Introduction
Peas,
beans and lentils are known as pulses. They are the seeds of plants belonging
to the family Leguminosae, which gets its name from the characteristic
pod or legume that protects the seeds while they are forming and ripening.
With approximately 13,000 species, the family Leguminosae is the second
largest in the plant kingdom and it is very important economically.
Different kinds of legumes
provide us with food, medicines, oils, chemicals, timber, dyes and
ornamental garden plants. Legume products include carob, senna, gum
arabic, balsam, indigo and licorice. Pulses are valuable because
they contain a higher percentage of protein than most other plant
foods.
Origins
Pulses
have been used as food for thousands of years. The lentil was probably
one of the first plants ever to be domesticated by humans. Most pulses
prefer warm climates but there are varieties which grow in temperate regions.
They can be eaten fresh or dried and come in a great number of varieties
with a range of colours, flavours, and textures. In spite of its common
name, the peanut or groundnut is also a legume rather than a nut.
Nutrition
All
pulses, except for soya beans, are very similar in nutritional content.
They are rich in protein, carbohydrate and fibre, and low in fat which
is mostly of the unsaturated kind. They are also important sources of
some B vitamins. Fresh pulses contain vitamin C, but this declines after
harvesting and virtually all is lost from dried pulses. Canned pulses
however, retain about half their vitamin C except for canned, processed
peas which have been dried before canning. Canning doesn't affect the
protein content, eliminates the need for soaking and considerably reduces
the cooking time compared with dried pulses. Frozen peas will have also
lost about a quarter of their vitamin C content.
Pulses are usually eaten for
their high protein content. A typical nutritional breakdown is that
for haricot beans which are used to make baked beans, contain, per
100g dried beans: 21.4g protein, 1.6g fat, 45.5g carbohydrate, 25.4g
fibre, 6.7mg iron and 180mg calcium.
The nutritional quality of
the soya bean is superior to that of other pulses. It contains more
protein and is also a good source of iron and calcium. The nutritional
breakdown of soya is per 100g of dried beans: 34.1g protein, 17.7g
fat, 28.6g carbohydrate, 8.4mg iron and 226mg calcium. Dried soya
beans are lengthy to prepare because they need at least 12 hours
soaking and 4 hours cooking time, boiling for the first hour, but
nowadays a large number of soya based foods including tofu, tempeh
and textured vegetable protein (soya mince or chunks) are available.
Storage & Cooking
One
advantage of dried pulses is that they will store very well for long
periods if kept in a dry, airtight container away from the light. However
it is best to eat them as fresh as possible. Pulses toughen on storage
and older ones will take longer to cook. Allow about 55g dried weight
per person, once soaked and cooked they will at least double in weight.
Most dried pulses need soaking for several hours before they can be cooked,
exceptions are all lentils, green and yellow split peas, blackeye and
mung beans. Soaking times vary from 4-12 hours, it is usually most convenient
to soak pulses overnight. Always discard the soaking water, rinse and
cook in fresh water without any salt, which toughens the skins and makes
for longer cooking. Changing the water will help to reduce the flatulence
some people suffer when eating pulses, also reputed to help is the addition
of a pinch of aniseeds, caraway, dill or fennel seeds.
Toxins in Pulses
Consumers should be aware that it is not safe to eat
raw or undercooked kidney and soya beans. There is no need to avoid them as
long as they are thoroughly cooked.
Red kidney beans: Incidents
of food poisoning have been reported associated with the consumption
of raw or undercooked red kidney beans. Symptoms may develop after
eating only four raw beans and include nausea, vomiting and abdominal
pain followed by diarrhoea. A naturally occurring haemaglutin is
responsible for the illness, but can be destroyed by high temperature
cooking, making the beans completely safe to eat. For this reason,
kidney beans must not be sprouted. Kidney beans should be soaked
for at least 8 hours in enough cold water to keep them covered. After
soaking, drain and rinse the beans, discarding the soaking water.
Put them into a pan with cold water to cover and bring to the boil.
The beans must now boil for 10 minutes to destroy the toxin. After
this the beans should be simmered until cooked (approximately 45-60
minutes) and they should have an even creamy texture throughout -
if the centre is still hard and white, they require longer cooking.
Soya beans: Contain
an anti-trypsin factor (or trypsin inhibitor) which prevents the
assimilation of the amino acid methionine. Soya beans also require
careful cooking to ensure destruction of this factor. They should
be soaked for at least 12 hours, drained and rinsed then covered
with fresh water and brought to the boil. Soya beans should be boiled
for the first hour of cooking. They can then be simmered for the
remaining 2-3 hours that it takes to cook them.
Soya flour should state heat
treated on its packaging. Other soya products (e.g. tofu, tempeh,
soya milk, soya sauces and miso) are quite safe to use. Soya beans
can be sprouted, but the sprouts should be quickly blanched in boiling
water to inactivate the trypsin inhibitor.
Pressure cooking: The
temperatures achieved in pressure cooking are adequate to destroy
both haemaglutins and the trypsin inhibitor. Pressure cooking also
considerably reduces cooking times - kidney beans 10-20 minutes,
soya beans 1 hour.
Canning: The temperature
achieved in the canning process also renders pulses quite safe.
Slow cookers: Pulses
must be soaked and boiled for 10 minutes before being added to a
slow cooker, as they do not reach sufficiently high temperatures
to destroy the toxins.
As beans and peas are all
very similar nutritionally, with the exception of soya, they can
be interchanged in most recipes if you want to experiment or have
run out of one kind, as long as you take into account the different
cooking times. If the beans are likely to need a lot longer to cook
than the other ingredients, try pre-cooking them in a separate pan
before adding to the other ingredients or using canned beans.
Click
here to find a selection of recipes that include pulses
Sprouting
Many
whole pulses (e.g. aduki, chickpeas, whole lentils, marrowfat peas, mung
and soya beans) can be sprouted which increases their nutritional value.
Further Information
The British Edible Pulse Association
- www.bepa.co.uk
Article - Beans:
A History
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