Dr Hector Perera       London

I think cooking and chemistry cannot be separated, they go together. Any food we eat such as bread, rice, pasta, chicken, beef, vegetables are made out of complicated organic chemicals. There are other inorganic chemicals such as salt to flavour the food. The molecules in chemicals in the food do not stay at one place, with the gain of temperature, they keep on vibrating, rotating and moving but we cannot see to the naked eye. There are other chemicals come and attack or try to live on them. If we leave a piece or a loaf of bread on the table for few days then after a few days it wouldn’t be the same because a few kinds of fungus have attacked it or call it covered with moulds. How about leaving a few fresh sardines or any piece of fish or chicken on the table for about two days. It will smell as it get rotten by attack of germs and bacteria, just like in bread and that is why we need to keep them in the fridge or in the freezer until it is used.

The problem is that when fish are killed, bacteria and fish enzymes convert TMAO into trimethylamine (TMA), which gives off the characteristic fishy” odour. This smell can be reduced in two ways. TMA on the surface of the fish can be rinsed off with tap water.

The cause of the stink

Fishes smell because of a natural process of decay. Bacterial enzymes attack the flesh of the fish. This triggers an oxidation reduction reaction. The muscle of the fish contain a substance called trimethylamine oxide (TMAO) which is broken down by decomposition. The result is trimethylamine and dimethylamine. The mixing of these two amines results in that characteristic fishy smell. In fact, it is the presence of trimethylamine that is used as an indicator of how fresh a fish is.

Do you know you can use acidic ingredients such as lemon, vinegar and baking soda to reduce the smell of the fish?

Back home in Sri Lanka, I have seen, fresh fish is washed with a mixture of salt, lemon juice and goraka” or Garcinia Indica.

Heard of the saying “something smells fishy”? Have you noticed how a fresh fish smells different from one that is not so fresh? Yes, once again it is chemistry that is the reason behind this.

Removing the smell

If you do have a very smelly fish and need to remove the fish smell, then chemistry can come to your aid once again. As mentioned above use lemon juice, vinegar or baking soda will reduce the smell of the mixing amines. Amines are alkaline based and lemon juice is acidic in nature, thus mixing the two neutralizes the effect of each other. Remember acid base neutralisation reaction is used in volumetric analysis. This is why lemon is added to fish preparations to remove the strong smell of fish. I wonder how did our kussi amma” knew this chemistry, it amazes me. Now you see chemistry cannot be separated from cooking.

Frying bacon

The volatile compounds in frying bacon reacted with sugars in the foodstuff are broken down by reaction with amino acids as heating occurs. In bacon, other volatile compounds are produced due to the thermal breakdown of fat molecules. As well as this, in the case of smoked bacon, nitrite used in the curing process can also react with the fatty acids and fats present in bacon on heating – this leads to a higher percentage of nitrogen-containing compounds than in standard pork meat.

So, what compounds give bacon its aroma?

The researchers compiled an exhaustive list of the volatile compounds present; they found that hydrocarbons, alcohols, ketones and aldehydes were present in large quantities in both the bacon and pork aromas. They also found some compounds present exclusively in bacon, and suggest that these play a major role in its scent.

These were all nitrogen containing compounds; they included 2,5-dimethylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-5-methylpyrazine and 2-ethyl-3,5-dimethylpyrazine. The researchers found that, individually, none of these compounds had the precise smell of bacon – however, they suspect that, combined, and in combination with other volatile compounds, it is most likely that they are responsible.

As well as these compounds, compounds which had previously been identified, from other meats, as having a ‘meaty’ scent were isolated. These included 2-pentylfuran, an oxygen-containing organic compound, and 3,4-dimethylpyridine, another nitrogen-containing compound. Although unsurprising, it’s perhaps a little disappointing that it’s not a lone compound that is responsible for bacon’s aroma.

Maillard Reaction

There’s one chemical reaction that, whether you have an interest in chemistry or not, we all carry out on a regular, maybe even daily, basis. That reaction? The Maillard Reaction. This is a process that takes place whenever you cook a range of foods – it’s responsible for the flavours in cooked meat, fried onions, roasted coffee, and toasted bread. The reaction’s name is a little deceptive, because it’s really an umbrella term for a number of reactions that can produce a complex range of products. The main stages, and some of the different classes of products, are summarised in this graphic.

The Maillard reaction takes its name from French chemist Louis-Camille Maillard, who originally described the reaction between amino acids and sugars in 1912. His study did not offer much in the way of analysis on the reaction’s impact on flavour and aroma in cooking, however; it was not until the 1950s that its mechanisms and culinary contributions would become more clearly understood.

In 1973, American chemist John E Hodge published a mechanism for the different steps of the reaction, categorising its stages and identifying a range of the different products produced as a result of these. He identified the first stage as being the reaction between the sugar and the amino acid; this produced a glycosylamine compound, which in the second step rearranged to produce a ketosamine. The final stage consists of this compound reacting in a number of ways to produce several different compounds, which can themselves react to produce further products.

Hundreds of other organic compounds are formed. A subset of these can contribute to the food’s flavour and aroma, and some of the different families of these compounds are detailed in the graphic. As a consequence of the complexity of the Maillard reaction, different amounts of different compounds can be formed in different foodstuffs, giving the wide variety of potential flavours. Cooking conditions can also influence the flavours produced; temperature and pH, amongst other factors, can have an influence.

Other products from Maillard reaction

The products of the Maillard reaction aren’t all good news, however. The carcinogenic compound, acrylamide, can also be produced as a result of the reaction, and the levels of it rise as food is heated for a longer period of time. A 2002 study found that fast food can contain particularly high levels of acrylamide, though measures have since been taken to try and reduce these levels. This gives some perspective to the discussion of carcinogens in food products; whilst, of course, we’d prefer to limit our exposure to these types of chemicals, in many cases carcinogenic compounds are already present as a natural consequence of cooking.

What chemicals are present in chicken cologne?

I wonder what chemicals are present in chicken cologne or the smell of cooking chicken, fried sardines, sprats and dry fish. There are far too many foods that give out nice mouth-watering smells but I have my doubts if these chemicals have been analysed and identified. When our Sri Lankan ladies cook by constantly opening and stirring the boiling chicken, fish and beef curries then walk up and down like as if they are on cat walk by shaking the hips in a stylish manner, I am sure the outsiders detect the cooking aroma on them. One thing they cover that Tandoori chicken smell by spraying a few different scents and colognes.

My energy & smell saving scientific cooking demonstration

When I demonstrated my energy and smell saving scientific cooking demonstration in that famous TV called Sirasa, I didn’t open the chicken curry to get that smell on me and on the two TV presenters Juliana and Sameera. That demonstration was to save about 60% energy and to stop chicken cologne depositing while cooking. If one millions of people followed my method of cooking, would you not think some energy is saved while cooking? One thing I have noticed that most of the British TV chefs love to shower with cooking aroma, they hardly care about energy wastage in cooking. Sometimes TV studio gets filled with smoke and cooking aroma but they do not care, why? Your comments are welcomed perera@hotmail.co.uk