Using an enzymatic galactose assay to detect lactose glycation extents of two proteins caseinate and soybean protein isolate via the Maillard reaction

BACKGROUND: Glycation of food proteins via the Maillard reaction has been widely studied in the recent years; however, the amount of saccharide connected to proteins is usually not determined. An enzymatic galactose assay was proposed firstly in this study to detect lactose glycation extents of caseinate and soybean protein isolate (SPI) during the Maillard reaction at two temperatures and different times. RESULTS: The separated glycated proteinswere hydrolysed to release galactose necessary for the enzymatic assay and glycation calculation. Caseinate and SPI both obtained the highest lactose glycation extents at 100 degrees C or 121 degrees C by a reaction time of 180 or 20 min. Short-and long-time reaction resulted in lower glycation extents. During the reaction, three chemical indices (absorbences at 294/490nm and fluorescence intensities) of reaction mixtures increased continually, but another index reactable -NH2 of glycated proteins showed the opposite trend. In general, changing profiles of the four indices were inconsistent with those profiles of lactose glycation extents of glycated proteins, implying practical limitation of the four indices in studies. CONCLUSION: This proposed enzymatic assay could directly detect lactose glycation of the two proteins, and thus was more useful than the four chemical indices tomonitor glycation of the two proteins. (C) 2016 Society of Chemical Industry