Construction Of Tartary Buckwheat Protein-Xanthan Gum Complex And Its Application In Pickering Emulsion

Pickering emulsion is a stable emulsion with solid particles instead of traditional emulsifiers,which has the advantages of strong stability,environmental friendliness,and high added value.In recent years,people are more and more interested in food grade particle stabilized Pickering emulsion due to its great potential in functional food,improving freeze-thaw stability and regulating processing characteristics of food.Compared with common non-protein groups(such as starch),protein-based particles have good hydrophilicity and lipophilicity,do not need too much surface modification,have the potential as natural emulsifiers,and have more advantages as Pickering stabilizers.As a high-quality source of plant protein,tartary buckwheat protein has balanced amino acid composition and high biological value,and its nutritional quality is superior to grain protein.At the same time,it has good functional properties,good emulsification,and potential to build Pickering emulsion.Therefore,this paper attempts to take tartary buckwheat protein as the research object,use ultrasonic crushing and shear homogenization technology to prepare tartary buckwheat protein nanoparticles,study the basic physical and chemical properties of the nanoparticles,and prepare tartary buckwheat protein Pickering emulsion stabilized by tartary buckwheat protein nanoparticles.However,the emulsification characteristics of tartary buckwheat protein are not ideal,and the stability of the prepared tartary buckwheat protein Pickering emulsion is poor,The interaction between protein and polysaccharide has a great impact on the structure and functional characteristics of protein,and is often used as an effective means to modify the structure of protein.Therefore,this topic takes tartary buckwheat protein as the research object,introduces xanthan gum to prepare tartary buckwheat protein xanthan gum complex,increases its emulsification,improves the stability of Pickering emulsion stabilized as a stabilizer,and determines the optimal ratio of tartary buckwheat protein and xanthan gum composite;The interaction mode of tartary buckwheat protein and xanthan gum in aqueous solution and emulsion was explored in order to improve the emulsification characteristics of tartary buckwheat protein and expand its application in food.The specific research contents and results are as follows:(1)Tartary buckwheat protein nanoparticles were prepared by ultrasonic crushing and shearing homogenization technology.Under suitable ultrasonic conditions(500 W,2 min),heating temperature of 80～100 ℃,pH of far away from the isoelectric point of tartary buckwheat protein,especially at pH 2.0 and pH 7.0,uniformly dispersed,clear and transparent nanoparticle solution with particle size of 97.55～165.2 nm and absolute potential of 27.23～32.3 m V can be obtained.At the same time,it was found that pH and pre-heating temperature had a great influence on the turbidity,average particle size,Zeta potential,surface hydrophobicity,sulfhydryl content,emulsification,etc.of tartary buckwheat protein nanoparticles.With the increase of heating temperature,the surface hydrophobicity and emulsification of tartary buckwheat protein increased,especially the heating temperature within the range of 80～100 ℃,and the effect was better.When the pH is far from the isoelectric point,tartary buckwheat protein has higher emulsification performance.Through spectroscopic analysis techniques(Fourier transform infrared spectroscopy,circular dichroism)and other characterization,it was found that these effects were mainly due to the expansion,rearrangement and aggregation of the secondary structure of tartary buckwheat protein molecules caused by heating and different pH treatments,thus affecting the ordered structure of the protein.(2)By analyzing the average particle size and Zeta potential of tartary buckwheat protein-xanthan gum complex,the pH environment range(neutral or alkaline)and preheat temperature range(80～100 ℃)suitable for the preparation of the complex were selected.Preheating treatment combined with pH had a significant effect on the structure and properties of tartary buckwheat protein-xanthan gum complex.Through the analysis of infrared spectrum and DSC,it was proved that the existence of xanthan gum changed the spatial structure of tartary buckwheat protein,promoted the expansion of the peptide chain of tartary buckwheat protein and the exposure of amino acid residues,increased the hydrophobic interaction between groups,and increased the denaturation temperature of tartary buckwheat protein.SEM results showed that the surface structure of tartary buckwheat protein changed from dense,dense and irregular block to smooth and uniform sponge structure after adding xanthan gum.Therefore,the addition of xanthan gum to tartary buckwheat protein can effectively improve its emulsibility,water and oil retention,and improve its application potential in Pickering emulsion.(3)The effects of the complex containing different xanthan gum concentrations(0 wt%,0.1 wt%,0.4 wt%)and the proportion of oil phase(10%,30%,50%)on the average particle size,Zeta potential,rheological properties,microstructure and storage stability of tartary buckwheat protein xanthan gum Pickering emulsion at different pH(7.0 and 9.0)were screened.The results showed that the emulsion was relatively stable and had good rheological properties under neutral(pH 7.0)conditions.However,compared with the pH 7.0 environment,the alkaline environment(pH 9.0)is more suitable for the preparation of tartary buckwheat protein xanthan gum Pickering emulsion.The proportion of oil phase also has a strong impact on the stability of emulsion.With the increase of the proportion of oil phase,the stability of emulsion increases.The stability results of emulsion show that when the pH is 9.0,the xanthan gum concentration in the complex is 0.4 wt%,and the oil phase proportion is50%,the emulsion prepared at this time has the best stability,smaller particle size,improved emulsification efficiency,stronger rheological properties,uniform dispersion of droplets,and basically the same size.Through observation of microscopic pictures,it is found that tartary buckwheat protein xanthan gum complex firmly wraps the oil phase droplets,The Pickering emulsion prepared at this time has the best stability.