Structure and antioxidant activity of Mail lard 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 alpha-lactalbumin (alpha-LA) or beta-lactoglobulin (beta-LG), heated at 95 degrees C, for up to 5 h. The pH of MRPs decreased significantly during heat treatment of alpha-LA-Ribose and beta-LG-Ribose mixtures from 8.4 to 5.3. The amino group content in MRPs, derived from the alpha-LA-Ribose and beta-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 beta-LG-Ribose than for alpha-LA-Ribose. During the Maillard reaction, the concentration of native and non-native alpha-LA, or beta-LG, decreased and the formation of aggregates was observed. Fluorescence intensity of the beta-LG-Ribose MRPs reached maximum within 1 h, compared to 2 h for alpha-LA-Ribose MRPs. Meanwhile, modification of the UV/vis absorption spectra for alpha-LA and beta-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 alpha-LA and beta-LG monomers via inter-molecular disulfide bridge, but also via other covelant bonds. MRPs from alpha-LA-Ribose and beta-LG-Ribose exhibited increased antioxidant activities, therefore theses MRPs may be used as natural antioxidants in food products. (C) 2012 Elsevier Ltd. All rights reserved.