Glycation of proteins by polysaccharides via the Maillard reaction improves the functional properties of proteins in foods, such as solubility, heat stability, emulsification, foaming, and gelation. Glycation is achieved by either the dry heating or the wet heating method, and considerable research has been reported on the functionality of the reaction mixture as tested in foods. While the characteristics of the glycates in foods have been well studied, the kinetics and equilibrium yield of the protein-polysaccharide glycation reaction has received little attention. Industrial manufacture of the glycates will require understanding the kinetics and yield of the glycation reaction. This work examined the glycation of whey protein isolate (WPI) and glycomacropeptide (GMP) by using dextran and the dry-heating method at 70 °C and 80% relative humidity. The disappearance of un-glycated protein and the creation of glycated protein were observed using chromatographic analysis and fluorescence laser densitometry of sodium dodecyl sulfate-polyacrylamide gels. Data were fit using a first-order reversible kinetic model. The rate constants measured for the disappearance of un-glycated protein by sodium dodecyl sulfate-polyacrylamide (SDS-PAGE) (k = 0.33 h-1) and by chromatographic analysis (k = 0.38 h-1) were not statistically different from each other for WPI-dextran glycation. Dextran glycation of GMP was slower than for WPI (k = 0.13 h-1). The slower rate of glycation of GMP was attributed to the 50% lower Lys content of GMP compared to WPI. Yield for the dry-heating dextran glycation method was 89% for WPI and 87% for GMP. The present work is useful to the food industry to expand the use of glycated proteins in creating new food products.
Keywords: carbohydrates; conjugation; dairy.