Enzymatic Or Glycosylation Modification Of Peanut Proteins And Its Related Structure-Function Mechamism

Peanut protein is one of the most important and underutilized protein resources in China. The aim of this study was to explore utilization means for proteins from peanut protrein. Physiochemical and functional properties of arachin and conarachin fractions was studied and compared, the related mechanism was elucidated. Enzymatic hydrolysis and conjugation with dextran were used to modify peanut protein isolate for improving its functional properties. The possible relationship between structure and functional properties of peanut protein isolate was also discussed. Main results are as follows:Arachin had higher thermal stability, more ordered structure and lower cooperativity of the thermal transition than conarachin. Most of free SH of arachin was buried in the interior while most of them of conarachin was located at the surface. The?H of arachin was remarkable higher than conarachin. The surface hydrophobicity of conarachin was higher than arachin. Compared with conarachin, arachin had the more compacted tertiary conformation. Conarachin had the higher solubility than arachin except at near pI. Conarachin had better emulision ability index, foam capacity and gel properties than arachin.Peanut protein isolate (PPI) was extracted by alkali dissolution and acid precipitation from defatted peanut flour. The effects of extraction conditions on the denaturation and functional properties of PPI were investigated. In comparison with native peanut protein (NPP) which was extracted by ammonium sulfate, the PPI extracted by alkali dissolution and acid precipitation had a higher extent of denaturation. Arachin was affected more easily by the extraction process than conarachin and led to a noticeable decrease of thermal stability of PPI. PPI contained much lower sulfhydryl and disulfide bond contents than NPP. The analyses of intrinsic fluorescence spectra indicated a more compacted tertiary conformation of NPP than PPI. Extraction process influenced the functional properties of PPI, such as protein solubility, emulsifying activity index and foaming capacity. The relatively poor functional properties of PPI might be associated with protein denaturation/unfolding and subsequent protein aggregation.Effects of limited enzymatic hydrolysis by Alcalase on the conformational and functional properties of peanut (Arachis hypogaea L.) protein isolate (PPI) were investigated. Acid subunits of arachin were most susceptible to Alcalase hydrolysis, followed by conarachin and the basic subunits of arachin. Enzymatic hydrolysis increased the thermal stability of arachin and led to a sharp increase of the number of disulphide bonds with a decrease of sulfhydryl group in PPI hydrolysates in comparison with PPI. The analysis of intrinsic fluorescence spectra indicated more loosed tertiary conformation of PPI hydrolysates than PPI. The limited emzymatic hydrolysis improved the functional properties of PPI, such as protein solubility and gel-forming ability, but impaired the emulsifying activity index.Reaction mixtures containing peanut protein isolate (PPI) and dextran (1:1 weight ratio) were dry-heated at 60?and 79% relative humidity for 7 days. SDS-PAGE analysis indicated PPI had become complexed with dextran to form conjugates of higher molecular weight. Arachin, accounting for over 50% of peanut proteins, was hard to glycosylate with dextran, which might limit the extent of glycosylation of PPI. The thermal stability of PPI has been remarkably improved by mixture/conjugation with dextran. Proteins in mixtures/conjugates might have a more compacted tertiary conformation than PPI. The protein solubility of conjugates at pH 4.5–6.0 was remarkably increased compared with the PPI/mixture. Mixture with dextran could significantly improve the emulsifying and foaming properties of PPI (p < 0.05). Conjugation with dextran could further enhance emulsifying and foaming properties of PPI on the base of mixture.Arachin can become complexed with dextran to form conjugates of higher molecular weight. Acid subunits of arachin were earier to glycosylate with dextran than basic subunits. The heat-pretreatment of arachin could not increase the speed of Maillard reaction with dextran. Proteins in mixtures/conjugates might have a more compacted tertiary conformation than arachin, which might limit the extent of glycosylation. The conjugation with dextran could improve the solubility and emulsifying properties of arachin, while it was hard to improve the functional properties of arachin. pretreated by heat.