Abstract: In this paper the antibacterial effect of tannin in vitro and its influencing factors are investigated. The minimal inhibitory concentration is measured through the agar dilution, and the antimicrobial properties are screened by filter disc method in food system. By using agar-comparing method, various antibacterial factors in food system such as pH value, sodium chloride concentration, sucrose concentration, metal ions and organic acids, on its bacteriostatic effect are screened. The results show that tannins have good antibacterial activities on Staphylococcus aureus and Micrococcus luteus, MIC of which is 0.39 mg/mL and 0.09 mg/mL respectively. Under the condition of acid, or under the synergism of citric acid and lactic acid, the antibacterial effects of tannic acid on food spoilage organisms increase; and the bacteriostatic effects are stable for NaCl, sucrose and metal ion. Compared with potassium sorbate, it seems to have a better effect on food and the MIC of which is lower than potassium sorbate. Tannins with organic acid together are more conducive to the antibacterial activity, which have a wide pH range. With added salt and sugar food, tannins can weaken the use of salt or sugar, and be beneficial for healthy living.

Key words: tannic acid; antibacterial agents; food additives; influencing factors