The effect of quercetin mediated photodynamic inactivation on apple juice properties at different temperature and its bactericidal mechanism

The inactivation efficacy, mechanism, and effect on apple juice properties of 405 nm blue light combined with quercetin in apple juice were investigated. At 60 J/cm2, Listeria monocytogenes and Escherichia coli O157:H7 cells experienced more than 5 log reduction at room temperature. The depolarized membrane potential and loss of succinate dehydrogenase enzyme activity showed that the membrane and protein were the targets of photody-namic inactivation (PDI). While all measured properties of apple juice were not significantly (P > 0.05) changed after PDI, the total phenolic and flavonol contents were significantly (P < 0.05) more preserved after PDI at 4<degrees>C than at room temperature. In conclusion, quercetin-mediated PDI can achieve an approximately 5 log bacterial reduction in apple juice and has no adverse effect on the juice properties. Therefore, quercetin-mediated PDI is a nonthermal technology that has the possibility of being an alternative to conventional nonthermal processing for juice.N