Maillard reaction

TheMaillard reaction(/maɪˈjɑːr/my-YAR;French:[majaʁ]) is achemical reactionbetweenamino acidsandreducing sugarsto createmelanoidins, the compounds that give browned food its distinctive flavor.Searedsteaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, falafel and many other foods undergo this reaction. It is named after French chemistLouis Camille Maillard, who first described it in 1912 while attempting to reproduce biologicalprotein synthesis.The reaction is a form ofnon-enzymatic browningwhich typically proceeds rapidly from around 140 to 165 °C (280 to 330 °F). Manyrecipescall for an oven temperature high enough to ensure that a Maillard reaction occurs.At higher temperatures,caramelization(the browning of sugars, a distinct process) and subsequentlypyrolysis(final breakdown leading to burning and the development of acrid flavors) become more pronounced.
The reactivecarbonyl groupof the sugar reacts with thenucleophilicamino groupof the amino acid and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavors. This process is accelerated in an alkaline environment (e.g.,lyeapplied to darken pretzels; seelye roll), as the amino groups (RNH+3→ RNH2) aredeprotonated, and hence have an increasednucleophilicity. This reaction is the basis for many of theflavoringindustry's recipes. At high temperatures, a probablecarcinogencalledacrylamidecan form.This can be discouraged by heating at a lower temperature, addingasparaginase, or injecting carbon dioxide.
In the cooking process, Maillard reactions can produce hundreds of different flavor compounds depending on the chemical constituents in the food, the temperature, the cooking time, and the presence of air. These compounds, in turn, often break down to form yet more flavor compounds.Flavor scientistshave used the Maillard reaction over the years to make artificial flavors, the majority of patents being related to the production of meat-like flavors.
In 1912,Louis Camille Maillardpublished a paper describing the reaction between amino acids and sugars at elevated temperatures.In 1953, chemistJohn E. Hodgewith theU.S. Department of Agricultureestablished a mechanism for the Maillard reaction.
The Maillard reaction is responsible for many colors and flavors in foods, such as thebrowningof various meats when seared or grilled, the browning andumamitaste infried onionsandcoffee roasting. It contributes to the darkened crust ofbaked goods, the golden-brown color ofFrench friesand other crisps, browning of malted barley as found inmaltwhiskey and beer, and the color and taste ofdriedandcondensed milk,dulce de leche,toffee,black garlic,chocolate,toasted marshmallows, androasted peanuts.
6-Acetyl-2,3,4,5-tetrahydropyridineis responsible for the biscuit or cracker-like flavor present in baked goods such as bread, popcorn, and tortilla products. The structurally related compound2-acetyl-1-pyrrolinehas a similar smell and also occurs naturally without heating. The compound gives varieties of cooked rice and the herbpandan(Pandanus amaryllifolius) their typical smells. Both compounds haveodor thresholdsbelow 0.06 nanograms per liter.
The browning reactions that occur when meat is roasted or seared are complex and occur mostly by Maillard browningwith contributions from other chemical reactions, including the breakdown of the tetrapyrrole rings of the muscle proteinmyoglobin. Maillard reactions also occur indried fruitand whenchampagneages in the bottle.
Caramelizationis an entirely different process from Maillard browning, though the results of the two processes are sometimes similar to the naked eye (and taste buds). Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They are both promoted by heating, but the Maillard reaction involves amino acids, whereas caramelization is thepyrolysisof certain sugars.
In makingsilage, excess heat causes the Maillard reaction to occur, which reduces the amount of energy and protein available to the animals that feed on it.
In archaeology, the Maillard process occurs when bodies are preserved inpeat bogs. The acidic peat environment causes atanningor browning of skin tones and can turn hair to a red or ginger tone. The chemical mechanism is the same as in the browning of food, but it develops slowly over time due to the acidic action on thebog body. It is typically seen onIron Agebodies and was described by Painter in 1991 as the interaction of anaerobic, acidic, and cold (typically 4 °C (39 °F)) sphagnum acid on thepolysaccharides.
The Maillard reaction also contributes to the preservation ofpaleofeces.
The open-chainAmadoriproducts undergo further dehydration and deamination to produce dicarbonyls.This is a crucial intermediate.
Dicarbonyls react with amines to produce Strecker aldehydes throughStrecker degradation.
Acrylamide, a possible humancarcinogen,can be generated as a byproduct of Maillard reaction between reducing sugars and amino acids, especiallyasparagine, both of which are present in most food products.