Maillard reaction

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 flavour molecules result. This reaction is the basis of the flavouring industry, since the type of amino acid determines the resulting flavour.

In the process, hundreds of different flavour compounds are created. These compounds in turn break down to form yet more new flavour compounds, and so on. Each type of food has a very distinctive set of flavour compounds that are formed during the Maillard reaction. It is these same compounds that flavour scientists have used over the years to create artificial flavours.

Although used since ancient times, the reaction is named after the chemist Louis-Camille Maillard who investigated it in the 1910s.

Products with Maillard reactions

The Maillard reaction is responsible for many colors and flavours in foodstuffs:

• caramel made from milk and sugar
• the browning of bread into toast
• the colour of beer, chocolate, coffee, and maple syrup
• self-tanning products
• the flavour of roast meat
• the color of 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) flavours aromatic varieties of cooked rice. Both compounds have odor thresholds below 0.06 ng/L ^[1].

The process

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. There are several ways for the ketosamines to react further:
   • Produce 2 water and reductones
   • Diacetyl, acetol, pyruvaldehyde and other short-chain hydrolytic fission products can be formed
   • Produce brown nitrogenous polymers and melanoidins

Factors

Pentose sugars react more than hexoses, which react more than disaccharides. Different amino acids produce different amounts of browning.

Since the Maillard reaction produces water, having a high water activity environment inhibits the reaction.

See also

• Baking
• Advanced glycation endproduct

External links

• Nice diagram
• Comprehensive list of books on Molecular Gastronomy

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