Effect of germicidal short wave-length ultraviolet light on the polyphenols, vitamins, and microbial inactivation in highly opaque apple juice
The aim of this investigation was to study the efficacy of UV-C light emitting diode system (LED) operating at 263 nm for the inactivation of Listeria monocytogenes and Escherichia coli O157:H7. Specified concentrations of bacteria were inoculated in apple juice and irradiated at the designated UV doses of 0 to 15 mJ{middle dot}cm-2. In addition, UV irradiation doses ranging from 0 to 160 mJ{middle dot}cm-2 were also delivered to apple juice and polyphenols and vitamins were profiled. LC-MS/MS analysis was conducted to assess the stability of polyphenols or vitamins in UV-C exposed apple juice. The polyphenol and vitamin results demonstrated that UV-C irradiation in apple juices at relevant commercial UV doses induced significant reductions in the concentrations of selected polyphenols and vitamins, p<0.05. Ascorbic acid was reduced to 32%, at 160 mJ/cm2 whereas 17% reduction was observed at 40 mJ/cm2. Riboflavin was observed to be relatively stable. Epicatechin and chlorogenic was significantly reduced at high exposure doses. In contrast minor changes were observed at 40 mJ/cm2. Results show that UV-C irradiation effectively inactivated pathogenic microbes in apple juice. The log reduction kinetics of microorganisms followed log-linear and with higher R2 (>0.95) and low RMSE values. The D10 values of 4.16 and 3.84 mJ{middle dot}cm-2 were obtained from the inactivation of Escherichia coli, and Listeria monocytogenes in apple juice. The results from this study imply that adequate log reduction of pathogens is achievable in apple juice and suggest significant potential for UV-C treatment of other liquid foods.