UV-C treatment using a Dean vortex technology — impact on apple juice enzymes and toxicological potential

Freshly squeezed apple juice (cultivar Gala) and commercially available naturally cloudy apple juice were treated with UV-C (254 nm, 0–53 kJ/L) using a commercial UV-C processing unit equipped with a Dean flow reactor. In this study the effect of UV-treatment on enzyme activities, as well as possible cytotoxic and genotoxic effects and furan formation in apple juice were investigated. Even at the highest dose applied (53 kJ/L) no significant effect on the activities of polyphenol oxidase, pectin esterase and polygalacturonase could be determined and residual enzyme activities above 95% were observed in all samples. By raising UV-C irradiation dose to 2.1 kJ/L, the upper limit of practical use, a slight increase in furan concentration from 2.3 to 3.7 μg/kg was observed. However, these concentrations are in the range of commercial, heat-treated juices available on the German market. UV-C treated (10.6 kJ/L) and non-treated apple juice showed no cytotoxic effect in the WST-1 assay when added in concentrations up to 20% (v/v). Furthermore, no difference on DNA strand break formations between treated and non-treated apple juice was observed. Thus, despite a slight increase in the concentration of a potentially genotoxic compound such as furan, UV-C treatment at dosages under investigation did not result in any change in the cytotoxic and genotoxic effects of apple juice on intestinal Caco-2 cells. Industrial relevance Ultraviolet treatment is a promising non-thermal technology for enhancing shelf life of liquid food. While the inactivation of food related microorganisms is well investigated little is known about the effect on compounds like enzymes and in particular the cyto- and genotoxicological potential of UV-C treated products. Our results provide useful information and assistance for regulatory authorities regarding risk and quality assessment of the emerging UV-C technology.