Science for All | What causes the browning of food?

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Updated - May 09, 2024 01:29 pm IST

Published - May 07, 2024 04:57 pm IST

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

Have you ever wondered why some foods, like meat, cakes, breads etc. turn brown when heated? Turns out, a chemical process called the Maillard reaction is responsible for it. 

What is the Maillard Reaction? 

Named after the early 20th-century French scientist Louis-Camille Maillard, the Maillard reaction is a chemical process that occurs when amino acids, which are the building blocks of proteins, and sugars are heated. The process affects the flavours, aromas, and textures of foods. 

The Maillard reaction is a form of non-enzymatic browning of food, which means that the colour change occurs without the activity of enzymes. 

How does the Maillard reaction cause browning of food? 

Maillard Reaction is a complex chemical mechanism that leads to the formation of multiple products through the process. Chemist J.E. Hodge in 1953 was the first to break down the reaction into steps for simplification. 

A variety of foods, including meats, bread, vegetables, coffee beans etc., contain both sugars and protein units. When food is heated, these sugars and proteins undergo a condensation reaction to form a protein-sugar compound called unstable Schiff base. 

When the Schiff base is rearranged and dehydrated, various intermediate compounds form. These compounds react further to produce important flavour compounds and contribute to the development of characteristic aromas in the food. 

Some of the intermediate compounds undergo a rearrangement, which results in the reorganisation of the atoms in the Schiff base, creating a more stable product. These products are important precursors for melanoidins, which are responsible for the brown coloration of the food. 

These compounds undergo further changes like condensation and polymerisation, leading to the formation of melanoidins — nitrogen-containing compounds that give food the distinct brown colour. 

The rate and extent of the Maillard reaction depend on several factors, including temperature, acidity, moisture content, and the types and concentrations of proteins and sugars in the food. Research suggests the ideal temperatures for the Maillard reaction are in the range of 110 degrees C and 170 degrees C, and temperatures higher than that can burn the food and render bitter flavours. 

Generally, higher temperatures accelerate the reaction while acidic conditions and the presence of water can inhibit it. This is why foods brown more quickly at higher temperatures and why dry foods, such as bread crusts, can develop a deep brown colour during baking. 

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