Novel Insights To Anti-oxidant Peptides Manufactured From Caragana Seed's Protein Which Are Available For Retarding Lipid Oxidation

Lipid oxidation has negative effects on food quality,leading to damage to flavor,color and nutrition.Thus,oxidation of lipid-enriched products has to be decelerated.Antioxidant peptides are an alternative,but their applications as oxidation resisitance agents are still limited due to the incomplete mechanism of action of the peptides.Caragana ambigua,one of leguminous plant species,is widely grown in the Three-North Shelterbelt area of China for the improvement of ecological environments.C.ambigua seeds are important plant protein sources and used traditionally as medical herb and animal feed.Its seed contains40%protein in addition to carbohydrate and fat.It is estimated that C.ambigua seeds produce 1965kg/ha protein.However,one of the production problems is that this plant has to be harvested every 3years to make it flourish.Turning the previously low-value C.ambigua seeds into a bio-economic resource would,therefore,be of considerable benefit to both farmers and the industry.This study was designed to investigate the potential of antioxidant peptides manufactured from the protein of C.ambigua seeds in protecting lipid against oxidation using bioinformatics,mass spectrometry,and spectroscopic techniques.The following are main results.1)The optimiziation of antioxidant peptides-producing parameters.C.ambigua seeds'protein was used as source of acidic amino acids for manufacturing antioxidant peptides.BIOPEP database as a bioinformatics tool firstly was applied to screen enzymes responsible for the preparation of protein hydrolysate.The optimal parameters were calcuated in terms of the activity of each antioxidant peptide.Theoretically,papain plus 100 g kg^-1of V-8 protease was regarded as the optimalcombination for hydrolyzing C.ambigua seeds'protein.The optimal parameters for hydrolyzing C.ambigua seeds'protein by the combined enzymes were incubation temperature of 45? for 2 h at pH5.0 with a 10 g kg^-1of[E]:[S].In this case,the inhibition rate of linoleic acid oxidation by C.ambigua seeds'peptide obtained active amino acids residues was 50.30%.2)Identification and purification of a novel decapeptide.The obtained antioxidant peptide purified from C.ambigua seeds'protein was identified as QITEGEDGGG,a novel decapeptide which has not been reported previously.The novel peptide has a superoxide anions scavengeing rate of86.46%,and 60.37%inhibition rate of linoleic acid oxidation.Its antioxidant activity was less affected at p H 3.0-4.0,but lost at p H 9.0-10.0.Heat treat has less effect on antioxidant activity of the C.ambigua seeds'peptide.3)Evaluation of the decapeptide that stops walnut oil from oxidation.Three ways,namely preventing the formation of lipid peroxides,scavenging radicals,and protecting phenolic compounds and polyunsaturated fatty acids of lipid,were used to deal with the potential of the C.ambigua seeds'peptide in retarding lipid oxidation.Compared to the peptide-free walnut oil as control,the peroxide value of walnut oil containing the peptide decreased by 8 meq kg^-1,the oxidation rate of that decreased by 50%,and the content of aldehydes of that decreased by 70%.The acidic amino acids residues are regarded to reduce the pro-oxidation reaction of metal ions by scavenging of oxygen radicals and alkyl radicals.Moreover,the amino acid combination ED in decapeptide is proved to be the key in improving the peptide's activity.Use of the C.ambigua seeds'peptide slowed down the fragment of unsaturated fatty acids in walnut oil,because van der Waals force and hydrogen bond took place between the decapeptide and unsaturated fatty acids.4)Establishement of novel antioxidant-modified technology.The new sequence C₈-ED was obtained by coupling the dipeptide ED with a fatty chain.It was seen that the modified peptides had 4times higher antioxidant activity than its original dipeptide ED.Its emulsification was 36.70%.Morphologically,the modified peptides is a complete spherical gel particle with a fibrous tubular fatty chain.As an antioxidant,the oxidation degree of the cooked flaxseed oil or the flaxseed oil-in-water emulsion was delayed during storage due to the addition of C₈-ED.As a surfactant,its emulsion stability should be the same as Tween-20 if p H of the emulsion was adjusted to 4.0.In summary,this current study provides new insights for the accurate screening of desirable antioxidant peptides technically,and clarifies the mechanism of a novel antioxidant peptide in curbing the oxidation of lipids theoretically.Moreover,this work will contribute more to promoting the ecological and economic benefits of C.ambigua planted largely in the arid region of China by transforming its seeds to value-added bioactive peptide products.