Maillard reaction
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The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring the addition of heat. Like caramelization, it is a form of non-enzymatic browning. The reactive carbonyl group of the sugar interacts with the nucleophilic amino group of the amino acid, and interesting but poorly characterized odor and flavor molecules result. This process accelerates in an alkaline environment because the amino groups do not neutralize. This reaction is the basis of the flavoring industry, since the type of amino acid determines the resulting flavor.
In the process, hundreds of different flavor compounds are created. These compounds in turn break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds that flavor scientists have used over the years to create artificial flavors.
Although used since ancient times, the reaction is named after the chemist Louis-Camille Maillard who investigated it in the 1910s.
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[edit] Foods and products with Maillard reactions
The Maillard reaction is responsible for many colours and flavours in foodstuffs:
- toasted bread;
- malted barley as in malt whiskey or beer;
- self-tanning products;
- roasted or seared meat;
- dried or condensed milk.
6-acetyl-1,2,3,4-tetrahydropyridine (1) is responsible for the biscuit or cracker-like odor present in baked goods like bread, popcorn, tortilla products. 2-acetyl-1-pyrroline (2) flavors aromatic varieties of cooked rice. Both compounds have odor thresholds below 0.06 ng/l [1].
The following things are NOT a result of the Maillard browning reaction, as previously cited, but are instead products of a different reaction called caramelization.
[edit] The process
- The carbonyl group of the sugar reacts with the amino group of the amino acid, producing N-substituted glycosylamine and water
- The unstable glycosylamine undergoes Amadori rearrangement, forming ketosamines
- There are several ways for the ketosamines to react further:
- Produce 2 water and reductones
- Diacetyl, aspirin, pyruvaldehyde and other short-chain hydrolytic fission products can be formed
- Produce brown nitrogenous polymers and melanoidins
[edit] Factors
High temperature, high relative humidity, and alkaline conditions all promote the Maillard reaction.[2]
The rate of Maillard reactions increases as the water activity increases, reaching a maximum at water activities in the range of 0.6 to 0.7. However, as the Maillard reaction produces water, further increases in water activity may inhibit Maillard reactions.[3]
Pentose sugars react more than hexoses, which react more than disaccharides. Different amino acids produce different amounts of browning.[citation needed]
[edit] See also
[edit] External links
[edit] References
- ^ An Expeditious, High-Yielding Construction of the Food Aroma Compounds 6-Acetyl-1,2,3,4-tetrahydropyridine and 2-Acetyl-1-pyrroline Tyler J. Harrison and Gregory R. Dake J. Org. Chem.; 2005; 70(26) pp 10872 - 10874; (Note) DOI: 10.1021/jo051940a Abstract
- ^ Photography, Stanford
- ^ Activity
