Maillard

The Maillard reaction is a non-enzymatic browning process that occurs when reducing sugars react with amino compounds, such as amino acids, peptides, or proteins, upon heating. It was first described by the French chemist Louis-Camille Maillard in 1912, who observed complex color and flavor changes in heated mixtures of sugars and amino compounds.

Mechanistically, the reaction begins with the condensation of a carbonyl group of a reducing sugar with a free amino group to form a Schiff base, which rapidly rearranges to more stable Amadori products. Through a cascade of dehydration, fragmentation, and rearrangement reactions, these intermediates generate a wide range of heterocyclic compounds and carbonyl-amine condensation products. The process eventually yields brown pigments known as melanoidins and numerous aroma-active compounds that contribute to flavor.

Conditions strongly influence the rate and extent of the Maillard reaction. It proceeds more rapidly at higher temperatures (typically in the range of 140 to 180°C), with lower moisture activity and, in many cases, slightly alkaline conditions. Availability of reducing sugars and reactive amino groups, as well as food composition and pH, also play key roles. The reaction is prominent in many cooked foods, including bread crusts, seared meats, roasted coffee and cocoa, cookies, and toasted nuts.

The Maillard reaction is distinct from caramelization, which involves sugar-only heating. While it enhances desirable flavors and browning, it can also lead to the formation of unwanted compounds under certain conditions, such as acrylamide, prompting mitigation strategies like controlling temperature and moisture, processing times, and formulation.