Microbiological Study of Tofu

The microbiological qualities of tofu juice and cake were studied. Seven brands of tofu from four grocery stores were tested, at day 1 and after 30 d of storage in a refrigerator. The microbial load at day 1 was different from brand to brand, but cell counts in juice and cake of the same brand were correlated. The number of cells observed at day 30 was different from brand to brand but was not related to the initial cell count. The pH had a great effect on the type of contaminating microorganisms present. All brands spoiled after 30 d of storage at 7°C; 112 isolates from both the fresh juice and cake at day 1 and at day 30 were obtained. The most common gram-positive organisms isolated were Streptococcus sp., Pediococcus sp., and Lactobacillus sp., and the most common gram-negative bacteria were Pseudomonas putida , P. aeruginosa , Enterobacter agglomerans , and E. cloacae .