Molecular Gastronomy

The chemistry behind baking

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The Maillard Reaction

This year marks the 100 year anniversary of the discovery of the Maillard Reaction – a key reaction in food science. Several hundred scientists met in the small French city of Nancy to attend a conference that was held to celebrate the anniversary of this great discovery. The scientists gathered together to present scientific papers related to this chemical reaction. So, how did this reaction come about?

It began 1912, when Louis-Camille Maillard conducted experiments based on the reasoning behind the production of carbon dioxide and change of color of raw ingredients when heated. He believed this reasoning would pave a new path for the world of medicine and diabetes, and did not bother to consider the importance of this discovery for food. Obviously, he was wrong, as his discovery proved to be a major milestone for food chemistry. The Maillard Reaction takes place in many cooking processes, and it is possibly the most favored and flavored chemical reaction.  Now, you may be wondering…what exactly is the Maillard Reaction and why is it so important?

The Maillard Reaction is actually a series of many complex reactions between reducing sugars (carbohydrates) and an amino acid (the basic foundation of all proteins). The Maillard Reaction is responsible for the browning of toast, nuts, hash browns, beer, roasted meat, etc. The glazing of milk and egg ingredients on baked goods lead to the Maillard reaction on the crusts of the baked goods, allowing for a browning on the surfaces.

The reaction takes place in several steps:

Step 1: A reducing sugar (such as glucose) reacts with an amino acid to form a product called the Amadori compound.

“The Amadori compounds easily isomerise into three different structures that can react differently in the following steps. As in food generally over 5 different reactive sugars and 20 reactive amino acids are present, only the first step theoretically already results in over 100 different reaction products.”

The size of the reducing sugar affects the rate of reaction. Larger reducing sugars generally conduct a slower reaction and a lighter resulting color, while smaller reducing sugars generate an opposite affect. In addition, there are certain types of reducing sugars (such as sugar alcohols or polyols) that do not take place in the Maillard reaction. In other words, baked goods using these products will not be affected in a change of color.

Step 2: Depending on the isomer of the Amadori compound, the amino acid can either be completely removed, or the isomer can be rearranged. This rearrangement is the main contributing factor towards the browning or change of color of the food during the reaction.

Depending on the rearrangement, there are three different possible pathways:

  1. dehydration reactions
  2. fission – production of short chain hydrolytic products
  3. strecker degradations – involves amino acids or the condensation to adols

The three different pathways usually end in the ultimate result of mixtures, which include flavour compounds and the brown pigments, melanoidins – the pigments often found in brown-colored foods.

This reaction usually takes place at high temperatures, so processes such as frying, roasting, grilling, and baking are heavily dependent on the Maillard Reaction. However, high temperatures are not the only contributing factor towards the reaction. There’s also:

  • time
  • water activity
  • pH level – (example: a higher pH value results in a faster Maillard reaction for a pretzel, giving a saltier taste and an even darker color of brown)
  • presence of oxygen
  • types of amino acids

Table 1 displays the effects of these conditions on the Maillard Reaction.

Table 1

These contributing factors make the already-complex Maillard Reaction even more complicated, as a small difference can affect the taste, aroma, and color of the product. These factors along with the reaction can also form acrylamide and furans, dangerous substances that could potentially cause cancer. Therefore, it is important to note the amino acids and contributing factors when using cooking methods involving the Maillard Reaction, as a small alteration can yield a completely different product.

Who knew a daily activity could contain a lot of chemistry with such complicated explanations?

The video above demonstrates the Maillard Reaction, while discussing caramelization – another type of nonenzymatic browning reaction.  This completely different process may be discussed later.

Author: Erica Rowane Bautista

Sources used (also includes sources of pictures):