Structure and antioxidant activity of Maillard reaction products from α-lactalbumin and β-lactoglobulin with ribose in an aqueous model system

Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 3% (w/w) ribose and 3% (w/w) of the dairy proteins α-lactalbumin (α-LA) or β-lactoglobulin (β-LG), heated at 95 °C, for up to 5 h. The pH of MRPs decreased significantly during heat treatment of α-LA-Ribose and β-LG-Ribose mixtures from 8.4 to 5.3. The amino group content in MRPs, derived from the α-LA-Ribose and β-LG-Ribose model system, was decreased noticeably during the first hour and did not change thereafter. The loss of free ribose in MRPs was higher for β-LG-Ribose than for α-LA-Ribose. During the Maillard reaction, the concentration of native and non-native α-LA, or β-LG, decreased and the formation of aggregates was observed. Fluorescence intensity of the β-LG-Ribose MRPs reached maximum within 1 h, compared to 2 h for α-LA-Ribose MRPs. Meanwhile, modification of the UV/vis absorption spectra for α-LA and β-LG was mainly due to a condensation reaction with ribose. Dynamic light scattering showed a significant increase in the particle size of the MRPs. Size exclusion chromatography of MRPs revealed the production of both high and low molecular weight material. Electrophoresis of MRPs indicated polymerization of α-LA and β-LG monomers via inter-molecular disulfide bridge, but also via other covelant bonds. MRPs from α-LA-Ribose and β-LG-Ribose exhibited increased antioxidant activities, therefore theses MRPs may be used as natural antioxidants in food products.