Research and Progress in the Application of Feed Proteases

Protein, carbohydrates, and fats are the three main constant nutrients that provide animals with the energy and essential nutrients needed for growth. Taking protein as an example, amino acids are the essential nutrients required, which are also necessary for the body and all biological metabolic processes.

Alkaline protease enzyme has a wider substrate specificity

Protein is a polymeric form of amino acids, composed of 20 different natural amino acids. For living organisms, amino acids are the most important building blocks of life. Amino acids are connected by peptide bonds to form polymeric structures called peptides. Based on the length of their peptides, they can be classified as short-chain peptides (oligopeptides, consisting of two to three amino acids), medium-chain (polypeptides), and long-chain peptides (proteins). The role of a protease enzyme is to hydrolyze the peptide bonds that connect amino acids and degrade proteins into polypeptides, oligopeptides, and even free amino acids. The dietary protein ingested by animals is first hydrolyzed into medium-chain polypeptides in the gastrointestinal tract, then further hydrolyzed into oligopeptides, tripeptides, dipeptides, or free amino acids. Free amino acids, dipeptides, and tripeptides are directly absorbed by the small intestine through the transport factors on the epithelial cell membrane of the small intestine, and finally enter the bloodstream.

The first protease enzyme to hydrolyze dietary protein in the gastrointestinal tract (also known as the digestive tract) is pepsin. Pepsin is secreted by the stomach of pigs or glandular stomachs of poultry. It belongs to acidic proteases and is activated and exhibits activity below a pH of 5.0, with the highest activity in low pH environments. In addition, although pepsin has broad substrate specificity, due to the limited time that dietary protein stays in the stomach and the fact that not all proteins can be effectively hydrated and dissolved in a low pH environment, dietary protein cannot be well hydrolyzed here.

Alkaline protease enzyme produces digestible peptides

In addition to the broad substrate specificity mentioned above, in vitro experimental results have also shown that alkaline proteases can hydrolyze protein in feed raw materials earlier, releasing peptides and nutrients that are enveloped and absorbed in the stomach and anterior intestine. Under low pH conditions (such as pH 3.7) in the stomach and upper digestive tract (duodenum), on an equal weight basis, alkaline protease hydrolyzed the substrate to produce an amount of small peptides (molecular weight below 3500 daltons) that is close to that produced by pepsin of equal weight. If protein hydrolysis activity can be exerted earlier in the stomach and intestine, protein anti-nutritional factors can be quickly processed by hydrolysis reaction, reducing negative effects on protein digestion, and optimizing the timing of hydrolysis of protein substrates. The latest data shows that alkaline protease has 2.8 times the activity of porcine pancreatic enzyme in terms of hydrolyzing oligopeptides and polypeptides, compared on an equal weight basis and based on the total quantity of oligopeptides and polypeptides generated. It can hydrolyze "digestible peptides" with a molecular weight smaller than 1100-1200 daltons, 1.7 times that of porcine pancreatic enzyme under small intestine pH conditions of 6.5. Digestible peptides are oligopeptides composed of ten or less than ten amino acid residues, with a molecular weight smaller than 1200 daltons. They diffuse more easily into the intestinal mucosal layer and are further degraded into directly absorbable dipeptides and tripeptides by the oligopeptide enzymes combined with the brush border of the small intestine.

To some extent, alkaline proteases can degrade plant protein inhibitors, plant coagulants, and other anti-nutrients, thus reducing the negative effects of these anti-nutrients on the digestion and absorption of feed protein.

Feed protease enzyme plays a very important role: it increases the value of feed raw materials, improves the retention of nitrogen in feed raw materials, improves the negative impact of animal production on environmental sustainability, and ultimately improves production efficiency and producers' profits. As a type of feed protease enzyme, alkaline protease complements internal proteases, including acid gastric enzymes such as pepsin in the acidic environment of the stomach and neutral or alkaline intestinal enzymes such as pancreatic enzymes, trypsin, chymotrypsin, and elastase in the intestinal environment, and can better cooperatively exert the role of a protease.

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