Evaluation of the possible non-thermal effect of microwave radiation on the inactivation of wheat germ lipase

To determine whether non-thermal effect exist during the process of enzyme inactivation by microwave radiation, the conformation and activity of wheat germ lipase (WGL) treated by microwaves and conventional heating were investigated, respectively. The results indicated that, when the WGL was maintained at 20 degrees C, its Tyr, Trp residues, the secondary and tertiary structures did not changed, even though the microwave was sustained for 1,800 s with power of higher than 80 W. While, when the temperatures were up to 45 and 60 degrees C, the activity of WGL decreased 60% and 100%, respectively, and the tertiary structure of WGL was totally changed by microwave at 60 degrees C. Moreover, the inactivation efficient of microwave radiation was about 10% more than that of conventional heating based on the thermal effects. In conclusion, microwave inactive WGL based on thermal effects rather than non-thermal effect, and was more effective than conventional heating. Practical ApplicationsMicrowave has been widely used in food thawing, drying, sterilization, enzyme inactivation and et al. In cereal industry, microwave is usually used to inactivate wheat germ lipase (WGL), which plays an important role in the storage of wheat products. However, because the effects of microwave was strongly interferes by the possible non-thermal effect and cannot be separated easily, the potential inactivation mechanism of microwave on enzyme was not clear enough to guide the inactivation process of lipase by microwave. In this study, the effects of microwave and conventional heating on the stability of WGL were investigated to detect the possibility of non-thermal effects during the inactivation process of lipase by microwave. The results make sure that, the microwave inactivated WGL based on thermal effect, rather than non-thermal effect. Thus, we can focus on the factors that influence the heating efficiency to improve the effect of inactivation of WGL or other lipase by microwave.