| In the development of new wheat-based products,it is particularly important to study the changes of product structural and physico-chemical properties caused by thermal interactions between macromolecular components.Starch and gluten are important macromolecular polymers in wheat flour,but their interaction mechanism during heating is still unclear.Therefore,it is difficult to clearly understand the basic regularity of wheat-based product quality,which also weakens the effectiveness of the current protocols in regulating the precise nutrition and personalized manufacturing of staple food products.In this research,the regulation mechanism of gluten,glutenin and gliadin on the gelatinization,retrogradation behavior and enzymolysis properties of wheat starch was studied;Then,the effects of heat-induced aggregation behavior,enzymolysis and gel properties of gluten proteins were revealed from the perspective of starch;Finally,the simulated dough system was used to verify the mechanism of multiple macromolecular components(including curdlan,wheat starch and gluten proteins),and the quality change during heating was analyzed.The main contents,results and conclusions are as follows:(1)The regulation mechanism of reconstituted gluten fractions(RGF)on the gelatinization behavior of starch were studied.The addition of RGF,irrespective of glu/gli ratios,significantly inhibited the gelatinization of starch,and this inhibition was enhanced with the increase of the gliadin proportion.The gelatinization properties of starch were characterized by rapid viscosity analyzer(RVA).The results showed that the peak and breakdown viscosity of starch decreased by 17.3%and 13.4%as the glu/gli ratio in RGF changed from 1:0 to 0:1,respectively.Glutamine(Gln)or tyrosine(Tyr)on the gluten molecular chains mainly combined with starch molecules through hydrogen bonding,which weakened the aggregation among the starch molecules.The particle size analysis found that gliadin reduced the diameter of gelatinized starch by 4.5%.Laser confocal microscopy(CLSM)also clearly observed that starch granules were effectively surround by gliadin,thereby stabilizing the granule structure better than glutenin.Additionally,the presence of gliadin reduced the amount of leached amylose by 22.2%,significantly decreased the viscoelasticity(G’ and G")of starch paste,resulting in a 27.1%decrease in the gel strength of starch.These results can provide a theoretical basis for the development of reconstituted wheat-based products with required texture.(2)The influence of RGF on retrogradation of starch was studied.The presence of RGF significantly inhibited the short-term and long-term retrogradation of starch.Rheometer and low-field nuclear magnetic resonance(LF-NMR)were used to analyze the short-term retrogradation of starch.The results showed that during storage at 4℃ for 8 h,the presence of gliadin reduced the G’ of starch gel and enhanced the water mobility.The hydrogen atom of amino group in Gln on gliadin molecules and the oxygen atom of a-1,4 glycoside bond on starch molecules,as well as the oxygen atom of carbonyl group in Gln and the hydrogen atom of hydroxyl group of C-3 on starch molecules could combine to form hydrogen bonding,which was the key to significantly inhibit the short-term retrogradation of amylose.During storage at 4℃ for 28 d,glutenin reduced starch retrogradation by 16.2%compared with gliadin.The oxygen atom of carbonyl group in Tyr on glutenin molecules could connect with the hydrogen atom of hydroxyl group of C-6 on starch molecules by hydrogen bonding,which led to the reduction of the retrogradation rate of amylopectin.It was also observed by atomic force microscopy(AFM)that glutenin significantly inhibited the aggregation of amylopectin molecules,indicating that glutenin was superior in retarding longterm retrogradation of amylopectin.This study suggested that by adjusting glu/gli ratios in RGF,the shelf-life of reconstituted wheat-based products during shortterm and long-term storage could be prolonged.(3)The effects of gluten and its different fractions on the enzymolysis properties of starch were studied.Compared with pure wheat starch,the hydrolysis rate of starch reduced by 39.9%,49.5%and 26.6%by addition of gluten,glutenin and gliadin,respectively.Thermogravimetric analysis(TGA)found that starch could interact with protein through hydrogen bonding,and the thermal stability of the complex was improved.Compared with gluten and gliadin,the addition of glutenin formed a denser physical barrier around the starch matrix,which inhibited the hydrolysis of starch by enzymes to a greater extent.In addition,the activity ofα-amylase was inhibited by various gluten fractions,with the highest inhibition percentages observed for glutenin(approximately 79%).This stronger binding between α-amylase and glutenin could be observed by CLSM.Therefore,the different gluten fractions could inhibit the digestion of starch,especially the addition of glutenin.The results can provide reference for the development of low glycemic index food by optimizing the proportion of gluten fractions.