Study On The Quality Improvement Of Textured Wheat Protein And The Mechanism Thereof

Wheat protein,commonly known as wheat gluten,is a nutrient-rich,safe and edible plant protein.Wheat protein contains considerable hydrophobic amino acids resulting in poor solubility,which leads to the limited application in food processing.The extruded wheat protein presents a fiber texture,which is similar to that of chicken breasts.Thus,textured wheat protein?TWP?can be used as a filler and substitute for meat products.As a result,extrusion can greatly broaden the application of wheat gluten in the food industry.However,textured wheat protein shows worse quality in terms of textural structure compared with meat.In this paper,the effects of additives on the quality characteristics of textured wheat protein were investigated.In order to provide theoretical guidance for the quality control of textured wheat protein,the mechanism of textured wheat protein quality improvement by additive was discussed,furthermore,the inner correlation between mechanism and the quality of textured wheat protein was considered as well.Firstly,the influences of sodium bicarbonate,sodium chloride,sodium tripolyphosphate and monoglyceride on the quality of textured wheat protein were studied.The results showed that with the increase of NaHCO₃ content,the bulk density and the rehydration rate of textured wheat protein increased gradually,the degree of texturization of TWP increased first and then decreased.When the addition of NaHCO₃ was 0.50%,the extruded products displayed the best texturization structure.The addition of NaCl and monoglyceride resulted in bulk density increased and rehydration rate and degree of texturization decreased,which were unconducive to the improvement of the quality.With the addition of sodium tripolyphosphate increased,the color of extruded products became bright and the degree of texturization significantly increased.When the addition of sodium tripolyphosphate was more than 0.50%,resulting in the rehydration rate decreased.Thus,the best addition content of sodium tripolyphosphate was 0.50%.Secondly,the effects of alkali?NaHCO₃,Na₂CO₃ and NaOH?and phosphate?sodium tripolyphosphate,sodium hexametaphosphate,sodium pyrophosphate?on the quality of textured wheat protein were studied.The results showed that compound modification with NaHCO₃ and three kinds of phosphate complexes was more efficient than single additive modification in terms of color,degree of texturization and elasticity of textured wheat protein.The color was lighter and the textured structure was more compact after compound modification than that of control sample.Compared with the other two kinds of phosphate?sodium hexametaphosphate and sodium pyrophosphate?,the effect of compound modification with NaHCO₃ and sodium tripolyphosphate was more obvious.The color was brighter and the degree of texturization and rehydration rate were up to 2.54 and 222 %,respectively.The degree of texturization and elasticity were 2.30².50 and 1.83⁰.92 respectively after extrusion with the addition of sodium tripolyphosphate and alkali?NaHCO₃,Na₂CO₃ and NaOH?.Thirdly,the protein cross-linking in the textured wheat protein added with alkali was investigated.The results showed that the contents of SDS extractable protein were significantly decreased?p<0.05?with the increase of alkali?NaHCO₃,Na₂CO₃ and NaOH?,furthermore,an obvious decrease in the intensity of the protein bands with lower molecular weight was observed in SDS-PAGE patterns,indicating that the alkali promoted protein cross-linking during the extrusion of wheat protein.In addition,when the level of NaHCO₃ was below 0.25%,SDSEPs were approximate to 100% under reduced condition,indicating that low level NaHCO₃ only promoted the disulfide cross-linking.While the addition of NaHCO₃ was more than 0.25%,the SDSEPs obviously decreased,indicating that high level NaHCO₃ induced non-disulfide cross-linking.According to the results of SDSEPs of the textured protein with Na₂CO₃ and NaOH,the degree of protein cross-linking was maximized when the additions of Na₂CO₃ and NaOH were 0.30% and 0.10%,respectively.Under reduced condition,SDSEPs decreased first and then increased with the increment of Na₂CO₃ and NaOH.The results were indicative of obvious non-disulfide cross-linking,but the cross-linking degree was weakened at higher concentration.Additionally,when gluten was extruded with alkali,the content of cystine,lanthionine,dehydroalanine and free sulfhydryl significantly changed,which suggested that the addition of alkali induced the formation of dehydroalanine-derived non-disulfide cross-linking.Finally,the application of textured wheat protein in sausage was studied.The results showed that appropriate amount?<10%?of textured protein did not decreased the elasticity and chewiness of the sausage.When the content of textured wheat protein reached 10%,the sensory evaluation was the best and the most popular.The elasticity,hardness and chewiness of sausage increased significantly?p<0.05?with the degree of texturization of TWP increased,but there were no obvious changes in cohesiveness and gumminess.Compared with the sausage made from commercial textured wheat protein,the homemade sausage was superior in the aspect of elasticity and chewiness.