Starch, as an important component of food, not only provides essential energy to the human body, but also affects quality attributes such as texture, mouthfeel, and acceptability of starchy foods. Most starchy foods undergo some form of processing or cooking, which results in the starch absorbing water and expanding to form a paste system with a certain viscosity, but during cooling and storage, starch molecules undergo rearrangement in their spatial conformation to form an ordered and stable gel structure, a phenomenon known as starch aging or regrowth.

Starch aging usually leads to the deterioration of starch food quality, such as deterioration of texture, decrease in transparency, roughness of taste, etc., which shortens the shelf life of starch food and reduces the acceptability of consumers. For example, in steamed buns, breads and pastries, due to the high starch content, with the prolongation of storage time, they will change from soft to hard, loose organization and loss of flavor.

However, the aging behavior of starch is also desirable in some processing applications, for example, in the production of breakfast cereals and dehydrated mashed potatoes, where starch aging can change the structural and sensory properties of the product and can lead to the formation of resistant starch. In view of this, how to rationally regulate the aging degree of starch and examine the aging characteristics of the system is important for both the processing of starchy foods and the improvement of eating quality.

Brief description of starch aging and its mechanism

Starch aging is a thermodynamic equilibrium process in which partially or completely pasted starch molecules are gradually transformed from a high-energy disordered state to a low-energy ordered state, i.e., the starch molecular chains are combined, aligned, and aggregated through intramolecular or intermolecular hydrogen bonding, constituting an ordered arrangement of aggregated structures.

The aging process of starch can be divided into short-term aging and long-term aging. Among them, short-term aging occurs in the initial stage after starch pasting, where the leakage of straight-chain starch molecules undergoes directional migration to form a three-dimensional network structure; long-term aging, on the other hand, generally takes more than a few weeks, mainly due to the fact that branched-chain starch has a highly branched structure, which is subjected to strong inhibition during polymerization, and the aging process is slower. Long-term aging plays a major role in the whole starch aging process and is the main cause of quality changes in starch systems.

For non-waxy starches, aging leads to the transformation of the starch paste into a firm gel with a three-dimensional network structure, whereas for waxy starches, aging leads to the formation of a soft gel, which contains aggregates but no three-dimensional network structure.

Usually, the strength of starch gels is related to the content of straight-chain starch. The network structure of straight-chain starch provides elasticity and deformation-resistant strength to starch gels, whereas soft gels containing only aggregates show better permeability, stronger viscosity and cohesion. Reduced availability of hydrogen bonds between straight-chain starch molecules disrupts long-range interactions within the soft gels, leading to a less cohesive network structure.

Starch aging is a continuous process that initially involves rapid recrystallization of straight-chain starch molecules followed by slow recrystallization of branched-chain starch molecules. Aging of straight-chain starches determines the initial hardness of the starch gel, as well as the viscosity and digestibility of starchy foods. Aging of breads and cakes is related to storage time and starch crystallinity, and is mainly caused by aging of branched-chain starches.

Additives and regulation of starch anti-aging

The aging of starch-containing food during storage is inevitable, at present, the world has not completely solved the problem of food aging, and aging can not be completely inhibited, but can be delayed by effective technical measures. According to the aging mechanism of starch and the factors affecting it, the following corresponding control technology can be used to slow down the aging.

I. Add enzyme preparation
Amylase and protease are widely used in starchy food, and amylase is divided into α-amylase, β-amylase, fungal amylase and so on. Among them, the best anti-aging effect is α-amylase. Due to the generation of low molecular weight dextrin during baking, α-amylase inhibits long-term aging of starch by interfering with the aging process of branched-chain starch. However, excessive amounts of α-amylase can make starchy foods sticky, affecting the texture and collapsing the structure.

Palacios et al. applied α-amylase to rice, which inhibited the aging of rice due to the increase of short side chain of branched starch. Chen Qiuping et al. added appropriate amount of bacterial α-amylase to steamed buns, which not only improved the sensory quality of steamed buns, but also inhibited the aging phenomenon of steamed buns during storage.Dang et al. extracted β-amylase from Ramie leaves also had an anti-aging post-effect on amylose foods.

G4 amylase is a new type of amylase, which can cut the starch branched chain short and produce tetrasaccharide, thus reducing the length of branched starch side chain. Kina et al. treated wheat starch with G4 amylase and found a significant anti-aging effect. In addition, you can also use the enzyme to decompose gluten or gluten protein, etc., the decomposition product will be added to starchy food, can also play a good anti-aging effect.

Add emulsifiers
Adding emulsifiers to food can not only delay the aging of starch, but also play a role in preserving freshness. After the paste of straight-chain starch molecules were double helix structure, at this time its internal is hydrophobic, the hydrophobic groups of emulsifier into its internal, the formation of insoluble inclusion complex, can be indirectly inhibited by inhibiting recrystallization of straight-chain starch branched-chain starch recrystallization and thus play a role in the anti-aging effect.

Emulsifiers can also retard aging by directly affecting the distribution of water in the food.Prakaywatchara et al. added four emulsifiers to gluten-free, all of which inhibited starch aging and the lowest enthalpy of aging was found in samples with 1% glycerol monoester and glycerol.

Fadda et al. concluded that emulsifiers indirectly hindered starch aging by decreasing the dough’s ability to absorb water and swell, allowing more water to be transferred to proteins and making the dough fluffy and soft.

Yu et al. added stearic acid and sodium alginate to wheat starch, which increased the initial temperature of pasting and effectively inhibited starch aging.

Li Lihua et al. investigated the effects of two emulsifiers, sodium stearoyl lactate and β-cyclodextrin, on the anti-aging of fresh wet noodles, and came to a new conclusion that the straight-chain starch-emulsifier-lipid complex inhibited the aging of fresh wet noodles.

