Suitability of ultraviolet-C irradiation for white grape must

Background and Aims: Ultraviolet (UV)-C irradiation is used for the reduction of microbial spoilage in food. Its effectiveness for the treatment of white grape must has been investigated considering different microbial species and modification of must composition. Methods and Results: Static and dynamic laboratory-scale systems emitting at 254 nm were used for the treatment of Vitis vinifera cv. Chardonnay and cv. Crimson grape juices of variable turbidity. The must samples were singularly inoculated with a pure culture of wine spoilage strains belonging to three species, Dekkera bruxellensis, Acetobacter aceti and Lactobacillus brevis, and treated with UV-C ranging from 300 to 1800 J/L. Cell counts and microbial reduction (derived from α values, according to the Weibull model), colour change, polyphenol oxidase (PPO) inactivation and formation of α-dicarbonyl compounds were evaluated. After treatment at the maximum UV-C dosage under static conditions, reductions of yeast counts of 4.91–5.99 log10 colony-forming units (CFU)/mL and bacterial counts of 4.12–5.05 log10 CFU/mL were achieved, depending on the strain being tested. Polyphenol oxidase activity decreased by up to 7.8 ± 1.4% with variation attributed to must turbidity, which indicated that clarification of must before UV-C treatment can lead to PPO inactivation. No significant variation in the colour or the concentration of α-dicarbonyl compounds was detected. Results were confirmed for grape juice with the continuous flow apparatus. Conclusions: The UV-C systems achieved microbial reduction without formation of oxidative compounds, suggesting that the experimental conditions employed did not cause any noticeable oxidative phenomena. Significance of the Study: The UV-C treatment of grape juice can be considered a potential alternative to sulfur dioxide addition for processing of white must. Improved efficacy of treatment can be achieved by increasing the flow rate and by clarification of must, making the system potentially applicable under industrial conditions.