Computational Fluid Dynamics Analysis and Biodosimetry-Based Microbial Validation for Continuous-Flow Pulsed UV Light Reactors for Processing of Model Liquid Foods

In this study, the effect of pulsed UV light (PUV) (emission wavelength: 200–1100 nm) treatment parameters (flow rate, 14.3–74.9 L/h; pulse frequency, 1–5 Hz; reactor configuration, annular (AT) and coiled tube (CT)) on microbial susceptibility in model liquids with different optical properties (water, water + red dye, water + green dye, skim milk) inoculated with test microorganisms (Escherichia coli, Listeria innocua, Clostridium sporogenes) was studied. Total delivered fluence during each treatment was computed using an innovative computational fluid dynamic (CFD) method and correlated with the analytical microbial inactivation kinetics data. D-value of microorganisms and corresponding reduction equivalent fluence in tested liquids were determined by collimated beam experiment. Total delivered fluence calculated using CFD were 5.45, 4.67, 4.47, and 4.46 J/cm² in AT reactor and 17.05, 25.83, 21.14, and 22.47 J/cm² for CT reactor in water, water + red dye, water + green dye, and skim milk, respectively. Microbial inactivation was a function of optical properties of the liquids (inactivation in water > water + red dye > water + green dye > skim milk) and reactor configuration (inactivation in CT reactor was significantly higher than AT reactor, p < 0.05). Reduction of > 7 log₁₀ for all the microorganisms was achieved for water and water + added dyes in CT reactor, whereas > 3.5 log₁₀ reduction was achieved for all the microorganisms in skim milk. Microorganisms D-value was significantly varied (p < 0.05) among the microorganisms (E. coli > L. innocua > C. sporogenes). Overall, these results demonstrate the applications of PUV for treatment of liquid food with different optical properties and shall serve as a benchmark for commercialization of PUV reactors for juices, and beverages.