A reactor engineering approach to describe bacterial inactivation during continuous UV-C light processing

Abstract

A reactor engineering approach was used to mathematically describe microbial inactivation during continuous UV-C light processing of liquid foods. The method was followed to analyze the survival curves of Lactobacillus rhamnosus inoculated into sucrose model solutions prepared at different concentrations (8, 10 and 12 g sucrose per 100 g of solution) and pH values (pH 3, 4.5 and 6), and further processed at two different residence times (4.85 and 29.9 min). The inactivation process was considered as an irreversible elemental reaction of unknown order occurring in a continuous stirred tank reactor. The proposed model was expressed in terms of the logarithmic reduction in microbial population and its straight-line form allowed the easy estimation of the inactivation rate constant and reaction order. Results indicated that inactivation of L. rhamnosus followed a variable order kinetic, moving from a first-order rate during unsteady-state operation to a near zero-order inactivation when steady-state operation was reached. Steady-state was reached faster (0.48 ± 0.11 min−1 vs. 0.37 ± 0.7 min−1, p < 0.05) and with a higher steady-state log reduction (5.9 ± 0.2 vs. 5.4 ± 0.6 log CFU/mL, p < 0.05) in experiments conducted with the lowest residence time, UV-C dose and power density (4.85 min, 12.8 J/cm2 and 6.6 J/cm3).