Add hydrocolloids
Hydrocolloids are mostly water-soluble natural polysaccharide macromolecules and their derivatives, which can form viscous solutions or gels when fully hydrated under certain conditions, and this characteristic makes them play a special role in foodstuffs, such as texture improvement and water control. Common food hydrocolloids include guar gum, xanthan gum, carrageenan and so on.

In general, hydrocolloids promote short-term aging and retard long-term aging mainly by affecting the interactions between straight-chain starch-straight-chain starch and branched-chain starch-branched-chain starch, and the inhibition of starch aging by hydrocolloids depends largely on the size of hydrocolloid concentration.

He Chengyun et al. investigated the anti-aging effects of xanthan gum, sodium alginate and carrageenan on steamed bread, and the optimal compound ratio was obtained by orthogonal experiment.

Ai et al. added three types of additives, namely enzyme, emulsifier and hydrocolloid, to rice cakes, and the comparison revealed that sodium alginate was the only additive that significantly reduced the hardening rate of rice cakes during storage.

Liu Haiyan et al. concluded that the moderate addition of colloids can significantly increase the specific volume of bread, improve the textural properties of bread, and effectively inhibit bread aging. However, no general conclusions have been drawn about the effect of hydrophilic colloids on starch aging.

Fourth, add modified starch
Different kinds of modified starch play different roles in the quality of cereal products, and the appropriate amount of modified starch can delay aging and improve product quality. Some modified starch is often introduced into modified hydrophilic groups, such as acetate, hydroxypropyl, etc. These hydrophilic groups can control the flow of water and exudation in the system; at the same time, they can also hinder the dehydration and condensation of the hydrogen bonding between starch molecules, thus delaying the aging.

In addition, some modified starches (e.g., potato modified starch) have good processing characteristics, such as good water retention, large swelling capacity, good low-temperature stability, and mild taste, which can not only delay the aging of cereal products, but also improve their quality.

Xie Shaomei et al. found that pregelatinized potato modified starch could improve the quality of bread, and with the increase of its addition, the anti-aging effect showed a tendency of increasing and then decreasing, but the reason for the trend was not studied.

Huang Li et al. studied the effect of hydroxypropyl di-starch phosphate (HPDSP) on the long-term aging characteristics of fresh and wet instant rice noodle, and found that the peak hardness of the sample group with the addition of 15% HPDSP decreased by 46.9% compared with that of the blank group; the relative crystallinity of the sample group was 2.22%, which was much lower than that of the blank group (10.17%); and the enthalpy of regeneration of the sample group decreased to 1.28 J / g, which was 72.1% lower than that of the blank group, showing that HPDSP could improve the quality of bread, but there was no research on the reason for this trend. 72.1%, it can be seen that HPDSP can significantly delay the aging of fresh and wet instant rice noodles.

V. Non-starch sugars
Non-starch sugars have an effect on the aging of cereal products by interacting with starch molecules to form complexes, or through the difference in water holding capacity of starch.Zeng et al. found that oligofructose has a good effect on the aging of wheat starch to slow down the aging of wheat starch.

Banchathanakij et al. found that different sources of β-glucan can delay the aging of rice starch, and the mechanism of delaying aging is to absorb water, which weakens the movement of starch molecules; the effect of different sources of β-glucan in delaying aging is different, and the β-glucan from barley and oats can be dissolved in water, which can hinder the starch molecules from moving to a greater extent, so it has a better effect on delaying aging.

Klinmalai et al. found that chitosan had no effect on the moisture content of rice noodles, but reduced their pH and whiteness, delayed the increase of hardness and viscosity of the rice noodle gel, and effectively maintained the adhesion and elasticity of the rice noodle gel. In addition, dietary fiber can also delay the aging of cereal products.

Six, other anti-starch aging methods
In addition to the use of traditional additives to achieve the anti-aging effect, there are some physical, biological and other methods can also be achieved. Zhang et al. studied the effect of tea polyphenols, tea water-soluble extracts, tea polysaccharides and green tea powder of four kinds of tea derivatives on the aging of wheat starch, and the results show that the four substances on the short-term aging of wheat starch and the long-term aging of wheat starch have inhibition effect.

Chunyuan Zhang studied the aging effect of tea polysaccharides on wheat starch and obtained the same results.Niu et al. studied the inhibitory effect of rice bran protein hydrolysate on rice starch. Xu Chen et al. added 5% proanthocyanidins to corn starch well inhibited starch aging.

Niu et al. obtained that porcine plasma protein hydrolysate has potential inhibitory effect on short-term aging of corn starch. Tian Yaoqi inhibited the aging of rice starch using ultrahigh pressure technology.

Xia Wen et al. used ultra-micro-milling technology to destroy the surface structure of cassava starch granules, which had a certain delaying effect on its short-term aging. There are also some applications of composite additives, which can effectively play the complementary role of various food additives, and compared with the addition of a certain single additive, it has a better flavor and texture, which is more easily accepted by consumers, and the effect of starch anti-aging is also better.

Therefore, the use of anti-aging agents and the research of new anti-aging agents are of great significance to inhibit starch aging.

This paper focuses on starch aging and the effect of different additives on regulating starch aging, starch aging is an irreversible process, which will have a great impact on food quality, starch modification is a very complex system, the current research is still very limited, and still use the traditional ways and methods, with the passage of time, these methods can not keep up with the development of the needs of the development, so there should be some new investigations and studies appear! .

Some aspects of inhibiting starch aging by adding different substances are still controversial, which requires research on the internal structure of starch to gain a deeper understanding of the aging mechanism, which is also the direction of future development.