Maillard Reaction Basics
The Maillard reaction is a set of complex reactions between amino acids and reducing sugars that occurs in both cooking and, to a lesser extent, spontaneously over time. When thinking of the Maillard reaction, the golden-brown pastries in a bakery or the sear on a steak come to mind. This browning is generally positive, creating delicious flavors and an appealing golden-brown appearance. However, Maillard browning is not always desirable. Browning can also occur in shelf-stable food products, influenced by factors such as temperature, pH, water activity, amino acid content, and the type of sugar present. Products with high carbohydrate content, like protein bars and cereals, can brown over time, which may become undesirable. This issue is common in foods with especially long shelf lives, such as combat rations.
As mentioned, the Maillard reaction requires a reducing sugar, meaning a sugar molecule with a free carbonyl group (such as an aldehyde or ketone) capable of reacting with amino groups. Reducing sugars can open into a chain form, exposing the reactive carbonyl group, allowing them to participate in the reaction.
During the Maillard reaction, when sugars and amino acids react, they produce melanoidins. These nitrogen-containing compounds are responsible for the brown color of foods that have undergone the Maillard reaction and contribute to flavors we associate with baked goods, seared meats, and more. The Maillard reaction is often confused with caramelization and dextrinization, which can occur simultaneously and sometimes cause confusion. Caramelization is specific to the browning of sugars that are heated and broken down, while dextrinization is the breakdown of starches into smaller chains, also leading to browning. All three reactions can occur at once.
A good example of a food that undergoes all three of these reactions is toasted bread. Temperature plays a major role in triggering the Maillard reaction and the other two reactions as well. As bread heats, the amino acids and sugars react, resulting in browning and the development of complex flavors. Meanwhile, the sugars melt and break down into smaller compounds that contribute to a caramel-like flavor, primarily diacetyl, furans, and aldehydes. The final reaction, dextrinization, also partially contributes to the browning of toast. This reaction occurs without water; when starches are heated, the large molecules break down into smaller dextrins.
Many aromatic compounds are direct products of the Maillard reaction—pyrazines, furans, oxazoles, and more—all of which contribute to aroma and flavor.
These reactions illustrate how food chemistry transforms simple ingredients into the flavors we know and enjoy. The Maillard reaction, in particular, is responsible for the rich taste and aroma in foods like toasted bread, roasted coffee, and grilled meats. It’s the science behind the browning and depth that make these foods so appealing.
https://www.sciencedirect.com/science/article/abs/pii/S0956713523003110
https://www.sciencedirect.com/science/article/abs/pii/S0963996917303265