Modelling microbial inactivation kinetics of combined UV-H treatments in apple juice

•Combined ultraviolet (UV)-heat (UV-H) treatments increased the UV inactivation in juice between 50 and 60 °C.•E. coli was the most UV-H-resistant microorganism in apple juice between 44 and 54 °C.•L. monocytogenes was the target microorganism at temperatures higher than 54 °C.•UV-H treatments reduced the UV dose required to achieve 5 Log reductions at 25 °C by 49.6–89.1%.

In this investigation, temperature's effect on the ultraviolet (UV) inactivation kinetics of pathogens of concern in juices – E. coli, Salmonella Typhimurium, L. monocytogenes, and S. aureus – was studied to establish the target microorganism and process criteria for pasteurizing apple juice using combined shortwave UV-C light and mild heat (UV-H) treatments. For this purpose, mathematical models based on Geeraerd et al.'s model, which predict UV-H inactivation at different treatment temperatures, were developed for each microorganism. For comparisons, inactivation models for heat treatments were also performed in the same juice and for the same microorganisms. The UV-C inactivation notably improved at treatment temperatures between 50 and 60 °C, but the thermodependence of the UV-H resistance differed among species. This behavior was related to the thermodependence of heat treatments for each bacterium so that the target microorganism for UV-H treatments was determined based on the most heat-resistant species at each treatment temperature. Thus, E. coli was the most UV-H-resistant microorganism between 44 °C and 54 °C, requiring a UV-C dose between 13.81 J/mL (12.71 min) and 5.20 J/mL (4.78 min) in order to achieve the 5 Log10 reduction that the U.S. Food and Drug Administration demands. Also, L. monocytogenes was the target microorganism at temperatures between 54 °C and 60 °C, requiring a UV-C dose from 5.20 J/mL (4.78 min) to 2.11 J/mL (1.93 min). The combination of UV-C and mild heat allowed for the UV-C doses and treatment times to be reduced from 49.6% to 89.1% in comparison with UV-C treatments at room temperatures.Industrial relevanceIn this manuscript, the target microorganism and process criteria for pasteurizing (5 Log10 reductions) apple juice using combined shortwave UV light (UV-C) and mild heat (UV-H) treatments have been established. E. coli and L. monocytogenes resulted as the limited pathogenic microorganisms of reference in apple juice. Combining UV light with mild temperatures permitted achieving the microbial inactivation required for safe apple juice with lower UV doses and treatment times than those needed for UV treatments alone, with the reduction of the UV doses ranging from 26 to 89% depending of the treatment temperature of the apple juice.