Effectiveness of pulsed light treatments assisted by mild heat on Saccharomyces cerevisiae inactivation in verjuice and evaluation of its quality during storage

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.