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Tofu is a traditional Chinese food with high edible value and rich nutrition, but the short shelf life of tofu not only restricts its industrialized development, but also causes food safety issues, especially in summer. Thus, it is necessary to develop an effective preservation technology, and adding the safe, efficient and dedicated preservative may offer an economical, resultful and feasible way to keep tofu fresh.In this study, spoilage bacteria were separated and characterized from firm tofu in bulk and boxed lactone tofu which were perishable, and the relationships between putrid phenomena and spoilage bacteria were preliminarily studied through pathogens inoculation experiments. Meanwhile, five food additives with bacteriostatic function including glycerol monolaurate (GML), sucrose monolaurate, glucono-δ-lactone, citric acid and nisin were chosen to inhibit the spoilage microorganisms. The minimum inhibitory concentrations (MIC) of each antibacterial agent and synergistic effects between GML and other antimicrobial agents were measured and compared. Then, preservatives mentioned above were applied in firm tofu to investigate the effect of preservation and the influence on moisture content, color and texture of firm tofu.Results showed that the main spoilage bacteria of firm tofu in bulk were Enter obacter-pyrinus, Lactobacillus-fermentum and Leuconostoc-mesenteroides. While Brevibacillus-parabrevis was the spoilage bacteria of boxed lactone tofu. The Enter obacter-pyrinus, Lactobacillus-fermentum and Leuconostoc-mesenteroides could cause sack expanding, clamminess and softening of tofu, respectively. Antibacterial activities of GML or nisin against each strain were better than the other preservatives. The synergistic effect of GML and nisin was the best, especially for gram-positive bacteria. The preservation results showed that adding0.04%GML+0.02%glucono-δ-lactone (w/w) or0.04%GML+0.02%citric acid (w/w) into firm tofu could significantly extend the shelf life of tofu at4℃,20℃,30℃for2d,1d and6h, respectively. Moreover, preservatives may impact the texture of firm tofu, like springiness increasing, cohesiveness and resilience reducing, and make the firm tofu less white and more yellow.
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