Evaluation of the Microbiological Safety of Tofu

Abstract

Studies were done to evaluate the safety of tofu inoculated with different bacterial pathogens and held at different temperatures. Clostridium botulinum (type A and/or B) toxin was produced in tofu after 1 and 3 wk of storage at 25 and 15°C, respectively, but not within 6 wk at 5 or 10°C. Compared with water-packed tofu, vacuum-packaged tofu did not increase the risk of botulinal toxin production at 15°C. Staphylococcus aureus and Salmonella typhimurium grew at similar rates at 10, 15 and 25°C, but decreased in number at 5°C. Staphylococcal enterotoxin was not produced within 4 wk at 10°C, 8 d at 15°C, or 2 d at 25°C, even though an S. aureus population of >107 CFU/g was present in most samples analyzed. Staphylococcal enterotoxin was detected in a 5-d sample held at 25°C. Toxin production may have been delayed because of the low amount of oxygen in water-packed tofu. Yersinia enterocolitica grew at all temperatures evaluated (5, 10, 15 and 25°C), including a 4- to 6-log10 increase within 14 d at 5°C. Results of these studies substantiate the need for: (a) implementing a high level of sanitary practices during tofu production, (b) pasteurizing tofu after packaging, and (c) properly refrigerating tofu during storage and display.