REDUCTION OF <i>SACCHAROMYCES CEREVISIAE, ESCHERICHIA COLI</i> AND <i>LISTERIA INNOCUA</i> IN APPLE JUICE BY ULTRAVIOLET LIGHT

Abstract

ABSTRACT 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 23.1–40.5, 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.