Pulses constitute essential
components of vegetarian diet. Pulses are major source of protein in Indian
vegetarian diet. These are main source of protein providing most of the
essential amino acids to a certain degree. Economically, pulses are
cheapest source of protein. Pulses are Bengal gram, pigeon pea, black gram,
green gram, lentil, etc. Pulses are mainly consumed in the form of dehusked
split pulses, as these are rich in proteins. In vegetarian diet pulses are
main source of protein.
Green gram, red gram, bengal
gram, horse gram, cluster bean, field bean, cow pea are some of the common
types of pulses.In general, their protein content is high and is commonly
more than twice that of cereal grains, usually constituting about 20 per
cent of the dry weight of seeds. The protein content of some legumes like
soyabean is as high as 40 per cent.
NUTRITIVE VALUE OF PULSES
|
Energy
Kcals
|
Moisture
g
|
|
Fat
g
|
Mineral
g
|
|
Fibre
g
|
Calcium
mg
|
Phosphorus
mg
|
Iron
mg
|
Bengal gram, whole
|
360
|
10
|
17
|
5
|
3
|
4
|
4
|
202
|
312
|
5
|
Bengal gram, dhal
|
372
|
10
|
21
|
6
|
3
|
1
|
1
|
56
|
331
|
5
|
Bengal gram, roasted
|
369
|
11
|
22
|
5
|
2
|
1
|
1
|
58
|
340
|
9
|
Black gram, dhal
|
347
|
11
|
24
|
1
|
3
|
1
|
1
|
154
|
385
|
4
|
Cow pea
|
323
|
13
|
24
|
1
|
3
|
3
|
4
|
77
|
414
|
9
|
Field bean, dry
|
347
|
10
|
25
|
1
|
3
|
1
|
1
|
60
|
433
|
3
|
Green gram, whole
|
334
|
10
|
24
|
1
|
3
|
4
|
4
|
124
|
326
|
4
|
Green gram dhal
|
348
|
10
|
24
|
1
|
3
|
1
|
1
|
75
|
405
|
4
|
Horse gram, whole
|
321
|
12
|
22
|
0
|
3
|
5
|
5
|
287
|
311
|
7
|
Kherasi dhal
|
345
|
10
|
28
|
1
|
2
|
57
|
2
|
90
|
317
|
6
|
Lentil
|
343
|
12
|
25
|
1
|
2
|
59
|
1
|
69
|
293
|
7
|
Moth beans
|
330
|
11
|
24
|
1
|
3
|
56
|
4
|
202
|
230
|
9
|
Peas green
|
93
|
73
|
7
|
0
|
1
|
16
|
4
|
20
|
139
|
1
|
Peas dry
|
315
|
16
|
20
|
1
|
2
|
56
|
4
|
75
|
298
|
7
|
Peas roasted
|
340
|
10
|
23
|
1
|
2
|
59
|
4
|
81
|
345
|
6
|
Rajmah
|
346
|
12
|
23
|
1
|
3
|
61
|
5
|
260
|
410
|
5
|
Redgram, dhal
|
335
|
13
|
22
|
2
|
3
|
58
|
1
|
73
|
304
|
3
|
Redgram tender
|
116
|
65
|
10
|
1
|
1
|
17
|
6
|
57
|
164
|
1
|
Soyabean
|
432
|
8
|
43
|
19
|
4
|
21
|
4
|
240
|
690
|
10
|
Pulse seeds are also sources of
other nutritionally important materials, such as vitamins and minerals.
Carbohydrates: Food pulses contain about 55-60 per cent of total
carbohydrates including starch, soluble sugars, fibre and unavailable
carbohydrates.
Minerals: Pulses are importantly sources of calcium,
magnesium, zinc, iron, potassium and phosphorus.
Vitamins: Pulses contain small amounts of carotene, the
provitamin A.
TOXIC CONSTITUENTS OF PULSES
The seeds of pulses include both
edible and inedible types. Even amongst the edible legumes toxic principles
occur and their elimination is important in order to exploit them for
edible purposes. Two thermoliable factors are implicated in toxic effects.
