|Liao, Ching Hsing|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 11, 2000
Publication Date: March 30, 2000
Citation: Liao, C., Sapers, G.M. 2000. Attachment and growth of salmonella chester on apple fruits and in-vivo response of attached bacteria to sanitizer treatments. Journal of Food Protection V.63 No. 7. p.876-883. Interpretive Summary: Apple juice has been implicated as the cause of several outbreaks of food- borne illness during the past few years. The source and route by which apple fruits become contaminated with disease-causing bacteria such as E. coli O157 and Salmonella are presently unknown. In this study, the authors showed that Salmonella became attached to the surfaces of apple fruits almost upon contact. They also found that Salmonella attached more efficiently and firmly to the surfaces of stem and calyx (floral) parts of fruit than to the unbroken skin. A majority (94%) of attached bacteria were found on the stem and calyx areas but a very small proportion (6%) were on the skin. Firm attachment of Salmonella to the stem/calyx cavities represents a major hurdle for developing effective methods of removing bacteria from contaminated fruits. The authors also demonstrated that four commercial disinfectants tested in the study were only partially effective in killing bacteria attached to the fruit. A small portion of bacteria attached to the stem and calyx areas were either resistant to or protected from the sanitizer treatment. Further investigation of the mechanism by which bacteria become attached to apple fruits and the mechanism by which attached bacteria become resistant to sanitizer treatment would lead to the development of more effective methods for cleaning and decontaminating apple fruits destined for juice production, fresh-cut, or fresh consumption.
Technical Abstract: Attachment and growth of Salmonella chester on fresh-cut apple disks or whole apple and in vivo response of attached bacteria to sanitizer treatments were investigated. Apple disks were immersed in a bacterial suspension and air-dried at room temperature. After two rinses, the population of S. chester retained on apple disks containing no skin peel was 13 to 19% higher than that retained on disks containing skin peel, indicating that S. chester attached more firmly to the surfaces of injured tissue than to the unbroken skin. The number of bacteria attached to the disk was not affected by the immersion time but was directly proportional to the concentration of bacteria in the suspension. The distribution of attached bacteria on the surfaces of three different parts of fruit was determined; 94% of bacteria were found on the stem and calyx cavity areas and 6% on the skin of the remaining fruit. Despite their acidic pH (4.10, apple disks supported the growth of S. chester at 20 degrees C, but not at 8 degrees C. All four sanitizers tested in the study, including 6% hydrogen peroxide, 2% trisodium phosphate, 0.36% calcium hypochlorite, and 1.76% sodium hypochlorite, were effective in reducing the population of S. chester on apple disks by 1 to 2 logs. Nevertheless, 5 to 13% of bacteria survived sanitizer treatment. Firm attachment of bacteria on calyx, stem and injured tissue and partial resistance of attached bacteria to sanitizer treatments are two major hurdles to be considered when developing methods for cleaning and decontaminating apple fruits.