• Maillard Reaction

When the top of your sponge cake turns into a beautiful golden brown colour or when your crumble develops a crackling crust, it is the work of Maillard reaction. Not only does it give food an appealing tint, distinct flavours are also developed when Maillard reaction is at work. In this article, we will take a closer look at the chemistry of Maillard reaction and how you could control it in your baked goods.

Process

The Maillard reaction occurs when heat is applied to foods containing sugars and proteins, typically within the temperature range of 140-165°C. Named after French chemist Louis-Camille Maillard, who first described it in 1912, this reaction involves the condensation of a reducing polysaccharide or sugar such as glucose and fructose with an amino group from proteins or peptides. In doing so, the reducing end carbonyl group would be bonded to the amino groups in the protein. The fluorescent compounds involved are the precursor for brown pigment that forms in the Maillard reaction.

  1. Initial reaction: A reducing sugar is reacted with an amino acid, forming glycosylamine.
  2. Amadori rearrangement: The glycosylamine undergoes an Amadori rearrangement to produce a more stable compound, an amino deoxy fructose derivative.
  3. Formation of Intermediates: The Amadori product breaks down into numerous fission products of the sugar-amino compound, forming very reactive intermediate substances including furan derivatives.
  4. Polymerisation: Furan derivate reacts with other compounds to polymerise into a dark-coloured insoluble nitrogen-containing compound. This includes melanoidins which are responsible for the brown pigments.

Dairy products are rich in proteins and lactose, which undergo the Maillard reaction. The acid hydrolysis of the Amadori product lactulosyllysine leads to the formation of the artificial amino acid furosine. When they break down into carboxymethyllysine, erthronic acid and galactose in the presence of oxygen, the nutritional quality of food could be impaired as some of the essential amino acids are destroyed. Harmful compounds such as acrylamide and hydroxymethylfurfural being formed in Maillard reaction could also pose a health risk.

There are significant differences between Maillard reaction and caramelisation, it is important to distinguish them despite both of them contributing to the browning and flavour development of food. Caramelisation is a complex group of reactions that occur due to direct heating of carbohydrates (typically above 160°C), causing them to break down and form complex flavour compounds and brown pigments. In comparison, Maillard reaction involves the condensation reaction between sugars and proteins, occurring at a slightly lower temperature.

Manipulating Maillard Reactions

  • Sugar

The choice of sugars used in baking can have a significant impact on Maillard reactions. Granulated sugar contains mainly sucrose, which do not participate well in Maillard reactions. In comparison, dark sugars such as molasses, honey and brown sugar contain a large amount of glucose and fructose which are beneficial for Maillard reactions.

  • Yeast

When yeast is added to bread dough, yeast would digest carbohydrates to produce carbon dioxide in the proofing stage, altering the amount of sugar present in the dough. In an over-proofed dough, yeast has taken up too much carbohydrates, reducing the amount of sugar available for amino acids to react to in the Maillard reaction. Hence, Maillard reaction would be limited.

  • Acidity

The optimum pH for Maillard reaction is 8-9. In sourdough, its acidity can hinder Maillard reactions, slowing the browning process. In comparison, baking soda or lye are added to the water bath to increase the pH, speeding up Maillard reaction when baking pretzels. As a result, deep brown, glossy pretzels with surface cracks can be produced.

  • Temperature

In cases where Maillard reaction is not desired, products can be cooked below 140°C so Maillard reaction would not occur. For example Japanese cheesecake is typically baked at a higher temperature, then at a temperature lower than 140°C to limit Maillard reaction.

  • Water

Similar to Japanese cheesecake, Maillard reaction is not desired in steamed buns as we want to make soft, fluffy and pale buns. Maillard reactions cannot occur in the presence of water so this prevents browning from occurring.

Reference