Effect of UV light on microbial proteases: From enzyme inactivation to antioxidant mitigation

Ultraviolet (UV) irradiation offers promise as an environmental friendly, non-thermal technology for sterilizing enzymes used in the food industry. However, UV light can diminish an enzyme's activity. Since enzymes can be easily inactivated by UV light, we tested the combined use of proteases and subsequent UV-inactivation for in-place cleaning in the dairy industry. We demonstrate the easy and rapid inactivation of five commercial proteases by monitoring the impact of UV light on enzymatic solutions using SDS-PAGE and densitometric analysis. We also examined whether addition of antioxidants such as threo-1,4-dimercapto-2,3-butanediol (DTT), cysteine, or ascorbic acid can enhance enzyme stability and protect against UV-induced loss of catalytic activity. Enzymes behaved differently upon UV-irradiation, probably due the effect of chromophoric groups and the characteristics of additives. In addition, the protective effect of ascorbic acid decreased with increasing concentration, while the protective effect of DTT and cysteine increased in a dose-dependent manner.Industrial relevance: This study and the corresponding results can be considered a starting point for further implementation of cleaning techniques combining proteolytic enzymes and UV light. More attention could be given to the additives included in the enzyme formulations to mitigate the effects of UV light during sterilization of enzymatic preparations.

► The effect of UV light on proteases was studied by SDS-PAGE and densitometry.
► Antioxidants were used to mitigate UV-induced decline in catalytic activity.
► Ascorbic acid exhibited concentration-dependent anti/pro-oxidant activity.
► Enzymes and UV light can be used for in-place cleaning in the dairy industry.