a b s t r a c tThe effectiveness of ozone in aqueous solution treatment on microbial inactivation was studied for three combinations microorganism/food: Listeria innocua/red bell peppers (artificially inoculated), total mesophiles/strawberries, and total coliforms/watercress, with two concentrations (0.3 and 2.0 ppm). Blanching treatments (50-60°C) were also individually applied and in combination with ozone, for studying possible synergistic effects. In relation to ozone treatments, the highest microbial reductions were obtained for the highest concentration with the highest treatment time (3 min). Under those conditions, L. innocua/peppers, total mesophiles/strawberries and total coliforms/watercress were reduced respectively 2.8 ± 0.5, 2.3 ± 0.4 and 1.7 ± 0.4 log-cycles. However, a substantial portion of the microbial populations were reduced by water washing alone, and the presence of ozone generally added an additional reduction of 0.5-1.0 log-cycles.If ozone at the highest concentration is used, the treatment impacts on L. innocua/peppers and total mesophiles/strawberries load reductions were equivalent to a blanching at 50°C (for the same treatment times).Combining blanching and ozone did not generate synergistic effects, and in some situations microbial reductions were lower than the ones observed when treatments were applied independently.
The impacts of ultraviolet-C radiation, blanching by heat, and combination of heat/ultrasounds (thermosonication) were studied for Listeria innocua (inoculated) in red bell peppers, total mesophiles in strawberries and total coliforms in watercress, in the temperature range 50-65°C. Quality attributes such as colour and firmness were studied for all products, and total anthocyanins content was additionally determined for strawberries. Results showed that ultraviolet-C radiation was the least effective treatment in terms of microbial load reduction and was equivalent to a simple water washing. Log reductions were 1.05±0.52 for L. innocua, 0.53±0.25 for total coliforms and 0.26±0.18 for total mesophiles. This treatment had the lowest impact on the quality parameters analysed. Thermosonication treatment was similar to heat blanching for all microorganism/product tested, excepted for total coliforms in watercress at 65°C, in which thermosonication had a higher effect (p<0.05). Heat blanching at 65°C allowed 7.43±0.12 log-cycles reduction, while loads were diminished by 8.24±0.13 log-cycles if thermosonication at the same temperature was applied. Thermosonication also allowed better quality retention, when compared to heat blanching at the same temperatures. The impact of thermosonication on microbial load reductions was statistically significant and thermosonicated samples retained quality attributes better than heat blanched ones at the same temperatures (p<0.05). Hence, it can be concluded that thermosonication is a promising process and may be a favourable alternative to the conventional thermal treatments.
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