The Regulatory Mechanism Of Water Extractable Arabinoxylan On The Gelatinization And Retrogradation Behavior Of Wheat Starch

As an important component of non-starch polysaccharides in wheat bran,arabinoxylan(AX)is mainly divided into water-extractable AX(WEAX)and water-unextractable AX(WUAX).WEAX can reduce the incidence of various chronic diseases such as cancer,cardiovascular disease,and type II diabetes.In the processing and storage of starchy foods,WEAX can significantly affect the starch gelatinization and retrogradation behavior,which is of great significance for the quality control of starchy foods.The interaction mechanism between WEAX and starch was unknown,this paper first studied the effects of WEAX with different molecular weights on the gelatinization and retrogradation of wheat starch in terms of swelling power,paste viscosity,microstructure and crystallinity.Then,WEAX with different structures was obtained using ?-L-arabinofuranosidase,and the chemical structure,rheological and thermal characteristics of tailored WEAX were determined.On this basis,the effects of WEAX with different structures on the gelatinization and retrogradation of wheat starch were studied.The purpose is to explain the interaction mechanism between WEAX and starch,and to provide a more comprehensive theoretical basis and technical support for effectively regulating the quality and shelf life of starch-based products.The main content and conclusion are as follows:The viscosity,viscoelasticity,thermal properties and crystallinity of wheat starch paste with and without WEAX were compared by rapid viscosity viscometer(RVA),rheometer,differential scanning calorimeter(DSC),laser confocal electron microscope(CLSM),and Xray diffractometer(XRD).The results indicated that the swelling power,solubility,peak viscosity,setback value,and viscoelasticity of wheat starch paste with WEAX were lower than those of the control(CK),which was mainly due to that WEAX inhibited the leaching of amylose and reduced the swelling of starch granules,and thus the recrystallization of amylose was hindered.The effect of L-WEAX on wheat starch was more significant than that of the H-WEAX.In the presence of WEAX,the wheat starch retrogradation kinetic parameters n was increased,and k was decreased,and the crystallinity was decreased,suggesting that WEAX mainly inhibited amylopectin recrystallization by changing its nucleation form and reducing the starch crystallization rate,wherein the effect of H-WEAX was more significant.The chemical structure,viscosity and thermal properties of WEAX under ?-Larabinofuranosidase treatment were compared by proton nuclear magnetic resonance(1HNMR),fourier infrared spectrometer(FTIR),high performance liquid chromatography,rheometer and thermogravimetric analyzer.The results showed that WEAX was hydrolyzed with ?-L-arabinofuranosidase AXH-m and AXH-d3 to obtain WEAX with only di-or monosubstituted side chains,and their degree of substitution were reduced.The viscosity of WEAX solution for directional removal of Ara side chain groups was lower than that of CK,which was attributed to the decreased molecular asymmetry of WEAX.After removing mono-substituted side chain Ara of WEAX,the thermal decomposition temperature of remained constant compared with CK.However,the weight loss rate decreased,and the thermal stability increased.Meanwhile removing the disubstitution of Ara at C-3 position,the thermal decomposition temperature and weight loss rate of WEAX were significantly lower than CK,indicating that the disubstituted C-3 Ara group on WEAX side chain had a more significant effect on the thermal characteristics of WEAX.The gelatinization viscosity,rheological properties,microstructure,and water distribution of wheat starch with the addition of WEAX with different structures were compared by RVA,rheometer,DSC,CLSM and 1H-NMR.The results showed that the substitution pattern of WEAX side chain Ara played an important role in affecting the gelatinization parameters of wheat starch and the fluidity of starch paste.The removal of side chain Ara groups reduced the number of side chain groups,leading to the reduction of the flexibility of the molecular chain of WEAX.Therefore,it was difficult to insert into the threedimensional structure of the starch network,and the inter-molecular entanglement and hydrogen bonding between debranched WEAX and wheat starch were weakened,resulting in their non-covalently cross-linked chain association and particle aggregation,which affected the swelling and overflow of wheat starch granules.Thus,the modified WEAX exerted less significant effect on starch gelatinization than unmodified WEAX.The more side chain groups of WEAX and the more complex its structure,the greater the influence on the gelatinization process of wheat starch.In addition,the disubstitution of Ara at C-3 had a more obvious effect on starch gelatinization.The retrogradation enthalpy,retrogradation kinetic parameters,long-range crystallinity,short-range crystallinity,and water distribution of wheat starch with the addition of WEAX with different structures were comparatively studied by DSC,XRD,FTIR and 1H-NMR.The results showed that the substitution pattern of WEAX side chain Ara played an important role in the thermal characteristics,crystallinity,and water distribution of wheat starch upom retrogradation.The side chain substitution pattern of WEAX was changed after removing Ara groups.The WEAX conformation with the single substituted Ara group removed was denser,and the unsubstituted Xyl aggregated between molecules,resulting in a stronger hydrogen bond between WEAX and starch.The WEAX conformation with the Ara group at the double substituted C-3 position removed was almost unchanged compared to unmodified WEAX,but the intermolecular hydrogen bond of WEAX was reduced,resulting in a weaker synergy with wheat starch.Moreover,debranched WEAX exerted less significant effect on restricting the free movement of water molecules in starch than unmodified WEAX,which promoted the precipitation of free water,and maked the effect of modified WEAX on starch retrogradation significantly weaker than unmodified WEAX.The more side chain groups of WEAX and the more complex its structure,the greater the influence on the gelatinization process of wheat starch.The disubstitution of Ara at C-3 had a stronger effect on the retrogradation behavior of wheat starch.