Processing zucchini (Cucurbita pepo L.) with low UV-C radiation

Recent developments regarding the antimicrobial properties of certain types of light sources have promoted a growing interest in these applications, especially with concern to their potentialities for food processing. Ultraviolet radiation in the range of 200-280 nm is lethal to most microorganisms, including bacteria, viruses, fungi and yeasts. Fresh and artificially contaminated zucchini (Cucurbita pepo L.), whole and cut into triangular prisms, was exposed to UV-C lamps (Philips TUV-TL mini 8W) for different periods of time with the objective of quantifying the germicidal effect of this treatment. Triangular prism cut samples of zucchini were processed for 5, 7.5, 10, 12.5 and 15 min with different energy discharges of UV-C radiation, respectively 2.1 and 8.4 watts, whereas whole zucchini were strategically exposed for maximum time/radiation conditions (15 min - 8.4W) due to larger surface area treatments. In freshly cut samples, total counts of mesophilic bacteria were assayed, although in the case of whole vegetables, these were initially inoculated with commercial strains of Enterococcus faecalis ATCC 29212, and consequently assayed for presence of this specific microorganism. In both cases, UV-C exposure significantly reduced microbial activity, however, in relation to the freshly cut samples, after initial reduction of mesophilic bacteria, observations of photoreactivation between 7.5 and 12.5 min were registered, with significant counts at 10 min. Decrease in bacterial growth was once again evidenced between 10 and 12.5 min but not confirmed at 15 min of exposure. As for whole contaminated vegetables, approximately 2 logarithmic reductions of the target microorganism (Enterococcus faecalis ATCC 29212) were achieved.