Maillard Reactions Of Proteins In Deep Eutectic Solvents

The deep eutectic solvent(Deep Eutectic Solvent,DES)is a mixture of two separate solids that forms a homogeneous liquid.The Maillard reaction is a series of reactions between carbonyl and amino compounds,which can be used for protein glycation to improve their functionalities.In the Maillard reaction,two methods are generally used:the dry-heat and wet-heat methods.The former is suffering from a long reaction time due to insufficient contacting between the sugars and proteins.The latter is suffering from a low degree of glycation due to the inhibiting effects of water to the Maillard reaction,where water is a reaction product.In this study,DES consisted of fructose and choline chloride was prepared and used for protein glycation.Fructose not only can act as a solvent,but also act as a reactant.Meanwhile,DES is free of water,and the moisture content can be effectively controlled to lower its inhibiting effect.It is expected by using DES for protein glycation,the problems of low degree of glycation in wet-dry method and the long reaction time in dry-method can be mitigated.The DES consisting of fructose and choline chloride was prepared.It was found that at mass ratios of fructose to choline chloride of 2:1,1.5:1,1:1,a stable homogeneous DES could be obtained.When the mass ratio of fhuctose to choline chloride was at 1:1.5,1:1.75,1:2,DES is unstable at room temperature and crystals were precipitated out easily.The effects of water dilution to reduce the viscosity of DES on the Maillard reaction was studied.It was found that the Maillard reaction was significantly affected by the dilution.High or low dilution ratio affected the Maillard reaction negatively.When the moisture content was at 20%,highest degree of Maillard reaction was observed.The longer the reaction time,the higher the color and the degree of browning.With the increase of reaction time,the pH value of the reaction system decreased,and the degree of glycation increased.Compared to fructose,the extent of protein glycation in DES system was higher.The physical and chemical properties of proteins after Maillard reaction were studied.The protein solubility and zeta potentials at different pH values remained rather constant after reaction.SDS-PAGE analysis found that high molecular weight compounds were formed,which might be caused by the crosslinking of protein in Maillard reaction.The free thiol content of protein decreased and the surface hydrophobicity increased after the Maillard reaction.CD analysis demonstrated that the content of a-helix decreased,and the content of ?-sheet increased,and the turn and random coil remained constant.The higher the degree of reaction,the lower the a-helix content,and the higher the ?-sheeting content was.The gel properties of the protein was changed after the Maillard reaction,and the viscosity,storage modulus and loss modulus of the gel decreased.