Study On The Antibacterial Stability Of Nisin And Its Application

Nisin as a potential kind of bacteriocin and biopreservatives has been widely applied in food processing. However, it is influenced by heat, alkali, substrate and storage time significantly. This paper firstly studied the components and antibacterial stability of nisin products. Protective materials and encapsulation technology were taken used of to improve the stability of nisin antibacterial activity. In addition, the application of nisin with compound preservative in food was studied. The main results were as follows.(1) Firstly the main component contents and titers of nisin samples were investigated. The 5 samples were all in line with the national standards. The colors of sample A and E were both light brown, darker than the other three. And there were a lot of carbohydrates and proteins in the samples. However, the titers of the two were 1280.0 IU/mg and 1401.9 IU/mg, respectively, which were higher than the qualified level (900 IU/mg) and with a good antimicrobial activity. In addition, the components, titers and solubility properties of smple B, C and D were close, and the NaCl contents were all higher than 70%. What’s more, with the pH increased from 2.0 to 9.0, the antibacterial circle diameter of sample A and B decreased about 31.25%　and 40.01%, respectively, which may implied that some components have protective effect on the antibacterial stability of nisin.(2) The antibacterial stability of nisin was studied that best antibacterial activity of nisin is in pH 2.0,25℃. As pH and temperature increased, the nisin titer loss rate rosed remarkably. While pH rose to alkaline level and even without heating, the antibacterial activity of nisin is unstable. Nisin solution was heated at 121℃ for 20 min, and then stored for one month, resulting in a significant downward trend on the titer. The titer loss rates were 65.20%　and 58.00%　in pH 4.0 and pH 6.0, respectively, resulting in a decreasing antibacterial stability of nisin.(3) Protective agents were used on the improvement of nisin antibacterial stabilty, and chitosan was the most significant protective agent, especially when nisin was at room temperature pH 6.0, the titer increased from 105.64 IU/mL of control to 154.72 IU/mL, and even it was heated to 121℃, the titer still represented a relevant better protective effect. VC and Tyr were both effective especially in acid region, when pH 4.0 nisin with 121℃, 20 min heating, the nisin titer increased 1.06-fold and 2.89-fold compared with control, respectively. In addition, FeSO4 was effective especially on weak acidic condition which can stabilize nisin antibacterial activity 4.20-fold than control after heating to 121℃ for 20 min.(4) Encapsulation technology was used to improve nisin antibacterial activity. The nisin-chitosan microcapsule was made through emulsification process and cross linking reaction. While it was processed at 25 C. CS/TPP (w/w) 3:1. CS/Nisin (w/w) 4:1, whose capsules were uniformly dispersed and particle size was 3.23 μm, the encapsulation rate and Zeta potential were 67.08% and 10.85%, respectively. While it was heated at 121℃ for 20 min, the antibacterial stability of pH 6.0 nisin-chitosan microcapsule was developed 47.95% compared to pH 2.0 free nisin.(5) Box-Behnken response surface design was used on nisin compound preservative of cooked pork, and the appropriate formula was that nisin 2.65 g/L, chitosan 4.50 g/L, D-sodium erythorbate 1.21 g/L and sodium citrate 0.15 g/L. While treated with the compound preservative, the aerobic plate count of cooked pork was 1.07×104 cfu/g, close to the theory value (1.49×104 cfu/g), which accorded with the national standard and verified a best formula.