Effect of UV-C and pulsed-UV treatments on reduction of Penicillium expansum spores and Escherichia coli K12 in a model apple juice

Pasteurization of fruits juices is essential for ensuring their safety and shelf stability. Penicillium expansum can cause significant health problems due to the production of patulin in apple juice. Ultraviolet (UV) light technology has been proposed as an alternative to thermal pasteurization process; however, the efficacy of UV light may be limited due to its low energy delivery and the physicochemical properties of the food treated. Pulsed UV technology is an alternative technology that may improve the treatment. The present study compares the effectiveness of UV-C and pulsed UV light treatments on the inactivation of P. expansum spores and E. coli K12 in model apple juices containing added ascorbic acid and malic acid, in the presence or absence of added fructose. Model juice samples were treated with UV-C for up to 100 min and with pulsed UV for up to 70 s. Log reductions for both microorganisms increased with time although resistance of P. expansum was greater compared to E. coli K12 for both UV treatments. In contrast to recent studies showing accelerated UV destruction of ascorbic acid in the presence of added fructose, log reductions for pulsed UV treatments for both microorganisms were significantly higher (p (0.05) in samples without added fructose than with added fructose. Moreover, there was no significant difference between log reductions for UV-C treated samples with or without added fructose for the UV-C treatment. For example, UV-C treatment for 100 min resulted in 2.99 and 3.05 log CFU/ml reduction of E. coli K12 with or without added fructose, respectively, whereas P. expansum populations were reduced by 1.97 and 2.04 log CFU/ml for 100 min of UV-C treatment with or without added fructose, respectively. Pulsed UV treatments resulted in observed reductions of 3.80 and 4.67 log CFU/ml of E. coli K12 with or without added fructose at 40 s, whereas the population of P. expansum was reduced by 3.16 and 3.85 log CFU/ml with or without added fructose at 60 s, respectively. These results show that pulsed UV can be more effective in reducing microbial populations in apple juices.