| Soybean meal as a plant source protein,high protein content and suitable amino acid ratio,has a high development and utilization value.At present,soybean meal is mainly fed directly to animals as feed,in which the soybean antigenic protein and anti-nutritional factors,greatly limit the digestion and absorption of soybean meal protein by animals.Enzymatic digestion of soybean meal overcomes the defects of soybean meal itself,improves the digestibility of the protein,reduces its allergenicity,and produces soybean small peptides with better functional properties.Soybean small peptides are mainly composed of 2～3 amino acids,and the molecular weight is mainly distributed in the range of 150～500 Da.Soybean small peptides are easier to be digested compared with intact proteins or free amino acids,and also have biological activities such as blood pressure regulation,inhibition of chronic kidney disease,immunomodulation,anticancer activity,antibacterial and antiviral,improvement of intestinal microbial activity,cholesterol reduction and antidiabetic,which are the best sources of protein absorption and utilization for human.This experiment intends to initially use physical and chemical methods to change the protein structure,and then use complex enzymes to enzymatically digest soybean meal to prepare peptides with a high percentage of small peptides to enhance the quality and nutritional value of soybean meal peptides.The main studies are as follows.(1)Semi-solid and liquid enzymatic methods were used to enzymatically digest soybean meal using five proteases: alkaline,papain,pancreatic,horn and neutral.The hydrolysis degree and peptide yield of soybean meal were changed by adjusting the enzymatic temperature,liquid-to-solid ratio,soybean meal volume,time,pH and enzyme addition,and the enzymatic results were optimized by single-factor and response surface experiments to achieve the optimal enzymatic conditions.It was found that the best enzymatic effect of trypsin in the semi-solid state enzymatic digestion was achieved: the highest peptide yield of 18.87% was obtained when the amount of soybean meal was 30 g,the liquid-solid ratio was 1 mL/g,the reaction temperature was 50 ℃,the hydrolysis time was 36 h,and the enzyme addition was 40mg/g;the best enzymatic effect of alkaline protease in the liquid state enzymatic digestion was achieved: the liquid-solid ratio was 14 mL/g,the reaction temperature was 50 ℃,the hydrolysis time was 11 h,and the enzyme addition was 50 mg/g.The highest peptide yield was obtained when the enzyme addition was 50 mg/g and the initial pH was 11,and the final peptide yield was 26.62%.(2)Soybean meal was treated with different power and time of ultrasonic extraction,different time and temperature of preheating,and different concentration of ethanol extraction as physicochemical methods to allow better solubilization of soybean proteins,to destroy and change the molecular structure of soybean proteins,and to enable better enzymatic digestion of soybean meal proteins by proteases.The results showed that the hydrolysis degree and peptide yield of soybean meal could be changed more significantly by heating soybean meal at 80 ℃ for 4 h;ultrasonication at 90 w for 20 min;and ethanol extraction at 40%.(3)Activated carbon with different content,temperature and time was used to decolorize and remove bitterness from the enzymatic digest,and the complex enzymatic digest was used to reduce the hydrophobic value of the enzymatic digest,improve the unpleasant flavor of the digest and enhance the flavor and sensory of the product.Using DA201-C macroporous adsorption resin,the enzymatic digest was desalted to achieve better desalination and higher peptide retention by changing the adsorption time and desorption solution.In the decolorization process,1.0% activated carbon decolorization was able to achieve 67.6% decolorization rate and 87.1%peptide retention rate.The best results were obtained by decolorization at 70 ℃ for40 min.In the desalination process,the highest desalination rate of 97.4% was achieved for the alkaline protease enzyme digestion product,and the desalination rates of the remaining enzyme digestion products were all higher than 90%,the peptide recovery was above 87%,and the desaccharide effect was about 20%.(4)The optimized pretreatment method and enzymatic conditions were used to compound enzymatic digestion of soybean meal,and the enzymatic effect of compound enzymatic digestion was investigated by molecular weight,hydrophobic value,antioxidant activity and amino acid content.The results showed that the composite enzymatic digestion of soybean meal had the advantages of high active substance,high percentage of dipeptide and tripeptide content,outstanding peptide conversion,palatable flavor and strong sensory.Among them,trypsin+neutral+alkaline protease had the best hydrolysis effect,with the degree of hydrolysis and peptide yield of 39.8% and 36.9%,respectively;the hydrolysis products contained the highest content of Glu and Asp,and also contained the seven essential amino acids;the highest content of dipeptide and tripeptide in horn+neutral+alkaline protease,reaching 49%.In the analysis of the activity of the enzymatic products,the enzymatic reaction involving trypsin had outstanding iron reduction ability;the scavenging ability of DPPH of the enzymatic products of trypsin + neutral + alkaline protease was at 34.4%,and the scavenging rate of superoxide radicals was 24.69%,which was at a high level;the scavenging ability of hydroxyl radicals was not much different among various enzymatic products,which were all around 30%.It was also found that neutral protease played an important role in the removal of bitterness and the color of finished soybean meal peptides. |
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