Assessing Microbial Quality of Tofu in Korea, Identifying a Dominant Bacteria Contaminating Tofu, and Characterizing the Growth in Tofu

Introduction: Tofu is susceptible to microbial spoilage as it contains carbohydrate, protein, fat, and water. In addition, microbial spoilage of tofu is highly related with the storage temperature and time.

Purpose: This study was to monitor the microbial safety of tofu in northern Seoul, to identify the dominant bacteria contaminating tofu, and to investigate the growth characteristics of identified bacteria.

Methods: The size of tofu specimens was 100. Total aerobic bacteria, Staphylococcus aureus, Salmonella spp., Bacillus cereus, Listeria monocytogenes, Escherichia coli, coliform bacteria, E. coli O157:H7 in tofu were tested. A dominant colony with the typical shape and color was isolated and subjected for the 16S rRNA bacterial identification. The growth characteristics of isolated bacteria in tofu as temperature was investigated.

Results: Aerobic bacteria was detected in 32 out of 100 tofus. The dominant bacteria contaminating tofu was identified as Bacillus cereus. Gompertz modeling of the growth of the Bacillus cereus in fresh tofu reveals that the microbial safety of tofu cannot be guaranteed if tofu contaminated with such bacteria is stored at 10°C for 4 days.

Significance: This study identified a dominant bacteria contaminating tofu and informed of its growth characteristics in tofu.