The reactivity of the individual protein-bound lysine residues of beta-casein a1 during the initial stages of the Maillard reaction
1993
Henle, T. | Klostermeyer, H. (Muenchen Technisch Univ. (Germany). Lehrstuhl fuer Milchwissenschaft)
A method was established to obtain information on the extent of the early Maillard-reaction between individual protein bound lysine residues of beta-casein A1 and reducing sugars. Comparing the tryptic maps of beta-casein A1 heated with and without lactose, we could determine via the calculation of relative peak areas at which positions and to what extent the 11 lysine residues were modified by the reaction with lactose. The reactivity of the individual lysine residues proved to be extremely different. A favourite glycosylation was observed on Lys28/29, Lys32, Lys99 and Lys107. In the primary sequence of beta-casein A1, these residues are located directly adjacent to charged side chains of glutamic acid and lysine, respectively. Amino groups adjacent to hydrophobic amino acids reacted significantly slower. Thus, the microenvironment might be principally responsible for the reactivity of a protein bound lysine residue during the early Maillard-reaction. But charged side chains an intermolecular catalysis of the Amadori-rearrangement could be affected, thus leading to an oriented formation of protein bound Amadori-products at specific reaction sites.
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