Preparation Of Peptides By Ultrasonic-Assisted Enzymatic Hydrolysis Of Wheat Germ Albumin And The Study On Its Microcapsules

Wheat germ is a part of wheat seed and is very nutritious,containing more than 30% of protein,including essential amino acids.and the biological potency of the protein contained in wheat germ is comparable to that of eggs,which is known as "plant eggs".The glutathione contained in wheat germ affects the baking quality and storage stability of flour,so modern milling processes often extract wheat germ,but it is usually used as feed or processed into primary products such as wheat germ flakes,resulting in the waste of wheat germ albumin and its bioactive peptides.At present,the enzymatic method for wheat germ albumin is mostly at the stage of traditional protease hydrolysis,but there are problems such as long time consuming and low efficiency,and there is less research on microencapsulation of wheat germ peptides.In this study,wheat germ albumin was extracted from wheat germ by water soluble acid precipitation method,followed by hydrolysis of wheat germ albumin by ultrasoundassisted papain;the enzymatic solution of wheat germ albumin was separated by ultrafiltration method,and the physiological activities of wheat germ albumin and different molecular weight peptides were studied;the wheat germ peptides with high physiological activities were microencapsulated,and the microcapsules were characterized and slow release experiments were conducted.(1)Four proteases of alkaline protease,acid protease,neutral protease and papain,were screened using the DPPH radical scavenging rate of wheat germ albumin enzymatic digest as the index.On the basis of single factor,the process parameters of ultrasound-assisted papain hydrolysis of wheat germ albumin were optimized by the response surface,and the physicochemical properties of wheat germ albumin before and after enzymatic digestion were measured.The results showed that the optimum process conditions were enzymatic time 20 min,5% substrate concentration,10000 U/g enzyme addition and 180 W ultrasonic power,and the DPPH radical scavenging rate of wheat germ albumin enzymatic solution could reach81.57% under these conditions.The water absorption,emulsification and solubility of wheat germ albumin were improved after ultrasound-assisted enzymatic digestion,while the foaming,foaming stability and emulsification stability were reduced.(2)Wheat germ protease hydrolysate was separated by ultrafiltration,and then the physiological activity and structural composition of four products,wheat germ albumin,peptides,peptides with molecular weights greater than 3 KDa and less than 3 KDa,were investigated by comparing the superoxide anion radical scavenging rate,reducing power,hydroxyl radical scavenging rate,DPPH radical scavenging rate and ACE inhibition rate of the four samples.The results showed that the peptides with molecular weight less than 3 KDa had higher antioxidant activity and anti-hypertensive activity.The structural composition of the four samples was studied and found that: the peptide bonds of wheat germ albumin were broken after enzymatic digestion,the secondary structure of the protein was changed,and the amino acid composition was also changed.The increase in the content of aromatic amino acids caused the red-shift phenomenon in the endogenous fluorescence spectra of the peptides,indicating that the increase in the physiological activity of the peptides was related to the structural changes.Sequence analysis of the most active peptides yielded the dominant peptide sequences as NIYLNFDALHGDKEHGGVR,TGGDGGPPGKPTT,DVFWIPRHFPFVQ,and EEEDKNDKWHRVE.(3)The process conditions of microencapsulation of wheat germ peptides were optimized by Box-Behnken response surface test on the basis of single factor.The results showed that the optimal process conditions were wall-to-core ratio of 20:1,homogenization time of 10 min,wall material ratio sodium starch octenyl succinate: sodium alginate(SSOS:SA)=3:1,and the microencapsulation rate of wheat germ peptide prepared under this condition was 65.33%.The in vitro digestion of the microcapsules showed that the release rate of the microcapsules in artificial simulated gastric juice was 26.54% and in artificial simulated intestinal juice was84.41%.The effect of slow release was achieved.