Culinary Chemistry

Featured, Science 2018-05-25

Chemistry is frequently likened to cooking, only involving more dangerous and inedible materials.

The comparisons are, to be fair, obvious. Both involve the conversion of starting ingredients into a final product that differs in appearance or chemical structure, be it cooking ingredients such as meat or vegetables, or chemical reagents with long complex names. Both require this conversion to be conducted after following a specific set of regimented instructions that maximise a delicacy’s flavour or the yield – total amount – of product formed.

The comparison ends when it comes to creating edible materials. As a general rule, one shouldn’t eat or drink in laboratories. It might not end well.

So yes, I conceive an argument can be made that chemists are scientific chefs.

But I would argue an extension to this logic. We are all chemists.

Now before I receive any hatred for insinuating such a statement, allow me to make an argument that we are all actually chemists even if we are currently unaware of the fact.

I am willing to bet that at some point in our lives every one of us will have cooked food. But aside from the need to create a sustaining meal, have we ever thought about what is happening in our pan or oven? Have we considered the detailed and complex chemical composition changes that are taking place as we cook our Sunday roast chicken dinner? Well, let me change your cooking perceptions as we understand the theory behind the chemical experiments we are all, guiltily or happily, performing on a daily basis.

 

Observing Science

To some the process of cooking might seem secondary, a means to an end. But I thoroughly enjoy it. My interests lie in the chemistry of everyday processes, including those individual chemical reactions that govern the fine line between a culinary delicacy and burnt cinders.

Let us take the cooking of a chicken breast as an example and apply the scientific method to the cooking process. So begins the (tasty) experiment. To cook chicken, we must apply heat, typically taking about 20-30 minutes at 200 °C in an oven. Now, throughout cooking we can make a series of observations about the exterior changes occurring. The most obvious changes are in colour and texture. The chicken breast turns from a soft rubbery pink colour to an entity with a harder white interior and a soft golden exterior (clearly assuming that it wasn’t burnt in some cooking mishap). While this might sound patronising to those who know how to cook chicken and how to tell when it is cooked, does everyone know why food turns a different colour when cooked?

The answer, of course, is chemistry. Whether you want to admit it or not, you, as the budding chef of your chicken dish, have just instigated, supervised and observed a chemical reaction. Or to be more specific, the cascading series of Maillard Reactions.

 

The Route to Culinary Prowess

In layman’s terms, Maillard reactions result in the distinctive flavours and textures of food. Have you ever wondered why chicken tastes like chicken and not beef? Well it all comes down to the specific chemicals created during the Maillard reaction. It is not just involved in the cooking of chicken. The beautiful brown glaze of cooked meat, browning bread in a toaster, roasting of coffee beans; the Maillard reaction forms an integral part of all of these processes.

The chemical process is named after the French chemist Louis-Camile Maillard whose initial research in 1912 detailed the series of reactions.1 So let’s get more specific. The Maillard reaction defines a set of chemical reactions between amino acids and reducing sugars in the presence of heat that create new molecules that are responsible for food’s distinctive flavours, colours and aromas.

But this reaction has been around for thousands of years, arguably since the discovery of fire and the subsequent cooking of meat. As our society has advanced, so too has our understanding of the complex chemistry being undertaken to the point where we are now able to control the reaction with such precision as to prevent unwanted side reactions and create the perfect palate pleasing flavour blend.

So, let us delve deeper into the individual components of the Maillard reaction, and understand what makes each component essential. Amino acids are the building blocks of life and exist in all foods. They are the individual building blocks of larger molecules known as proteins, which are large complicated biological molecules responsible for swathes of life’s processes. A large variety of proteins exist, with specific types found only in certain foods. This diversity is the reason for the different flavour molecules, known as flavouroids, in food. The second essential component is the reducing sugar, such as glucose. Heating the raw food initiates a cascade of reactions and sees the formation of a variety of different functional group molecules including aldehyde, ester, and amine products that form the basis of flavouroids. The chemistry is extremely detailed and complicated and has been discussed further in several other sources.2 The longer food is heated, the more diverse these flavour compounds become. One particularly important class of molecules are known as Strecker Aldehydes, which are responsible for flavours in coffee, beers and other foods.3

But how do you explain the colour change? Well towards the end of the Maillard process compounds known as melanoidins are formed. These are long polymeric molecules and act as brown pigments, hence turning food brown as it cooks. This results in an alternative name for the Maillard reaction as a method of non-enzymatic browning. This classification distinguishes it from enzymatic browning where enzymes are responsible for the browning colour, as for example is the case in avocado browning.

Maillard reactions produce hundreds of different compounds, specific to the amino acids and sugars present in the raw food and the conditions in which cooking occurs. We can imagine several examples of this process. The reason chicken tastes like chicken and not beef comes down to the protein structure and how this structure changes throughout the cooking process. This structural rearrangement is temperature dependent, making the process of developing flavour differ depending on the cooking process. Different cooking conditions can lead to the formation of different molecules and thus potentially new flavours and textures.

 

Undesirable Maillard Reactions

Perfecting cooking depends on one’s ability to strike the right balance in the Maillard reaction. Cooking, as Goldilocks would say, must be just right. Everything discussed so far has involved favourable Maillard reactions. But this is not always the case. Excessive cooking has been known to result in the formation of toxic by-products such as acrylamide or furans.4 Acrylamide in particular is a molecule worthy of its own discussion. Animal studies investigating the effects of acrylamide and its metabolite glycidamide, have suggested they are genotoxic – meaning they affect genetic information – and carcinogenic.5 Since these molecules accumulate in overcooked or processed foods, there have been several mainstream news reports that have referred to the cancer-causing effects of burnt toast to name just one. However, before we all make the sudden decision to never eat toast (or to be more extreme, cooked food) again, human studies on the effects of acrylamide are inconclusive.

 

We are all chemists at heart

Cooking is a complex chemical process. Such a simple task such as heating a chicken breast in the oven results in a variety of chemical reactions that distinctly change the flavour and aroma of certain foods. Food science is a fascinating topic that coalesces the fields of chemistry and biology. But I think you will now agree that in the heart of every kitchen lies a good chef chemist.

Do you agree that we are all chemists, or did I whet your appetite for more chemistry cooking facts? Let me know your thoughts at @JoeAtNotch
 

References:

  1. Maillard, L. C., R. Acad. Sci. 1912, 154, 66
  2. OK I’m a chemist so I must discuss the, initially simple, chemical reactions that cascade into complex products, that occur during the Maillard reactions. A model of the reactions was described by John Hodge in 1953 as a three-stage process. First, the carbonyl group of the sugar undergoes nucleophilic attack by an amine group of the amino acid to produce an unstable glycosylamine intermediate. This intermediate undergoes a rearrangement (known as Amadori rearrangement) to produce several aminoketose compounds. Then finally, these aminoketose compounds undergo further rearrangements and reactions to produce the final flavour, aroma, colour and other compounds. The chemistry is, as you can now probably understand, extremely complex.
    maillardreaction

    1. Compound Chem: The Maillard Reaction
    2. C&En: Maillard Reaction Turns 100
    3. Agric. Food Chem., 1953, 1, 928
    4. Future Learn
    5. Van Boekel M. A. J. S., Biotechnology Advances, 2006, 24, 230 Link
  3. Lund M., Ray C., J. Agric. Food Chem., 2017, 65, 4537 Link
  4. Tareke E., et al., Agric. Food Chem. 2002, 50, 4998 Link
  5. European Food Safety Authority: Acrylamide