The Maillard Reaction [Oxford Scientist Submission]

Unfortunately I did not win, but annoyingly had written about the same topic as the highlighted student on the list. We had pretty much identical content (mine was slightly more scientific), but to be fair she had a nicer writing style and addressed the question in hand more directly ("One Way Science Affects Your Daily Life") 

My submission is pasted below:

I can’t imagine my stir-fry tasting like stir…. steam? Or my steak tasting boiled rather than roasted. How does, essentially a raw cow shoulder, become appetizing? What is responsible for the aromatic smells and plethora of tastes in the foods I eat on a day to day basis?

The answer is the Maillard Reaction (incorrect term! It is a series of complex reactions, rather than one). The series of reactions occur between amino acids and reducing sugars, using heat to initiate.

It all starts with the carbonyl group on a reducing sugar (e.g. glucose, fructose, galactose etc.) reacting with a nucleophilic amino group present on an amino acid, to form a glycosylamine (a biochemical compound whereby a glycosyl group has attached to an amino group).  The unstable glycosylamine then undergoes Amadori rearrangement, i.e. isomerises, to form a ketosamine, a molecule combined of a ketose (monosaccharide with one ketone group per molecule) and an amino group.

This ketosamine reacts further in several ways to produce a range of products that give our food flavour and colour:

• ·         Known as a non-enzymatic browning reaction due to the formation of the brown, nitrogenous polymer known as melanoidin without the need of any enzymes - seen in bread as it turns into toast
• ·         Production of multiple heterocyclic compounds, such as pyrazines and thiophenes which are linked to savoury flavours, alkylpyridines which are linked to bitter tastes and furanones which convey sweet/caramel like flavours.

The wide variety of possible compounds that can be formed from the ketosamine results in a myriad of potential flavours which we experience daily. Factors such as temperature (>145°C is ideal for Maillard but increasing temperature too high can lead to other processes), and pH (Maillard is accelerated in an alkaline environment compared to acidic) also influence which flavours are expressed. Food manufacturers exploit these in order to achieve specific flavours.

Although, there is a darker side to the Maillard reactions. A carcinogenic compound, known as acrylamide is formed when starchy foods are cooked at high temperatures (>120°C) for prolonged periods of time – for example, with burnt toast or potatoes. It has been known for years that acrylamide is capable of causing nerve damage, accelerating muscular atrophy and impairs coordination whilst also being a risk factor for kidney, endometrial and ovarian cancer. This is why I never eat that piece of burnt toast, no matter how rushed I am   in the mornings.

Nutritional value of a product may be reduced through Maillard reactions, as the availability of amino acids and carbohydrates are substantially reduced.  A study by the Department of Food Science & Technology, University of Rhode, has shown that there is a “significant decrease in the nutritional value of foods which undergo the Maillard Reaction” – most of this is because of the loss of the basic amino acid, lysine, which is an essential nutrient in our diet, or because of the decrease in digestibility of proteins when they are heated with reducing sugars. The department undertook an investigation, where they fed rats for three months with a browned protein diet, compared to another control group of rats being fed a diet which did not involve the Maillard Reaction in preparation of the foods. The rats who had been fed the browned diet showed “physiological and biochemical changes” e.g. degradation of quality of connective tissues, due to collagen degeneration.

Surprisingly, a form of the Maillard Reaction also takes place in our bodies, but at a much slower rate (we simply cannot get our core temperature up to >145°C!) It does however lead to damage in extracellular proteins which is associated with ageing, and it has been suggested that it has a role in the formation of cataracts (when the lens becomes cloudy, as a result of age-related changes in the eye.)

This is known as the “the most important flavour-producing reaction” – something that we all carry out on a daily basis without realising. It is truly amazing about how such a simple act of cooking can have such in-depth, varied and complex chemistry behind it.