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Pasteurization of verjuice by UV-C irradiation and mild heat treatment
Verjuice is a highly acidic juice and more prone to yeast spoilage. In this study, the efficacy of individual and combination processes of UV-C irradiation (UV) and mild heat treatment (MH) for pasteurization of verjuice were assessed. Saccharomyces cerevisiae (NRRL Y-139) was selected as the target microorganism and kinetic parameters for MH, UV, and combined UV + MH inactivation treatments were determined. The UV treatment alone at a UV dose of 0.57 J/cm(2) (energy of 2.30 J/mL), provided only 0.54 +/- 0.02 log CFU/mL reduction of S. cerevisiae. In contrast, the combined treatment (UV + MH2) substantially reduced the number of S. cerevisiae in verjuice, 5.16 +/- 0.24 log CFU/mL reduction was achieved at 0.25 J/cm(2) UV dose (energy of 1.01 J/mL) and 51.25 +/- 1.47 degrees C. The percentage of synergism for the UV + MH inactivation of S. cerevisiae in verjuice was maximized at 51.25 degrees C (50.79% of synergistic effect). Inactivation kinetics of S. cerevisiae was best described by Weibull model with the smallest RMSE and AIC values. D value was decreased from 13.66 to 1.94 min when UV was combined with mild heating. The results showed that UV-C light assisted by mild heat treatment can be a potential alternative to thermal pasteurization of verjuice. Practical applications Fruit juices are prone to spoilage by yeasts, molds, and some acid-tolerant bacteria. Saccharomyces cerevisiae is a heat resistant spoilage microorganism and found in some spoiled juices. Thermal pasteurization is widely used for the preservation of fruit juices but results in losses of essential nutrients and changes in physicochemical and organoleptic properties. This study illustrated that the combined UV-C light assisted by mild heat treatment can deliver the required microbial reduction in verjuice. The synergistic effect of two processing methods is suggested for controlling the growth of spoilage microflora of fruit juices.