Storage Characteristics, Isolation and Identification of Spoilage Bacteria, and Spoilage Characters of Boxed Tofu

In order to explore the effects of spoilage microorganisms on the quality of boxed tofu and their spoilage characteristics, sensory score and aerobic plate count were used as indexes to study the effect of storage temperature (4, 25 and 37 ℃) on the storage life of boxed firm tofu and lactone tofu. The spoilage bacteria in boxed tofu were isolated and identified, and their spoilage and growth characteristics were observed. The results showed that the storage life of boxed firm tofu and lactone tofu stored at 4 ℃ was both more than 30 days. The storage life of boxed firm tofu and lactone tofu stored at 25 ℃ was about 36 and 48 h, respectively. The storage life of boxed firm tofu and lactone tofu stored at 37 ℃ was about 12 and 30 h, respectively. Fifty-two strains of spoilage bacteria were isolated and identified from fresh and spoilage boxed firm tofu and lactone tofu, including 43 strains of Bacillus sp. and 9 strains of other genus bacteria, which indicated that Bacillus sp. were the main microorganisms that caused spoilage of boxed tofu. The diversity of spoilage bacteria was affected by storage temperature, and the species of spoilage bacteria were more abundant when the boxed tofu were stored at 4 and 25 ℃. The quality of boxed tofu was greatly affected by Bacillus sp. when stored at 25 ℃, in which Bacillus cereus could cause browning of boxed firm tofu, and Bacillus subtilis and Bacillus licheniformis could cause boxed firm tofu to swell. The spoilage characteristics of boxed lactone tofu back inoculated Bacillus subtilis and Bacillus cereus were basically the same as those of the control sample. The final spoilage characters of tofu were caused by the comprehensive action of various bacteria. This study further enriched the species of Bacillus sp. and other bacteria from tofu on the basis of previous studies, and it had good theoretical significance for guiding soybean products enterprises to take targeted measures to control the number of Bacillus sp. in boxed tofu in the process of production, storage and transportation, so as to delay its spoilage and prolong its storage life.