As an important component of food, starch not only provides the energy necessary for the human body, but also affects the texture, taste, acceptability, and other quality attributes of starch-based foods.
Most starchy foods have undergone some form of processing or cooking, causing the starch to absorb water and swell to form a paste-like system with a certain viscosity. However, in the process of cooling and storage, after the starch molecules are rearranged in space conformation, they will form an orderly and stable gel structure. This phenomenon is called starch aging or retrogradation.
Starch aging usually leads to deterioration of starch food quality, such as texture deterioration, reduced transparency, rough taste, etc., thereby shortening the shelf life of starch foods and reducing consumer acceptance. For example, in steamed bread, bread, and cakes, due to the high starch content, with the extension of storage time, it will turn from soft to hard, loosen the organization, and lose the flavor.
However, the aging behavior of starch is also desirable in certain processing applications. For example, in the production process of breakfast cereals and dehydrated mashed potatoes, starch aging can change the structure and sensory properties of the product, and can form resistant starch. In view of this, how to reasonably control the aging degree of starch and examine the aging characteristics of the system is of great significance for the processing of starchy foods and the improvement of edible quality.
Brief Introduction of Starch Aging and Its Mechanism
The essence of starch aging is a thermodynamic equilibrium process in which partially or completely gelatinized starch molecules gradually transform from a high-energy disordered state to a low-energy ordered state. That is to say, starch molecular chains form an orderly arranged aggregated structure through the combination, arrangement, and aggregation of intramolecular or intermolecular hydrogen bonds.
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 gelatinization, and the leaked amylose molecules undergo directional migration to form a three-dimensional network structure; long-term aging generally takes more than a few weeks, mainly due to the high branching structure of amylopectin. It is strongly inhibited during polymerization, and the aging process is slower. Long-term aging plays a major role in the entire starch aging process and is the main cause of changes in starch system quality.
For non-waxy starch, aging will cause the starch paste to transform into a firm gel with a three-dimensional network structure; for waxy starch, aging will cause the starch paste to form a soft gel, which contains aggregates but does not have a three-dimensional network structure.
Generally, the strength of the starch gel is related to the amylose content. The network structure of amylose can provide the starch gel with elasticity and resistance to deformation, while the soft gel containing only aggregates shows better permeability, stronger viscosity, and cohesion. The decrease in the availability of hydrogen bonds between amylose molecules will destroy the long-range interactions within the soft gel, resulting in a decrease in the cohesiveness of the network structure.
Starch aging is a continuous process that initially involves the rapid recrystallization of amylose molecules and then the slow recrystallization of amylopectin molecules. The aging of amylose determines the initial hardness of starch gel, as well as the viscosity and digestibility of starchy foods. The aging of bread and cakes is related to storage time and starch crystallinity, mainly caused by the aging of amylopectin.
Starch Anti-aging Additives and Control Methods
The aging of starch-containing foods during storage is inevitable. At present, the problem of food aging has not been completely solved in the world. It cannot be completely suppressed, but it can be delayed by effective technical measures.
According to the starch aging mechanism and influencing factors, the following corresponding control techniques can be used to delay aging.
1. Adding Enzyme Preparations
Amylases and proteases are widely used in starchy foods. Amylases are divided into α-amylase, β-amylase, fungal amylase, etc. Among them, the best anti-aging effect is α-amylase. Due to the low molecular weight of dextrin produced during the baking process, α-amylase inhibits the long-term aging of starch by interfering with the aging process of amylopectin. However, excessive α-amylase can make starchy foods sticky, affect the taste, and collapse the structure. Palacios et al. applied α-amylase to rice. As the side chains of amylopectin increased, the aging of rice was inhibited. Chen Qiuping added an appropriate amount of bacterial α-amylase to the steamed bread, which not only improves the sensory quality of the steamed bread, but also inhibits the aging of the steamed bread during storage. The β-amylase extracted from ramie leaves by Dang et al. also has anti-aging effects on starchy foods.
G4 enzyme is a new type of amylase, which can shorten the starch branch chain to produce tetrasaccharides, thereby reducing the length of the side chain of amylopectin. When G4 amylase is used to treat wheat starch, it is found to have a significant anti-aging effect. In addition, enzymes can also be used to decompose bran or gluten proteins, etc., and the decomposition products can be added to starchy foods, which can also play a good anti-aging effect.
2. Adding Emulsifiers
Adding emulsifiers to food can not only delay the aging of starch, but also play a role in preserving freshness. The gelatinized amylose molecule has a double-helical structure. At this time, its interior is hydrophobic, and the hydrophobic group of the emulsifier enters its interior to form an insoluble inclusion complex, which can be indirectly inhibited by inhibiting the recrystallization of amylose The amylopectin is recrystallized and has an anti-aging effect.
Emulsifiers can also delay aging by directly affecting the distribution of water in the food. Adding four emulsifiers to gluten-free can inhibit starch aging, and the lowest aging enthalpy was found in samples with 1% monoglyceride and glycerin.
Fadda believes that emulsifiers reduce the ability of the dough to absorb water and swell, so that more water is transferred to the protein and the dough becomes fluffy and soft, which indirectly prevents starch aging.
Yu adds stearic acid and sodium alginate to wheat starch to increase the initial temperature of gelatinization and effectively inhibit starch aging.
