Attachment and growth of Salmonella Chester on apple fruits and in vivo response of attached bacteria to sanitizer treatments

Attachment and growth of Salmonella Chester on fresh-cut apple disks and in vivo response of attached bacteria to sanitizer treatments were investigat ed. Apple disks (14 mm in diameter and 3 to 4 mm in thickness) were immerse d in a bacterial suspension that contained 8.17 log CFU/ml of Salmonella Ch ester and air dried at room temperature for 10 min. After two rinses, the p opulation of Salmonella Chester retained on apple disks that contained no s kin was 13 to 19% higher than that retained on disks that contained skin, i ndicating that Salmonella Chester attached more firmly to the surfaces of i njured tissue than to the unbroken skin. The number of bacteria attached to the disk was not affected by the immersion time but was directly proportio nal to the concentration of bacteria in the suspension. The distribution of artificially inoculated Salmonella Chester on the surfaces of three differ ent parts of whole fruit was determined; 94% of attached bacteria was found on the stem and calyx cavity areas and 6% on the skin of the remaining are a of the fruit. Despite their acidic pH (4.1), apple disks supported the gr owth of Salmonella Chester at 20 degrees C but not at 8 degrees C. All four sanitizers tested in the study, including 6% hydrogen peroxide, 2% trisodi um phosphate, 0.36% calcium hypochlorite, and 1.76% sodium hypochlorite, we re effective in reducing the population of Salmonella Chester on apple disk s by 1 to 2 logs. However, 5 to 13% of bacteria survived the sanitizer trea tments. Hydrogen peroxide, which reduced the population of Salmonella Chest er on skin by 3 to 4 logs and the population of bacteria on stem or calyx b y 1 to 2 logs, was the most effective among the four sanitizers tested. Fir m attachment of bacteria on calyx, stem, and injured tissue and partial res istance of attached bacteria to sanitizer treatments are two major obstacle s to be considered when developing methods for cleaning and decontaminating apple fruits destined for juice production and fresh consumption.