Determination of free carbohydrates and Amadori compounds formed at the early stages of non-enzymic browning

Abstract

α-N-acetyl, ϵ-N-(1-deoxy- d-lactulos-l-yl)- l-lysine (ALL) was prepared as a model of protein-bonded lactose, and characterized by NMR. An HPLC method was designed to determine it. Milk model systems containing lactose, α-N-acetyl- l-lysine and salts were heated at 120°C (in the liquid state) or freeze-dried and stored at 45°C and 0·44 a w. Free carbohydrates formed were determined by GC, and ALL by HPLC. Lactulose was formed at higher levels than ALL when heating, whereas the opposite was true during the storage of lyophilizates. It was shown that enolization is the main pathway of lactose degradation at high temperature, and that addition to amino groups predominates at low temperatures and a w.