Preparation Of Antioxidant Peptides From Brewer's Spent Grains And Its Composite Film Study

Brewer's spent grains(BSG)as the main by-product of beer brewing,are the main solid waste produced after saccharification and filtration.They are rich in protein,crude fiber and other complex nutrients,and have good physical and chemical properties.In this paper,protein extracted from brewer's spent grains was used to prepare brewer's spent grains antioxidant peptides(BSGPH)by enzyme hydrolysis method.After ultrafiltration,the antioxidant activity of antioxidant peptides of brewer's spent grains with specific molecular weight was measured in vitro,and chitosan composite film was prepared with them as active additives.Firstly,the basic components of brewer's grains were determined,the protein content was 18.94%and the amino acid composition was rich.The protein of brewer's grains was extracted by alcohol-alkali method.The best extraction process was obtained by single factor experiment and orthogonal experiment:The ratio of alcohol-alkali is 1:4,the ratio of solid-liquid is 1:30,the extracting solution was heated for 90 min at 50?.Under these conditions,the protein extraction rate of brewer's spent grains was 70.54%and the protein purity was 58.24%.Using brewer's spent grains protein as substrates,the degree of hydrolysis and DPPH radical scavenging activity of enzymatic hydrolysate as they were used as the evaluation index,the optimal enzyme for preparing the antioxidant peptides from brewer's spent grains was determined to be alkaline protease among four kinds of proteinases.Through single factor experiment and orthogonal optimization,optimum process conditions were determined as follows:enzymatic hydrolysis temperature 46?,E/S 5%,enzymatic hydrolysis time 92min and p H 9.5.Under the conditions,the DPPH radical scavenging activity was 82.47%,and the protein hydrolysis degree could reach up to 30.55%.The antioxidant peptides of brewer's spent grains were ultrafiltered,and the antioxidant peptides with molecular weight less than 10 k Da were intercepted for in vitro antioxidant activity experiment.The results showed that it had strong in vitro antioxidant activity,the IC₅₀values of DPPH radical scavenging rate,ABTS radical scavenging rate and linoleic acid autoxidation inhibition rate were 2.43,0.12 and 1.11 mg/ml,respectively,and the AC_0.5value of reducing ability is 2.16 mg/ml.Finally,the CS/BSGPH composite film was prepared by using the obtained antioxidant peptides less than 10k Da.The mechanical properties,barrier properties,moisture resistance,antioxidant and antibacterial properties of the composite films were studied.With the increase of the content of antioxidant peptides in brewer's spent grains,the basic properties of other composite films were enhanced to a certain extent in addition to the tensile strength.CS/BSGPH composite film was applied to the storage experiment of plant oil to detect the carbonyl value and peroxide value of plant oil during storage.Both of them decreased with the increase of antioxidant peptide content in brewer's spent grains,and decreased significantly compared with unsealed plant oil,indicating that CS/BSGPH composite film can effectively inhibit the oxidation of plant oil.