Study On Preparation Of Wheat Protein Fibers

Wheat gluten is the protein after the starch and other water-soluble substances are washed from the wheat flour and then dried. Its production is huge and has a rising trend year by year. Nowadays, its application is mainly on food and food field, but there are few studies on the production of wheat protein fiber. In this study, glutenin and gliadin were purified from wheat gluten and defatted at first. Then study the effect of different factors on the rheological properties of wheat protein solution and the effect of protein on the mechanical properties of fibers. We also used different modification methods to improve the mechanical properties and measured the structure and properties of modified fibers.Firstly, after the purification of glutenin and gliadin, effects of proportion of gliadin and glutenin, aging time of the protein solution, temperature, protein concentration and p H on the rheological properties of wheat protein solution were studied. We found that the wheat protein solution was a non-Newtonian fluid and belonged to a shear-thinning fluid. With the increase of proportion of gliadin and glutenin, aging time, protein concentration and p H of protein solution, its non-Newtonian index decreased gradually and the structural viscosity index increased gradually while temperature had the opposite effect. The preliminary suitable preparation conditions of fibers were as follows: gliadin: glutenin(w/w) should be greater than 1:3; the temperature should not lower than 20℃; protein concentration should be lower than 20%; p H should be between 6 and 9; aging time depended on the proportion of gliadin and glutenin, temperature, p H and protein concentration but the non Newtonian index of the protein solution should be controlled in the range of 0.15-0.25 and the structural viscosity index should be controlled in the range of 15-17.Secondly, the process conditions of without microwave and microwave treated fibers were optimized. The preparation conditions of non-microwaved fiber were gliadin: glutenin(w/w) =1:1, p H 7, protein concentration of 15%, and the coagulation time of 20 min. The preparation conditions of microwaved fiber were microwave power of 20.6 W/m L, microwave time of 3 min, and p H 8.Under this condition the prepared fiber had the breaking strength of 0.69±0.01 c N/dtex and the elongation at break of 23.37±1.20%. Compared with the non-microwaved fibers, the breaking strength increased by 23.21% and the elongation increased by 302.43%. The result showed that the increased elongation was more obvious which indicated the toughness of microwaved fiber was increased.To study the mechanism underlying the effect of microwave treatment on the improvement of mechanical properties, microwave could increase the content of disulfide bond, covalent crosslinking caused by non-disulfide bond, crystallinity and α-helix, which played a positive role in the improved mechanical properties of microwaved fibers. The SEM observation showed that microwaved fiber had a smoother and denser surface and less pores. Microwave also increased surface hydrophobicity and thermal stability, while the standard moisture regain decreased but still had good moisture absorption performance close to silk.Finally, on the basis of microwave treatment, we studied the effect of glutaraldehyde on the fibers’ mechanical properties. Through single factor and orthogonal experiment, the optimum process conditions were glutaraldehyde concentration of 1%, crosslinking time of 5 h, temperature of 40℃, and p H 9. Under this condition, the crosslinked fiber’ breaking strength was 1.04 ± 0.01 c N/dtex and the elongation was 31.70 ± 0.80%, which was close to the mechanical properties of wool. Compared with the non-crosslinked fiber, breaking strength increased by 46.48% and the elongation increased by 35.64%, which indicated that the toughness of crosslinked fibers was futher increased. Compared with non-microwaved and noncrosslinked fibers, breaking strength increased by 85.71% and the elongation increased by 449.39%.To study the mechanism underlying the effect of crosslinking treatment on the improvement of mechanical properties, the results showed that glutaraldehyde and the protein molecules did crosslinked and glutaraldehyde could further increase the content of crystallinity and α-helix, which played a positive role in the improved mechanical properties of crosslinked fibers. The SEM observation showed that after crosslinking the distance between protein moleculars was closer and fibrous protein was more obvious. Surface hydrophobicity of the crosslinked fiber was decreased but higher than the wheat protein. The thermal stability and the standard moisture regain were increased.