Functional Properties Of Modified Heat-denaturated Peanut Protein From Defatted Flour By Physical And Enzymatic Treatment

In China, most of the defatted peanut flour (DPF), a by-product containing 47–55 % protein, are underutilized in developing countries and only used for animal feed, due to the poor functional properties caused by heat denaturation. The aim of the present study was to modify heat peanut meal protein by enzymatic hydrolysis and physics for improving its functional properties and extending utilization. Physics and hydrolysis modifications were used to modify DPF for improving its functional properties. Main results are as follows:Comparison of the dry roasting and moist heat treatments on peanut protein isolate (PPI) the impact of structural and functional properties. The results showed that the proportion of conarachin in PPI was decreased with heat time and arachin was more heat resistant than conarachin. Heat aggregation or breakdown of arachin during roasting after 30min. Roast and moist heat treatments both decreased sharply the quantity of extractable protein in defatted flour but increased significantly protein solubility of PPI in pH 7.0; the isoelectric point of peanut protein isolate shifted to acidic pH compared with control. The emulsifying properties of PPIs decreased toward 15 min and then increased; moist heat treatment from 0min to 75 min resulted in a decrease in EAI and ESI, while an increase was observed after 75 min. All of samples (including control) could not form the strong gells. On the moist heat treatment samples, the value of foaming capability was increased towards 75 min then decreased. However, for foaming stability, the value first showed a decrease, then an increase.Optimal conditions of heat and alkali extraction of peanut protein, yield of peanut protein was 54.83 %. Compared functional properties of extracted peanut protein, nature peanut protein and Commercial soy protein isolate, the solubility, emulsifying properties and foaming properties of peanut meal protein are significantly better than the other two proteins.The effects of microfluidization on functional properties as well as conformational properties of PPI were investigated by solubility and emulsifying properties, foaming properties, gel properties, DSC, free sulfhydryl and far-UV CD. When the pressure is 120 MPa, the microfluidization led to dissociation of insoluble aggregates, thus improved NSI, EAI and FA of PPI. Free sulfhydryl and far-UV CD spectrum analyses showed that both the tertiary conformation and the secondary structure of the proteins in PPI were nearly unaffected by the microfluidization treatment. DSC analysis indicated the microfluidization-treated PPI samples presented similar Td and?H, relative to that of untreated PPI.Four proteases (alcalase, protamex, pancreatin and papain) were used to hydrolyze heat peanut meal and hydrolytic conditions were optimized. When using protamex to hydrolyze the heat peanut flour, its hydrolysate was modified slightly. The hidrolysate just had a little of low-molecular weight of peptide and most was large-molecular weight of peptide. Compared to the control, the hydrolysates of protamex just had little change of its structure. Hydrolysate of other three enzyme had large change of theirs structure and all had much low-molecular weight peptide. After hydrolyzing, the heat denaturation peanut flour protein which had no sensitive to heat was sensitive to heat. For the function characteristic, some was improved. All the hydrolysates'solubility were over 80 %, and was just little less than the control. Except the hydrolysate of papain, all the hydrolysate had improvement in foamability and the maximum was 140 % which was four times to the control. Although all the hydrolysates'foam stability was over 80 %, it was still little lower than the control. Hydrolysates of protamex whose hydrolysis degree was under 3.4 % and hydrolysates of trypsin whose hydrolysis degree was under 1.76 % had improvement on the emulsibility. But the emulsion stability was worse than the control.Peanut protein concentrate (PPC) was extracted from commercial defatted peanut flour (DPF), a severely denatured byproduct, by combined protease pretreatment and alkali solution with isoelectric precipitation. The effect of proteolysis by Alcalase, Papain and Protamex at various degree of hydrolysis (1-8 % DH) on the yield and functional properties of PPC were investigated. Alcalase was the most efficient protease for hydrolyzing of DPF, followed by Protamex and Papain. Proteolysis remarkably increased the nitrogen solubility of DPF in acidic and basic condition. Enzymatic degradation of acidic subunits (AS) of denatured and insoluble arachin was mainly responsible for the increase of nitrogen solubility index (NSI). Compared with the control, the yield of PPC was significantly increased by enzymatic pretreatment. In terms of the functional properties, PPCs prepared by Papain and Protamex at 4 % or 8 % DH were considered good emulsifiers with emulsifying activity index (EAI) larger than 120 m2/g. For all three enzymatic treatments, foaming capacity (FC) and foaming stability (FS) were significantly improved at various DH (p < 0.05). Alcalase treatment at 1 % DH could remarkably enhance water holding capacity (WHC) to 6.2 mL/g. This study demonstrated that the PP-ASIP method could be a highly effective way to obtain PPC with good functional properties from denatured DPF.