Study On The Regulatory Mechanism Of Wheat Water-Extractable Arabinoxylan On The Polymerization Behavior Of Gluten During Thermal Processing

As the second largest crop in China,about 90%wheat is used for production of wheat flour.About half of the residents treat the pasta food as their staple food.Although the increasingly sophisticated grain processing in our country can satisfy the taste of consumers,the lack of nutrients such as dietary fiber is serious.As an important component of wheat dietary fiber,water-soluble arabinoxylan(WEAX)is regarded as a techno-functional improver for dough,due to its prominent interactions with gluten proteins.Although large amount of studies focus on the WEAX and gluten interactions during dough development stage,heating stage is the last but most critical step during bread making.However,the detailed mechanism of WEAX on the heat-induced aggregation process of gluten remained far more to be elucidated.The complex structural characteristic of WEAX is also one of the main obstacles to reveal its interaction mechanism with gluten.Against this background,current study starts from the perspective of the structure of WEAX,and selected the WEAX with different Mw and different FA contents.Their effects on the heat-induced aggregation process of gluten were detailed studied.The interactions between WEAX and gluten were comparatively assessed at the macroscopic,microscopic and molecular levels to reveal the regulatory mechanism of WEAX on the heat-induced aggregation behavior of gluten,and the results may further provide the theoretical guidance for selecting the optimum structure of WEAX to regulate gluten quality,improve the quality of cereal products and develop functional ingredients.The specific research contents and conclusions are as follows:The viscoelasticity and thermal properties of gluten protein with low(L-)and high(H-)Mw under heat treatment were compared and studied by rheometer,differential scanning calorimetry,and thermogravimetric analyzer.The results showed that addition of WEAX,especially L-WEAX could improve elastic modulus and viscous modulus of gluten during heating.WEAX significantly enhanced the denatured temperature and enthalpy of gluten,indicating that the heat stability of gluten was improved and the structure of gluten was more ordered with WEAX.The particle size analyzer,Ubbelohde viscometer,laser confocal microscope,and atomic force microscope were used to compare the particle size,intrinsic viscosity,microstructure,surface topography of gluten protein before and after the addition of WEAX during heating.During the temperature rose from 25℃to 95℃,L-WEAX increased the median particle diameter of gluten protein to the maximum.Moreover,the Huggins constant reached the peak value at 95℃ in the presence of 1%L-WEAX,indicating that L-WEAX was more effective to induce the aggregation of glutenin-gliadin.WEAX evoked the reinforced glutenin network and heterogeneous distribution of gliadin,with a more uniform molecular surface developed for gluten during heating.The changes of protein molecular weight and subunits of gluten protein before and after the addition of WEAX during the heating stage comparatively investigated by size exclusion high performance liquid chromatography,sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE),reversed phase high performance liquid chomatography,ultra high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS).Land H-WEAX could dramatically enhance the glutenin-gliadin aggregation at 90℃ and 95℃,respectively.The promoted heat-induced aggregation behavior of gluten by WEAX was predominantly attributed to the enhanced aggregation ability of x-type HMW-glutenin subunit,LMW glutenin subunits(mainly i-and s-type),γ-gliadin and CSB_α gliadin 9/18.L-WEAX was more effective in promoting the heat-induced aggregation of α-and γ-gliadin into glutenin,whereas H-WEAX decreased the polymerizing temperature of glutenin and gliadin from 95℃to 70℃.Meanwhile,surface hydrophobicity,amino acid environment,disulfide(SS)conformation,non-covalent forces,and the secondary structure of WEAXgluten protein during heating were studied by fluorescence spectrophotometer,Fourier Raman spectrometer and Fourier transform infrared spectroscopy.L-WEAX could develop more hydrogen bonds with tyrosine of gluten and stabilize the secondary structure more evidently than H-WEAX upon heating.Compared with SS bridge formation,hydrophobic interactions were not the driving force involved in the heat-induced polymerization behavior affected by WEAX.Different fractions of WEAX were extracted from wheat bran by ethanol fractionation precipitation method,and WEAX obtained by precipitation with 50%(v/v)ethanol was subjected to alkaline treatment(0s,50s and 8h)to obtain WEAX with different FA contents.The effect of FA on the heat-induced gluten protein aggregation behavior were studied in terms of the M W,SH content,composition and secondary structure of protein.Gluten in the presence of WEAX with high FA content showed the largest increase in viscoelasticity,illustrating that FA could improvethe viscoelasticity of gluten during heating.Gluten with the medium and high FA content of WEAX showed the greatest increase in the degree of crosslinking at 75℃～90℃ and 90℃～95℃,respectively.This indicated that the presence of FA on the side chain promoted the formation of glutenin-gliadin crosslinking.EF50 mainly promoted the aggregation capacity of HMS,LMS,α-,β-and ω-gliadin.FA promoted the conversion of α-helix to β-sheet and intermolecular β-sheet.Meanwhile,WEAX with FA could also inhibit the degree of changes in all secondary structures of gluten protein during heating.