| Wheat gluten is an important byproduct of the wheat starch industry.It is a kind of high quality plant protein with rich amino acids.The utilization of wheat gluten in food industry is limited by its insolubility in water.Glycosylation of protein is a kind of chemical modification,which has the advantages of simple reaction condition,low cost and high safety.In this study,the mechanisms to facilitate the glycosylation of wheat gluten and glucose by ultrasound,microwave and ultra-high pressure(UHP)treatments respectively were studied.In addition,the process conditions,functional and structural properties of wheat gluten were investigated,which may provide theoretical basis for wheat gluten high-value application.Firstly,the process conditions of wheat protein glycosylation by damp-heat treatment were studied.The optimum condition was obtained by using single factor method and response surface analysis.The results showed that the degree of grafting(GD)of wheat protein reached the maximum of 15.47% when reaction temperature/time/pH was 80℃/60 min/10,and the ratio of wheat protein to sugar was 1:1.Ultrasound treatment could facilitate the glycosylation of wheat gluten and glucose.Results suggested that grafting degree and the in-process products content(A294)increased to the maximum of 29.83% and 0.328,respectively at 40 min and then decreased when further increasing the ultrasound pretreatment time whereas the browning degree increased continuously with increasing the ultrasound treatment time.Furthermore,the solubility of ultrasound-glycosylation modified wheat gluten significantly improved at a wide range of pH and reached the maximum value when the ultrasound treatment at 40 min,and the isoelectric point of modified wheat gluten decreased.The emulsification and emulsion stability reached to 56.82 m2g-1 and 36.27 min respectively.In addition,the structure of glycosylated wheat gluten altered.Ultrasound treatment could increase the surface hydrophobicity of wheat gluten and thus its conformation and facilitate the glycosylation.FTIR spectra indicated that the a-halixs decreased concomitance with b-sheets increasing,and the glucose combined to wheat gluten molecules by covalent bonds.SDS-PAGE suggested that there were macromolecules formed in modified wheat gluten,and the gel revealed red glycosylation band after PAS stained,which demonstrated that the glycosylation occured between wheat gluten and glucose.Fluorescence spectra also showed that ultrasound-glycosylation composite modification altered the conformation of wheat gluten.Microwave treatment could improve the glycosylation of wheat gluten and glucose.Results suggested that grafting degree and the in-process products content(A294)first increased to the maximum of 23.75% and 0.702,respectively at 350 W and then decreased with further increasing the microwave power,from 0 W to 700 W,whereas the browning degree increased continuously with increasing the microwave power.Moreover,the solubility of ultrasound-glycosylation modified wheat gluten significantly improved at a wide range of pH and reached the maximum at 350 W,and the isoelectric point of modified wheat gluten decreased.The emulsification and emulsion stability reached to 41.65 m2g-1 and 11.99 min respectively,and antioxidation activity continuously increased with increasing the microwave power.The structural analysis showed that an appropriate microwave treatment could impair the inter-and/or intra-molecular noncovalent interactions and destroy disulfide bonds,which resulted in unfolding wheat gluten structure and increasing the surface hydrophobicity,and therefore facilitating the glycosylation between wheat gluten and glucose.SDS-PAGE revealed that there were macromolecules formed in microwave-glycosylation composite modified wheat gluten,and the gel revealed red glycosylation band after the PAS stained,and the color of the band was the deepest when microwave power is 350 W,which demonstrated that the glycosylation occurred between wheat and glucose.Fluorescence spectra also showed that microwave-glycosylation composite modification altered the conformation of wheat gluten.UHP treatment could improve the glycosylation of wheat gluten and glucose.Results suggested that grafting degree and the in-process products content(A294)first increased to the maximum of 27.44% and 0.313,respectively at 300 MPa and then decreased with further increasing the pressure whereas the browning degree increased continuously with increasing the pressure.Moreover,the solubility of UHP-glycosylation modified wheat gluten significantly improved at a wide range of pH and reached the maximum at 300 MPa,and the isoelectric point of modified wheat gluten decreased.Compared with the vital wheat gluten,the emulsification and emulsion stability increased by four times and three times respectively,and the reducing activity and DPPH free radical scavenging ability continuously increased with increasing the pressure.The structural analysis showed that an appropriate UHP treatment could weaken the inter-and/or intra-molecular noncovalent interactions,which resulted in unfolding wheat gluten structure and thus exposing the hydrophobic groups and increasing the surface hydrophobicity.SDS-PAGE revealed that there were macromolecules formed in UHP-glycosylation composite modified wheat gluten,and the gel revealed red glycosylation band after PAS stained,and the color of the band was the deepest when the pressure is 300 MPa,which demonstrated that the glycosylation occured between wheat gluten and glucose.In addition,fluorescence spectra indicated that UHP-glycosylation composite modification altered the conformation of wheat gluten,which facilitated the glycosylation and improved the functionalities of the products. |
