Answer: Common preservatives in food are: benzoic acid and its sodium salt, sorbic acid and its potassium salt, parabens, nisin and natamycin.

Benzoic acid is widely used and is very effective against yeast and bacteria, but slightly less effective against mold. The optimal pH range is 2.5 to 4.0, with the strongest antibacterial effect at pH 3.0; above pH 5.5, It has little effect on many molds and yeasts, so it is most suitable for use in foods such as carbonated beverages, juices, wines, pickles and sour pickles. Sorbic acid has inhibitory effects on molds, yeasts and aerobic bacteria, but is almost ineffective against anaerobic spore-forming bacteria and acidophilic bacteria. Generally speaking, when the pH value of the solution is lower than 4, the antibacterial activity of sorbic acid is high; when the pH value is higher than 6, the antibacterial activity is low. However, sorbic acid is still effective when the pH is as high as 6.5. Parabens are effective inhibitors of mold and yeast, but have no effect on bacteria, especially gram-negative bacteria. The antibacterial scope of nisin: Gram-positive bacteria, Lactobacillus, Staphylococcus aureus, Clostridium botulinum, Bacillus, etc. It has no effect on Gram-negative bacteria, yeast and mold; the antibacterial pH value is between 6.5～6.8. Nisin is often used in cheese and cream products. Scope and dosage of natamycin: cheese, pastries, meat products, Western hams, fruit and vegetable juices (slurry) and other foods, the maximum dosage is 0.3g/kg; when used in fermented wine, the maximum dosage is 0.01g /kg, and should be used on the surface, sprayed or soaked with suspension, and the residual amount should be less than 10mg/kg.