LC/MS Analysis and Antioxidative Efficiency of Maillard Reaction Products from a Lactose−Lysine Model System

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Abstract
Aqueous solutions of lactose and lysine were refluxed for up to 4 h without pH control. Samples were collected every hour, and the reaction was monitored by measuring the pH, the optical density at 420 nm, and the relative antioxidative efficiency (RAE). The greatest change in optical density and antioxidative efficiency occurred for the mixture heated for 4 h. The 4 h solution was separated into three fractions according to the molecular weights of the components and tested for RAE. The high molecular weight fraction was more colored, and it had the highest antioxidative activity. The low molecular weight fraction was separated by high-performance liquid chromatography (HPLC). RAE values were measured for each purified compound. HPLC coupled with diode array and electrospray mass spectrometry allowed a rapid screening of the solutions and a tentative identification of several peaks. Nuclear magnetic resonance analysis allowed the identification of galactosylisomaltol and pyrraline. The resonance assignments for these compounds were revised. Keywords: Maillard reaction; lactose; lysine; antioxidative efficiency; pyrraline; galactosylisomaltol; HPLC/MS