Maillard reaction

The Maillard reaction ( named after the French scientist Louis Camille Maillard; pronunciation: [ majaʁ ] ) is a non-enzymatic browning reaction. Here, amine compounds ( such as amino acids, peptides and proteins ) with reducing compounds under heat converted to new compounds. It is not to be confused with caramelization, but both reactions can occur together.

Unlike typically suggested by name reactions, it is not about a single specific chemical reaction, but a complex whole of many both side by side as well as successively running reactions that leads to a variety of reaction products, many of which are still not precisely identified were.

• 2.1 influencing the Maillard reaction

Chemical basis

The Maillard reaction is important for the cooking and the food industry, because the brown melanoidins mentioned end products are intense flavor and is responsible for the typical aroma and the color of protein-rich roasted, baked and fried. The reaction also retards spoilage because the melanoids / melanoidins as the Pronyl -lysine bind oxygen. Scientists also found a weak antibacterial ( bacteriostatic ) effect. The Maillard reaction can also cause undesirable flavor changes in sterilizing such as meat or dairy products, and occur even without the effect of heat during long storage protein-containing foods. Through the Maillard reaction, the amino acid content of foods can reduce up to 20%, which may be regarded as an impairment.

In the multi-stage reaction, an amino acid and reducing sugars such as aldoses (e.g., glucose) or connected acyloins (e.g., fructose) from about 140 ° C first with elimination of water. The result is a Schiff base, which rearranges in several steps. At a reaction with aldoses done an Amadori rearrangement, in acyloins a Heyns rearrangement. It formed from the Amadori and Heyns products highly reactive alpha - dicarbonyl compounds such as Deoxyosone designated 1 -, 3 -, and 4- Deoxydicarbonyle and from many others. Partial arise cyclic compounds and heterocyclic compounds. 1- Deoxyosone For example, to Norfuraneol ( caramel aroma ) and maltol ( Röstgeruch ) react, while from the 3- Deoxyosonen e.g. furfural ( pentoses ) or 5- hydroxymethylfurfural ( from hexoses ) and 4- Deoxyosonen z. example maltol or acetylformoin be formed. By further reactions with amine compounds are formed, for example, pyrroles and pyridines. Also caused by a Strecker degradation odorous aldehydes such methional, phenylacetaldehyde, 3 - and 2- methylbutanal and 3 - and 2- methyl propanal and colored compounds, which are called melanoidins. Continue to emerge with the amino acid cysteine ​​sulfur-containing reaction products of cyclic characteristic odor, such as bis-2- methyl-3- furyldisulfid. Among the necessary conditions for the Maillard reaction of an anhydrous heat runs parallel to the Maillard reaction from the caramelization of carbohydrates contained in food. From 180 ° C also begin Verkohlungsprozesse.

Formation of acrylamide

Example of undesirable Maillard reaction is the enhanced held at temperatures from 170-190 ° C formation of the carcinogen acrylamide from the amino acids asparagine and glutamine (as in potato and cereal products). With Temperature control below the critical temperature, this reaction can be reduced. Reduction of acrylamide formation in potatoes is also possible through the use of boiled potatoes and dark and cool.

Unwanted Maillard reactions lead to numerous other potentially mutagenic and / or carcinogenic compounds acting. The relationships are still partially unknown.

In the food manufacturing

The Maillard reaction influences taste, texture and smell of many foods, for example:

• Roasted products such as coffee beans, cocoa beans, malt or onions
• Deep fried foods such as french fries
• Baked goods such as bread, toast or biscuits
• Fried foods like steak

Many flavors are prepared by using the Maillard reaction industrially. For various amino acids and sugars wide variety of flavors are produced in a combination of heat duration, and type of heating. Thus, the combination of the amino acid cysteine ​​and the sugar glucose in long warming aroma of Bratz Wiebeln, with short heating time the aroma of roast.

Influencing of the Maillard reaction

An effect on the Maillard reaction (formation rate share Maillard compounds in the final product ) are a number of factors, such as the pH, proportion of protein / amino acids, water, or sugar, the temperature and cooking time in the food production.

Examples of application:

• Increasing the pH by liquor in the production of pretzel.
• Reduction of the water content in bread crust by dry heat.
• Butter biscuits or rolls with egg white and sugar solution before baking.

Medical aspects

The Maillard reaction plays a role in certain aging processes in the human body and in diabetes mellitus. These oxidative reactions lead to damage to the body tissues. In the summer of 2004, however, surprising interim results of an EU study were presented (since 1998) to a Hamburg conference, which also demonstrate antioxidant effects of Maillard products. A group of Italian scientists led by Vincenzo Fogliano of the University of Naples discovered, moreover, that melanoidins can counteract the formation of metastases.

Generated in the laboratory Maillard products block certain proteins, lectins, which effect the cohesion of cancer cells and thereby accelerate the formation of metastases. On the other hand, patients with diabetes or renal dysfunction to an increased Melanoidinspiegel. Here are the exact relationships are still unclear.