Study On The Emulsifying Properties And The Emulsification Mechanism Of Limited Enzyme-modified Wheat Gluten

Wheat gluten, the by-products during the production of wheat starch, is thehigh-quality and inexpensive plant-based protein. Due to the presence of hydrophobicamino acids, wheat gluten had poorer functional properties such as dispersion andemulsification which limits its application in the food and non-food industries. Thelimited modification of wheat gluten using acid protease to improve its emulsificationproperties was studied, and the mechanism of the emulsifying property improvementof wheat gluten was preliminarily explored.During the process of wheat gluten hydrolysis, fixed substrate concentration of15%(W/V), the effects of enzyme concentration, time, temperature and pH on theemulsification properties of wheat gluten were studied, and the process condition wasoptimized by response surface test. The transglutaminase (TG) was added on the basisof modification using acid protease at optimal technology to further research on theeffect of TG on the emulsification of wheat gluten by response surface test. Thefunctional properties of raw material and hydrolysates prepared by spray drying weredetermined and compared. The fundamental physical properties and the changes inprotein structure of the hydrolysates prepared by six different technologies weredetermined to explore the relationship between structure and function. The followingresults were obtained.The emulsifying capacity of wheat gluten increased after enzymatic hydrolysis,and the effect of the various factors on emulsion stability of hydrolysates changedlittle.The optimal reaction conditions of acid protease were that substrate concentration15%, the protease usage (E/S)1.60%, pH3, the temperature48.9℃and the reactiontime2.5h. The theory emulsifying capacity of wheat gluten hydrolysate was60.25m2/g,and the emulsification significantly improved.The optimal reaction conditions for the subsequent transglutaminase (TG) werethat the protease usage (E/S)5‰, pH7, the temperature50.8℃and the reaction time2.5h. The theory emulsifying capacity of wheat gluten was59.41m2/g.Transglutaminase treatment could not improve the emulsification of the wheat glutenhydrolyzate further.The solubility, emulsification, hygroscopicity, water holding capacity and oil holding capacity of wheat gluten after hydrolyzed by acid protease were significantlyincreased compared with the raw material. But there was no significant change in thestability of the emulsion. The foamability and foam stability of wheat gluten afterhydrolyzed by acid protease were all reduced, but the foamability and foam stability ofwheat gluten after hydrolyzed by acid protease and transglutaminase were all increased.The physical properties of hydrolysates were studied. It was found that there wasno close relationship between viscosity and emulsification. The conductivity also hadnothing to do with emulsification, but it is related with ash content. The greater theemulsifying power of hydrolysates was, the lower the critical micelle concentration ofwheat peptides was.Total content of amino acid before and after enzymatic hydrolysis was almostunchanged. Emulsifying property of wheat gluten is affected by the molecular weightdistribution. The emulsification of wheat gluten hydrolyzed by acid protease is well,which has higher content of medium molecular weight and other relatively equalmolecular weight distribution of peptides that can contribute to the improvement ofrheological properties of Interfacial film. The degree of hydrolysis of wheat gluten thathas high emulsification was controlled to about5%.It was found that secondary structure of wheat gluten was dominated by β-foldingby Fourier infrared spectrum technology. The content of β-folding of wheat gluten wassignificantly increased and the content of α-helix and β-sheet of wheat gluten wassignificantly reduced after hydrolyzed by acid protease.The total thiol content of wheat gluten was almost the same before and aftermodified by acid protease. The disulfide content of wheat gluten was increased and thefree thiol content was reduced after modification, which is due to the conversionbetween disulfide and thiol. The ratio of thiol and disulfide controlled within a certainrange may play an important role to improve emulsification of wheat gluten.