Study On The Emulsifying Property Of Pea Proteins And Its Influencing Mechanism

Pea protein,a kind of plant protein with high nutritional value,has many advantages,including the wide source,low cost,not easy to cause allegy,as well as the well-balanced amino acid profiles.Thus,the application of pea proteins has a good prospect.The emulsifying property is one of the important functional properties of pea proteins.This paper aimed at investigating the emulsifying properties of pea proteins and the molecular mechanism that affects the emulsifying properties in order to provide theoretical foundation for the application of pea proteins as a natural emulsifier in food.First and foremost,key factors including protein concentration,pH,ion strength and heat treatment temperature,were investigated for their effects on the emulsifying properties of pea proteins.To achieve this,pea protein powders were used to prepare emulsions with soy bean oil by homogenizing technique.Parameters of the emulsions studied included the particle size distribution,flocculation index,microstructure,heat stability and storage stability.The results indicated that when protein concentration was higher than 10.0 mg/mL,pea proteins had a good emulsifying ability,could effectively inhibit the flocculation of emulsions.In addition,pea proteins could the oil droplets at pH 5.0.At pH 7.0 and pH 9.0,pea proteins had a good emulsifying ability.Salt ions,such as Na~+and Cl~-,had a negative influence on the emulsifying properties.After heat treatment at 90?,the emulsifying ability and stability improved.Secondly,the solubility,composition and structure of pea proteins were investigated,and the results indicated that pea protein powders obtained by spray drying were partly denatured,and the solubility was poor.The emulsifying ability of pea proteins at different pH or ionic strength were mainly affected by the solubility.The emulsifying property of pea proteins after heat treatment at different temperature were affected by the solubility,protein aggregates,and surface hydrophobicity.In addition,to increase the efficiency of the application of pea proteins,the emulsifying ability of pea proteins extracted at 90?was studied,and the results showed that the soluble proteins had a good emulsifying ability:when protein concentration was 10.0mg/m L,pea proteins had the best emulsifying ability,while the average diameter of oil droplets was less than 0.60?m.To investigate the effects of soluble protein aggregates on the emulsifying properties,the emulsifying properties of pea proteins soluble at different temperatures were studied.The results indicated that,at the same protein concentration,compared with the proteins soluble at 30?and 60?,the pea proteins soluble at 90?had a slightly poor emulsifying ability,but the emulsions had a higher viscosity and elastic modulus,which increased the stability of emulsions.Thirdly,in order to study the molecular mechanism that affected the emulsifying properties,the interfacial adsorption properties of pea proteins were investgated.The results indicated that the insoluble fraction had a negative effect on the interfacial adsorption,while the competitive adsorption components of pea proteins,including aggregates,vicilin and legumin,further affected the emulsifying properties.When protein concentration was within 1.0 to 30.0 mg/mL,with the increasing of concentration,there were more proteins adsorped to the water-oil interface,and protein aggregates were losing the superiority in competitive adsorption,while the proportion of vicilin and legumin increased.When protein concentration was higher than20.0 mg/mL,the interfacial adsorption would reach the saturation state,and there were more vicilin than legumin in surface proteins,while the proportion of aggregates was very low.The proportion of vicilin was higher than 45.30%,while the proportion of aggregates was less than16.31%.Although the proportion of aggregates increased to 37.21%when the heat treatment temperature was increased to 90?,the soluble vicilin and legumin could adsorbed to the interface at a fast speed and improved the emulsifying ability greatly.Also,the interfacial adsorption properties of pea proteins soluble at different temperatures were studied.The results showed that,proteins soluble at 90?could stabilize larger water-oil interface area and make the interfacial membranes more tight.When the extraction temperature increased from 30?to90?,there were more soluble aggregates affecting the adsorption of vicilin and legumin on the interface,but increased the interfacial elastic modulus,which improved the emulsifying stability.Meanwhile,to study the interfacial adsorption property of insoluble fractions,pea proteins were pre-treated by homogenizing technique,and then were used to prepare emulsions.The results indicated that at low protein concentration,the insoluble fraction adsorbed to interface in the form of big particles,and when there were enough proteins,the soluble fraction,together with the insoluble fraction,which had been treated into smaller particles,could cover and stabilize the oil droplets well.