Effect of UV-C treatment on the microbial population of white and red wines, as revealed by conventional plating and PMA-qPCR methods

Abstract

Abstract Ultraviolet C (UV-C) irradiation is one of the emerging techniques for the inactivation of microorganisms in liquid food products, and it holds considerable promise also for treatment of wine. This application can be of particular interest to reduce or even eliminate the use of sulphur dioxide as a preservative in winemaking, given its potential health risks. In this study, UV-C light treatment was applied to ten different white and red wines during winemaking, for the first time at industrial scale, using a commercial turbulent flow system. The effect of 1.0 kJ/l dosage treatment on the viability of the natural microbial population, i.e., total yeasts, lactic acid bacteria and acetic acid bacteria, was investigated both with conventional plating and optimized specific propidium monoazide (PMA)-qPCR. Results of the two methods were mainly concordant for control and UV-C treated samples, and, in some cases, PMA-qPCR was able to detect small amounts of viable cells, probably in the VBNC state. Remarkably, PMA-qPCR allowed to obtain reliable results much faster than conventional plating methods. Data indicated that the UV-C irradiation was effective in reducing microbial counts for up to five log CFU/ml, depending on the wine (white or red) and on the microbial load of the sample. The treatment was much more effective in white wines: a statistically significant decrease was observed for putative spoilage-related bacteria, besides the most pronounced effect on yeast cells. Outcomes strongly support the applicability of UV-C treatment for white wine production, thanks to its efficacy towards all the microbial groups considered.