Inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium in apple juices with different soluble solids content by combining ozone treatment with mild heat.

Abstract

This study evaluated the combined effects of ozone and heat treatment to inactivate Escherichia coli O157:H7 and Salmonella Typhimurium in three types of apple juice of different soluble solids content. Three types of apple juice (18, 36, 72 °Brix) inoculated with pathogens were subjected to ozone (3·0 l min(-1) flow rate and 2·0-3·0 g m(-3) concentration) and heat treatment (25, 45, 50 and 55°C) simultaneously for 20, 40 and 60 s. Initial populations of pathogens in inoculated apple juice were approximately 10(5)-10(6) CFU ml(-1). Heat treatment alone (25, 45, 50 and 55°C) for 1 min reduced populations of E. coli O157:H7 by 0 to 4·75 log CFU ml(-1) in three types of apple juice. The combination of ozone and heat treatment for 1 min at 25 and 45°C reduced E. coli O157:H7 by 0·93-3·87 log CFU ml(-1) and below the detection limit (>1 log CFU ml(-1)) at 50 and 55°C. A similar tendency was observed for S. Typhimurium. In several instances, results showed a synergistic effect of ozone and heat treatment. Colour values were not changed during ozone and heat treatment. These results show that the combination of ozone and heat treatment can be used as a potential inactivation intervention for E. coli O157:H7 and S. Typhimurium in apple juice. The combination of ozone treatment and mild heat can be used as an alternative intervention for pasteurization of varying soluble solids content apple juice in food industries.