . So sterilization is a necessary step to be done in the productive process of various dairy. Microwave sterilization was employed to process milk to reach safe level high quality in terms of main nutritional ingredients, flavor, color in short time. In this study, the effect of microwave sterilization parameters quality of milk and design of microwave sterilization machine were completed.Non-thermal effect of microwave on the results of milk sterilization was found, which became much obvious with the increasing temperature. Microwave sterilization is more efficient than thermal sterilization because it effect directly on microorganism to make its internal structure destoryed. Results from single factor experiment showed that survival amount of the total bacteria counts decreased with the increase of mocrowave power, decrease of milk mass, increase of sterilization time. Coliform bacteria is killed completely except that mocrowave power is 4 kW, which shows that sterilization effect of microwave is very significant for coliform bacteria. Protein, lactose, vitamin C are not destoryed significantly. The regression models between the different factors and survival amount of the total bacteria counts was obtained by using responding surface methodology:Y = 3. 65-1.67A+0.95B-0.63C+0.9A~2 -0.18B~2-0.38C~2+0.37AB-0.21AC+0.12BC A, B, C is mocrowave power, milk quality, sterilization time respectively. The sequence of the effect of single factor on survival amount of the total bacteria counts was that mocrowave power > milk quality > sterilization time. A microwave sterilization technological parameter is obtained according to the regression models: mocrowave power, milk mass, sterilization time is 7 kW, 5.4 kg, 117 s, respectively. The final temperature of milk is 61℃in this process. Compared with the time of microwave sterilization in temperature of 61℃, water bath sterilization cost 39 min to attatin same survival amount of the total bacteria counts with the microwave sterilization process. The mocrowave sterilization had no obvious effect on the content of protein, lactose, vitamin C, and color, turbidity of milk. Howerve, the content of vitamin C, turbidity of milk changed obviously in water bath sterilization, and the content of protein, lactose, color were lower than those of microwave sterilization. A microwave sterilization machine was designed to achieve continuous microwave sterilization for milk on the basis of microwave sterilization process. The machine can produce 3.5,7,10.5 kW by 15 magentron of 700 W, and microwave oven was composed of 5 cavity oven, and dimension of every cavity oven is 78, 55, 60 cm. Microwave suppressor was designed on inlet and outlet of the microwave oven. A door was designed on every cavity oven to observe pipeline and service equipment, and four choke groove on the door to weaken the microwave. Sterilization pipe, the diameter and length of which was 24.5, 11130 mm respectively, folded 3 times in the oven. The amplification of equipment is studied by using similarity theory method to extend research results.