Studieson Characteristics Of Aggregation Of Wheat Flour Protein During Ripening Process

The aggregation behavior of protein was researched in this study,changes of the content of each protein component,the content and particle size distributions of the glutenin macropolymer(GMP),the molecular weight distribution and the secondary structure of protein,the microstructure of dough was included.The rheological properties of wheat flour and the dynamic rheological properties of dough,dough sheeting and batter was studied during ripening,so as to characterization the aggregation properties complementally.At the same time,the influence of the addition of glucose oxidase,xylanase,lipoxygenase,and the heat treatment at 37?for 1 h in the wheat flour and its products quality was researched to seek a safe and effective method to accelerate ripening.In this research,three new grinding wheat flour with high,medium and low gluten were used and different ripening time(0-90d)were considered.The protein composition,the GMP content and particle size distribution,the free sulfhydryl group(-SH)content,disulfide bond(S-S)content,and the molecular weight distribution of protein were researched to analyse the protein characteristics and further explore the after-ripening mechanism of flour.In addition,the transformation of protein secondary structure and the microstructure of dough were observed.The results showed that the content of glutenin increased,while the gliadin decreased significantly in the process of after ripening,however,the content of crude protein and salt soluble protein appeared no significant change as a whole.The content of glutenin reached the maximum value,and the gliadin reduced to the minimum in the 40 days.However,the trend of the above indexes were stable after 50 days of storage.The GMP content increased significantly at the 40 th day of storage.The GMP content increased by 38%,31%,and 28%,respectively,for high,medium and low gluten flour,but no significant change in particle size of GMP were observed.Similarly to the changes of protein component,after ripening for 50 days,this change was not evident any more,and finally tend to be stable.For the three kinds of flour,the free sulfhydryl group content decreased by 5.5%,4.1% and 4.4%,the disulfide bond(S-S)content increased by 1.6%,1.8% and 2%,respectively.The proportion of ?-helix increased,while the proportion of ?-pleated sheet and ?-turn decreasedfor both of the three different kinds of flour,which indicating that the secondary structure of protein changed to a certain degree,and this was the main reason that led to the difference in the quality of products.The result of molecular weight distribution showed that the content of high molecular weight glutenin macropolymer increased,while the content of gliadin decreased.In summary,the gliadin cross-linked with glutenin by the disulfide bond,and then formed the glutenin with higher molecular weight,which increased the content and particle size of GMP,and help developed stronger gluten network.According to the principal component analysis,the equation model of aging degree of flour was established.Changes of moisture content,whiteness,gluten index,pasting properties were determined,in particular,the empirical rheology and dynamic rheological properties were observed,respectively,and then the relevance among indicators were analysed.The results showed that in the process of after ripening,the gluten index of high and medium gluten flour increased at first and decreased later on,and the gluten index of low gluten flour was gradually increased,it indicated that the quality of gluten protein was improved gradually.The change of water absorption of high gluten flour was not significant,for the medium and low gluten flour the water absorption rate increased at first and decreased later on,which mainly influenced by water content and gluten.The weakening degree of high gluten flour was firstly increased and then decreased,for the medium and low gluten flour the weakening degree was reduced gradually,it revealed that the stability of dough was improved.Correlation analysis showed that the peak viscosity,minimum viscosity,final viscosity,and the breakdown value were significantly positive(p<0.01)related with the ripening time.Frequency sweep test showed that the storage modulus(G')and the loss modulus(G�)of dough,dough sheeting,and batter both increased with ripening time.The flow characteristic profile of batter showed that the apparent viscosity of batter decreased as the shear rate increased,and the batter showed shear thinning properties in the process of ripening.Yield stress test showed that for the high,medium and low gluten flour,the maximum yield stress were achieved at the fortieth day,the seventieth day and the sixtieth day,respectively.At this time,the resistance to the stretch of batter reached the maximum value,it indicated the best gluten strength.In order to explore the way to accelerate the ripening of flour,the influence of the addition of glucose oxidase,xylanase,lipoxygenase,and the heat treatment at 37?for 1 h in the wheat flour and its products quality were researched.Results showed that no significant difference were observed between the natural aging for 40 days and adding glucose oxidase,and lipoxygenase in terms of the effect on the flour color,gluten properties and flour pasting properties.The dynamic rheological characteristics of dough and batter showed that the viscoelastic of flour dough and the batter was improved,and the elasticity increased after treatment.Adding lipoxygenase had the best effect on flour color and improved the brightness of flour to a great extent,represented the significant effect on the content and particle size of the glutenin macropolymer,showed the biggest extent of increase in high molecular weight protein,and the greatest impact on the secondary structure of flour protein.The effect of glucose oxidase on gluten index and the elasticity of dough was the most significant,it also can effectively delay the deteriorate of dough sheet color,at the same time the batter showed the maximum yield stress,the dough appeared the highest swelling height,and the fermentation ability of gluten was the strongest.Heat treatment had the most significant effect on the content of thiol and disulfide bond.