29G-17 |
Pathogen population dynamics of rice cake |
S. Y. LEE1, P. M. Gray1, R. H. Dougherty2, and D. H. Kang1. (1) Dept. of Food Science & Human Nutrition, Washington State Univ., PO Box 646376, Pullman, WA 99164-6376, (2) Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164 Rice cakes are typically held at room temperature prior to sale since refrigeration dramatically reduces their quality. This factor, along with a high water activity and pH>4.6, provides an environment conducive to pathogen growth. To date, no studies have been published regarding survival of pathogens in rice cakes. This study was undertaken to investigate the levels of selected pathogens in raw materials used in rice cake manufacture and to evaluate the effect of cooking on their survival and subsequent growth. Regular rice flour (RR), sweet rice flour (SR), commercial white rice flour (WR), and tapioca flour (TP), red bean paste (RB) and mung bean product (MB) were evaluated. Twenty-five g samples from 10 sources of each cake ingredient were assayed for Bacillus cereus. Each ingredient was inoculated with non-spore forming (Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus) or spore forming (B. cereus) bacteria and were cooked by steam (100°C) for 30 min. Zero/ten (samples positive/samples assayed) RR, 0/10 SR, 10/10 WR, 10/10 TP, 5/10 RB, and 5/10 MB samples were positive for B. cereus. Levels of non-spore forming pathogens were significantly reduced (> 6 log10 CFU/g) in all samples by cooking for 30 min at 100°C, while spores of B. cereus were reduced by about 2 log10 CFU/g by the same heat treatment. After room temperature storage (22 ± 2°C), levels of B. cereus in RR, SR, WR, and, TP increased by 1.2, 1.7, 2.4, and, 1.7 log10 CFU/g after 1 day, respectively. Those populations were maintained within 0.5 log10 through 3 days storage. B. cereus in RB decreased by 1.3 log10 after 1day, and maintained that level. However, in MB, B. cereus increased by 4 log10 after 1 day. This information will be useful to commercial rice cake manufacturers.
Session 29G, Food Microbiology: General
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