Bacterial Contamination of Soybean Curd (Tofu) Sold in Thailand

Abstract

Soybean curd (Tofu) is a popular food for many people, especially those with health concerns. The objective of this study, therefore, was to evaluate the contamination rate and types of foodborne pathogens and food spoilage bacteria in packaged and unpackaged tofu sold in Thai markets. A total of 133 tofu samples (59 packaged tofu samples and 74 unpackaged tofu samples) were collected from open markets and supermarkets in Thailand. The predominantly identified Gram-negative bacteria were coliforms (67% in tested samples), Pseudomonas spp. (56%) and Escherichia coli (28%) and the predominantly identified Gram-positive bacteria were Enterococcus spp. (77%), lactic acid bacteria (68%), Bacillus cereus (41%) and Staphylococcus spp. (26%). No Listeria spp. were found in any of the tofu samples. The contamination rates of E. coli, Salmonella spp. and Enterococcus spp. in unpackaged tofu were significantly higher than those in packaged tofu (P < 0.05). Three kinds of Gram-negative pathogenic bacteria, Cronobacter sakazakii, Salmonella spp. and Yersinia enterocolitica (serotype 0:5), were found only in unpackaged tofu samples. Of 54 B. cereus isolates, four isolates from three unpackaged tofu samples and one packaged tofu sample were found to produce diarrheal enterotoxin. The most common Enterococcus spp. isolates were Enterococcus faecium and Enterococcus faecalis. These results suggested that the improvement of hygienic practices might be required for reducing the risk of food poisoning and food spoilage of tofu in Thailand.