Microbial inactivation and quality of grapes treated by plasma-activated water combined with mild heat

Abstract

Saccharomyces cerevisiae is often associated with spoilage of fresh fruits and vegetables. This study aimed to evaluate the synergistic effect of plasma-activated water (PAW) and mild heat on the survival of S. cerevisiae and quality attributes of grapes. The combination of PAW and mild heat (50, 52.5, and 55 °C, 30 min) showed full synergistic fungicidal activity against S. cerevisiae on grapes. For S. cerevisiae cells, maximum inactivation was 5.85 log10 CFU/g after the PAW treatment at 55 °C for 30 min, which was significantly higher than that of individual treatment of PAW at 25 °C (0.39 log10 CFU/g) or sterile distilled water at 55 °C (2.39 log10 CFU/g) (p < 0.05). The levels of H2O2 and NO2− in PAW significantly decreased, while NO3− content remarkably increased after the mild heating at 25–55 °C for 30 min. Meanwhile, no significant changes were observed in the total soluble solids, reducing sugar, pH, titratable acidity, firmness, surface color, total phenolics, vitamin C, and antioxidant properties of grapes treated with PAW at 25–55 °C for 30 min. In summary, the combination of PAW and mild heat may be considered as an alternative to traditional preservation methods for fresh produce.