The Comparative And Modification Study On The Emulsion Stabilities Between Soybean Protein Isolate And Concentrates

Soybean is a valuable source of plant proteins,which contains a large number of essential fatty acids,phosphorus and calcium,phosphorus and other essential amino acids.Its amino acid composition is close to that of animal protein.The digestion and utilization rate of soybean is more than 90%.In a word,soybean has high nutritional value.Soy protein is also good at emulsifying and gel properties,so can be used to prepare emulsion.However,the poor stability limits its application in food systems.In order to improve the stability of soy protein emulsion,the difference between SPI and SPC emulsion was studied first in this research.Then the stability of SPC emulsion was improved by adding polysaccharide and through ultrasonic assisted enzymatic hydrolysis.Soy protein emulsion was formed firstly by stirring and shearing emulsification,followed by high pressure homogenization.Four factors and three levels orthogonal experiments were designed by four single factors,and the optimized experimental conditions were:SPI emulsion:protein concentration 5g/100mL,oil content 25%,the shear time 30s and the homogeneous intensity 200bar.The SPI emulsion stability was 88.46%in further validation experiments.While at the conditions of protein concentration 4g/100mL,oil content 15%,the shear time 120s and the homogeneous intensity 500bar,the SPC emulsion stability was 58.47%in further validation experiments.The stabilities of the SPI and SPC emulsion were studied,the result showed that no creaming and flocculation were observed for SPI emulsion at all levels of concentration after16 days of storage in 4^oC.For SPC emulsions,however,the flocculation was shown along with the decreasing of protein concentrations.At the same protein levels,the particle sizes of SPI emulsion were all significantly less than that of SPC.Under the optimum preparation conditions,the particle sizes of SPI,SPC emulsions were 281.2nm,600.2nm respectively;and the zeta-potential was-33.9mV for SPI,and-26.2mV for SPC emulsion,SPI emulsion was more stable than SPC emulsion.According to the microcapsule figure by LCSM,it was showed that SPI droplets are dispersed uniformly to embed oil particles with sphere shape.Effect of polysaccharide on the stability of SPC emulsion was studied:Under the condition of pH3.0,soybean polysaccharide or xanthan gum produced better emulsions with the highest emulsion activity 59.07m²/g and the smallest particle size 4.747?m;while at pH7.0,emulsions formed with carrageenan or xanthan gum showed good stabilities with the maximum emulsion activity 87.05m²/g and the smallest particle size 2.375?m.It was also found that no creaming and flocculation were observed with the above emulsions after storage for 16 days at 4^oC.The structure and morphology of the complex emulsions were also studied.According to the microcapsule figure by TEM,it was showed that the polysaccharides were well fixed on the surface of the liquid droplets to maintain the emulsions with excellent long-term stability and dispersion property.Effect of ultrasound assisted with enzymatic hydrolysis on the stability of SPC emulsion was investigated.Comparing with SPC,the enzyme sensitivity of the proteins with pre-ultrasound?400W or 600W?was improved markedly.Ultrasound assisted with enzymatic hydrolysis can also improve the solubility and emulsifying ability of SPC,better than that of enzymatic or ultrasonic modification alone.Solubility of SPC-400W-Pap and SPC-600W-Pap reached 21.67%and 23.43%respectively,SPC-400W-Pap-3.4%and SPC-600W-Pap-3.9%had higher solubility under neutral and acidic conditions.SPC-400W-Pap-2%emulsion showed good stabilities with the smallest particle size 2.375?m,the emulsifying activity41.68%,the emulsion stability 94.57%,the zeta-potential-38.4mV,F_adsds 85.35%and?_sat1.81kg/m³.It was also found that no creaming and flocculation were observed for the above emulsions after storage for 60 days at 4^oC.Effect of ultrasound assisted with enzymatic modification on the structure of SPC was further studied.Comparing with SPC,the structures of the proteins modified with SPC-400W-Pap-2.0%changed as follow:the peak at wave 1450-1540 cm^-1,1620-1670 cm^-1and 3100-3400 cm^-11 enhanced,the proportion of?-strand and random coil increased,the molecular weight decreased,the surface hydrophobicity enhanced,-SH content increased,the-S-S content decreased.In conclusion,ultrasound assisted with enzymatic hydrolysis promoted the extension of polypeptide chain and enhanced its flexibility.As a result,solubility and emulsifying capability of the proteins were improved.