Raw vegetables, unlike meat, can be eaten raw. However vegetables are generally cooked to soften
their texture and thus improve their digestibility, as well as intensify their flavour (compare the taste of
raw and steamed broccoli!).
However cooking also has some less desirable consequences – such as loss of their natural colour
and reduction in nutrient value.
Flavour changes on cooking
High temperatures make the aromatic molecules contributing to the flavour more volatile and therefore
more easily detected. However overcooking will cause these volatile molecules to be evaporated or
destroyed, so vegetable soups that have been cooked for a long time often need to be generously
seasoned at the end of cooking to make up for the loss of flavours. The odour of vegetables also
develops as a vegetable is cooked – this is also because the volatile odour molecules become more
volatile and easier to detect. Equally heating can result in odourless smell molecules being
transformed into highly aromatic molecules. Cabbages and leeks are especially common for their
potent smell released on cooking.
Texture changes on cooking
Some vegetables, especially those that are tubers or storage parts of the original plant, contain large
amounts of starch, and cooking, like for rice and pasta, therefore is essential to gelatinize their starch
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and improve digestibility. Vegetables of this type include the potato family and have been considered
in another section.
Other vegetables have a particularly tough cell wall and these vegetable are often preferentially
cooked because cooking causes their cell walls to weaken, improving digestibility of the vegetable.
These vegetables include carrots and beetroot. Equally, vegetables with a softer cell wall, such as
lettuce, should not be cooked at all – raw, their digestibility is fine.
Plant cell walls are made up of complex carbohydrate molecules - cellulose, pectin, and
hemicelluloses. Each of these molecules is affected differentially by heat. Because the cell walls of