What is the significance of starch aging, pasting and to food?

Overview
1, the general characteristics of starch: as we all know, starch belongs to the natural polymer carbohydrates, according to its molecules contain α-1,4 glycosidic bonds and α-1,6 glycosidic bonds and is divided into two kinds of straight chain starch and branched chain starch which have great differences in properties. Straight-chain starch is unstable when heated and pasted in water, and will age rapidly and gradually form a gel, which is hard and can only be transformed in the opposite direction at a temperature of 115-120 degrees. Branched-chain starch in aqueous solution is stable, the rate of gelation is much slower than straight-chain starch, and the gel is soft.
2, the paste of starch: starch is insoluble in water at room temperature, but when the water temperature rises to 53 ℃ or more, the dissolution occurs, the collapse, the formation of a uniform viscous paste solution. The essence is the starch grain in the ordered and disordered state of the starch molecules between the hydrogen bond broken, dispersed in water to form a colloidal solution. Starch at high temperatures to dissolve, split to form a uniform paste solution characteristics, known as starch pasting.
3, aging of starch: aging of starch refers to the aging of starch after pasting at room temperature or below room temperature, it will become opaque or even coagulation and precipitation. Aging is the inverse process of pasting, the essence is that in the process of pasting, the starch molecules that have been dissolved and swollen are rearranged and combined to form a substance similar to the structure of natural starch. Factors affecting the pasting and aging of starch
1, pasting 1) starch itself: branched starch is easy to paste because of its many branches and easy penetration of water, but they have poor heat resistance and will produce desizing phenomenon after excessive heating. Straight chain starch is more difficult to paste, has better “cooking resistance”, has a certain gel, can produce elasticity and toughness of the gel structure in the dish.
(2) Temperature: the pasting of starch must reach its solubility point, i.e. the pasting temperature, the pasting temperature of various starches is different, generally when the water temperature rises to 53 degrees, the physical properties of starch undergoes obvious changes.
(3) Water: the pasting of starch requires a certain amount of water, otherwise the pasting is incomplete. Under normal pressure, it is difficult to paste completely with less than 30% water.
(4) pH value: when the PH value is greater than 10, reduce the acidity will accelerate the pasting, add acid can reduce the viscosity of starch, alkali is conducive to starch pasting, for example, adding a small amount of alkali when boiling thin rice can make it viscous.
(5) coexisting substances: high concentration of sugar can reduce the degree of starch pasting, lipids can form a complex with starch to reduce the degree of pasting.
2, aging 1) the type of starch: straight chain starch is easier to age than branched chain starch, for example, glutinous rice, sticky corn in the branched chain more, not easy to age.
2) Water: water content between 30% and 60%, easy to aging phenomenon, water content below 10% or higher than 60% of the food, not easy to aging.
3) Temperature: the optimal temperature for aging is 2-4 degrees, higher than 60 degrees or lower than 20 degrees do not occur aging.
(4) Freezing speed: the rate of temperature drop of starch solution has a great influence on aging. Slow cooling can make the starch molecules have time oriented arrangement, which can aggravate the aging degree, while rapid cooling can reduce the aging degree.
(5) PH value: PH in the range of 5-7, the most easy to aging, in the acidic or alkaline environment below 4, starch is not easy to aging.
6）Expansion treatment：Grains or starch can be preserved for a long time without aging after high pressure or expansion treatment.
In addition there are inorganic salts and coexisting substances, etc. on starch aging also has a certain effect.
Application of starch pasting and aging in life
Starch pasting and aging are both relatively common chemical phenomena in our daily life, examples are as follows.
The fact that soft-tasting rice is better for digestion than hard-tasting rice shows that the pasting of starch can improve the digestion and absorption rate of food. Secondly, the pasting of starch can also be applied in the process of hanging, sizing and thickening of dishes.
In addition, the production of some foods also uses the principles related to starch pasting. For example, when making vermicelli, the starch with more straight chain starch and better aging degree should be selected, such as mung bean starch. And when making rice cakes, Lantern, dumplings and other pastries, the starch that contains almost no straight chain starch, is not easy to be aged, easy to absorb water and swell, easy to be pasted, and has high viscosity should be chosen, such as glutinous rice flour.
The aging of starch is mainly applied in the process of making vermicelli and vermicelli, starch can only have strong toughness after aging, produce luster on the surface, not easy to break after heating and have strong taste, so it should be chosen bean starch with high content of straight-chain starch as the raw material.