Inactivation Kinetics of Alicylobacillus acidoterrestris Spores and Determination of Spore Germicidal Fluences Under UV-C Treatment

The aim of this study is to measure the UV-C inactivation kinetics and determine the fluences required for incremental inactivation of Alicyclobacillus acidoterrestris (AAT). Spores from five strains of AAT (ATCC 49025, DSM 2498, VF, SAC, and WAC) were suspended in clear phosphate-buffered saline (PBS) and individually treated with UV-C doses up to 100 mJ/cm2. A collimated beam device emitting UV-C at 254 nm (from a monochromatic low-pressure mercury lamp [LPM]) and at 268 nm (from UV light-emitting diodes [UV-LEDs]) was used for UV treatments. The log reduction from each treatment was plotted against the UV-C fluence. Curve fitting using the GInaFiT tool for Excel was attempted using both linear and nonlinear regression models. The goodness-of-fit and model performances, assessed using Akaike's Information Criterion and Bayesian Information Criterion, revealed that the Weibull model provided a better fit for the inactivation data and was thus used to determine UV-C doses required for 1-log inactivation and incremental log inactivation. Similar AAT spore inactivation efficacy was observed at both 254 and 268 nm. A UV-C dose of 100 mJ/cm2 at 254 nm inactivated >4-log CFU/mL, while at 268 nm, a 3.7-5.08-log CFU/mL reduction was observed for AAT strains ATCC 49025, DSM 2498, WAC, and VF. Among the five strains of AAT tested, spores of WAC demonstrated greater resistance, requiring UV-C doses of 2.76 mJ/cm2 and 100 mJ/cm2 for 1-log (D10-value) and 4-log inactivation at 254 nm, and 5.89 mJ/cm2 and >100 mJ/cm2 at 268 nm. In contrast, spores of SAC showed greater sensitivity, with UV-C doses of 1.87 mJ/cm2 and 47.92 mJ/cm2 required for 1-log and 4-log inactivation at 254 nm, and 6.20 mJ/cm2 and 44.61 mJ/cm2 at 268 nm. This study lays the foundation for designing a successful UV-based nonthermal pasteurization system.