Preparation Of Soybean Protei Isolate-Xanthan Gum-Tea Polyphenols And Its Application In Nanoemulsion

Soybean protein isolate(SPI)is a kind of high-quality plant protein,which is often used in food industry because of its availability,low price,rich nutrition,easy digestion and absorption.However,the stability of SPI is easily affected by environmental factors such as temperature,ion concentration and pH,which limits its application in food processing.In this study,the commercial soy protein isolate was used as raw meterials to prepare the complex added with xanthan gum and tea polyphenol.The effects of different preparation methods on the emulsifying properties of the composites were studied.The mode of combining of the three components and the mechanism of polyphenol binding to protein and polysaccharide were preliminarily discussed.By using the three component complexes as emulsifier,the nano emulsion of flaxseed oil was prepared.In addition,the nano emulsion was further applied to the cream to evaluate the emulsifying properties of three component complex and its antioxidation in food system.The main results are as follows:The ternary composites SPI-XG-TP and SPI-TP-XG were prepared by changing the order of addition and proportion of raw materials.It was found that there were significant differences in the structure and emulsifying characteristics of the two composites.By analyzing the gel electrophoresis patterns,UV absorption spectra and endogenous fluorescence spectra of protein complexes with polysaccharides and polyphenols,it was found that protein and polyphenols and polysaccharides were cross-linked to form macromolecular substances.After reaction,the spatial structure of SPI was destroyed,the natural conformation and the functional properties of the proteins were changed.The nanoemulsions were prepared with the composites by different compounding modes.It was found that the SPI-XG-TP stabilized emulsion had smaller particle size,higher absolute potential and higher emulsifying activity,but the emulsion stability was slightly lower than that of SPI-TP-XG stabilized emulsion in the three component complex.On the basis of SPI-XG binary complex prepared with SPI and XG as raw materials,SPI-XG-TP ternary complex was prepared by changing the concentration of TP.The influence of TP on the bonding mode of SPI-XG was studied by analyzing the grafting degree,carbonyl content,disulfide bond,hydrogen bond and hydrophobic interaction.It was found that the degree of Maillard reaction increased with the increase of TP concentration,the natural conformation of protein was opened,the internal hydrophobic groups were exposed to aqueous solution,and the complex interactions among protein,polysaccharides and polyphenols were formed.Atomic force and particle size analysis were used to observe the appearance of the complex.It was found that the particle size of the ternary complex was smaller and the particle size distribution was more uniform.The addition of polyphenols could make the complex presenting a more compact shape.The flaxseed oil nanoemulsion was prepared by means of SPI-XG-TP complex used as emulsifier and linseed oil was used as oil phase.Taking protein concentration,oil content and ultrasonic power as the influencing factors,emulsifying activity as the evaluation index,the single factor experiment was carried out.The optimum conditions for preparation of flaxseed oil nanoemulsion were as follows:when the protein content was0.81%,the oil content was 9.58%,and the ultrasonic power was 719.54 W,the emulsification activity of nano emulsion reached the highest value at 181.72 m~2/g.Under the optimum technological conditions,the flaxseed oil nanoemulsions were prepared by using different composites.The entrapment efficiency,laser confocal images and their changes in peroxide value of different nano emulsions were compared.It was found that the encapsulation efficiency of nano emulsion prepared by SPI-XG-TP was higher than that of other composites,and the oil droplet distribution was uniform and the particle size was smaller.During storage,SPI-XG-TP could also reduce the peroxide value and inhibit the oxidation of the oil.When the flaxseed oil nanoemulsion was added to the cream powder and then whipped into butter,the whipping property of the butter was improved after adding the complex.The texture and rheological analysis of the butter between different groups showed that there was a certain difference between the texture and rheological properties of the samples.Among the cream samples,the acceptance of milk K and SPI XG TP+E was the highest in sensory evaluation experiment,which showed the greast potential in food applicatiopn.The acid value and peroxide value of SPI XG TP and SPI XG TP+E cream are low and the progress of rancidity is slow in storage.This is because SPI XG TP can inhibit the accumulation of oil droplets and prevent from oil oxidation.TP can also inhibit the growth and reproduction of microorganisms,extending the shelf life of the product,but it has a certain influence on the color of the product.