Evaluating the growth of Listeria monocytogenes that has been inoculated into tofu containing background microflora

Tofu is a popular food choice for people with health concerns, especially vegetarians. In this study, the survival and growth of Listeria monocytogenes was investigated after it had been inoculated into various tofu products. Three kinds of pre-packaged tofu products were purchased, and a mixture of four strains of L. monocytogenes was injected into these products before storage treatment at either 4–7 °C or 22 °C. During storage treatment, the inoculated L. monocytogenes (starting at the level of approximately 3 log CFU/g) competed to grow among the background microflora that is inherently present in the tofu samples. The L. monocytogenes flora reached the concentrations of 7.1–7.9 log CFU/g after 24 days at 4–7 °C treatment or 6.9–7.5 log CFU/g after 48 h at 22 °C treatment. Nevertheless, compared to other single species of the indigenous microflora within the three kinds of tofu samples, the inoculated L. monocytogenes strains were the numerically dominant population. These results indicate that L. monocytogenes contamination in tofu products at the manufacturing process or at the retail level poses a potential risk to human health.