Effect Of Physicochemical Pretreatment On Transglutaminase-Set Wheat Gluten And Soy Protein Isolate Mixture Gel

The objective of the research is wheat gluten?WG?and soy protein isolate?SPI?.The effects of physical and chemical pretreatment on the solubility and structure of wheat gluten were studied.The effects of physical and chemical pretreatment on the solubility,structure of soy protein isolate and the properties of gel induced by transglutaminase?TGase?were studied.The TGase-induced gelation properties of WG and SPI mixtures with pretreatment and unpretreatment were investigated.The main conclusions are as follows:?1?Wheat gluten was pretreated with Na₂SO₃,urea,ultrasonic and microwave,solubility results under the condition of optimum pretreatment were figured out as Na₂SO₃ 32.8%,addition of urea 41.96%,addition of ultrasonic 29.4%,addition of microwave 35.6%,while original wheat gluten 15%.The pretreatment all can reduce the particle size of the protein particles,and the ultrasonic pretreatment had the greatest effect on the protein particle size.Except urea pretreatment,the other pretreatments significantly enhanced the surface hydrophobicity of wheat gluten,and the degree of microwave change was the most obvious.Na₂SO₃,ultrasonic and microwave pretreatment had a significant increase in the free SH content of wheat gluten,and the degree of Na₂SO₃ change was the most obvious,the free SH content of wheat gluten increased by 6.5 times.Na₂SO₃ pretreatment improved the ionic bond effect of wheat gluten,and urea,ultrasonic,microwave pretreatment reduced the hydrophobic interaction.Fourier transform infrared spectrometry?FTIR?analysis of wheat gluten showed that Na₂SO₃,ultrasonic and microwave pretreatment increased the content of?-helix and random coil,and decreased the content of?-sheet.?2?Soy protein isolate?SPI?was pretreated with sodium sulfite,ethanol,ultrasonic and microwave,the changes of solubility and structure were investigatied,and the properties of gel induced by TGase were studied.The results showed that pretreatments could increase solubility and reduce particle size,and the degree of microwave change was the most obvious.Ultrasonic,microwave and sodium sulfite pretreatment had a significant increase in the free SH content of SPI,and the sodium sulfite was the best pretreatment.Except ethanol pretreatment,the other pretreatments significantly enhanced the surface hydrophobicity of SPI,followed by microwave treatment,sodium sulfite treatment,ultrasonic treatment.Ethanol pretreatment significantly increased hydrogen bonding.Sodium sulfite,ultrasonic and microwave pretreatment reduced the hydrophobic interactions.Pretreatment reduced the content of?-helix of SPI,increased the content of random coil,and the more obvious physical pretreatment act.SPI gels induced by TGase could be promoted by pretreatment,and the gel had denser and more uniform microstructure when compared with the untreated gel.When treated by microwave,the gel strength and water-holding capacity?WHC?were 278.33g/cm² and96%,respectively.?3?Wheat gluten and soy protein isolate were added with TGase after Na₂SO₃/microwave pretreatment to make mixed protein gel,TGase?10,20,30,40,50,60 U/g?significantly improved the gel strength,water holding capacity?WHC?and storage modulus?g'?values of WG/SPI gels.When TGase concentration reached 50 U/g,the gel strength was 600.3 g/cm²,which was 3.8 times higher than the unpretreated gel,and WHC was 93%.Moreover,the TGase crosslinking reaction reduced the soluble protein content of protein and hydrophobic interaction and promoted the formation of disulfide bond,thus reducing the content of free SH group.The intermolecular forces that form the network structure of WG/SPI gel include the covalent interaction??-??-glutamyl?lysine bond,disulfide bond?and noncovalent interactions?ionic bond,hydrogen bond,hydrophobic interaction?.In addition,secondary structure studies showed that Na₂SO₃/microwave pretreatment reduced the content of?-sheet and random coil of TGase-induced gels,but increased the content of?-helix and?-turn.Results from scanning electron microscopy?SEM?indicated that TGase promoted the formation of a compact and homogeneous WG/SPI gels,and the pretreated TGase-induced gel was smoother and the network structure was denser than that of untreated gel.