Influence of UV treatment to inactivate microorganisms on the molecular-chemical and sensory properties of wine

UV-C technology is a chemical-free, non-thermal method for microbial stabilization of food and beverages. It is discussed as a possible alternative for wine preservation methods based on additives. The objective of this work was to examine the UV C technology for microbial stabilization of wine with a focus on investigating the influence of UV-C treatment on the chemical and sensory characteristics of wine. It was evident that UV-C treatment can effectively inactivate the typical harmful microorganisms in wine, such as Brettanomyces bruxellensis or Acetobacter aceti. The Weibull function was identified as the appropriate model to describe the inactivation kinetics of microorganisms in wine. Therefore, it should be used to determine the microbial required UV-C dose. Factors like wine absorption, cell count, and type of microorganisms could be determined as parameters influencing the effectiveness of UV C treatment. Increasing UV C doses caused several photochemical reactions in wine, which eventually could result in the formation of off-flavors such as 2aminoacetophenone (2 AAP) and acetaldehyde as products of light-induced reactions. Besides that, increasing UV-C doses caused the degradation of aroma-active substance classes such as C13 norisoprenoide, monoterpene, and esters. Phenolic compounds were also affected by UV C, as shown by decreasing concentrations of hydroxycinnamic acids and flavanoids. Hydrolyzable tannins and sulfur dioxide (SO2) were examined as possible antioxidants to mitigate the photo-induced oxidative reactions. Counterintuitively, the addition of SO2 promoted oxidative processes, and caused an increase of 2 AAP and acetaldehyde levels, while hydrolyzable tannins showed strong antioxidative effects, reducing oxidative reactions. To ensure the best quality of wine, high concentrations of SO2 should be avoided before UV C treatment. Vice versa, hydrolyzable tannins are preferable to be added before UV C application. In detail, the photo-induced reaction pathway of the formation of 2 AAP was investigated in combination with oxygen and transition metals. Research has shown that increasing oxygen concentrations promotes the formation of 2 AAP and decreases the degradation of photosensitizer riboflavin (RF). For the first time, a link between the photo-induced formation of 2 AAP and the photo-Fenton reaction was found: the photo-Fenton reaction, which is catalyzed by transition metals, stands in direct competition with 2 AAP formation. To ensure the long-term microbial protection of UV C, the microbial stability of UV C treated wine was investigated over a 12 week storage. A reincrease of Brettanomyces bruxellensis cells after UV C treatment could not be observed in wine during the storage period. UV-C application at 280 nm instead of 254 nm was exanimated as an alternative wavelength. The wavelength of 280 nm enables the use of LEDs instead of ecologically harmful mercury-vapor lamps. The research has shown higher inactivation efficiency at 280 nm . Chemical and sensory analysis revealed that aroma-active compounds were similarly affected at both wavelengths. However, the absorbance of phenolics is more pronounced at 280 nm, and therefore, they were more strongly affected at 280 nm than at 254 nm, which in turn led to a higher impact on the sensory properties of the wine at 280 nm . Accordingly, the inactivation of harmful microorganisms in wine should not be conducted with UV treatment at 280 nm . Since the application of UV C technology at 254 nm can be safely used for wine preservation, the next step of future studies should investigate the technology on an industrial application scale.