Study On The Mechanism Of Tea Polyphenols Influencing Gluten Network Structure

As the increase of aging population in our country,various chronic diseases have become the main factors limiting the improvement of quality of life.Many studies have shown that tea polyphenols are functional ingredients that are beneficial to the human health with their function in preventing chronic diseases.Therefore,studying the effect of tea polyphenols on the gluten protein network in bread and dough systems and its mechanism of action are important to its utilization in bread and other pasta products.In this paper,through the study of the effect of tea polyphenols on the structure of the gluten network in bread and dough systems,the results were as follows:First,by adding 0%,0.5%,1%,and 2%(w/w)tea polyphenols to the bread system,the specific volume,color difference,texture,internal structure,water retention and sensory scores of the bread were measured.The results showed that the addition of tea polyphenols deteriorate the quality of the bread and reduce its sensory property,which were correlated to the amount of tea polyphenols.When the amount of tea polyphenols was 2%,the specific volume of bread decreased by 30.7%,the hardness increased by 103.5%,the whiteness decreased by 24.2%,the water retention rate decreased by 0.6%,and the water loss rate increased by 2.3% after 7 days of storage.However,the addition of tea polyphenols was beneficial to improve the nutritional properties of bread.Apparently,the addition of 2% tea polyphenols increased the polyphenol content in the bread crust and bread core compared with the blank control group,which was 17.4 mg/g and 18.7 mg/g(GAE).The results of in vitro simulated digestion experiments of starch also showed that tea polyphenols reduced the digestibility of starch in the bread system,which was beneficial to the control of postprandial blood glucose.Secondly,the effect of the addition of tea polyphenols on the properties of the dough system was investigated.The results of the farinograph and extensograph experiments of the dough indicate that tea polyphenols weaken the processing characteristics of the dough.When the amount of tea polyphenols was 2%,the water absorption of the flour and the stability and develop time of the bread dough were decreased,which led to an increase of the softening degree of the dough.When the amount of tea polyphenol was 3%,the structure of the dough was severely broken,and the normal stretching experiment cannot be performed.Dynamic rheological experiments showed that the addition of tea polyphenols enhanced the elastic modulus(G')and viscous modulus(G”)of the dough.During dough fermentation,the addition of tea polyphenols did not affect the viability of yeast,but significantly reduced the gas holding capacity,resulting in a reduction in its volume.When the amount of tea polyphenols was 2%,the volume of dough was reduced by 10.8 mL(27.0%),12.9 mL(29.7%),and 13.9 mL(30.6%)after fermentation for 30 min,60 min,and 90 min,respectively.Gluten is the basis of the structure and physical properties of bread and dough.The addition of gluten can improve the quality of tea polyphenol-bread(2% tea polyphenol).The results showed that when gluten amount was added to 12%,the specific volume of tea polyphenol bread was comparable to that of the control group,the bread hardness was reduced by 31.6%,the internal structure was improved,and the sensory score was also increased.The interaction between gluten and tea polyphenols may be the mechanism by which tea polyphenols affected the physiochemical property of bread and dough systems.The results of the water distribution experiment showed the disappearance of the bound water peak,and an increase of adsorbed water and free water by 17.3% and 0.4%,respectively.Simultaneously,the disulfide bond content was decreased by 9.9 ?mol/g(24.2 %),and the stability of disulfide bonds were also reduced evidenced by a reduction(15.0%)of the relative content of the gauche-gauche-gauche structure.Analysis of the secondary structure of gluten protein showed that tea polyphenols increase the ratio of random coil and ?-folding,which indicated that the addition of tea polyphenols reduces the stability of the protein structure,destroys the formation of gluten protein network,and reduces the wet gluten content(93.3%).Consistently,the results of scanning electron microscope and laser confocal microscope also showed the same results.The analysis of the internal chemical bonds of the dough showed that the addition of tea polyphenols increased the internal hydrogen bonds and the hydrophobic interaction among the dough proteins and improved the thermal stability of the dough.Tea polyphenols also reduced the peak viscosity and retrogradation viscosity of wheat flour,indicating that the interaction between tea polyphenols and starch may also be another factor affecting bread quality.