Maillard reaction

The Maillard reaction (/maɪˈjɑːr/ my-YAR; French: [majaʁ]) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and many other foods undergo this reaction. It is named after French chemist Louis-Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis.[1][2]

The crusts of most breads, such as this brioche, are golden-brown due to the Maillard reaction.
Effects of the Maillard reaction on a starch-rich material (potato slice). The substrate is shown before (left) and after (right) being exposed to hot dry air (503 K, approx. 230 °C/445 °F).

The reaction is a form of non-enzymatic browning which typically proceeds rapidly from around 140 to 165 °C (280 to 330 °F). Many recipes call for an oven temperature high enough to ensure that a Maillard reaction occurs.[3] At higher temperatures, caramelization (the browning of sugars, a distinct process) and subsequently pyrolysis (final breakdown leading to burning) become more pronounced.

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of 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., lye applied to darken pretzels; see lye roll), as the amino groups (RNH3+ → RNH2) are deprotonated, and hence have an increased nucleophilicity. This reaction is the basis for many of the flavoring industry's recipes. At high temperatures, a probable[4] carcinogen called acrylamide can form.[5] This can be discouraged by heating at a lower temperature, adding asparaginase, or injecting carbon dioxide.[4]

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 new flavor compounds. Flavor scientists have used the Maillard reaction over the years to make artificial flavors.

History

In 1912, Maillard published a paper describing the reaction between amino acids and sugars at elevated temperatures.[1] In 1953, chemist John E. Hodge, with the U.S. Department of Agriculture, established a mechanism for the Maillard reaction.[6][7]

Foods and products with Maillard reactions
6-Acetyl-2,3,4,5-tetrahydropyridine
2-Acetylpyrroline

The Maillard reaction is responsible for many colors and flavors in foods, such as the browning of various meats when seared or grilled, the browning and umami taste in fried onions, and coffee roasting. It contributes to the darkened crust of baked goods, the golden-brown color of French fries and other crisps, of malted barley as found in malt whiskey and beer, and the color and taste of dried and condensed milk, dulce de leche, the Sri Lankan confection milk toffee, black garlic, chocolate, and roasted peanuts.

6-Acetyl-2,3,4,5-tetrahydropyridine is responsible for the biscuit or cracker-like flavor present in baked goods such as bread, popcorn, and tortilla products. The structurally related compound 2-acetyl-1-pyrroline has a similar smell, and also occurs naturally without heating and gives varieties of cooked rice and the herb pandan (Pandanus amaryllifolius) their typical smells. Both compounds have odor thresholds below 0.06 ng/l.[8]

Roast pork, browned using the Maillard reaction
The preparation of French fries at high temperature can lead to the formation of acrylamide.[5]

The browning reactions that occur when meat is roasted or seared are complex, and occur mostly by Maillard browning[9] with contributions from other chemical reactions, including the breakdown of the tetrapyrrole rings of the muscle protein myoglobin.

Caramelization is 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, as discussed above, whereas caramelization is simply the pyrolysis of certain sugars.

Maillard reactions also occur in dried fruit.[10]

In making silage, excess heat causes the Maillard reaction to occur, which reduces the amount of energy and protein available to the animals that feed on it.

Chemical mechanism
  1. The carbonyl group of the sugar reacts with the amino group of the amino acid, producing N-substituted glycosylamine and water
  2. The unstable glycosylamine undergoes Amadori rearrangement, forming ketosamines
  3. Several ways are known for the ketosamines to react further:

The open-chain Amadori products undergo further dehydration and deamination to produce dicarbonyls.[11] This is a crucial intermediate.

Dicarbonyls react with amines to produce Strecker aldehydes through Strecker degradation.[12]

Acrylamide, a possible human carcinogen,[13] can be generated as a byproduct of Maillard reaction between reducing sugars and amino acids, especially asparagine, both of which are present in most food products.[14][15]

See also

References
  1. Maillard, L. C. (1912). "Action des acides amines sur les sucres; formation de melanoidines par voie méthodique" [Action of amino acids on sugars. Formation of melanoidins in a methodical way]. Comptes Rendus (in French). 154: 66–68.
  2. Chichester, C. O., ed. (1986). Advances in Food Research. Advances in Food and Nutrition Research. 30. Boston: Academic Press. p. 79. ISBN 0-12-016430-2.
  3. Bui, Andrew (2017-09-29). "Why So Many Recipes Call for a 350-Degree Oven". Tasting Table. Retrieved 6 November 2017.
  4. Tamanna, N; Mahmood, N (2015). "Food Processing and Maillard Reaction Products: Effect on Human Health and Nutrition". International Journal of Food Science. 2015: 526762. doi:10.1155/2015/526762. ISSN 2314-5765. PMC 4745522. PMID 26904661.
  5. Tareke, E.; Rydberg, P.; Karlsson, Patrik; Eriksson, Sune; Törnqvist, Margareta (2002). "Analysis of acrylamide, a carcinogen formed in heated foodstuffs". J. Agric. Food Chem. 50 (17): 4998–5006. doi:10.1021/jf020302f. PMID 12166997.
  6. Hodge, J. E. (1953). "Dehydrated Foods, Chemistry of Browning Reactions in Model Systems". Journal of Agricultural and Food Chemistry. 1 (15): 928–43. doi:10.1021/jf60015a004.
  7. Everts, Sarah (October 1, 2012). "The Maillard Reaction Turns 100". Chemical & Engineering News. 90 (40): 58–60. doi:10.1021/cen-09040-scitech2.
  8. Harrison, T. J.; v, G. R. (2005). "An expeditious, high-yielding construction of the food aroma compounds 6-acetyl-1,2,3,4-tetrahydropyridine and 2-acetyl-1-pyrroline". J. Org. Chem. 70 (26): 10872–74. doi:10.1021/jo051940a. PMID 16356012.
  9. McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner. pp. 778–79. ISBN 978-0-684-80001-1.
  10. Miranda, Gonzalo; Berna, Angel; Mulet, Antonio (4 February 2019). "Dried-Fruit Storage: An Analysis of Package Headspace Atmosphere Changes". Foods. 8 (2): 56. doi:10.3390/foods8020056. PMC 6406843. PMID 30720722.
  11. Nursten, Harry (2007). "The Chemistry of Nonenzymic Browning". The Maillard Reaction. pp. 5–30. doi:10.1039/9781847552570-00005. ISBN 978-0-85404-964-6.
  12. Stadler, Richard H.; Robert, Fabien; Riediker, Sonja; Varga, Natalia; Davidek, Tomas; Devaud, Stéphanie; Goldmann, Till; Hau, Jörg; Blank, Imre (August 2004). "In-Depth Mechanistic Study on the Formation of Acrylamide and Other Vinylogous Compounds by the Maillard Reaction". Journal of Agricultural and Food Chemistry. 52 (17): 5550–5558. doi:10.1021/jf0495486. PMID 15315399.
  13. Acrylamide. Cancer.org. Retrieved on 2016-07-24.
  14. Virk-Baker, Mandeep K.; Nagy, Tim R.; Barnes, Stephen; Groopman, John (29 May 2014). "Dietary Acrylamide and Human Cancer: A Systematic Review of Literature". Nutrition and Cancer. 66 (5): 774–790. doi:10.1080/01635581.2014.916323. PMC 4164905. PMID 24875401.
  15. Mottram, Donald S.; Wedzicha, Bronislaw L.; Dodson, Andrew T. (October 2002). "Acrylamide is formed in the Maillard reaction". Nature. 419 (6906): 448–449. Bibcode:2002Natur.419..448M. doi:10.1038/419448a. PMID 12368844.

Further reading
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