Inhibitors of the enzymes trypsin, chymotrypsin and amylase
haemagglutinins, which impede the absorption of the products of digestion
in the gut. In addition, legumes also contain a goitrogen, a toxic saponin,
cyanogenic glycosides and alkaloids.
Elimination of Toxic Factors
It has already been
indicated that soaking, heating and fermentation can reduce or eliminate
most of the toxic factors of the pulses. Correct application of heat in
cooking pulses can eliminate most toxic factors without impairment of
nutritional value. Cooking also contributes towards pulse digestibility.
Heat causes the denaturation of the proteins responsible for trypsin
inhibition, haemagglutination and the enzyme responsible for the hydrolysis
of cyanogenic glycosides. The mode of application of heat is important.
Autoclaving and soaking followed by heating are effective. Another way of
eliminating toxic factors is by fermentation, which yields products more
digestible and of higher nutritive value than the raw pulses.
Processing: Processing of pulses is of primary importance in
improving their nutritive value. The processing methods used are soaking,
germination decortications, cooking and fermentation.
Soaking: Soaking in water is the first step in most methods
of preparing pulses for consumption. As indicated above, soaking reduces
the oligosaccharides of the raffinose family. Soaking also reduces the
amount of phytic acid in pulses.
Germination: Germination improves the nutritive value of food
pulses. The ascorbic acid content of pulses increases manifold after 48
hours germination. Germinated and sprouted pulses have been used to prevent
and cure scurvy. The riboflavin, niacin, choline and biotin contents of all
pulses increase during germination. The germination process reduces and/or
eliminates most of the antinutritional and toxic factors in several pulses.
Decortication: A simple method is to soak the seeds for a short
time in water; the husk takes up more water than the seeds and may be
easily separated by rubbing while still moist. In the alternative, the
soaked grains may be dried and the husk removed by pounding and winnowing.
Roasting also renders the husk easier to separate. Roasted legumes like those
of Bengal gram and peas are widely used in India.
Cooking: Cooking destroys the enzyme inhibitors and thus
improve the nutritional quality of food pulses. Cooking also improves the
palatability.
Fermentation: The processing of food pulses by fermentation increases
their digestibility, palatability and nutritive value. Fermentation process
improves the availability of essential amino acids and, thus, the
nutritional quality of protein of the blend. In general, the nutritive
value of the legume based fermented foods has been shown to be higher than
their raw counterparts.
Pulse milling
Pulses are usually converted
into Dhal by decutilating and splitting. Both dry and wet milling processes
are employed. By and large carborundum emery rollers are used for dehusking
and burr grinders for splitting. Decuticling is seldom complete in single
pass requiring multiple passes, each pass producing 1.5 to 2% fines
reducing recovery of dal.
Basic processes in dhal milling
are cleaning, dehusking, splitting, separation and bagging. Major variation
is involved with dehusking process only. Dhals like Arahar, urad, moong and
lentil are difficult to dehusk as a result repeated operations by dehusking
rollers are required. Rewetting and drying is done to loosen portions of
husk sticking after repeated rolling. Linseed oil is used to impart shine
or better appeal to the milled dal.
The removal of the outer husk
and splitting the grain into two equal halves is known as milling of
pulses. To facilitate dehusking and splitting of pulses alternate wetting
and drying method is used. In India trading milling methods produce
dehusked split pulses. Loosening of husk by conditioning is insufficient in
traditional methods. To obtain complete dehusking of the grains a large
number of abrasive force is applied in this case as a result high losses
occur in the form of brokens and powder. Yield of split & pulses in
traditional mills are only 65 to 75% due to the above losses compared to 82
to 85% potential yield.
Milling of Pulses
In India, there are two
conventional pulses milling methods ; wet milling method and dry
milling method. The latter is more popular and used in commercial mills.
