Effect Mechanism Of ?-polyglutamic Acid On Rheological Properties Of Wheat Dough

?-polyglutamic acid[Poly(?-glutamic acid),?-PGA]as a natural food additive,has been widely used in the field of cereal products,improving the quality of noodle products in many ways.At present,most studies tend to explore the functionality of y-PGA in noodle products,but there are few studies on related mechanisms,so that it cannot provide theoretical basis and technical guidance for the better application of ?-PGA to the food industry.Adding different concentrations of?-PGA to flour to make dough.The three aspects of dough rheological properties,changes in dough composition,and the quality of buns and biscuits were studied.The main research contents and results are as follows:(1)From the perspective of empirical rheology(farinographical properties)and basic rheology(uniaxial stretching,dynamic oscillation,stress relaxation),it was found that ?-PGA has a significant effect on the rheological properties of dough.Farinographical properties experiments indicated that ?-PGA can significantly increased the water absorption of flour,and the highest water absorption was obtained when the amount of 0.50%y-PGA was added,which was 5.93%higher than that of the control.The dough developing time and stabilizing time were significantly extended,from 4.04 min to 7.87 min,4.40 min to 12.79 min,and the degree of weakening gradually decreased with the increase of ?-PGA addition,from the initial 132 to 42,68.19%reduction.?-PGA reduced the maximum resistance of dough stretching,the degree of elongation increased,the area of stretching decreased first and then increased.It indicated that ?-PGA reduced the tensile properties of the dough and enhanced the overall fluidity of the dough.?-PGA caused the dough's elastic modulus and viscous modulus to decrease,and the loss factor became larger.The effect of adding 1.00%?-PGA was most obvious.It indicated that the addition of?-PGA maked the dough more moist and slack.A larger loss factor indicated that the dough had become more relaxed.In order to verify this,a stress relaxation experiment of the dough was conducted.The results showed that ?-PGA significantly reduced the stress of the dough.When the amount of ?-PGA was 1.50%,the maximum stress and equilibrium stress were reduced by 24.8%and 34.8%,respectively,and the general elastic modulus was reduced from 4.16 × 104 Pa to 2.77 × 104 Pa,high elastic modulus reduced from 11.04×103 Pa to 7.20 × 103 Pa,damping coefficient reduced from 5.41 × 105 Pa·S to 3.50 × 105 Pa·S,relaxation time shortened from 12.99 min to 12.61 min,the degree of deformation increased significantly.It was verified again that the relaxation characteristics of the dough became larger,and the stress,elasticity and initial viscosity of the dough became smaller.(2)The effect of y-PGA on dough rheological properties was the result of the interaction between ?-PGA and dough ingredients.Moisture was the main component of the dough.Using pulsed nuclear magnetic resonance technology to study the moisture characteristics of the dough,it was found that the T22 value decreased and the activity of the semi-bound water in the dough decreased,indicated that the binding force of ?-PGA to the semi-bound water of the dough was enhanced.Using laser confocal scanning microscope to observed the dough formation,it was found that the protein network had aggregation,the connection between the network was weakened,the pores became smaller,and the starch granules swelled resulting in irregular shapes,This indicates that ?-PGA has a negative effect on protein and interacts with starch.From the electron microscopy image of the dough powder,it can be seen intuitively that the particles of the dough powder added with ?-PGA at the same grinding strength became smaller,the protein coated on the starch surface decreased,the number of exposed starch particles increased,and the starch structure was damaged.When the added amount of ?-PGA was 0.75%,the flour particles were the smallest,indicating that ?-PGA maked the freeze-dried dough easier to grind into powder,the protein structure became weaker,and the degree of starch damage became larger.According to the determination of the solvent retention of dough powder,y-PGA has a significant effect on the solvent retention of these four solutions.?-PGA increased the SRC values of the trace water SRC,trace sodium carbonate SRC,and trace sucrose of the dough powder,and reached the maximum value when 1.00%?-PGA was added,y-PGA reduced the amount of trace lactic acid SRC,indicated that?-PGA improved the water absorption capacity of the dough powder,maked the wheat flour easier to be in a high-sugar environment,had a weakening effect on the properties of wheat gluten,and interacted with starch and gliadin effect.(3)?-PGA changed the spatial structure of protein and weakened gluten.y-PGA had no significant effect on crude protein content.Different amounts of ?-PGA had different effects on the dry and wet gluten content of the dough powder.A small amount of ?-PGA(0.25%to 0.50%)increased the gluten content,0.75%?-PGA reduced the dry and wet gluten content of dough powder,and excessive addition of?-PGA(1.00%to 1.50%)increased the dry and wet gluten content.According to the glutenin macropolymer(GMP)content test and SDS soluble protein liquid chromatography analysis,it can be seen that ?-PGA reduced the GMP content and the SDS soluble protein content increased.This shows that ?-PGA depolymerizes glutenin macropolymer and degrades them into SDS soluble proteins.The measurement of the free thiol and disulfide bond content of wheat dough showed that the free thiol content decreased and the disulfide bond content did not change.The analysis of Fourier infrared spectroscopy result showed that the addition of ?-PGA changed the secondary structure of wheat protein,the protein structure was stretched,the ?-helix and ?-turn structure were reduced,and the ?-sheet structure was increased.The wheat protein was analyzed by SDS-PAGE,and the addition of ?-PGA did not destroy the primary structure of the protein.(4)?-PGA had an improving effect on cooking products(buns)and baking products(biscuits).0.50%?-PGA increased the specific volume of steamed buns,but the specific volume of steamed buns decreased as the amount of ?-PGA continues to increase.The steamed bread made by adding 0.50%?0.75%y-PGA had the lowest hardness and chewability,and the responsiveness of steamed bread made by 1.00%?1.50%?-PGA was reduced.When the added amount of ?-PGA was 0.25%?0.75%,the distribution of pores inside the steamed bread became more and more uniform,and the diameter of pores was mostly small,spots appeared on the skin of buns.As the amount of ?-PGA added increased,the hardness of the biscuits decreased,and the brittleness decreased first and then rised.?-PGA improved the color of the biscuit,became more white and bright,the weight of the biscuit became larger,the yield rate was improved,the surface was smooth and delicate.