Nisin is a polypeptide synthetic by a number of amino acids, white or slightly yellow crystalline powder or particles, slightly salty, it is currently the world's only allowed to be used in food preservative antibiotics, is widely used in dairy products, meat products, sauce products, condiments and beverages and other food production, play a preservative and fresh-keeping effect.
The water solubility of nisin increased with the decrease of pH value. When pH is equal to 2.5, the solubility is 12%. When pH is 5.0, the solubility is 4%. When the pH is greater than or equal to 7, it is almost insoluble, which makes it easier to dissolve under acidic conditions, thus playing a better anti-corrosion effect.
The thermal stability of nisin in acidic conditions is also very strong, for example, in dilute hydrochloric acid with pH less than 2.0, it can withstand sterilization at 115.6℃ or even higher without losing life, when the pH value exceeds 4, especially under heating conditions, the decomposition rate of nisin in aqueous solution will be accelerated, and the vitality will be reduced. However, it is worth noting that when it is added to food, its stability will be greatly improved due to the protection of large molecules such as milk and broth.
In practical application, the nisin in acidic food shows a good anti-corrosion effect, for example, it (such as 0.05g/kg) added in pH4 yogurt, fruit milk, after 90℃, 20 minutes of sterilization treatment, the product shelf life can be extended from 6 days at room temperature to more than one month.
Nisin has high stability under acidic conditions, which is due to its unique solubility and thermal stability characteristics, which make it have a wide range of application prospects and important value in the field of food preservation. At the same time, it is also necessary to pay attention to the use of food according to the specific situation and needs to choose the appropriate amount of addition and treatment.