Effectiveness of pulsed light treatments assisted by mild heat on Saccharomyces cerevisiae inactivation in verjuice and evaluation of its quality during storage
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The effects of pulsed light (PL) processing parameters such as depth of juice layer (1, 3, 5 mm), distance from the lamp (5, 10 cm) and number of pulses (0-50 pulses) on the inactivation of Saccharomyces cerevisiae in verjuice, a clarified beverage obtained from freshly-squeezed unripe grapes, were investigated. A reduction of 0.96 +/- 0.27 log CFU/mL was achieved by applying a dose of 34 J/cm(2) (1-mm layer depth, 5-cm distance, 50 pulses). PL was combined with mild heating (MH) at 43, 45 and 47 degrees C to increase its inactivation efficacy. Pasteurization was achieved by applying 17 J/cm(2) at 45 degrees C (PLMH45-3) and 6.12 J/cm(2) at 47 degrees C (PLMH47-3) to a 3-mm juice layer with S. cerevisiae reductions of 5.10 +/- 0.24 and 5.06 +/- 0.08 log CFU/mL, respectively. Quality properties of PLMH47-3-pasteurized verjuice were monitored during 6 weeks of storage at refrigerated (5 degrees C) and room temperature (25 degrees C), The results were compared to those of untreated and thermally pasteurized (72 degrees C/18 s) samples. Untreated juice spoiled within 2 weeks at 25 degrees C. No growth was detected in other conditions for 6 weeks. Among quality characteristics, only optical properties changed slightly during storage. It was concluded that mild MH-assisted pulsed light treatments have potential for verjuice pasteurization compared to conventional thermal pasteurization due to the better preservation of its fresh-like characteristics.