Effects Of Alkaline Extractable Arabinoxylan On Wheat Dough And Dough Components Properties

Arabinoxylan?AX?,as a predominant non-starch polysaccharide of wheat bran,produces significant impact on the mechanical and rheological properties of wheat dough because of the interaction between Arabinoxylan,gluten and starch.In this study the effect of structural differences of arabinoxylan on wheat dough gluten network and mechanical properties was investigated.For that purpose alkaline extractable arabinoxylan?AEAX?was extracted from wheat bran by using different alkaline extractants and hydrolyzed by xylanase and the effects of AEAX with different molecular mass on the gluten and starch properties were studied,as well as the effects of AEAX on the wheat steamed breadFirstly,AEAX was extracted from wheat bran by using different alkaline extractants?NaOH,NaOH with 0.88%H2O2,saturated Ba?OH?₂ and saturated Ba?OH?₂ with 0.26 mol/L NaBH4?.On the basis of extraction purity,yield,composition and relative molecular mass distribution all extracts were compared and discussed.Comparison results showed that the extracts extracted by Ba?OH?₂,which is a highly selective extractant for AEAX,had higher purity of 85.83%,ratio of Ara/Xyl?0.755?and higher relative molecular mass while the extracts extracted by NaOH had lower purity of 72.38% and lower ratio of Ara/Xyl.Mixolab results showed that AEAX with higher relative molecular mass and ratio of Ara/Xyl significantly improved the dough absorption and decreased setback value?P<0.05?,as well as inducing the decrease of dough stability.Rheological results showed that the addition of 3% AEAX extracted by NaOH with 0.88%H2O2 would increase the dough loss modulus while other extracts would induce the decrease of dough storage and loss modulus.Secondly,xylanase was used to prepare different relative molecular mass AEAX.HPSEC was used to determine the relative molecular mass distribution of AEAX,meanwhile LF-NMR,CLSM,Mixolab and Rheometer were used to investigate the effects of AEAX with different relative molecular mass on the moisture distribution,microstructure,thermo-mechanical properties and rheological properties of dough.The solubility result showed that hydrolyzed AEAX owned higher solubility and more stable rheological behavior.With the addition of AEAX with lower relative molecular mass,dough stability and storage modulus significantly increased?P<0.05?,meanwhile the value of T21 decreased from 2.0092 ms to 1.5199 ms and the area proportion of T21 and T22 increased.CLSM graphs indicated that the presence of hydrolyzed AEAX could weaken the physical barriers and eliminate the negative effects on the process of protein network formation to a certain degree.These results indicated that the hydrolyzed AEAX could diminish the competition for water between dough components and polysaccharide,meanwhile reinforce the combination between dough components and water.Then,AEAX-gluten mixtures and AEAX-starch mixtures were built to investigate effect of AEAX with different relative molecular mass on rheological properties of wheat gluten and gelatinization and retrogradation properties of starch.The water holding capacity of AEAX-gluten mixture significantly increased compared with that of control gluten,as well as the storage modulus,loss modulus and critical temperature?P<0.05?.These results indicated that AEAX would interfere with the gluten network formed by glutenins and gliadins,and hydrolyzed AEAX would eliminate the negative effect caused by polysaccharide on disulphide/sulphhydryl interchange reactions and spatial structure change.RVA results showed that with the addition of AEAX especially hydrolyzed AEAX setback value and viscosity of AEAX-starch mixtures decreased significantly compared with control wheat starch?P<0.05?.DSC results showed that pasting temperature of AEAX-starch mixtures increased from 62.64? to 65.18?,as well as the gelatinization complexity.Rheological tests showed that the presence of AEAX improved storage modulus of starch mixtures.These results indicated that AEAX especially hydrolyzed AEAX could restrain the swelling and pasting process,and strengthen the formation of starch gel network.Finally,3.0% AEAX was added into wheat flour and steamed bread were prepared.The specific volume and gas cell characteristic of wheat steamed bread was tested,as well as the texture properties of steamed bread during storage.The results showed that with the addition of hydrolyzed AEAX hardness of steamed bread decreased to 1 119.762 g,and specific volume increased compared to control.The storage test showed that AEAX especially hydrolyzed AEAX could significantly decrease the hardness increment of steamed bread?P<0.05?.