The
Maillard reaction (also known as dextrinisation) is a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
between an
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
and a
reducing sugarA reducing sugar is any sugar that, in an alkaline solution, forms some aldehyde or ketone. This allows the sugar to act as a reducing agent, for example in the Maillard reaction and Benedict's reaction.-Examples:...
, usually requiring
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
. It is vitally important in the preparation or presentation of many types of food, and, like
caramelizationCaramelization is the oxidation of sugar, a process used extensively in cooking for the resulting nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor....
, it is a form of non-enzymatic browning. The reaction is named after the chemist
Louis-Camille MaillardLouis Camille Maillard was a French physician and chemist.-Early days:He was admitted to the Faculty of Science in the University of Nancy at the age of 16...
who discovered it in the 1910s while attempting to reproduce biological
protein synthesis, although it has been used in practical cooking since prehistoric times.
The reactive carbonyl group of the sugar reacts with the nucleophilic
amino groupAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
of the amino acid, and forms a variety of interesting but poorly characterized molecules responsible for a range of odors and flavors.
The
Maillard reaction (also known as dextrinisation) is a
chemical reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
between an
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
and a
reducing sugarA reducing sugar is any sugar that, in an alkaline solution, forms some aldehyde or ketone. This allows the sugar to act as a reducing agent, for example in the Maillard reaction and Benedict's reaction.-Examples:...
, usually requiring
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
. It is vitally important in the preparation or presentation of many types of food, and, like
caramelizationCaramelization is the oxidation of sugar, a process used extensively in cooking for the resulting nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor....
, it is a form of non-enzymatic browning. The reaction is named after the chemist
Louis-Camille MaillardLouis Camille Maillard was a French physician and chemist.-Early days:He was admitted to the Faculty of Science in the University of Nancy at the age of 16...
who discovered it in the 1910s while attempting to reproduce biological
protein synthesis, although it has been used in practical cooking since prehistoric times.
The reactive carbonyl group of the sugar reacts with the nucleophilic
amino groupAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
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
aminoAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
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 scientistsA flavorist, also known as flavor chemist, is someone who uses both chemistry and art to engineer artificial and natural flavors. The tools and materials used by flavorists are almost the same as that used by perfumers with the exception that flavorists seek to mimic or modify both the olfactory...
have used over the years to create artificial flavors.
Foods and products with Maillard reactions
The Maillard reaction is responsible for many colors and flavors in foods:
- Toasted bread
Toast is sliced bread which has been browned by exposure to dry heat . This browning reaction is a form of the Maillard reaction. Toasting warms the bread, making it more pleasant to eat for some, and makes it crisp such that it holds toppings more securely. Toasting is also a common method of...
- Biscuit
A biscuit is a kind of small, flat-baked bread product that is usually made with a chemical leavener such as baking powder. The exact meaning varies markedly in different parts of the world, and the meanings in British English and American English are quite distinct...
- Malted barley as in malt
Malting is a process applied to cereal grains, in which the grains are made to germinate by soaking in water and are then quickly halted from germinating further by drying/heating with hot air. Thus, malting is a combination of two processes: the sprouting process and the kiln-drying process...
whiskey or beerBeer is the world's oldest and most widely consumed alcoholic beverage and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize , and rice are widely...
- Onion
Onion is a term used for many plants in the genus Allium. They are known by the common name "onion" but, used without qualifiers, it usually refers to Allium cepa. Allium cepa is also known as the "garden onion" or "bulb" onion...
s
- Roasted
Roasting is a cooking method that uses dry heat, whether an open flame, oven, or other heat source. Roasting usually causes caramelization or Maillard browning of the surface of the food, which is considered a flavour enhancement. Meats and most root and bulb vegetables can be roasted...
or searedSearing is a technique used in grilling, roasting, braising, sautéing, etc. that cooks the surface of the food at high temperature so that a caramelized crust forms. A similar technique, browning, is typically used to sear or brown all sides of a particular piece of meat, fish, poultry, etc....
meat
- Dried or condensed milk
Condensed milk, also known as sweetened condensed milk, is cow's milk from which water has been removed and to which sugar has been added, yielding a very thick, sweet product that can last for years without refrigeration if unopened...
