The aging of starch: After the starch solution is slowly cooled or the starch gel is left for a long time, it will become opaque or even precipitate. This is called the aging of starch. The essence is that the molecules after gelatinization will automatically Arranged in order to form highly dense, crystallized, insoluble molecular micro-bundles.

Factors affecting starch aging

(1) Type of starch. Amylose ages more easily than amylopectin; amylose with a small molecular weight ages easily; amylose with a degree of polymerization between 100 and 200 is the most susceptible to aging.

(2) Starch concentration. The solution concentration is high, there are many opportunities for molecular collision, and it is easy to age. However, when the moisture content is below 10, starch is difficult to age. When the moisture content is 30 to 60, especially around 40, starch is most susceptible to aging.

(3) Types of inorganic salts. Inorganic salt ions can hinder the orientation of starch molecules.

(4) pH value of food. When the pH is between 5 and 7, the aging rate is fast, while when it is acidic or alkaline, the aging is slowed down due to the same charge.

(5) Freezing speed. When gelatinized starch is cooled slowly, aging will be aggravated, while quick freezing can reduce the degree of aging.

(6) The level of temperature. The optimal temperature for starch aging is 2 to 4°C. It is not easy to age above 60°C or below -20°C. However, aging will still occur when the temperature returns to normal temperature.

(7) The influence of deposits. Lipids and emulsifiers can resist aging; polysaccharides (except pectin), surfactants or polar lipids with surface activity are added to bread and other foods to extend the shelf life. Completely gelatinized starch is cooled naturally at a lower temperature or slowly dehydrated and dried, which will cause hydrogen bonds to recombine between the starch molecules, causing the water molecules in the starch latex to gradually escape, resulting in water precipitation. At this time, the starch molecules are rearranged into orderly crystals and condensed, and the starch milk ages back to form a gel. This kind of starch that regenerates into crystal after gelatinization is called aged starch. Aged starch is difficult to rehydrate and harden, so it is difficult to digest rice that has been cooked, roasted and then cooled.