Formation of whey protein isolate-dextran conjugates by Maillard reaction with ethanol-water pretreatment

A simple, efficient, and low-cost Maillard reaction method was developed through ethanol-water pretreatment. The formation of whey protein isolate (WPI)-dextran conjugates was confirmed using the degree of glycosylation, ultraviolet absorbance, browning intensity, color, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The significant conformational changes were illuminated because of the higher wavenumber shift of absorption peaks of FTIR amide I, II, and III bands, the reduction of fluorescent signal, and the decrease of surface hydrophobicity. Scanning electron microscopy revealed the morphological transition of WPI from a smooth sphere to an inhomogeneous block structure with rough and uneven surface before and after covalent grafting of dextran. The strong steric hindrance and abundant hydrophilic hydroxyl groups from covalently conjugated dextran dramatically inhibited the aggregation between conjugate molecules which exhibited low turbidity and good solubility in a wide pH range from 2.0 to 10.0. Emulsifying activity and emulsifying stability of WPI were significantly improved after glycosylation. This work will be beneficial to control the formation of light-colored Maillard reaction products under high substrate concentration, high reaction rate, and low water content at mild temperatures for short processing time, and to facilitate the large-scale preparation of glycosylated protein with desirable physicochemical properties.