RICE
Rice is the staple food in southern India, Assam and
Kashmir. It is also the staple food of Bangladesh, Sri Lanka, Burma, China and
Japan. Where rice forms the major source of calories, the nutritive value of the
diet depends on the processing undertaken before it is marketed. Depending on
the mode of processing, different parts of the rice grain may be removed.
STRUCTURE
HUSK
This is the loose covering of
rice. It has not nutritive value and is always removed before cooking. The
process of removing the husk is called milling.
BRAN
This is the outermost coat of
the grain. It contains nutrients and cellulose; the latter interferes with the
absorption of other foods, hence this layer is best removed.
ALEURONE LAYER
This is thin layer underneath
the bran. It contains vitamins, minerals, proteins and fats.
EMBRYO (GERM)
The germ is at the base of the
grain, and is rich in nutrients and vitamin E.
ENDOSPERM
The endosperm forms 75% of the
grain. It consists mainly of starch, which is the principal source of calories.
COMPOSITION
Rice is
rich in starch, moderate in proteins, and poor in fat, iron and calcium. During
cooking, it absorbs a considerable amount of water.
CALORIES
Rice provides about 350 kcal (1.47MJ) per
100g dry weight.
PROTEINS
Rice contains about seven per cent proteins;
these are deficient in the amino acid lysine, which can be supplemented with Soya
bean and pulses. The Chinese custom of eating rice with Soya bean provides
proteins of high biological value. Eating rice with dal (pulses) or a
preparation of rice and dal (khichdi), or eating rice with milk or milk products
like curd and buttermilk, is also helpful in balancing the diet.
PROCESSING
The processes employed for the removal of the
husk and bran are described below.
HAND-POUNDING
This is mainly done by farmers
who cultivate rice for their own consumption. Rice is placed in a large mortar
and pounded with wooden or iron pestles. Hand-pounding does not remove the bran's
completely as milling, and so vitamins are better preserved.
M,ACHINE-MILLINO
Most of
the rice sold in the market is machine-milled, a process which removes bran,
the aleurone layer, and embrye. These constituents are collectively called the polishing; they are nutritious, and constitute 10% of the
weight of the grain.
Advantages : Milled rice
(i) keeps
better, as it is less likely to be contaminated by insects which destroy stored
grain;
(ii) looks clean and attractive for marketing;
(iii) is easily digested
and absorbed; and
(iv) contains little
phytate, and hence minerals from other
foods are better absorbed.
Disadvantages : According to the mode
of milling, variable proportions of vitamin B-complex, calcium, iron, proteins
and fats are removed. It is possible to remove over 75% of thiamine during
milling. When rice constitutes the main source of food, this loss leads to
beriberi. In the West, vitamin B is supplied from other sources; hence, an
occasional helping of highly-polished rice has no deleterious effect.
In the states of Tamil Nadu,
Bengal and Goa, parboiled rice is consumed. The methods of parboiling vary but
essentially consist of the following steps:
(i) paddy (rice with husk) is soaked
in water;
(ii) the water is brought to boil;
(iii) the water is drained off and
the paddy is dried;
(iv) the dried paddy is either machine-milled or
hand-pouched, as described above, to separate the husk.
Advantages
(i) The grain is harder
after parboiling;
(ii) parboiled rice can be preserved better, both in the
uncooked and cooked states;
(iii) when parboiled rice is processed, the outer
bran is more easily removed without the aleurone layer, and hence polishing is
easier while nutrients are better preserved (it is, therefore, better to
machine-mill parboiled rice than raw rice); and
(iv) when parboiled rice is
washed prior to cooking, the loss of nutrients is far less than from raw rice.
Disadvantages
(i) It involves an
additional process before polishing: and
(ii) parboiled rice may emit an
unpleasant smell during cooking. However, the addition of anhydrous ferric
chloride (2.9 g to one kg paddy) during parboiling prevents the foul odour it
also provides 1g (17.9 mm oles iron to the rice).
FERMENTED RICE
Fermented rice provided
better nutrition. Rats fed on two parts rice and one part black gram (urad
dal), with a high-fat, low-protein diet, showed fatty changes in the liver;
when rice was previously fermented (idli), these fatty changes were prevented.
Fermented ricer has a higher content of choline and folic acid. The fact
that Tamils in southern India often eat fermented rice as idli may explain why
liver damage does not occur among them, despite a low intake of proteins.
DIGESTION
Rice is easily digested. When
properly chewed, digestion begins with ptyalin in the mouth and is completed by
the pancreatic and intestinal juices. If eaten with dal (pulses), it produces
too much bulk. Smaller feeds, of a couple of tablespoons of rice with milk or
milk products, are easily digested even during an acute illness.
ABSORPTION
Almost all the rice is
completely absorbed from the intestine, as the polished grain is not covered
with cellulose. The low phosphorus content of rice allows better absorption of
the minerals calcium and iron, which partly compensates for the low content of
these elements in rice. Iron absorption is considerably increased on a
rice-based diet when 40 g (or even less) of fish is also eaten.
DEFICIENCY (BERIBERI)
Rice has a high vitamin B
content, mainly thiamine. Despite this, the discovery that lack of vitamins
could lead to deficiency diseases was first made in rice-eating populations
suffering from beriberi
When rice is the principal
food, it becomes the main source of the vitamin B group. During milling, washing
and cooking of rice, over 75% of thiamine may be lost. Added to this, when the
main source of calories is carbohydrate, the demand for B-group vitamins is
increased. Sub-clinical or clinical vitamin B deficiency can occur when the
diet consists mainly of highly polished rice.
