Efficacy of ultraviolet radiation as an alternative technology to inactivate microorganisms in grape juices and wines

Since sulphur dioxide (SO2) is associated with health risks, the wine industry endeavours to reduce SO2 levels in wines with new innovative techniques. The aim of this study was, therefore, to investigate the efficacy of ultraviolet radiation (UV)-C (254 nm) as an alternative technology to inactivate microorganisms in grape juices and wines.A pilot-scale UV-C technology (SurePure, South Africa) consisting of an UV-C germicidal lamp (100 W output; 30 W UV-C output) was used to apply UV-C dosages ranging from 0 to 3672 J l−1, at a constant flow rate of 4000 l h−1 (Re > 7500). Yeasts, lactic and acetic acid bacteria were singly and co-inoculated into 20 l batches of Chenin blanc juice, Shiraz juice, Chardonnay wine and Pinotage wine, respectively. A dosage of 3672 J l−1, resulted in an average log10 microbial reduction of 4.97 and 4.89 in Chardonnay and Pinotage, respectively. In Chenin blanc and Shiraz juice, an average log10 reduction of 4.48 and 4.25 was obtained, respectively.UV-C efficacy may be influenced by liquid properties such as colour and turbidity. These results had clearly indicated significant (p < 0.05) germicidal effect against wine-specific microorganisms; hence, UV-C radiation may stabilize grape juice and wine microbiologically in conjunction with reduced SO2 levels.

Research highlights
► Investigate ultraviolet radiation (UV)-C as an alternative technology to inactivate microorganisms in grape juices and wines.
► UV-C dosages ranging from 0 to 3672 J l−1, at a constant flow rate of 4000 l h−1 was applied.
► Yeasts, lactic and acetic acid bacteria were singly and co-inoculated into 20 l batches of grape juices and wines.
► A dosage of 3672 J l−1, resulted in an average log10 microbial reduction of 4.97 and 4.89 in Chardonnay and Pinotage, respectively.
► In Chenin blanc and Shiraz juice, an average log10 reduction of 4.48 and 4.25 was obtained, respectively.
► Results showed that UV-C radiation may stabilize grape juice and wine microbiologically in conjunction with reduced SO2 levels.