A NOSE FOR TASTE
Elusive and distinctive flavours are often due to one special chemical, as in the case
of vanilla, originally derived from the vanilla orchid and now generally synthesized.
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In truth there are only really five
flavours: sweet, sour, bitter, salt and savoury. What we call flavour is a subtle
combination of these five blended with the odours that foods give off Flavour is
the essence of food, and flavour chemistry one of the most fascinating studies. Some may
be surprised to hear that there are five flavours; traditionally there were four. In
recent years it has come to be realised that the flavour given to food by the natural
amino acid glutamic acid and certain nucleotides constitutes a new taste. This flavour is
best known in the form of monosodium glutamate. The Japanese gave the name umami to the
new taste; 'savoury' is the nearest equivalent in English. Monosodium glutamate was once
suspected as the cause of so-called 'Chinese Restaurant Syndrome'. This is no longer
accepted.
Essentially when we talk about taste we are talking about smell. Natural products
contain many aroma chemicals. Tarragon essential oil, for example, contains up to 77
components and coffee over 800. Some, on the other hand, contain fewer major components.
For example, vanilla contains the major ingredient vanillin, which was synthesized in
1874. Whilst some synthetic flavourings are prepared by using such major components as the
key ingredient, the majority are complex mixtures of the many important aroma chemicals
found in nature.
Flavours can be powerful chemicals; e.g. capasaicin, the active ingredient of chili
peppers; and some should be treated with care: safrole, the aromatic oil of sasafras, a
natural product, was found to be carcinogenic and was banned in the USA in 1958 and the UK
in 1965.
Many of our favourite flavours are the result of specific chemical processes:
fermentation (cheese, yogurt, alcoholic drinks) or roasting and frying (meat, chocolate,
toast, deep-fat-fried food). Fermentation, roasting and toasting create specific chemical
reactions in the foodstuffs, and the chemicals concerned have been identified. The sweet
caramelly taste of fried onions for example, or gravy, or the crackling on pork can be
traced to a single process; the browning reaction; discovered by a French chemist, L. C.
Maillard, in 1912. This process involves a chemical reaction between proteins and
carbohydrates. Variations on the browning reaction produce many of the most delicious
flavours: chemicals associated with particular flavours have been identified:
allylpyrazine gives a roasted nutlike flavour; methoxypyrazines earthy vegetables;
2-isobutyl-3 methoxypyrazine gives green pepper, and acetyl-l-pyrazines popcorn; 2-acetoxy
pyrazine produces toasted flavours.
Despite the appeal of the flavours produced there are some worries about browning
reaction, because it undoubtedly produces heterocyclic amines (HA) which are cancer
producing. Up to 20 HAs have been found in cooked meats. Well-cooked meat is most likely
to contain HAs and, strangely enough fast food the least likely. It is certain that the
body has defence mechanism against HAs, its natural antioxidants,
but obviously it makes sense not to overload the system. The foods most likely to contain
HAs are barbecued meat; chicken roasted over an open flame contains up 5000 parts per
billion of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, a potent carcinogen. On
current evidence, a barbecue is a far greater health hazard than any additive. |
