Research On Techniques And Mechanism Of Microwave Sterilization In Process Of Beer Production

With the development of the beer production industrial technology and national standards of living, consumers of beer flavor stability and freshness requirements gradually enhance. To ensure the biological stability, it must be adopted proper sterilization methods to kill bacteria in beer. The advantages of microwave sterilization are the short heating time, fast speed, sterilization uniformity etc, to keep physiological activity of food functional component, colour, fragrance, taste, nutrients, and no chemicals residue, high safety. Research on sterilization of bottled beer has important practical and theoretical significance. It not only realizes energy conservation and emission reduction, but also generalizes to drinking water and recycled water disinfection. In this paper, microwave sterilization technique of beer, microwave sterilization influencing factor of indicator bacteria and the mechanism of microwave sterilization were discussed by using adapted power and temperature controlled microwave experiment oven.In the study of microwave sterilization process of beer, the optimal continuous sterilization conditions were obtained. When total bacteria was 103 and microwave power was 780 W, the optimal irradiating temperature, time of 600 mL bottled beer were 72℃and 180 s, respectively. After this treatment, bacteria in beer can be completely sterilized. Under these conditions, the loss rate of reducing sugar, total acid and original wort concentration in beer which was less than the index treated by pasteurization. Meanwhile, the time consuming and energy expenditure of microwave sterilization method are superior to those of pasteurization. Two ways sterilization of beer between continuous microwave sterilization and intermittent microwave sterilization showed that the latter has lower energy consumption and short-term efficient advantages. It saves energy and time were 16.67 % and 30 s.Microwave sterilization influencing factor of indicator bacteria in beer was discussed. Difficulty of microwave inactivation was as follows: Saccharomyces cerevisiae < Escherichia coli < Bacillus subtilis. The effect of microwave sterilization was affected by various factors. The higher concentration of bacterial suspension, irradiation time and irradiation power, the longer time of microwave complete sterilization, the better effect of microwave sterilization. The more deviated from the microbial optimum growth pH, the better effect of microwave sterilization.The mechanism of microwave sterilization was also discussed. With Escherichia coli as the research object, coomassie brilliant was used to determine soluble protein of bacteria leakage content treated by microwave sterilization and water-bath heating. The results showed that microwave action to make proteins leaks out more at the same time, explained that microwave action to make membrane permeability have significantly changed. Atom force microscope was used to observe the cell morphology after microwave irradiation; the results show that microwave can rupture the cell wall and membrane, which leads to cytoplasm leakage.