INHIBITION OF BROWNING BY SULFUR AMINO-ACIDS .1. HEATED AMINO-ACID GLUCOSE SYSTEMS

Amino acids interact with carbohydrates to form Maillard browning products. Such reactions reduce the nutritional value of foods containing amino acids and carbohydrates and may lead to the formation of compounds that are mutagenic and clastogenic or chromosome-damaging. A need therefore exists to inhibit these heat-induced interactions. To demonstrate whether SH-containing sulfur amino acids minimize nonenzymatic browning, β-alanine, Nα-acetyl-L-lysine, glycylglycine, and a mixture of amino acids were each heated with glucose in the absence and presence of the following potential inhibitors: N-acetyl-L-cysteine, L-cysteine, reduced glutathione, sodium bisulfite, and urea. Inhibition was measured as a function of temperature, time of heating, and concentration of reactants. The extent of browning was estimated by absorbance measurements at 420 nm. Inhibition was independent of the amino group containing reactant. The minimum concentrations for optimum inhibition, in moles of inhibitor per mole of D-glucose, were as follows: sodium bisulfite, 0.02; L-cysteine, 0.05; iV-acetyl-L-cysteine, 0.2; reduced glutathione, 0.2; urea, 8. An “index of prevention” (IP) was used to calculate the inhibition at the optimum mole ratio range, where IP = 100 - [molar absorptivity value (MAV) of the amine compound + glucose + inhibitor] X 100/(MAV of the amine compound + glucose). The calculated values were about 90% in all cases. Possible mechanisms of browning prevention are discussed. © 1990, American Chemical Society. All rights reserved.