Effect Of Glutamine Transaminase On Structure And Functional Properties Of Whey Protein

Whey protein is a recovered product of whey,which is very rich in nutritional value.In this paper,whey protein was used as the raw material and cross-linked with transglutaminase to prepare modified whey protein samples.On this basis,the effects of concentration,action time and action temperature on the microstructure,apparent structure and functional properties of whey protein were studied.The whey protein gel was prepared,and the mechanism of gel formation was preliminarily explored.Response surface analysis was performed to obtain the enzyme-modified whey protein gel with the best gel strength.The analysis explored the modification of transglutaminase.Changes in texture,moisture status and digestibility of whey protein gel before and after sex.The main research contents and results are as follows:(1)The effect of transglutaminase on the microstructure of whey protein was studied.The content of free sulfhydryl groups in whey protein cross-linked by transglutaminase decreases,and the disulfide bond content first increases and then decreases.The disulfide bond content is closely related to the gel strength;the degree of cross-linking shows that transglutaminase induces The formation of?-(?-glutamyl)lysine bond leads to a decrease in the free amino content of whey protein and therefore an increase in the degree of cross-linking of the protein.Infrared spectroscopy analysis shows that whey protein is dominated by?-helical structure.Transaminase treatment leads to a decrease in the?-helical structure,while increasing the rigid?-sheet and?-turn structures;fluorescence spectroscopy results show that whey protein has the maximum fluorescence intensity when the enzyme concentration is 12 U/g,and then gradually decreases;X-ray diffraction pattern shows that after the action of transglutaminase,the intensity of the diffraction peak on the left side of whey protein is weakened,and the intensity of the diffraction peak on the right side is enhanced.The peak shifts slightly to the left and becomes wider,indicating that the protein structure is affected.damage.(2)Optical microscope showed that whey protein was modified by transglutaminase to form a polymer;scanning electron microscope results showed that whey protein was cross-linked by transglutaminase and formed a three-dimensional network,and certain transglutaminase The whey protein network structure treated by concentration,action time and action temperature is more compact,with moderate pore size and uniform distribution;the particle size and Zeta potential results show that when the concentration of transglutaminase,the action time and the action temperature are 16 U/g,At 1.0 h and 40~oC,whey protein forms the largest polymer.(3)The effects of different concentrations of transglutaminase,action time and action temperature on the functional properties of whey protein were studied.The results showed that the foamability,foaming stability,emulsification,water retention,oil absorption,turbidity and freeze-thaw stability of whey protein all increased with the concentration of transglutaminase,the action time and the action temperature.The increase first increases and then decreases.When the enzyme concentration is 16 U/g,the foamability,emulsification,water retention,oil absorption,and turbidity of whey protein reach the maximum;when the enzyme concentration is 20 U/g,whey protein has the highest foaming stability and Freeze-thaw stability;because the net negative charge of the whey protein molecule first decreases and then increases,the emulsion stability also shows a trend of first decrease and then increase,and the viscosity increases with the increase of the concentration of transglutaminase.(4)The effects of the concentration of transglutaminase,the action time and the action temperature on the strength of whey protein gel were studied.On the basis of single-factor experiments,taking gel strength as an indicator,a response surface model was established to optimize the parameters,and the best process parameters for preparing whey protein gels by transglutaminase cross-linking were obtained:the concentration of transglutaminase was 16.33 U/g,the action time is 1.06 h,and the action temperature is39.99~oC.Under these conditions,the gel strength of whey protein can reach 53.06 gf·mm.The texture,moisture state and digestibility results of the whey protein gel before and after modification show that the cross-linked modified whey protein gel has better gel strength,elasticity,water retention and digestibility than before modification rate.