Influence of the Maillard reaction on the structure of β-casein using a simulated cooking system

Abstract

Glycation during food processing can change the structural characteristics of dietary protein and endow a variety of functionalities. Milk β-casein (MC) with five different types of carbohydrates (i.e., glucose, sucrose, amylose, amylopectin, and soluble starch) in a simulated cooking system at 98 and 115 °C was investigated. The changes in ultraviolet absorption, endogenous fluorescence intensity, surface hydrophobicity, particle size, free amino group, free sulphydryl group, and circular dichroism were measured. For the glucose-added group, the lowest free amino content and most significant spectral changes among all groups were observed after heating at 115 °C for 6 hr (OH-MC-Glu). Results showed that glycation activities of five sugars were glucose > sucrose > soluble starch> amylopectin ≈ amylose. Under the simulated cooking system, the secondary structure and conformation of glycated MC changed to different degrees, which were affected by the glycation degree. Moderate glycation (0-2 hr of heating) may promote the conversion reaction of sulfhydryl-disulfide bond (SH-SS) in MC, causing cross-linking and self-aggregation of MC, and induce the particle size increase of MC. Excessive glycation (2-6 hr of heating) can further reduce the surface hydrophobicity of MC, inhibit self-aggregation of MC, and reduce the particle size of MC.