Performance Assessment of an Ultraviolet Light Emitting Semi-Conductor Device in Treating Apple Juice: Microbial Inactivation and Biochemical Assessment Study

Abstract

Inactivation of Listeria monocytogenes ATCC 19115 and Salmonella enterica serovar Muenchen ATCC BAA 1764 by a light emitting diodes (LED) operating at 279 nm was investigated. In addition, this investigation assessed the poly-phenolic and vitamin content of UV irradiated apple juice (AJ). Specific concentrations of bacteria were inoculated in AJ and irradiated at the designated UV doses of 0 to 10 mJ{middle dot}cm-2 for Salmonella Muenchen and 0 to 12 mJ{middle dot}cm-2 for Listeria monocytogenes.Results show that UV-C irradiation effectively inactivated pathogenic microbes in AJ. The log reduction kinetics of microorganisms followed log-linear and with higher R2 (>0.95). The D10 values of 3.50 and 3.56 mJ{middle dot}cm-2 were obtained from the inactivation of Salmonella Muenchen, and Listeria monocytogenes in apple juice. In addition, quantifiable UV-C doses ranging from 0 to 160 mJ{middle dot}cm-2 were also delivered to AJ and polyphenols and vitamins were profiled. LC-MS/MS analysis was conducted to assess the stability of polyphenols or vitamins in UV-C exposed AJ. The polyphenol and vitamin results demonstrated that UV-C irradiation in AJ can cause significant reductions (p<0.05) if not properly delivered. Chlorogenic acid was reduced to 56%, at 80 mJ/cm2 whereas 12% reduction was observed at 40 mJ/cm2. Choline was observed to be relatively stable as a function of UV-C dosage. In contrast thiamine was significantly reduced at higher doses. In addition, Epicatechin was significantly reduced at high exposure doses. In contrast minor changes were observed at 40 mJ/cm2. The results from this study imply that adequate log reduction of pathogens is achievable in AJ and suggest significant potential of using LED devices for UV-C treatment of highly turbid fluids.