The physical and chemical properties of peptides are important factors that affect the processing, storage stability, taste quality and the nutritional and biological effects of the final products. In the process of hydrolysis, the degradation of peptide bond results in three main changes. (1) The increase of the number of dissociatable groups (NH4 +, COO -) results in the increase of hydrophilicity and electrostatic charge; (2) the change of molecular structure results in the exposure of hydrophobic residues embedded in the interior; (3) the decrease of polypeptide chain length and molecular weight results in many key parameters of peptide, such as solubility, viscosity, emulsification, foaming, gelling and flavor, etc White is totally different.

However, it is related to the molecular size or DH (degree of hydrolysis), the characteristics of protease used, the physical and chemical properties of mother protein and hydrolysis conditions, and also related to the composition factors of the final product, such as pH value, ionic strength, product type and other components in the product.

Solubility
One of the most important physical and chemical properties of soybean polypeptide is its solubility in a wide range of pH value, temperature, ionic strength and nitrogen concentration. Many scholars have shown that even limited or partial hydrolysis will increase the solubility of the final hydrolysate, especially at the isoelectric point of soybean protein, the soybean protein will form precipitation, but the soybean polypeptide will remain dissolved. The increase of solubility may be due to the decrease of molecular weight of hydrolysate and the increase of hydrophilicity of hydrolysate due to the new dissociative amino and carboxyl groups. The stability of stable protein hydrolysate refers to the thermal stability of products containing hydrolysate, the stability when coexisting with other components and the storage stability.
Even when it was co stored with CaCl2 () in ph3-11 system, 80% of the hydrolysates of whey trypsin with very low degree of hydrolysis (8%) remained soluble after being treated at high temperature for a long time (134 ℃, 5min). At this time, the solubility of protein was very poor. The trypsin and chymotrypsin hydrolysate (2% - 5%) of casein remained stable after being treated at 100 ℃ for 30 minutes. Storage stability is very important for the application of soy peptides in cool drinks.

Soybean polypeptide can strengthen nitrogen in transparent juice drink, and its stability is excellent. Emulsifying property

Many researchers have systematically studied the emulsification of hydrolysates obtained by different enzymes under different hydrolysis conditions. It is generally believed that the emulsification of protein hydrolysates can be improved by properly controlling the degree of hydrolysis (DH). Hydrolysis exposes the hydrophobic residues embedded in the interior, improves the adsorption at the interface, and forms an cohesive membrane. At the same time, hydrophobic residues interact with oil, while hydrophilic residues interact with water.

However, with the increase of hydrolysis degree, the extreme degradation of protein will also lead to a sharp decline in the emulsification of hydrolysates. This is because the molecular weight of hydrolysate is too small. Because peptide chain should have at least more than 20 amino acid residues to have good emulsification. Although small peptides can spread rapidly and adsorb at the interface, they can not fold and orientation as protein at the interface, so they can not effectively reduce the interfacial tension, and small peptides can be replaced by large peptide molecules with stronger adsorption trend at the interface, so the emulsification stability of small peptide molecules is poor. The choice of protease has a great influence on the emulsification and stability of the product.

Turgeonetal. believed that the clustering of hydrophobic residues in the distance (3~5 residues) is necessary for the effective adsorption, good emulsification and interface performance of peptides at the interface. The emulsification and stability of the hydrolysates of hydrophilic amino acid residues and peptide bonds are higher than those of hydrophobic amino acid residues.

Osmolality is the amount of permeable particles dissolved in 1kg solvent, usually expressed as (mOsm / kg). Hyperosmolar solution, i.e. high pressure or high osmolar pressure product, will absorb a lot of water from the small intestine, cause severe diarrhea, even dehydration and damage the electrolyte balance, and also cause nausea, vomiting and abdominal distention.

Obviously, for osmolality, there are: free amino acid > peptide > protein. Therefore, the substitution of amino acids by peptides will greatly reduce the osmotic pressure of the final product and the possibility of causing discomfort. The cleavage of peptide bond in rheological property protein reduces the hydrophobicity of peptide product, increases the net charge, and makes peptide product lack the strict balance between hydrophobicity, attraction and repulsion force when protein gelling. Compared with mother protein (soybean protein), the viscosity of peptide solution drops sharply, and the viscosity of peptide solution is usually not affected by heat treatment, and constant temperature heating will not produce gelling.

Therefore, the production of peptide products can not be restricted by the production of protein products, such as contamination of heat exchangers, pumps, agitators and spray drying, which is of great significance for the production of high nitrogen content products.
Protein restriction enzyme hydrolysis is also an effective method to increase solid concentration before spray drying. In addition, the viscosity of soybean protein increased sharply with the increase of its concentration, but for low molecular soybean polypeptide, the change was very small, even at a high concentration of 50%, it was still full of liquidity. The results showed that when the concentration of soybean protein increased to 10%, the viscosity increased in a straight line, while the viscosity of 30% soybean peptide was the same as that of 10% soybean protein, even when it reached 50%, its fluidity was still good. In addition, about 10% of the aqueous solution of soybean protein will coagulate once heated, while the aqueous solution of soybean polypeptide will not coagulate. (Note: This article is excerpted from the monograph on enzymatic peptide by Zou Yuandong, a world famous peptide scientist)

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Chengdu Shengnuo Biotechnology Co., Ltd. has "Chengdu polypeptide drug engineering technology research center" in Chengdu, mainly engaged in polypeptide, polypeptide drug and beauty peptide research. Our zero defect has passed the FDA certification, and now it has become the first-class professional peptide drug and product development, technology transfer, technical service and peptide drug industry in the scale production and export of China's parks.