Research On Techniques And Mechanism Of Microwave Sterilization In Starch Wastewater Recycling Utilization

Starch production in China is the second-largest in the world which is just after the United States. Starch wastewater is about 40 ton per ton of starch. Soluble starch, protein, fiber, ash, salts and vitamins are main components in waste water. Starch wastewater is acidic and with non-toxic materials. Resource on starch wastewater utilization has important practical and theoretical significance.The nutritional composition of starch wastewater is suitable for the needs of microorganisms to grow and reproduce. Early experiments in the laboratory, the wastewater as a medium has already been used to ferment L-lactic acid by Lactobacillus. Prior to that, sterilization for waste water is necessary to ensure aseptic conditions of the medium. Microwave sterilization is short, energy saving and convenient, which is suitable for the sterilization process link in resources utilization of starch wastewater. In this paper, microwave sterilization technique of starch wastewater, microwave sterilization influencing factor of indicator bacteria and the mechanism of microwave sterilization were discussed.In the study of microwave sterilization process of starch wastewater, the optimal sterilization conditions were obtained. When microwave power was 500 W, 100 mL wastewater placed in 250 mL flask was irradiated for 3 min. Then adding 5% glucose into wastewater, the water was irradiated for 3 min again. After this treatment, wastewater can be completely sterilized. Under these conditions, the loss rate of total sugar, reducing sugar and protein in wastewater was 3.11%, 3.04% and 16.29%, which was less than the index treated by high pressure steam sterilization. Meanwhile, the energy expenditure and time consuming of microwave sterilization method are superior to those of high-pressure steam sterilization method.Microwave sterilization influencing factor of indicator bacteria was discussed. Difficulty of microwave inactivation was as follows: Saccharomyces cerevisiae < Staphylococcus albus < Geotrichum candidum < Escherichia coli < Bacillus subtilis. The effect of microwave sterilization was affected by various factors. The higher the concentration of bacterial suspension, glucose and NaCl, the longer the time of microwave complete sterilization. The more deviated from the microbial optimum growth pH, the better the effect of microwave sterilization.The mechanism of microwave sterilization was also discussed. Transmission electron microscope was used to observe the cell morphology after microwave irradiation, and DNA gel electrophoresis experiment was used to analyse the damage of bacterial DNA after microwave irradiation. The results show that microwave can rupture the cell wall and membrane, which leads to cytoplasmic leakage. Microwave also can lead to protein denaturation and DNA breakage of the cell. These types of effect simultaneously make inactivated bacteria showed broken, distortion and many other states.