Conformation And Functional Properties Of Wheat Gluten Hydrolysate/Polysaccharide Conjugates Synthesized By Ultrasound

Wheat gluten is a byproduct of the wheat starch industry. The use in food is limited by its water-insoluble characteristic. The aim of the present study was to modify wheat gluten by graft reaction of gluten hydrolysate and polysaccharide subjected to ultrasound treatment for improving its functional properties and extending utilization. Optimal technological conditions and some rules of functional properties of the modified glutens changing were studied. Relation of composition/structure of the modified glutens to functional properties was analyzed. Moreover, the conjugates were also used in the milk emulsions.Two proteases (Protamex and Papain) were used to hydrolyze gluten protein. The conditions of graft reaction of gluten hydrolysate and polysaccharide were optimized. In single factor experiments, the effects of the degree of hydrolysis, weight ratio of polysaccharide to gluten hydrolysates, reaction time and pH value on the degree of graft reaction (DG) were investigated. Optimal conditions of gluten hydrolysate and Arabic gum for graft reaction were obtained by surface response design. The conjugate with the highest degree of graft(DG=23.56%) using DH8.8% of Protamex hydrolysate and Arabic gum could be obtained, when the most optimum conditions were as follows: the weight ratio of protein to polysaccharide 10:1, time 19min, pH9.2, temperature 80℃.The functionality of conjugates of Protamex hydrolysate and Arabic gum was studied. Solubility, thermal stability, emulsifying and foaming properties of the resultant conjugate were significantly (P<0.05) improved compared the hydrolysate and control. Solubility curve kept relatively plateau at pH3-10. No obvious pI was noticed. Nitrogen Solubility Index (NSI) was about 30% increases in acidic condition compared to the control. Emulsifying Stability (ES) had a clear improvement; it was about 2.7 times of the control when DG is the maximum. Foam Stability (FS) in acidic condition was about 3.2 times of the control when DG is 14.8% and FS reached maximum.In secondary structure based on FT-IR, modification led to decrease and increase inα-helix andβ-structure ratio, respectively. The conjugate had the lowestα-helix/β-sheet ratio and the highest molecular flexibility. Microstructure of the modified glutens had great change based on SEM observation. The conjugates had less edges and corners than control. According to SDS-PAGE analysis, new broad bands of the conjugate subunits compared to control appeared in the upper regions of the separation gel and the glycosyl bands were seen more clearly. These illustrated macromolecular grafts emerged. Change in molecular weight distribution and structure of the modified gluten proteins resulted in improvement of flexibility and surface properties. These changes play an important role in improvement of functional properties.The conjugates were used as partial substitute for sodium caseinate in the imitated neutral emulsions. It was an effective replacer to slow down enlargement of the d3,2 at the top and bottom of emulsions, creaming rate and centrifugal sedimentation rate when replaced about 10%-30% of the sodium caseinate. The imitated acidic emulsions showed low creaming rate and centrifugal sedimentation rate when conjugates were used as skim milk powder replacer in the emulsions to replace about 30% or 40% of the skim milk powder.