Traditional dry milling method
('DHAL' MILLING)
There is no common processing
method for all types of pulses. However, some general operations of dry
milling method such as cleaning and grading, rolling or pitting, oiling,
moistening, drying and milling have been described in subsequent
paragraphs.
Cleaning and grading
Pulses are cleaned from dust,
chaff, grits, etc., and graded according to size by a reel type or rotating
sieve type cleaner.
Pitting
The clean pulses are passed
through an emery roller machine. In this unit, husk is cracked and
scratched. This is to facilitate the subsequent oil penetration process for
the loosening of husk. The clearance between the emery roller and cage
(housing) gradually narrows from inlet to outlet. As the material is passed
through the narrowing clearance mainly cracking and scratching of husk
takes place by friction between pulses and emery. Some of the pulses are
dehusked and split during this operations which are then separated by
sieving.
Pretreatments with oil
The scratched or pitted pulses
are passed through a screw conveyor and mixed with some edible oil like
linseed oil (1.5 to 2.5 kg/tonne of pulses). Then they are kept on the
floor for about 12 hours for diffusion of the oil.
Conditioning of pulses
Conditioning of pulses is done
by alternate wetting and drying. After sun drying
for a certain period, 3-5 per cent moisture is added to the pulse and
tempered for about eight flours and again dried in the sun. Addition of
moisture to the pulses can be accomplished by allowing water to drop from
an overhead tank on the pulses being passed through a screw conveyor. The
whole process of alternate wetting and drying is continued for two to four
days until all pulses are sufficiently conditioned. Pulses are finally
dried to about 10 to 12 per cent moisture content.
Dehusking and Splitting
Emery rollers, known as Gota
machine are used for the dehusking of conditioned pulses About 50 per cent
pulses are dehusked in a single operation (in one pass). Dehusked pulses
are split into two parts also, the husk is aspirated off and dehusked,
split pulses are separated by sieving. The tail pulses and unsplit dehusked
pulses are again conditioned and milled as above The whole process is
repeated two to three times until the remaining- pulses are dehusked and
split.
Polishing
Polish is given to the dehusked
and split pulses by treating them with a small quantity of oil and / or
water.
Commercial milling of pulses by
traditional methods
The traditional milling of
pulses is divided into two heads, namely, dry milling and wet milling. But
both the processes involved two basic steps : (i) Preconditioning of
pulses by alternate wetting and sun drying for loosening husk and (ii) subsequent
milling by dehusking and splitting of the grains into two cotyledons
followed by aspiration and size separation using suitable machines.
100 per cent-dehusking and splitting of pulses are seldom achieved
particularly in cases of certain pulses like Red gram, black gram and green
gram. Of them Red gram is the most difficult pulses to dehusk and split.
Only about 40 to 50 per cent Red gram grains are dehusked and split in the
first pass of preconditioning and milling. As sun drying is practiced the traditional
method is not only weather dependent but also it requires a large drying
yard to match with the milling capacity. As a result it takes 3 to 7 days
for complete processing of a batch of 20 to 30 tonnes of pulses into dhals.
Moreover milling losses are also quite high in the traditional method of
milling of pulses.
In general, simple reciprocating or rotary sieve cleaners are used for
cleaning while bucket elevators are used for elevating pulses.
Pitting or scratching of pulses
is done in a roller machine. A worm mixer is used for oiling as well as
watering of the pitted pulses.
Blowers are used for aspiration
of husk and powder from the products of the disc sheller or roller machine.
Split dhals are separated from the unhusked and husked whole pulses with
the help of sieve type separators.
Sieves are also employed for grading of dhals.
In general, the raw pulses may
contain 2 to 5 per cent impurities (foreign materials), some insect
infested grains and extra moisture. Though the clean pulses contain
about 10-15 percent and 2-5 per cent germs, the yield of dhals commercial
dhal mills varies from 68-75 per
cent. It may be noted that the average potential yields
of common dhals vary from 85 to 89 per cent. These milling losses in
the commercial pulses mills can be attributed lo small brokens and fine
powders found during scoring and simultaneous dehusking and splitting
operations.
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