Functional And Structural Properties Of Cottonseed Protein And The Antioxidant Activity Of Peptides

Cottonseed meal rich in protein is a co-product of the cottonseed oil processing industry.The variety of cotton,planting environment,and oil extraction process impact on the development and utilization of cottonseed meal directly.Therefore,it is necessary to investigate structural and functional properties of proteins and antioxidant activity of peptides.The results can be used to provide theoretical basis and guide for the development and utilization of cottonseed meals.In this paper,four kinds of hot-pressed solvent extraction cottonseed meal?HCM?,two kinds of cold-pressed solvent extraction cottonseed meal?CCM?and subcritical fluid extraction cottonseed meal?SCM?had been selected as the specimens and peanut meal and soybean meal?cold-pressed solvent extraction?as control material to systematically analyze the physicochemical properties of flours.Then cottonseed protein isolated by ultrasonic-assisted alkaline extraction method study the ultrasonic treatment parameters on the extraction yield,as well as the structural and functional properties of proteins.Hydrolyzed and fermentation peptides of HCM and CCM were investigated antioxidant capacity,then the high antioxidant capacity of peptides were isolated,purified and sequenced.The main conclusions are as follows:?1?The protein content of HCM were 56.23%⁶0.86%,which were lower than CCM and SCM.And free gossypol content of HCM were 38¹23 mg·kg^-1,which were not detected in CCM and SCM.HCM displayed high?E and bulk density,indicating HCM exhibited dark color,poor dispersibility.SCM showed lowest water absorption capacity and highest oil absorption capacity.Low emulsifying activity and high emulsion stability were observed in HCM.The minimum solubility of cottonseed meals was reached at pH 3.0,and the solubility increased with further increase in pH.The solubility of peanut meal and soybean meal were higher than those of CCM and SCM,and HCM had lowest solubility.?2?The optimum conditions of cottonseed protein by ultrasonic-assisted alkaline extraction were 11.0 of pH,20:1?V/W,m L/g?of liquid-solid ratio,20min of ultrasonic time,45°C of ultrasonic temperature,and 600W of ultrasonic power.Under the optimum conditions,the extraction yield of cottonseed protein was 87.64%.It proved that the model was highly significant?R²=0.9956?and could fit experimental data well and be applied in the prediction of extraction yield of cottonseed protein.Compared with the alkaline method without ultrasonic treatment,ultrasonic-assisted alkali extraction method of cottonseed protein showed shorter time,lower temperature and higher extraction yield.?3?Two major high-intensity bands were found at approximately 50 and 45 kDa for CPIs,and in the presence of?-mercaptoethanol?reducing condition?many additional minor bands appeared between 14 and 35 kDa.The emergence of these minor bands under reducing condition suggests the presence of intermolecular disulfide bond in CPIs.CPIs showed two diffraction peaks at approximately 8.5°and 19.5°.The diffraction profile showed partial crystallinity of the CPIs.Protein gelatinization parameters,such as T_d,and?H,were94.31°C⁹7.72°C,and 3.51⁷.87 J/g,respectively.Proteins of HCM showed relatively more?-sheet?38.3%⁴0.5%?,less?-turn?22.2%²5.8%?and?-helix?15.8%¹9.5%?,indicating the presence of highly denatured protein molecules.The analysis of surface hydrophobicity and intrinsic fluorescence spectra in CPIs of CCM and SCM with high surface hydrophobicity and fluorescence intensity showed a less denatured and more folded conformation.?4?All CPIs presented the minimum solubility and the lowest foaming capacity and foaming stability value at pH 5.0,while the highest foaming capacity and foaming stability value were observed at pH 7.0.Proteins of HCM exhibited lower water/oil absorption capacity than CCM.Proteins of SCM with high water/oil absorption capacity,emulsifying abilities,and foaming capacity/stability,exhibited desirable functional properties due to lesser degree of denaturation.?5?The DPPH·scavenging capacity and total reducing power of the hydrolyzed and fermentation peptides in HCM were higher than that of CCM,while the hydroxyl radical?·OH?scavenging ability,ABTS⁺·scavenging ability and ferrous(Fe²⁺)chelating ability of the hydrolyzed and fermentation peptides in CCM were higher than that of HCM.The DPPH·scavenging capacity,·OH scavenging ability and total reducing power of cottonseed fermentation peptides were higher than that of hydrolyzed peptides,while the ABTS⁺·scavenging capacity and Fe²⁺chelating ability of cottonseed hydrolyzed peptides were higher than that of fermentation peptides.The total reducing power and DPPH·scavenging ability of cottonseed hydrolyzed peptides were stronger than those of peanut and soybean hydrolyzed peptides.?6?Hydrolyzed peptides of HCM were fractionated into three fractions[UF-I??10kD?,UF-II?3kDa¹0kDa?,UF-III?<3kDa?]by using an ultrafiltration?UF?membrane bioreactor system.Among them,UF-III showed the highest antioxidant activity.UF-III was further fractionated with Sephadex G-25 gel into three fractions?F1,F2,and F3?and F3 exhibited the strongest antioxidant activity.F3 was further fractionated with Sephadex G-15 gel into two fractions?F3-1 and F3-2?and F3-2 showed the stronger antioxidant activity.The DPPH·scavenging capacity,·OH scavenging ability,ABTS⁺·scavenging capacity,Fe²⁺chelating ability,and total reducing power of F3-2 were 67.9%,32.76%,57.78%,61.20%,and 0.24,respectively.The amino acid sequence of F3-2 which contains 21 peptide sequences were identified,and the number of amino acids and the molecular weight range of 23 peptide were4¹1 and 307¹148 Da,respectively.