modified during cooking.
Another important material in vegetables and fruits is starch. Not all plant tissue contain it. For
example, carrots contain almost no starch. Want proof? Just play with iodine in the following
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Iodine is a chemical element discovered in the XVIII th century by the French chemist M. Courtois. It
dissolves well in ethanol (the alcohol present in wine, liqueurs, and so called alcohols. It is being used
in chemistry, but it is also helpful in kitchens to discover which food ingredients contain starch.
Just begin by cutting a potato into two parts, and place one drop (use a drop counter) onto the cut
surface. The brown solution slowly turns blue.
On the contrary, put one drop on a slice of carrot: no blue colour appears (the iodine solution remains
This test is the basis of the game of recognizing which food ingredients contain starch. Use it on raw
or cooked food.
Although it is obvious that fruits contain some sugars (there are many kinds, not just sucrose, which
makes white table sugar), it is less visible that vegetables also contain some. But one should know
that boiling carrots, for example, in water, also primarily releases sugars. No wonder that cooking
carrots can produce a “caramel” when all the water has evaporated.
Another important particularity of vegetables and fruits: colour!
Green colour is known to come from “chlorophyll”, but there are also red colours, blue colours, yellow
Have you also noticed that the colour of vegetables can change once cut? The vegetable turns
brown in some minutes, depending on the exact vegetable or fruit. For example, mushrooms,
avocados, some varieties of apples… all turn brown very fast. Generally, cooks prevent this browning
using lemon juice, but it this wise, and if so why? Let’s carry out a simple experiment.
Firstly, is lemon juice useful to prevent the browning of fruits and vegetables? Let us cut an apple into
slices that we put on a white plate (to see the browning better).