Abstract
Formation of dialkylpyrazinium radical cations in aerated 70 % aqueous glycerol solutions of glucose and lysine during heating resulting in browning (90, 110, and 130°C, investigated) was more dependent on temperature than formation of brown colour. Activation energy (Ea) for radical formation was ~83 kJ mol–1, compared with ~70 kJ mol–1 for browning, and was unaffected by methyl linolenate. Low-temperature browning was influenced by non-radical degradation of Amadori products, whereas radical processes were prominent at higher temperatures and were unaffected by unsaturated lipids. In contrast, methyl linolenate reacts with lysine in the absence of glucose to form fluorescent products at a slow rate (Ea 25 kJ mol–1). Glucose increased the rate of formation of fluorescent products (Ea ~60 kJ mol–1), in agreement with Maillard reactions at low temperatures involving glucose as a rate-determining reagent. Lipid oxidation does not have a direct effect on lysine and glucose browning reactions at conditions relevant for food; effects of lipids on Maillard reactions are matrix-related.
Published Version
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