- Roasted coffee
Coffee is a brewed beverage prepared from roasted seeds, commonly called coffee beans, of the coffee plant. They are seeds of "coffee cherries" that grow on trees in over 70 countries. It has been said that green coffee is the second most traded commodity in the world behind crude oil. Due to its...
- Dulce de leche
Dulce de leche in Spanish or doce de leite in Portuguese , is a milk-based sauce. Found as both a syrup and a caramel candy, it is prepared by slowly heating sweetened milk to create a product that is vaguely similar in taste to caramel...
6-Acetyl-2,3,4,5-tetrahydropyridine6-Acetyl-2,3,4,5-tetrahydropyridine, with the IUPAC name 1-ethanone, is an aroma compound and flavor that gives baked goods such as white bread, pop corn, or tortillas their typical smell, together with its structural homolog 2-acetyl-1-pyrroline.6-Acetyl-2,3,4,5-tetrahydropyridine and...
is responsible for the biscuit or cracker-like flavor present in baked goods like
breadBread is a staple food prepared by cooking a dough of flour and water and possibly more ingredients. Doughs are usually baked in the Western world , but in some cuisines breads are steamed, fried, or baked on a hot skillet. It may be leavened or unleavened...
,
popcornPopcorn or popping corn is a type of corn which explodes from the kernel and puffs up when heated. Corn popping was originally discovered by Native Americans, but became popular as a snack food during the United States Great Depression, especially in movie theaters.Corn is able to pop because,...
,
tortillaIn Mexico and Central America, a tortilla is a type of thin, unleavened flat bread, made from finely ground maize . In Mexico, there are three colors of maize dough for making tortillas: white maize, yellow maize and blue maize.A similar bread from South America is called arepa...
products. The structurally related compound 2-acetylpyrroline has a similar smell and occurs also naturally without heating and gives varieties of cooked
riceRice is the seed of a monocot plant Oryza sativa, of the grass family . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East, South, Southeast Asia, the Middle East, Latin America, and the West Indies...
and the
spiceA spice is a dried seed, fruit, root, bark, leaf, or vegetative substance used in nutritionally insignificant quantities as a food additive for the purpose of flavour, colour, or as a preservative that kills harmful bacteria or prevents their growth....
pandan (
Pandanus amaryllifoliusPandanus amaryllifolius is a tropical plant in the screwpine genus which is known commonly as pandan and used widely in Southeast Asian cooking. It is an erect green plant with fan-shaped sprays of long, narrow, bladelike leaves and woody aerial roots...
) their typical smell. Both compounds have odor thresholds below 0.06 ng/
l
.
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,
myoglobinMyoglobin is a single-chain globular protein of 153 amino acids, containing a heme prosthetic group in the center around which the remaining apoprotein folds. It has eight alpha helices and a hydrophobic core. It has a molecular weight of 16,700 daltons, and is the primary oxygen-carrying pigment...
. Thus, the browning of meat is technically not a Maillard browning since it does not involve the reaction with a reducing sugar.
CaramelizationCaramelization is the oxidation of sugar, a process used extensively in cooking for the resulting nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor....
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
pyrolysisPyrolysis is the chemical decomposition of condensed organic substances by heating. The word is coined from the Greek-derived elements pyro "fire" and lysys "decomposition"....
of certain sugars. The following things are a result of the Maillard browning reaction:
- Caramel
Caramel is a beige to dark brown confection made by heating sugar. It is used as a flavor in puddings and desserts, a filling in candies and chocolates, and a topping for ice cream and custards....
made from milkMilk is an opaque white liquid produced by the mammary glands of mammals. It provides the primary source of nutrition for young mammals before they are able to digest other types of food. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce...
and sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
, 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
Chocolate comprises a number of raw and processed foods produced from the seed of the tropical cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America, with its earliest documented use around 1100 BC...
and maple syrupMaple syrup is a sweetener made from the sap of some maple trees. In cold climate areas, these trees store sugar in their roots before the winter and the sap which rises in the spring can be tapped and concentrated. Quebec, Canada, produces most of the world's supply of maple syrup...
