61C-37 |
Antibacterial effect of crude extracts of tea on foodborne pathogens in liquid medium |
S. KIM and D. Y. C. Fung. Animal Sciences and Industry, Kansas State University, Call Hall 202, Manhattan, KS 66506 Naturally occurring phenolic compounds from various plants act as antioxidants and antimicrobial agents. Extracts of tea, such as Black or Green, have been shown to have antibacterial activities, against pathogenic bacteria. Microbial growth of four foodborne pathogens (Escherichia coli O157:H7, Salmonella enteritidis, Listeria monocytogenes, and Staphylococcus aureus) was determined in Brain Heart Infusion (BHI) broth with tea extracts. Ten grams of each tea (Black, Jasmine, Green, Oolong, and Dungglre) were brewed separately in 90 ml of boiling BHI broth for 10 min. The cocktail of four pathogens was inoculated into the cooled BHI-tea extracts at ca. 3 log cfu/ml. After incubation at 35 ̊C for 0, 1, 3, and 5 d, a viable cell count of each pathogen was performed on its selective agar. This experiment was performed in triplicate. All pathogens grew from ca. 3 log cfu/ml to ca. 7-8 log cfu/ml after the first day in BHI without tea extracts (control). E. coli O157:H7 and S. enteritidis increased to 7 log cfu/ml in all tea extracts in 1 d indicating that the gram-negative cells were not affected by tea extracts. S. aureus remained at 3 log cfu/ml in Oolong tea and reduced to ca. 1.5 log cfu/ml in Green, Jasmine, and Black tea from 1 d to 5 d. In Jasmine tea, L. monocytogenes reduced to log 2 cfu/ml in 1 d and 3 d but increased to 5.5 log cfu/ml in 5 d. In Green tea, the cells grew steadily from 3 log cfu/ml in 1 d to 5 log cfu/ml in 5 d. These data indicated that some tea extracts can inhibit and suppress the growth of gram-positive cells. From this study, tea extracts may be applied to ready-to-eat foods or other commodities directly or as a spray to prevent growth of gram-positive bacteria.
Session 61C, Food Microbiology: General I
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