Reduction of Saccharomyces cerevisiae, Escherichia coli and Listeria innocua in apple juice by ultraviolet light

Apple juice was inoculated separately with Saccharomyces cerevisiae, Listeria innocua (ATCC 51742) or Escherichia coli (ATCC 11775) for treatment in a double tube ultraviolet (UV) disinfection system. The apple juice was treated at six flow rates (0.073-0.548 L/min),for selected fluences (75-450 kJ/m(2)). The juice was also inoculated with a mixture of these three microorganisms and UV light treated,from. 0.548 to 0.735 L/min for 30 min. The microbial reduction was described with. a first order kinetic model. Average D-uv values of 23.1-10.5, 8.2-20.6 and 6.0-17.7 min were obtained for S. cerevisiae, L. innocua and E. coli, respectively. A linear model was used to describe the relationship between log D-uv versus flow rate for S. cerevisiae and L. innocua. However; a third order polynomial model was more adequate for describing the E. coli D-uv values versus flow rate. Less than 10 (no growth), 190 and 200 cfu/mL of S. cerevisiae, L. inocua and E. coli, respectively; were observed in UV-treated apple juice inoculated with a mixture of microorganisms.