- lightly roasted peanut
The peanut, or groundnut , is a species in the legume family native to South America, Mexico and Central America. It is an annual herbaceous plant growing 30 to 50 cm tall...
s
In making
silageSilage is fermented, high-moisture fodder that can be fed to ruminants or used as a biofuel feedstock for anaerobic digesters. It is fermented and stored in a process called ensilage or silaging, and usually made from grass crops, including corn or sorghum or other cereals, using the entire green...
, 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
- The carbonyl group of the sugar reacts with the amino group of the amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
, producing N-substituted glycosylamineGlycosylamine is a biochemical compound consisting of an amine with a β-N-glycosidic bond to a carbohydrate thus forming a cyclic hemiaminal ether bond .Examples include nucleosides such as adenosine....
and water
- The unstable glycosylamine undergoes Amadori rearrangement
The Amadori rearrangement is an organic reaction describing the acid or base catalyzed isomerization or rearrangement reaction of the N-glycoside of an aldose or the glycosylamine to the corresponding 1-amino-1-deoxy-ketose...
, forming ketosamineA ketosamine is a compound word used to describe the combination of two organic chemistry functional groups, derived from ketose and amine....
s
- There are several ways for the ketosamines to react further:
- Produce 2 water and reductones
- Diacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C
4H
6O
2...
, aspirinAspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
, pyruvaldehyde and other short-chain hydrolytic fission products can be formed
- Produce brown nitrogenous polymers and melanoidin
Melanoidins are brown, high molecular weight heterogeneous polymers that are formed when sugars and amino acids combine at high temperatures and low water activity. Melanoidins are commonly present in foods that have undergone some form of non-enzymatic browning, such as barley malts , bread...
s
Factors
High temperature, low moisture levels, and alkaline conditions all promote the Maillard reaction. 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.
The rate of Maillard reactions increases as the
water activityWater activity is a dimensionless quantity used to represent the energy status of the water in a system. It is defined as the vapor pressure of water above a sample divided by that of pure water at the same temperature; therefore, pure distilled water has a water activity of exactly one...
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.
PentoseA pentose is a monosaccharide with five carbon atoms.They either have an aldehyde functional group in position 1 , or a ketone functional group in position 2 ....
sugars react more than
hexoseIn organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C
6H
12O
6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position...
s, which react more than
disaccharideA disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only...
s. 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 endproductAdvanced Glycation End products are the result of a chain of chemical reactions after an initial glycation reaction. The intermediate products are known, variously, as Amadori, Schiff base and Maillard products, named after the researchers who first described them. Advanced Glycation End products...
s. It is tracked by measuring
pentosidinePentosidine is a biomarker for advanced glycation endproducts, or AGEs. It is a well characterized and easily detected member of this large class of compounds.-Background:...
.
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
neurodegenerationNeurodegeneration is the umbrella term for the progressive loss of structure or function of neurons, including death of neurons. Many neurodegenerative diseases including Parkinson’s, Alzheimer’s, and Huntington’s occur as a result of neurodegenerative processes. As research progresses, many...
.
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
corneaThe cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43...
, 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
retinaThe vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, 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.
See also
- Advanced glycation endproduct
Advanced Glycation End products are the result of a chain of chemical reactions after an initial glycation reaction. The intermediate products are known, variously, as Amadori, Schiff base and Maillard products, named after the researchers who first described them. Advanced Glycation End products...
- Baking
Baking is the technique of prolonged cooking of food by dry heat acting by convection, and not by radiation, normally in an oven, but also in hot ashes, or on hot stones. It is primarily used for the preparation of bread, cakes, pastries and pies, tarts, quiches, and cookies. Such items are...
- Beer
- Wok hei
External links