reaction between the lysine in a protein with a reducing sugar to form a brown compound

Browning reaction involving combination of an amino group (2NH2) from a protein and an aldehyde group from a sugar, which then leads to the formation of many complex substances.

This chemical reaction between amino acids from protein and carbohydrates exposed to high temperatures produces both browning and pleasant flavor changes in foods that are not made primarily of sugars: Bread crusts, roasted coffee beans and nuts, beer, and dry-heat cooked (roasted, fried, baked, sauteed) meats, for example. The reaction was first described by French biochemist Louis-Camille Maillard in 1912. The Maillard reaction happens quickly only at high temperatures, which is why foods that are cooked in boiling water, which has a maximum temperature of 212 degrees, do not brown on the exterior. In foods composed primarily of sugars, the chemical reaction that accounts for browning (and its culinary term) is “caramelization.