| Our previous studies have found that gluten protein and ?-glucan are important factors affecting the baking quality of barley bread.In gluten,barley flour contains a lot of glutenin and gliadin,but it can not form a viscoelastic gluten network structure like wheat flour.In the aspect of ?-glucan,the presence of a large amount of?-glucan could inhibit the formation and development of gluten protein network structure and affect the distribution and migration of water in dough.However,it is not clear how ?-glucan affects water migration in dough and its weakening mechanism in the formation and development of gluten network structure.Therefore,it is of great significance to further study the mechanism of water transfer between ?glucan and gluten protein,and the interaction mechanism between ?-glucan and gluten protein,so as to fully reveal the mechanism of the rich ?-glucan in barley to weaken the quality of barley fermented flour products.In this paper,the effects of barley ?-glucan on the macroscopic properties and microstructure of dough,the Weakening Mechanism of gluten system by ?-glucan were studied and the binding-dissociation of water with ?-glucan and gluten protein was also discussed,and the mechanism of reducing the quality of the barley fermented flour products was revealed.The main results are as follows:1.Taking dough without adding ?-glucan as blank control and mixed system of ?glucan and dough in different proportions as research objects,the effects of ?-glucan on wet gluten content,gelatinization properties,rheological properties and microstructures of wheat flour were studied.The results showed that when the addition of ?-glucan was more than 0.1%,the wet gluten content of wheat flour decreased significantly(P<0.05).The peak viscosity,minimum viscosity,disintegration value,final viscosity and retrogradation value of the system decreased significantly,while the peak time increased significantly(P<0.05).The addition of ?-glucan decreased significantly(P<0.05)the maximum expansion height of dough and the maximum gas release.The degree of yeast production and dough gas holding capacity decreased,and the dough fermentation performance decreased.The addition of ?glucan can significantly increase the viscoelasticity of fermented dough,hinder the expansion and extension of dough fermentation process,and significantly change the microstructure of dough.When a large amount of ?-glucan is added,the gluten protein becomes discontinuous and irregular,and the structure becomes more and more compact.2.The mixed flour dough of barley(30%)and wheat(70%)was used to sample the dough before,in the middle,at the later stage and in the early stage of dough wakefulness.The dynamic distribution of ?-glucan in mixed flour dough was studied by laser confocal microscopy(CLSM).The results showed that the addition of ?glucan reduced the formation of gluten reticular structure during stirring.In the early stage of fermentation,gluten became irregular,discontinuous,a large number of starch granules were exposed,and ?-glucan covered the gluten network structure.3.The effect of ?-glucan on the mechanism of gluten weakening was studied in the mixed system of ?-glucan and gluten.Macroscopically,when the addition of ?glucan was more than 0.1%,the elongation resistance of gluten protein increased significantly(P<0.05),and the elongation decreased significantly(P<0.05),so that the dough hardness increased and the gluten strength decreased.The addition of ?glucan could change the rheological properties of gluten protein.At a given frequency,the addition of ?-glucan increased the viscoelasticity and mechanical strength of gluten protein.Temperature affects the rheological properties of gluten,and the interaction between gluten and ?-glucan is enhanced by temperature.Microscopically,the addition of ?-glucan significantly reduced the ratio of gluten protein to beta-folding and increased the ratio of irregular curling;with the increase of?-glucan content(P<0.05),the content of free thiol group increased significantly(P<0.05),the content of total thiol group and disulfide bond decreased significantly.When the addition of ?-glucan was 2.0%,the content of disulfide bond was 0,33mol/g in the blank group decreased to 0.07 mol/g;denaturation temperature Td and enthalpy change value ?H decreased significantly(P<0.05),and gluten thermal stability decreased;with the increase of ?-glucan content,gluten holes began to become smaller and less,and became very irregular.When ?-glucan content was 2.0%,gluten appeared serrated edges,and the size of holes became very uneven.13C NMR showed that carbonyl group(C=O)and double bonded carbon group(C=C)on the side chain of ?-glucan acted on the carbon atoms on the tyrosine phenyl ring,causing changes in chemical shifts.4.The mechanism of the effect of ?-glucan on gluten formation and development can be summarized as follows:first,?-glucan reduces disulfide bond between glutenin molecules to free mercapto groups,which hinders the cross-linking and aggregation of glutenin molecules.,reducing the stability of disulfide bond affects the formation and viscoelasticity of gluten.Second,?-glucan transforms the ?-folding structure of protein into unordered irregular curl structure,which makes the network structure of gluten protein loose and disordered.Third,the competitive water absorption of ?glucan desiccates gluten protein through hydrogen bonding,which leads to redistribution of water in dough,hinders the aggregation of gluten molecules,and makes gluten protein difficult to form a viscoelastic gluten network.5.?-glucan/dough,?-glucan/fermented 40min dough and ?-glucan/gluten protein mixed system were used to study the binding and dissociation of water between ?-glucan and gluten protein.The results showed that,with the increase of the amount of the ?-glucan,the time of T21,T22 and T23 of the dough increased,and when the amount of the ?-glucan was 2.0%(P<0.05),the combined water in the dough and the free water showed a tendency to decrease,and the semi-binding water had a tendency to increase.When the addition amount is 2.0%,the proportion of the combined water and the free water is significantly reduced(P<0.05),and the semibinding water is significantly increased(P<0.05).Before and after fermentation,the transverse relaxation time T21 is basically between 0.19?0.29ms,the transverse relaxation time of weakly bound water is about 1?15 ms,and the lateral relaxation time of free water is obvious.With the increase of ?-glucan content,the content of tightly bound water in gluten protein decreased,the weak bound water showed an increasing trend,and there was no free water distribution. |
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