Characteristics Of Native Nisin And Its Application In Meat Preservation

This paper consisted of two parts some characteristics of native nisin were studied in part I, and the application of native nisin in preservation of fresh pork and salted duck in part II. Experiments were conducted to study the effects of temperature, pH, protease and storage condition on the activity of native nisin, and to study the inhibitory spectrum. The results indicated that nisin activity was affected significantly by temperature and pH. Under acidic condition nisin was stable to temperature, but as p1-I was increased, the higher the temperature was, the more the losses of nisin activity were. The lower temperature was of advantage to nisin storage. Storage effect of dry nisin was better than its solution. It was observed that native n~sin was sensitive to trypsin, but insensitive to pepsin. The results of inhibitory spectrum experiment revealed that native nisin was effective against Gram-positive bacterium, however, there was no effect on the inhibition of Gram-negative bacterium, yeast and molds. The effectiveness of nisin in preservation of fresh pork was assessed through microbiological assay, pH and TVBN value examination and sensory evaluation during storage under vacuum-package and low temperature (5?.5 C) conditions. According to the microbiological index, the results showed that the shelf-life of normal pork (control) was 4 days, while the addition of 200mglkgnisin, or 2%sodiumlactate (NaL), I %potassium sorbate, 200mg/kgnisin-2%NaL combination prolonged the shelf-life to 6, 6, 8 and 8 days respectively. The combination of 200mg(kgnisin and 1%potassium sorbate appeared to have a best effect, and prolor ed the shelf-life to more than 12 days. pH value appeared to have a decline trend after au initial ascent. TVBN value increased gradually during storage, which wasn related to corresponding microbiological results completely. Sensory evaluation showed that the addition of nisin. NaL, and potassium sorbate had no negative effect on sensory quality of fresh pork. Another experiment was conducted to study the effect of nisin and other preservatives , combined with vacuum-package and microwave treated, on the storage of salted duck at 30C. The result showed that the effects of additions of natural preservatives such as nisin, nisin-NaL combination were limited. By further adding some chemical-compound preservatives such as potassium sorbate and sodium bcnzoate, the shelf-life was prolonged significantly, and to more than 25 days at high dosing. The use of icrowave-enhancing agent(MEA) alone prolonged the shelf-life of salted duck to more than 15 days, while to more than 25 days combined with I g/kgnisin and 3.5%NaL, At that time TBA value was still normal. Sensory evaluation revealed that the addition of nisin, NaL, MEA, or combination of the three preservative had no negative effect on the sensory quality of salted duck, which was found acceptable at the 25th day by adding the combination of MEA, lglkgnisin and 3.5%NaL.