Effect Of TGase Modification With The Physicochemical Pretreatment On The Wheat Gluten

The low dispersibility and solubility of wheat gluten in aqueous solution limit the crosslinking reaction of Transgluaminase （EC 2.3.2.13 TGase） to enhance its gelation performance, which in turn hamper its applications. The purpose of this study was to determine and optimize the optimal technological parameters of the physicochemical pretreatments and to observe the effect of TGase on the gelation of wheat gluten. Moreover, the structural characteristics of both modified and native proteins （wheat gluten, gladin and glutenin） were investigated by SDS-PAGE, scanning electron microscopy （SEM）, FTIR spectra, circular dichroism （CD）, as well as other techniques. The results suggested that:（1） Sodium sulfite（Na₂SO₃）, urea/Na2SO3 and Na2SO3 pretreatments noteworthily improved the solubility of wheat gluten. After the pretreatment the solubility of wheat gluten were 33.33%（by Na2SO3）,40.89%（by urea/Na2SO3） and 28.84%（by urea）, The physicochemical pretreatments further promoted the solubility and the optimal parameters of the physicochemical pretreatments was determined:concentration of urea（0.5mol/L）, concentration of Na2SO3（800mg/L）, pretreating with urea and Na2SO3 for 30min at 60℃ with ultrasonic pretreatment of which the time and temperature were 60℃,50min, and the final solubility was 45.82%.（2） By single factor and orthogonal experiments, the optimal parameters toseparate wheat gliadin and glutenin were determined:For gliadin, ethanol concentration 65%, liquid-solid ratio 30:1, extraction time 2.5h and temperature 35℃; For glutenin, pH 10, liquid-solid ratio 30:1, extraction time 2.5h and temperature 35℃. In these conditions, the yield of gliadin and gluten was 29.33% and 39.99% respectively.The solubility of wheat gluten was changed after the pretreatments, so was the structure of the wheat gluten. After treatments by urea/ultrasonic, Na2SO3/ultrasonic and urea/Na2SO3/ultrasonic respectively the solubility of wheat gluten increased from 8% to 30%,35% and 48% respectively. After the treatment by urea/ultrasonic, the contents of hydrogen bond of all of the three proteins（gluten, gliadin and glutenin）dropped. When the Na2SO3 was added, the content of ion bonds of the gluten increased, while the content of ion bonds in both gliadin and glutenin decreased. After pretreatment by urea, Na2SO3 and ultrasonic, the hydrophobic interactions of the gluten, the gliadin and the glutenin increased. The contents of disulfide bond of the three proteins decreased when the Na2SO3 was added, but the content of sulfhyedryl （SH） group increased. However, the pretreatment of urea had little effect on the content of the sulfhyedryl group and the disulfide bond of the three proteins. The ratio of small particle protein of the three proteins raised after the pretreatmentby urea, Na2SO3 and untrasonication, and urea/Na2SO3/ultrasonication had a significant effect on the particle of the three protein. The SDS-PAGE results showed that:after the treatment by urea, Na2SO3 and ultrasonication, the optical density of small molecular weight protein of the gluten was increased; the LWM-GS bands was brightened and the HWM-GS bands was dimmed; the gliadin bands were more clear, but the optical density had little change. The SEM result demonstrated that the surface structures of three proteins had more inhomogeneous clusters and pore sizes after pretreatment of urea, Na2SO3 and ultrasonication, and the surface structure was seriously damaged with urea/Na2SO3/ultrasonic treatment. The FTIR and the CD results suggested that the formation of β-sheet structure was one of the major secondary structures of the three proteins and some changes occurred in the pretreatment of the three proteins, with the content of β-sheet decreasing and the content of random coil increasing.（3） The gel strength of wheat gluten increased from 149g/cm2 to 170 g/cm2,254 g/cm2、344g/cm2 and 277g/cm2 respectively after being treated by TGase, urea/ultrasonication/TGase,Na2SO3/ultrasonication/TGaseand,urea/Na2SO3/ultrasonic ation/TGase. After being modified by TGase, the hydrophobic interactions and the content of disulfide bond increased and the content of the sulfhyedryl group decreased. The laser particle size results showed that the ratio of large particle protein of the three pertreated protein raised after being modified by TGase. The SDS-PAGE results indicated that high molecular weight particle that insoluted SDS solution of the pretreated gluten were generated after modificated; the HWM-GS fraction was the major participants in the TGase cross-linking reaction of the glutenin; after the cross-linking reaction, largemolecule ωb-gliadin and the insoluble large-molecule protein were generated. The SEM results declared that the network formed by the wheat gluten was transformed from inhomogeneous clusters and pore sizes to a dense and homogenous structure after the modificationby TGase. The FTIR and CD results demonstrated that:in term of the secondary structure of the three proteins, the β-turn transformed to α-helix and β-sheet, the content of α-helix and β-sheet increased and the content of β-turn and random coil decreased.