(4)The relationship between the thermal aggregation behavior of gluten proteins induced by starch and enzymolysis properties of gluten proteins was studied.With the gluten-starch proportion changed from 1:0 to 1:1,the hydrolysis rate of gluten proteins increased by 21.5%.Using DSC and TGA techniques,the thermodynamics behavior of protein was assessed.The results suggested that the presence of starch delayed the thermal aggregation reaction and reduced the thermal stability of gluten proteins.Protein network analysis confirmed that the junction density and branching rate of gluten proteins significantly decreased by 29.9%and 25.1%,and lacunarity increased by 1.92 times,thereby weakening gluten network structure.The sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)was used to study the molecular weight(Mw)of gluten proteins.It was found that the increase of starch ratio inhibited the crosslinking of disulfide bonds and reduced the formation of gluten aggregates(Mw≈130-200 kDa).Therefore,the presence of starch promoted the enzymatic hydrolysis of gluten proteins,which was related to the loose and open gluten protein structure induced by starch after heat treatment.The results are helpful to develop gluten products with high digestibility by changing the proportion of starch in the reconstituted system.(5)The effect of starch debranching on the quality and structure of gluten gel was studied.With the extension of the debranching time from 0 h to 8 h,the molecular weight of DBS increased from 3.5 × 107 g/mol to 1.7 × 105 g/mol.Compared with gluten gel(G),the viscoelasticity and water holding capacity of the composite gel(G+DBS)were significantly enhanced.The strength of the composite gel was increased by 24.9%with the increase of starch debranching degree.TGA showed that the weight loss rate of gluten increased by 4.4%with the increase of starch debranching degree,which was related to the structural changes and aggregation behavior of gluten proteins.The increase of starch debranching degree reduced the β-sheet structure at the expense of the α-helical,and decreased the fluorescence intensity of tryptophan,leading to the protein molecules tend to expand.Meanwhile,gliadin or low molecular weight glutenin(Mw<44 kDa)was also significantly inhibited,leading to the transition of disulfide bond conformation changes from a stable g-g-g configuration to a t-g-g configuration.AFM also observed that the average height and width of gluten molecular chains decreased with the increase of starch debranching,which improved the compatibility between DBS and gluten molecular chains and was conducive to the formation of uniform gel system.(6)The interaction mechanism of multiple macromolecular components(curdlan,starch and gluten proteins)in the simulated dough system was studied,and the influence of curdlan on the stability of dough processing quality was analyzed.When heating temperature exceeded 60℃,0.6%curdlan increased the stiffness of dough with a maximum storage and loss modulus.The thermodynamic behavior of dough components was analyzed by DSC.It was found that the curdlan delayed the thermal denaturation of gluten proteins and the gelatinization of starch granules.SEM and CLSM results also confirm that curdlan gradually expanded and homogenously filled into the gluten matrix and adhered to discrete starch granules,which could contribute to the development of a stable connection of starch,gluten and curdlan.For starch,the barrier effect of curdlan formed on the surface of the starch granules inhibited its breakdown,and reduced the peak breakdown viscosity of starch by 28.1%and 24.5%,respectively,accentuating the dough strength.Regarding gluten,hydrogen bonding and hydrophobic interactions were involved in curdlan-gluten interactions.Some random coils of gluten were transformed into a-helix structure,which reduced the content of disulfide bonds and inhibited gluten aggregation,resulting in the structural weakening of dough.In conclusion,this study revealed the mechanism of the heat-induced wheat starch-gluten interactions,and their interactions were critical to the overall dough structure and its related processing properties and alleviated in vivo digestion.On the one hand,gluten and its fractions could significantly inhibit the gelatinization,retrogradation and enzymatic hydrolysis of starch.Gliadin significantly inhibited starch gelatinization and short-term retrogradation,while glutenin could effectively inhibit the long-term retrogradation and enzymatic hydrolysis of starch.On the other hand,the presence of starch inhibited the thermal aggregation of gluten proteins,and endowed gluten with higher digestibility and better gel quality.Based on the above research,in the simulated dough system with multiple macromolecular components,it was found that an appropriate amount of curdlan was the key to enhance the strength and viscoelasticity of the dough during heating,which was the result of stronger interactions among curdlan,gluten proteins and starch.The research in this paper has guiding significance for the design and development of reconstituted wheat-based products. |
