Why is cooking considered a chemical change

Roasting, baking, caramelizing - the chemistry of good taste

Have you ever wondered why a steak turns brown when grilled or roasted? And do you also know the myth that the pores close when roasting meat? The BESSERwisser analyze these processes and explain the science behind them.

Maillard reaction: browning and aroma

Behind the browning process during heating - not only when grilling, but also when baking, roasting, caramelizing, roasting coffee or even brewing beer - there is a chemical reaction: the Maillard reaction, first described by Louis Maillard in 1912, which takes place between reducing sugars and protein components . This chemical process is a highly complex matter, but the basic principle behind it is relatively simple: During the heating of meat, bread or other foods containing protein and carbohydrates, certain amino acids - these are small units of protein - combine with sugar molecules in the carbohydrate chains. Starting at 100 ° C, then effectively from 150-180 ° C [1], the so-called Maillard products and the brown color develop as a result. The latter is created by pigments called melanoidins. Depending on which sugar or amino acids are present in the heated food, characteristic tastes result. Ultimately, the temperature during roasting determines the flavoring substances formed and thus the taste [1].

There are a large number of possible starting materials for Maillard reactions and thus also a large number of possible secondary products [2]. Typical end products and their taste characteristics are shown in the following graphic.

Source: Open Science - Life Sciences in Dialogue; (cc / by-nc-sa 4.0)

The smells and flavors of the Maillard reaction can also be generated artificially in the laboratory. For example, if you heat the amino acid cysteine ​​and the sugar glucose with a Bunsen burner in a reaction glass, the smell of a steak quickly arises. If you use the amino acid glycine instead of cysteine, you can smell caramel. If you heat the substances proline and glucose, it smells like fresh bread. [1] The Maillard reaction is also involved in beer brewing: here the products of the Maillard reaction have a major influence on various properties of the beer such as malt aromas and color. The malt contains a large number of reducing substances that react in a Maillard reaction at high temperatures during the malting process, or more precisely during the drying process. The color-imparting property of the melanoidins formed is the most striking property. There are a large number of compounds that are formed in the course of the Maillard reaction, some of which are aroma-active, with which the master brewer can specifically control the character of the beer through the selection of the malt and the temperature. [3]

Roasting: the myth of meat pores

There are many rumors about how to properly roast meat. The most persistent myth is that the “pores” of the meat close up when roasting. That is why, as one hears and reads often, one should also sear the meat before cooking it in a casserole, for example. The fact is, however, that meat has no pores at all, because it consists mainly of muscle cells. Therefore, searing meat only serves to create a taste due to the high temperatures and the Maillard reaction that takes place, which would not result from low-temperature cooking. Whether the resulting Maillard products stay in the meat or go into the gravy is completely irrelevant for enjoyment. The main thing is that all tastes are preserved for consumption. [1], [4]

Acrylamide in the Maillard reaction

Acrylamide is formed when glucose or fructose reacts with the amino acid asparagine, both in industry and in conventional cooking and baking processes at home or in restaurants. Several factors are decisive for the amount of acrylamide produced: the amount of these substances in the food to be processed, the preparation temperature and the duration of heating. Larger amounts of acrylamide are therefore formed, especially when high-level heating (e.g. deep-frying) of foods rich in carbohydrates and starch, such as potatoes or cereals. The same applies to industrially manufactured foods. In addition, processing steps such as the addition of additives such as glycerine play an important role. [5, 6, 7, 8]

For over fifteen years it has been known and scientifically proven that acrylamide is formed when foods rich in starch or carbohydrates are heated and converted to glycidamide in the body. This in turn is supposed to change the genetic make-up and cause cancer to develop, i.e. potentially mutagenic and carcinogenic. In animal experiments, acrylamide caused cancer, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) classifies acrylamide as likely carcinogenic for humans, which was confirmed in a scientific assessment of the risk assessment published in 2015 by the European Food Authority (EFSA). [9]

The awareness that foods that are fried, baked or deep-fried too dark are potentially carcinogenic has spread throughout society. To what extent this is reflected in a pack of chips is questionable. In any case, the topic of acrylamide keeps fueling burgeoning debates. The EU regulation [10], which has been in force since April 2018, obliges food business operators to implement measures to reduce the acrylamide content, and new, reduced guide values ​​now apply in individual foods.

How useful these guidelines are is controversial, because despite everything, the responsibility rests with the consumer. As a responsible end consumer, one would have to analyze the acrylamide content of every finished product consumed using guideline values ​​[9], true to the motto “the dose makes the poison”. In addition, you should know what is actually going on in your own pans, ovens or deep fryers. It is obvious that this is hardly practicable. What remains is the option of using the above-mentioned factors such as the preparation temperature and starch or carbohydrate content of the processed food as a basis when preparing food at home and keeping the consumption of industrially processed products with these properties low.

Conclusion

The Maillard reaction is one of the most interesting and diverse chemical reactions in the kitchen. It also plays an important role in the food industry and in the chemical production of flavorings today. This process, in which sugar and protein components react with one another at high temperatures, not only gives us hours of enjoyment. At high temperatures, especially with potato and grain products, but also when grilling meat and heating other foods, acrylamide is produced, which is potentially harmful to health.

It can be concluded that food that is grilled, fried or deep-fried that is too hot and too long can develop carcinogenic effects in the long term. The amount of acrylamide produced is not only dependent on the preparation temperature, but also on the composition of the food.

credentials

[1] Vilgis Thomas, The Molecule Kitchen, Physics and Chemistry of Fine Taste, Hirzel Verlag, 2013, 9th corr. Edition, 53-55, ISBN 978-3-7776-2330-6

[2] van Boekel M A J S, Formation of flavor compounds in the Maillard reaction (2006), Biotechnology Advances 24, 2006, 230-233, doi: 10.1016 / j.biotechadv.2005.11.004

[3] Spieleder E, Dissertation: Systematic investigations of reducing substances in malt and their influence on the brewing process, Technical University of Munich, Chair of Brewery I Technology and Beverage Technology, 2006, accessed on March 16, 2017

[4] Coultate T.P., Food: The Chemistry of Its Components, Royal Society of Chemistry Publishing, 2009, 5th edition, p. 36

[5] Tareke E, Rydberg P, Karlsson P, Eriksson S, Törnqvist M., Analysis of Acrylamide, a Carcinogen Formed in Heated Foodstuffs, J Agric Food Chem., 2002, 50 (17): 4998-5006., Doi: 10.1021 / jf020302f

[6] Smarrito-Menozzi C., Matthey-Doret W, Devaud-Goumoens S., Glycerol, an Underestimated Flavor Precursor in the Maillard Reaction, J. Agric. Food Chem., 2013, 61 (43), pp 10225-10230, DOI: 10.1021 / jf3050044

[7] German Research Foundation (DFG) Senate Commission for the Health Assessment of Food, Thermally Induced / Process-Related Contaminants: The Example of Acrolein and the Comparison to Acrylamide (2012), accessed on May 7, 2018

[8] Haase, N. U., Matthäus, B. and Vosmann, K .: Approaches to minimize acrylamide formation in plant-based foods - demonstrated using the example of potato chips. German Food Review, 2003, 99, 87-90

[9] Austrian Food Safety Agency, publication on acrylamide from April 19, 2018; accessed on May 3rd, 2018

[10] EU regulation on minimization measures and judge values ​​for lowering the acrylamide content in food. VO (EU) 2017/2158, accessed May 7, 2018

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