A delicious Chemical Reaction

Most of us have tried our hand at a new activity during the lockdown and cooking has been the most popular pastime. A lot of us has been turned into culinary enthusiasts and with social media at our fingertips, we have been busy searching for good recipes. Ever wondered why we are often told to fry the onions until it turns brown? Why do we have to waste our valuable time in waiting for onions to get brown? What kind of reaction is taking place inside it? 

Browning of onions

Let's delve deeper to learn about one of the world's most delicious chemical reactions.

Chemical reactions affect many of the foods we consume everyday. Some of the reactions adversely affect the food and eventually turn them undesirable for consumption whilst others greatly enhance the desirability of the food. There are mainly two types of reactions which lead to the browning of food: Enzymatic and Non-enzymatic reactions. 

Enzymatic reactions: These reactions occur in freshly cut fruits and vegetables, containing a specific enzyme, which reacts with the oxygen present in the atmosphere, overtime to produce undesirable brown colored compounds. Browning of Apple, avocados are main consequences of the enzymatic reactions. This mechanism causes unappealing browning of food.

This image shows apple turning brown in color by Enzymatic mechanism

Then which reactions make food so enticing?

Non-enzymatic reactions: These reactions are responsible for inducing pleasant aromas and flavours in foods upon treatment of heat. These are further classified into two categories:

Caramelization: This chemical reaction occurs when sugar is heated at a temperature greater than its melting point. Solution of sugar syrup (चाशनी), Marshmellow toasted over fire are some classical examples of foods whose color and flavour is result of Caramelization.

Formation of sugar syrup
showing caramelization

Malliard reactions: This is a chemical reaction involving reducing sugars (glucose , fructose) and amino acids (building blocks of proteins) present in food to react in the presence of heat which results in browning of foods while producing aromas and flavours. 

Malliard reaction is followed by a cascade of reactions in foods leading to formation of compounds inducing aroma components and is responsible for wonderful taste of cooked food. These reactions were first described by a French Scientist, Louis-Camille Maillard in 1912.  The end product of this reaction is melanoidins. These are long, polymeric compounds, which act as brown pigment, produced by rearranging amino acids and sugars in various rings like structures that reflect light in such a way as to give the food a brown color and pleasant flavours. 

This reaction occurs in almost every kind of food we cook. But, due to presence of different reactants, the aromas and flavours of different foods vary. Foods undergoing roasting (Coffee and cocoa), baking (breads and cakes), or grilling (meats and cheese) are classical examples of Maillard reactions. The brown color of beer is also due to Maillard reaction.

The image shows that Malliard reaction is taking place

What are the key factors that affect Maillard reaction?

• Maillard Reaction is accelerated by heat, as the temperature increases, the water starts to boil leaving behind the high concentrations of  proteins and sugars which leads to speeding up the reaction. If the food is wet, high heat cooking techniques can dry out the food enough to raise temperatures sufficiently. However, Malliard reactions still readily occur at low temperature but the rate is slower.  It is highly unlikely that we will be cooking a single meal which takes 8-12 hours. Therefore, it is imperative to make sure that your food is dry (you can use paper towel for that).  You might be thinking that raising the temperatures even higher would enhance Malliard reactions. However, above 180°C, a different set of reactions occur: Pyrolysis also known as charring which creates a bitter taste. The compounds formed with such kinds of reactions are carcinogenic (cancer causing).

• pH (potential of Hydrogen) can also affect the rate of malliard reaction. Try adding a pinch of baking soda to the onions and they will start browning soon. (It's a hack)

So, you might be thinking that Maillard reaction is really good. From now onwards, this is my favourite chemical reaction so far (obviously, because it makes my food delicious). But what if I tell you, this reaction also produce some hazardous compounds which are carcinogenic and adversely affect our body. Yes, I am no joking. Malliard reaction produces Acrylamide, formed during roasting, frying, baking, is a human health concern as it can cause cancer. Boiling and steaming do not typically form acrylamide. It is typically found primarily in plant-based food cooked through with heat. Certain potato products especially potato chips and french fries, food made of grains such as cookies and toast, coffee  contain high levels of Acrylamide. The question here arises, what can we do to keep ourselves safe whilst enjoying our favourite foods. Here are some practices which you can employ to reduce the levels of Acrylamide in your foods:

• Don't store potatoes in the refrigerator since it can result in increased acrylamide during cooking. Therefore, it is highly recommended to store potatoes outside the refrigerator, preferably in a dark and cool place.
• Fry the potato to a golden yellow color rather than a brown color helps reduce acrylamide formation. 
• Acrylamide levels in toasted bread  can  be reduced by toasting it to a light brown color, rather than a dark brown color.
• Acrylamide can also be mitigated by soaking raw potato slices in water for 15-30 minutes before frying or roasting. (these should be blotted dry before cooking)

Fry your potatoes to golden yellow color and toast your bread to light brown.

What type of browning is involved in baked foods? 

The wonderful smelling, golden brown flavorful and slight crisp surface of breads and cakes is result of both Malliard reaction and Caramelization.

Sometimes, despite your best efforts, your recipes fall slightly short of your expectations but by understanding key factors affecting Malliard reactions, you can bring that extra oomph to your dish like restaurants do.