Effect of ozone, treatment temperature, and antimicrobials on inactivation of Escherichia coli O157:H7 and Salmonella spp. in apple cider and orange juice

The studies presented in this dissertation were conducted to determine the effect of ozone, treatment temperature, and antimicrobials on the inactivation of Escherichia coli O157:H7 and Salmonella spp. in apple cider and orange juice. In the first experiment, inactivation of£. coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone was evaluated. A five-strain mixture of E.coli O157:H7 or Salmonella was inoculated (7 log cfu/ml) into apple cider and orange juice. Ozone (0.9 g ozone/h) was pumped into juices maintained at 4°C, ambient temperature (~20°C), and 50°C for up to 30 min (Salmonella/50°C), 75 min (E. coli/50°C), 180 min (apple cider/4°C) or 240 min (orangejuice/4°C and ambient). Samples were withdrawn, diluted in 0.1 % peptone water, neutralized with 1.0 N NaOH, and surface plated onto recovery media. Recovery of£. coli O157:H7 was compared on tryptic soy (TSA), sorbitol MacConkey (SMAC), hemorrhagic coli (HC), and modified eosin methylene blue (MEMB) agars; recovery of Salmonella was compared on TSA, bismuth sulfite (BSA), and XLT4 agars. After treatment at so·c, £. coli O157:H7 populations were reduced to the limit of detection ( 1.0 log cfu/ml) in 45, 30, 45, and 30 min in apple cider, and 75, 60, 60, and 45 min in orange juice, as determined on TSA, HC, MEMB, and SMAC, respectively.