Jump to content

Maillard reaction

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by AlexDitto (talk | contribs) at 02:00, 27 June 2009 (Switching sausage picture for toast picture). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A slice of bread, contrasting untoasted and toasted; the toasted section is brown due to the Maillard reaction

The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring heat. It is vitally important in the preparation or presentation of many types of food, and, like caramelization, it is a form of non-enzymatic browning. The reaction is named after the chemist Louis-Camille Maillard who discovered it in the 1910s while attempting to reproduce biological protein synthesis[1]: 79 , although it has been used in practical cooking since prehistoric times.

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a variety of interesting but poorly characterized molecules responsible for a range of odors and flavors. This process is accelerated in an alkaline environment as the amino groups are deprotonated and hence have an increased nucleophilicity. The type of the amino acid determines the resulting flavor. This reaction is the basis of the flavoring industry.

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.

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:

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

The browning reactions which occur when meat is roasted or seared have often been referred to as Maillard reaction browning. However, lean meat contains very few, if any, reducing sugars. Furthermore, red meat undergoes more extensive browning than does white meat. The browning reactions in lean meat are most likely due to the breakdown of the tetrapyrrole rings of the muscle protein, myoglobin. Thus, the browning of meat is technically not a Maillard browning since it does not involve the reaction with a reducing sugar.

Caramelization is an entirely different process from Maillard browning, though the results of the two processes are sometimes similar to the naked eye (and tastebuds). Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They both are promoted by heating, but the Maillard reaction involves amino acids, as discussed above, while caramelization is simply the pyrolysis of certain sugars. The following things are a result of the Maillard browning reaction:

  • Caramel made from milk and sugar, especially in candies; NB: milk is high in protein (amino acids) and browning of food involving this complex ingredient would most likely include Maillard reactions. See references below.
  • Chocolate and maple syrup
  • lightly roasted peanuts

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.

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:

Factors

High temperature, low moisture levels (low moisture levels are mainly necessary because water boils into steam at 212 Fahrenheit (100 Celsius), whereas the Maillard reaction happens noticeably around 310 Fahrenheit (155 Celsius): by the time something is in fact browning, all the water is vaporized), and alkaline conditions all promote the Maillard reaction.[3]

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.[4]

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

Physiology

The Maillard reaction also occurs in the human body. It is a step in the formation of advanced glycation endproducts.[5] It is tracked by measuring pentosidine. Although the Maillard reaction has been studied most extensively in foods, it has also shown a correlation in numerous different diseases in the human body, particularly degenerative eye diseases. These diseases are generally due to the accumulation of advanced glycation end products, or AGEs, on nucleic acids, proteins, and lipids. Though AGEs have numerous origins, they notably can form from the oxidation and dehydration of Amadori adducts, which themselves are products of nonenzymatic Maillard reactions. Apart from ocular diseases, whose correlation with Maillard chemistry has been more recently studied, the formation of AGEs has also proven to contribute to a wide range of human diseases which include diabetic complications, pulmonary fibrosis, and neurodegeneration.

It has been suggested that receptor systems in the body have evolved in order to remove glycation-modified molecules such as AGEs in order to eliminate their effects. The adverse effects of AGE accumulation appear to be mediated by numerous different AGE receptors. Examples include AGE-R1, galectin-3, CD36, and most notably RAGE, the receptor for AGEs.

Advanced glycation in numerous different locations within the eye can prove detrimental. In the cornea, whose endothelial cells have been known to express RAGE and galectin-3, the accumulation of AGEs is associate with thickened corneal stroma, corneal edema, and morphological changes within patients with diabetes. Within the lens, Maillard chemistry has been studied extensively in the context of cataract formation. Advanced glycation is known to alter fiber membrane integrity in the lens, and dicarbonyl compounds are known to cause increased aggregate formation within the lens. This effect is exacerbated by both diabetes and aging. Furthermore, it is thought that AGE-inhibiting compounds are effective in preventing cataract formation in diabetics.

Glycation in Maillard reactions may lead to destabilization of the vitreous gel structure within the eye via unnecessary cross-linking between collagen fibrils. Again, this process is more strongly observed within diabetic patients. Within the retina, the accumulation of AGEs in the drusen and Bruch’s membrane has been associated with age, and has also been observed at a higher level among patients with age-related macular degeneration, or AMD. This is manifested by the thickening of the Bruch’s membrane. Furthermore, it has been observed that AGE levels increase with age within the lamina cribosa, and the products of the Maillard reaction have been observed there as well.

It is believed that a wide range of ocular diseases, particularly diabetic retinopathy, may be prevented by the inhibition of the Maillard reaction. This may be achieved in numerous ways: prevention the formation of AGEs, reducing the effectiveness of the AGE signaling pathway and the receptor-ligand interactions, or breaking the AGE crosslinks. This latter method, the breaking of crosslinks, has already been achieved to some extent by the breaker ALT-711, though its effectiveness against retinopathy is unknown. Another method is by the use of Amadorins, which are able to prevent the reaction of Amadori intermediates which form into AGEs by scavenging the reactive carbonyls.[6]


See also

References

  1. ^ Chichester, C. O. (1986). Advances in Food Research (Advances in Food and Nutrition Research). Boston: Academic Press. ISBN 0-12-016430-2.
  2. ^ T. J. Harrison, G. R. Dake (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): 10872–10874. doi:10.1021/jo051940a. PMID 16356012.
  3. ^ "Albumen Photography". Stanford.
  4. ^ "A beginner's course in water activity". Decagon Devices.
  5. ^ SK Grandhee and VM Monnier (1991). "Mechanism of formation of the Maillard protein cross-link pentosidine. Glucose, fructose, and ascorbate as pentosidine precursors". J. Biol. Chem. 266 (18): 11649–11653. PMID 1904866. Retrieved 2007-12-14. {{cite journal}}: Unknown parameter |day= ignored (help); Unknown parameter |month= ignored (help)
  6. ^ Alan W. Stitt (2005). "The Maillard Reaction in Eye Diseases". Annals of the New York Academy of Science. 1043: 582–597.
  7. ^ Bravo, Adriana (2008-06-11). "Formation of α-dicarbonyl compounds in beer during storage of Pilsner" ([dead link‍]). Journal of Agricultural and Food Chemistry. 56 (11): 4134–4144. doi:10.1021/jf703696p. ISSN 0021-8561. Retrieved 2008-06-16. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Peter J. Van Soest, 1982. Nutritional Ecology of the Ruminant published by Cornell University Press
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Maillard_reaction&oldid=298863445"