Inactivation by ozone of Listeria innocua on salmon-trout during cold-smoke processing

This study was conducted to evaluate the efficacy of gaseous ozone exposure on Listeria innocua 2030c growth during cold-smoke processing of Oncorhynchus mykiss (salmon-trout). Three sets of experiments were performed: inoculation with L. innocua 2030c followed by a 20 min ozone exposure were applied to (a) fresh salmon-trout after filleting, (b) to fresh whole fish, and (c) to fresh whole fish after removal of the fish slime. In sets (a) and (b) fillets were subsequently cold-smoked but not in set (c). The ozone concentration inside the exposure chamber after 20 min reached 0.1 X 10(-3) g/l. Counts of L. innocua 2030c were performed after treatment for sets (a), (b) and (c), after smoking and weekly during 21 days in vacuum packs at 5 degrees C, for sets (a) and (b). Sampling for total Aerobic Plate Counts (APC) of non-inoculated samples was also performed in set (a). The percentage of salt in the water phase, peroxide values and the effect of treatment oil sensory properties of cold-smoked salmon-trout fillets were also determined in the first and second set. In the first set, a decrease of less than 1 log(10) in L. innocua numbers occurred oil ozone treated samples in all sampling occasions. APC was slightly lower on fresh fillets after treatment and oil smoked fillets at 3 weeks of storage at 5 degrees C (less than I log(10) CFU/g). In the second set, a reduction greater than I log(10) L. innocua/g Occurred oil smoked fillets at the end of the storage period. In the third set, the slime removal resulted in a I log(10) L. innocua/g reduction on fresh treated samples. Ozone treatment had no significant (p > 0.05) effect oil L. innocua counts on samples compared to those on untreated fish. In both sets, no significant differences among ozone treated/untreated samples were noticeable by sensory evaluation (p > 0.05). (c) 2005 Published by Elsevier Ltd.