Li Lihua studied the anti-aging effects of two emulsifiers, sodium stearoyl lactylate, and β-cyclodextrin, on fresh wet noodles, and concluded that the amylose-emulsifier-lipid complex inhibits the aging of fresh wet noodles.
3. Add Hydrocolloid
Hydrocolloids are mostly natural polysaccharide macromolecules and their derivatives that are soluble in water. Under certain conditions, they can be fully hydrated to form viscous solutions or gels. This feature makes it have special effects such as texture improvement and water control in food. Common food hydrocolloids include guar gum, xanthan gum, carrageenan, and so on.
Generally speaking, hydrocolloids mainly promote short-term aging and delay long-term aging by affecting the interaction between amylose-amylose and amylopectin-amylose, and hydrocolloids can greatly inhibit starch aging. The extent depends on the size of the hydrocolloid concentration.
He Chengyun studied the anti-aging effects of xanthan gum, sodium alginate, and carrageenan on steamed bread, and obtained the best combination ratio through orthogonal experiments.
Ai added enzymes, emulsifiers, and hydrocolloids to the rice cakes. It was found that sodium alginate was the only additive that significantly reduced the hardening rate of rice cakes during storage.
Liu Haiyan and others believe that adding a proper amount of colloid can significantly increase the specific volume of bread, improve the texture characteristics of bread, and effectively inhibit bread aging. However, no general conclusions have been drawn regarding the influence of hydrocolloids on starch aging.
4. Add Modified Starch
Different types of modified starches have different effects on the quality of cereal products. An appropriate amount of modified starch can delay aging and improve product quality. Some modified starches often introduce modified hydrophilic groups, such as acetate, hydroxypropyl, and so on. These hydrophilic groups can control the flow and exudation of water in the system. At the same time, it can also hinder the dehydration and condensation of the hydrogen bonds between starch molecules, thereby delaying aging.
In addition, some modified starches (such as modified potato starch) have good processing characteristics, such as good water holding capacity, high swelling ability, good low-temperature stability, and mild taste, which can not only delay the aging of cereal products, but also improve their quality.
Xie Shaomei’s research found that pre-gelatinized potato starch can improve the quality of bread. With the increase of its addition, the anti-aging effect shows a trend of first increase and then decrease, but the reason for this trend has not been studied.
Huang Li studied the effect of hydroxypropyl distarch phosphate (HPDSP) on the long-term aging characteristics of fresh and wet instant rice noodles, and found that the sample group with 15% HPDSP added to the blank group had a 46.9% reduction in the peak hardness; The crystallinity is 2.22%, which is much lower than the blank group’s 10.17%; the retrogradation enthalpy value of the sample group drops to 1.28 J/g, which is 72.1% lower than that of the blank group. It can be seen that HPDSP can significantly delay the aging of fresh and wet instant rice noodles.
5. Non-starch Sugars
Non-starch sugars interact with starch molecules to form complexes, or through the difference in the water holding capacity with starch, affect the aging of cereal products. Zeng’s research found that oligofructose has a good delaying effect on the aging of wheat starch.
Banchathanakij’s research found that β-glucans from different sources can delay the aging of rice starch. The mechanism of delaying aging is to absorb water and weaken the movement of starch molecules; β-glucans from different sources have different effects in delaying aging, which come from barley. The β-glucan of oatmeal and oatmeal can dissolve in water and hinder the movement of starch molecules to a greater extent, so the effect of delaying aging is better.
Klinmalai’s research found that chitosan had no effect on the moisture content of rice noodles, but reduced its pH and whiteness, delayed the increase in the hardness and viscosity of the rice noodle gel, and effectively maintained the cohesiveness and elasticity of the rice noodle gel. In addition, dietary fiber can also delay the aging of cereal products.
6. Other Anti-starch Aging Methods
In addition to using traditional additives to achieve anti-aging effects, there are some physical and biological methods that can also be achieved. Zhang et al. studied the effects of tea polyphenols, tea water-soluble extracts, tea polysaccharides, and green tea powder on the aging of wheat starch, and the results showed that the four substances have inhibitory effects on the short-term and long-term aging of wheat starch.
Zhang Chunyuan studied the aging effect of tea polysaccharides on wheat starch and got the same result. Niu et al. studied the inhibitory effect of rice bran protein hydrolysate on rice starch. Xu Chen et al. added 5% proanthocyanidin to corn starch to inhibit starch aging well.
Niu research has shown that porcine plasma protein hydrolysate has a potential inhibitory effect on the short-term aging of corn starch. Tian Yaoqi uses ultra-high pressure technology to inhibit the aging of rice starch.
Xia Wen uses ultra-fine pulverization technology to destroy the surface structure of tapioca starch granules, which can delay the short-term aging to a certain extent. In addition, there are some composite additives that can effectively play the complementary role of various food additives. Compared with adding a single additive, it has a better flavor and taste, and is easier to be accepted by consumers. Starch is anti-aging. The effect 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 article focuses on the effects of starch aging and different additives on regulating starch aging. Starch aging is an irreversible process that will have a huge impact on food quality. Starch modification is a very complex system, and current research is still limited. The traditional methods are still used. As time goes by, these methods have been unable to keep up with the needs of development, so some new investigations and studies are needed.
It is still controversial in some aspects to inhibit starch aging by adding different substances. This requires studying the internal structure of starch to gain a deeper understanding of the mechanism of aging, which is also the direction of future development.
