Answer: There are many methods of food preservatives. Among them, the method of adding food preservatives has low investment, quick results, does not require special instruments and equipment, and does not change the form and quality of food, so it is widely used. When adding food preservatives, they must first be used in strict accordance with the dosage and scope stipulated in the Food Hygiene Law, on the premise that they are non-toxic and harmless to the human body. In order to achieve the best use effect of food preservatives, we must pay attention to various factors that affect the preservative effect: (1) pH value and water activity. In water, acid-type preservatives are in an ionization equilibrium state. In addition to H+ ions, they mainly rely on Unionized acids act as preservatives, and these preservatives work best when the pH is low. High water activity is conducive to the growth of bacteria and mold. The activity of water where bacteria live is above ..9 and for mold is above 0.7. Reducing the activity of water is beneficial to the anti-corrosion effect. Adding electrolytes or other soluble substances to water can reduce the activity of water and play a synergistic effect when it reaches a certain concentration. (2) Dissolution and dispersion For fruits, potatoes, and refrigerated foods, spoilage generally starts from the surface, and the preservatives only need to be evenly dispersed on the food surface; for beverages, the preservatives need to be mixed into a solution and evenly dispersed in the beverage. middle. (3) Combined use of preservatives No preservative can inhibit all putrefactive microorganisms, so preservatives with different scopes of action should be used together. Preservatives used together can have synergistic or synergistic effects; additive or additive effects; antagonistic or antagonistic effects. Generally, the same type of preservatives are used together, for example, acidic preservatives are used together with their salts, several esters of the same acid, etc. (4) The use time of preservatives. The same kind of preservatives may have different effects due to different adding occasions and times. First, ensure that the food itself is in good hygienic conditions, and add preservatives during the induction period of bacteria. If the bacterial proliferation enters the logarithmic phase, the preservative will lose its original effect. Preservatives should be added as early as possible. If added early, the effect will be good and the dosage will be small. The more serious the food is contaminated with bacteria, the less effective the preservatives will be. If the food has deteriorated, any preservatives will be irreversible. (5) Influence of food raw materials and ingredients The effect of preservatives is affected by the raw materials and ingredients of food. For example, aromatics, seasonings, emulsifiers, etc. in food have antibacterial effects. Salt, sugar, and ethanol can reduce the concentration of water. Activity, contributes to preservatives. Salt can also interfere with the activity of enzymes in microorganisms, but it will change the distribution coefficient of preservatives and make them unevenly distributed. Certain ingredients in food react chemically with preservatives, causing some or all of the preservatives to become ineffective or cause side effects. Preservatives are also easily decomposed by microorganisms in food