Study On The Application And Mechanism Of Enzymes In The Quality Improvement Of Whole Wheat Chinese Steamed Bread

Chinese steamed bread(CSB)is a traditional fermented staple food in China while whole wheat CSB has higher nutritive value and deserves further development.However,there is rarely acceptable whole wheat CSB due to its rough texture and poor taste.Pentosanase(Pn)and glucose oxidase(GOX)were applied to the quality improvement of whole wheat CSB.And the modification mechanism of the enzymes was investigated on molecular,microstructure and macroscopic level respectively.The quality of whole wheat CSB treated with Pn and GOX got improved significantly.The dosages of Pn and GOX were 60 μg/g flour and 40 μg/g flour respectively.Pn and GOX individually led to the increase of specific volume by 22.05%,35.38% and the decrease of hardness by 29.51%,37.76%.The internal structure of CSB was affected with Pn increasing the pores size while GOX increasing the porosity.The scores of sensory evaluation of CSB treated with Pn and GOX were 14.5%,17.0% higher than that of control CSB.Pn and GOX could catalyze the degradation/solubilization and oxidation of water extractable arabinoxylan(WEAX)and water un-extractable solids(WUS).WUS had a lower purity but higher yield than WEAX.The ferulic acid content and Ara/Xyl-ratio of WUS were higher as well.Pn provoked the degradation of WEAX with the decrease of weight average molecular weight(Mw)and viscosity.The dissolution degree of WUS increased while the Mw and viscosity of arabinoxylan solubilized decreased as the dosage of Pn was on the increase.Pn preferred to work on the position where Ara/Xyl-ratio of WUS was lower.GOX resulted in the oxidative gelation of WEAX.As the amount of GOX increased,the gelling time got shortened and gel strength increased significantly.The effects of Pn and GOX on the characteristics of proteins in the whole wheat dough were studied.Both Pn and GOX could increase the solubility of albumin and globulin,gliadin and SDS-soluble glutenin significantly.Pn had little influence on the glutenin macropolymer(GMP)content as well as the protein molecular weight.But Pn increased the free sulfhydryl content only when the dosage of Pn was 120 μg/g flour.GOX not only provoked the decrease of free sulfhydryl and increase of GMP content at the same time,but also forced the albumin and globulin to form large protein aggregates and protein-polysaccharide conjugates through non-disulfide covalent bonds.Besides,the secondary structure of gluten isolated from whole wheat dough with GOX got more stable with more β-sheet and less α-helix.The composition and physiochemical properties of dough liquid obtained from whole wheat dough with Pn and GOX differed a lot from the control.Pn and GOX at lower dosage could increase the yield and viscosity of dough liquid,but the viscosity would reduce when the amount of Pn and GOX got higher.As Pn dose was 60 μg/g,WEAX content of dough liquid was 43.10% higher than control.The protein concentration increased by 22.70% and there were large protein aggregates and protein-polysaccharide aggregates generated in the presence of GOX.When the dose of GOX was 40 μg/g,there was no significant difference among the foam capability of the dough liquids,with both original height and final height of foam similar to the control.But the bubble size got much smaller than that of control,which was accompanied by more bubbles.Pn weakened the foam capability of dough liquid and decreased the final height of foam significantly even though Pn got the bubble size reduced as well.Besides,GOX slowed down the drainage rate while Pn was on the contrary.Finally,the effects of Pn and GOX on the rheology and microstructure of whole wheat dough were investigated.Pn-treated dough exhibited higher extensibility,in which the gluten matrix was more open and starch granules were more visible.The dough with GOX got significantly strengthened and more tenacious,which was accompanied by a more continuous and highly dense gluten network.Both of Pn and GOX at appropriate dosages could improve the dough fermentation capability,such as the maximum and final height of dough and tolerance.