According to the "import and export of canned food inspection regulations" definition,acidified food(acidified foods)YesRefersBy adding acid or acid production, the final equilibriumpH less than or equal4.6, water activity (Aw) greater0.85Low acid foods.
Acidified foods generally meet four conditions:
1、 Product shelf-life stability, non-refrigerated or frozen storage;
2、 The product shall be packed in sealed containers;
3、 The water activity of the product (aw) is greater0.85;
4、 If by adding acid or acidic substances, the final equilibriumpH less than or equal4.6.
ForpHValue greater4.6and water activity (aw) is greater0.85After acid impregnation, acid and other artificial acidification treatment, there are usually two ways to achieve the purpose of inhibiting microbial reproduction:
1、 Thermal sterilization:The production, sterilization and packaging of acidified food must be balanced within the time specified in the sterilization process.pH reached4．6or below, and keeppHValue. Must comply with the sterilization process procedures for productionFoodFull thermal sterilization,Make the food in a commercially sterile state during the shelf life.
2、 Use of permitted preservatives to inhibit the proliferation of microorganisms harmless to health(as an alternative to thermal sterilization)。
In layman's terms, for some foods with low acidity, we hope to allow them to obtain a longer shelf life at room temperature without adding preservatives. The current international practice is to artificially acidify, seal and package the food. Thermal sterilization, thereby extending the shelf life of food. The lactic acid introduced in the previous issue is an acid commonly used in artificial acidification procedures.
Acidity refers to the concentration of hydrogen ions in a solution, usuallypH is expressed, I .e.PH = -lg[H ]
In aqueous solution, strong acids and strong bases can be completely ionized into the corresponding cations and anions; for weak acids, the acidity of weak base solutions is[H]. Similarly, alkalinity is usuallypOHindicates that for aqueous solutions (25℃), thenpH pOH = 14.0
 indicates the equilibrium concentration of a component after ionization, such[H ]and[OH-]means in solutionH andOH-The equilibrium concentration of, in unitsmol/L.
2、 Water activity:
Water activity refers to the ratio of the vapor pressure of water in food to the saturated vapor pressure of pure water at the same temperature. Available formulas (1-1) is expressed as follows:
Aw = p / p0 (1-1）
In the formula:Aw is water activity;pThe partial pressure of water vapor when the food reaches equilibrium in a closed container, that is, the partial pressure of water vapor over the food, generally speakingpwith the increase of the free water content in the food which is easy to be evaporated;p0is the saturated vapor pressure of pure water at the same temperature.
water activityAw value is of great significance to food preservation. The storage stability of foods containing water is different due to the difference of water activity.