Ultraviolet inactivation kinetics of Escherichia coli and Yersinia pseudotuberculosis in annular reactors

Terrorist threats have precipitated the need for information on the ultraviolet (UV) resistance of potential biothreat agents in food processing, such as Yersinia pestis. The objective of this study was to characterize the resistance of the Yersinia species to UV treatment using a single-lamp annular UV reactor. A novel method is proposed to measure the inactivation kinetics of Yersinia pseudotuberculosis, a surrogate of Y. pestis. This proposed method can overcome the disadvantages of the traditional collimated beam approach for liquids with high absorptive properties, such as liquid foods. As a reference, an inactivation rate of Escherichia coli K12 in caramel model solutions was measured first. Both first-order and series-event inactivation models were used to fit UV inactivation data. For the series-event model, an inactivation constant of k(SE)= 0.675 cm(2)/mJ and threshold n= 4 were obtained for E. coli K12 with the coefficient of determination R(2)= 0.987 and the standard deviation of log(10) reductions sigma(y)= 0.133. For Y. pseudotuberculosis, k(SE)= 0.984 cm(2)/mJ and n= 3 were obtained with R(2)= 0.972 and sigma(y)= 0.212. In contrast, for the first-order inactivation model, the first-order inactivation constant k(1)= 0.325 cm(2)/mJ with R(2)= 0.907 and sigma(y)= 0.354 was found for E. coli; and k(1)= 0.557 cm(2)/mJ with R(2)= 0.916 and sigma(y)= 0.402 was obtained for Y. pseudotuberculosis. Based on R(2), sigma(y), and the maximum absolute and relative errors, the series-event inactivation model describes the UV inactivation kinetics of Y. pseudotuberculosis and E. coli better than the first-order model. It is apparent that Y. pseudotuberculosis is less resistant to UV light than E. coli K12.