Application of Amylase in Animal Feed

Starch is the main source of animal energy, with 60% to 80% of animal energy coming from starch in feed. Starch enzymes are key enzymes for the digestion and absorption of starch. Adding starch enzymes to feed can improve animal digestion and absorption of starch, improve production performance, and increase feed utilization.

Types and mechanisms of starch enzymes used in animal feed

The different amounts and ratios of amylose and amylopectin in straight-chain and branched-chain starches affect the speed and completeness of starch digestion in animals. Studies have found that the higher the proportion of straight-chain starch, the worse the performance of starch digestion. In vitro digestion experiments have also shown that the proportion of straight-chain starch has a significant effect on the formation of resistant starch. Among the same types of starch, the higher the proportion of straight-chain starch, the higher the proportion of resistant starch. The digestive speed of corn with different proportions of straight-chain starch is: glutinous corn > ordinary corn > high straight-chain corn, indicating that straight-chain starch is more difficult to digest than branched-chain starch. This is mainly because the side chains of straight-chain starch molecules are longer than those of branched-chain starch, and the hydrogen bonds connecting glucose chains are stronger, making straight-chain starch more difficult to be acted upon by starch enzymes.

Starch enzymes are key enzymes for starch digestion and absorption

The digestion and absorption of starch by animals mainly rely on the hydrolysis of salivary amylase enzyme and pancreatic amylase enzyme secreted by themselves. Salivary amylase is an α-amylase secreted by salivary glands. Its optimum pH is 6.8, and it mainly hydrolyses the α-1,4 glycosidic bonds in starch chains. Salivary amylase enzyme can decompose starch into maltose and dextrin in small amounts. However, feed stays in the oral cavity for a short time, and starch enzymes have little digestive function in the oral cavity. Pepsin is not present in pig gastric juice, but there is still a certain degree of starch digestion in pig stomach, which mainly depends on salivary amylase enzyme and starch enzymes contained in plant feed. When the pH in the stomach drops below 5.0, the environment is no longer suitable for salivary amylase to function, and salivary amylase enzyme itself will also be hydrolyzed by gastric protease and lose its activity.

Application of starch enzymes in animal feed

The rumen of adult ruminants is rich in microorganisms. The starch in feed is fermented and utilized by rumen microorganisms to produce volatile fatty acids, methane, carbon dioxide and other gases, and very little starch enters the intestines. The energy required by ruminants mainly comes from the oxidation of volatile fatty acids. The application of starch enzymes in the feed of ruminants is rarely reported. Before the rumen of young ruminants matures, the digestion of starch still mainly relies on the action of pancreatic amylase enzyme, and adding starch enzymes to feed can supplement the deficiency of endogenous starch enzymes. Fish have poor utilization and metabolic ability for glucose, and mainly rely on the decomposition of protein to provide energy. The enzyme activity is severely destroyed by the high temperature during the production and pelleting of aquaculture feed. The use of starch enzymes in aquaculture feed is also rare. Starch enzymes are mainly used in the feed of monogastric animals such as pigs and chickens.

Currently, the most commonly used starch enzymes in feed are middle-temperature α-amylases. Middle-temperature α-amylase is an industrial enzyme widely used in food, chemical fiber, printing and dyeing industries. Due to the lack of starch enzymes specifically targeted at the digestive physiology of animal gastrointestinal tract in the feed industry, middle-temperature α-amylase is added to feed. The optimum working temperature of middle-temperature α-amylase is 70 to 80°C, and the activity is very low under the conditions of animal body temperature; the acid resistance of middle-temperature α-amylase is poor, and it is seriously inactivated below pH 5.0; its activity is severely damaged by pepsin, so it cannot pass through the stomach and function in the intestines.

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