detailed description of pulse composition and milling

1. Composition of Pulses
By
Er. Nadiya Rashid Malik

2. Pulses
• Pulses are the edible fruits or seeds of pod bearing
plants belonging to the family of Leguminosae and are
widely grown throughout the world.
• They have 20-40% of protein and this makes them
important in human food from point the point of view
of nutrition.
• Pulses are the poor man’s meat.
• The per capita availability of pulses has declined
from 64 g per day(1951-56) to less than 40 g per day
as against the FAO/WHO’s recommendation of 80 g of
protein per day.

3. Composition
• The chemical composition of edible pulse
seeds depends upon the species.
• In general, their protein content is high and is
commonly more than twice that of cereal
grains, usually constituting about 20% of the
dry weight of seeds.
• The protein content of some legumes like
soyabean is high as 40%.

4. Pulse Proteins
• Pulse are chiefly globulins but albumins are also present in
a few species.
• Pulse proteins are deficient in sulphur- containing amino
acids, particularly in methionine and in tryptophan.
• Only soya-bean has tryptophan levels equal to the FAO
pattern.
• All pulses contain sufficient amounts of leucine and
phenylalanine.
• Lysine and threonine contents are low only groundnuts.
• A majority of pulse proteins have high molecular weights
and are very compact molecules, and this reduces the
digestibility of the native protein.
• Proteins also form complexes with phytin and polyphenols
present in pulses, contributing to their low digestibility.

5. Carbohydrates
• Food pulses contain about 55-60% of total
carbohydrates, including starch, soluble sugars, fibre
and unavailable carbohydrates.
• Starch accounts for the major proportion of
carbohydrates in legumes.
• The unavailable sugars in pulses include include
substantial levels of oligosaccharides of the raffinose
family of sugars which cause flatulence production in
man and animals.
• These escape digestion, when they are ingested, due to
the lack of alpha-galactosidase activity in mammalian
mucosa.

6. • Oligosaccharides are not absorbed in the
blood and are digested by the microflora of
inner intestinal tract, resulting in production
of carbon dioxide,hydrogen and small amount
of methane.
• Germination,soaking, cooking, autoclaving
and fermentation reduces considerable
amount of oligosaccharides.

7. Lipids
• Lipids form about 1.5 % of dry matter in
pulses except in groundnut, soyabean and
winged bean.
• Most of the pulse lipids contains poly-
unsaturated acids. They undergo rancidity
during storage resulting in undesirable
changes, such as loss of protein solubility, off
flavor development and loss of nutritive
quality.

8. Minerals
• Pulses are important sources of calcium,
magnesium, zinc, iron, potassium and
phosphorus.
• 80% of phosphorus in many pulses is present
as phytate phosphorus.
• Phytin complexes with proteins and minerals
and renders them biologically unavailable to
human beings and animals.
• Processing can reduce the phytin levels.

9. vitamins.
• Pulses contain small amount of carotene, the
provitamin A.
• Many Pulses contain 50-300 IU of Vitamin A per
100g.
• Thiamine content of pulses is approximately
equal to exceeds whole of cereals, the average
value of thaimin being 0.4 -0.5 mg per 100 g of
pulses.
• Pulses are rich in niacin.
• Poor in riboflavin.

10. Milling of Pulses
• Introduction
• Pulses are rich in proteins and are mainly consumed in the
form of dehusked split pulses.
• Pulses are the main source of protein in vegetarian diet. There
are about 4000 pulses mills (Dhal mills) in India.
• The average processing capacities of pulses mills in India
vary from 10 to 20 tons/day.
• Milling of pulses means removal of the outer husk and
splitting the grain into two equal halves.
• Generally, the husk is much more tightly held by the kernel
of some pulses than most cereals. Therefore, dehusking of
some pulses poses a problem.

11. • The method of alternate wetting and drying is used to
facilitate dehusking and splitting of pulses. In India, the
dehusked split pulses are produced by traditional methods
of milling.
• In traditional pulses milling methods, the loosening of husk
by conditioning is insufficient.
• Therefore, a large amount of abrasive force is applied for
the complete dehusking of the grains, which results in high
losses in the form of brokens and powder.
• Consequently, the yield of split pulses in traditional mills is
only 65%–70% in comparison to 82%–85% potential yield.
• It is, therefore, necessary to improve the traditional
methods of pulses milling to increase the total yield of
dehusked and split pulses and reduce the losses.

12. Varieties, Composition, and Structure
• Green gram, red gram, Bengal gram, horse
gram, cluster bean, field pea, and arhar are
some of the common types of pulses.

13. Traditional Dry Milling Method
(Dhal’s 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 then 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 take place by friction between pulses and
emery.

14. • Some of the pulses are dehusked and split during this operation, which are then
separated by sieving.
• Pretreatment with Oil
• The scratched or pitted pulses are passed through a screw conveyor and mixed
with some edible oils like linseed oil (1.5–2.5 kg/ton of pulses).
• Then they are kept on then floor for about 12 h for diffusion of the oil.
• Conditioning
• Conditioning of pulses is done by alternate wetting and drying.
• After sundrying for a certain period, 3.5% moisture is added to the pulses and
tempered for about 8 h 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 2–4 days until
all pulses are sufficiently conditioned.
• Pulses are finally dried to about 10%–12% moisture content.
• Dehusking and Splitting
• Emery rollers, known as Gota machine, are used for the dehusking of conditioned
pulses.
• About 50% pulses are dehusked in a single operation (in one pass).

15. • 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 mentioned
earlier.
• 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 for the production of grade I
dehusked and split pulses known as “dhal.”

16. Commercial Milling of Pulses by
Traditional Method
• It is discussed earlier that the traditional milling of pulses are 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 sundrying for
loosening husk.
• (ii) subsequent milling by dehusking and splitting of the grains into two
cotyledons followed by aspiration and size separation using suitable
machines.
• The 100% dehusking and splitting of pulses can seldom be achieved,
particularly in cases of certain pulses like tur, black gram, and green
• gram.

17. • Of them, “tur” is the most difficult pulses to dehusk and split.
• Only about 40%–50% “tur” grains are dehusked and split in the first pass
of preconditioning and milling.
• As sundrying is practiced, the traditional method is not only weather
dependent but also requires a large drying yard to match with the milling
capacity.
• As a result, it takes 3–7 days for complete processing of a batch of 20–30
tons of pulses into “dhal.” 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.

18. • The machines used for dehusking are either power-driven disk-
type sheller or emery-coated roller machine, which is commonly
known as “gota” machine.
• The emery roller is encaged in a perforated cylinder. The whole
assembly is normally fixed at a horizontal position.
• Sometimes, either a cone-type polisher or a buffing machine is
employed for removal of the remaining last patches of husk and for
giving a fine polisher to the finished “dhal.”
• Blowers are aspiration of husk and powder from the products of
the disk sheller or roller machine.
• Split “dhals” are separated from the unhusked and husked whole
pulses with the help of sieve-type separators.
• Sieves also employed for grading of “dhals” mills vary from 68% to
75%.

19. • It may be noted that the average potential
yields of common “dhals” vary from 85% to
89% .
• These milling losses in the commercial pulses
mills can be attributed to small brokens and
fine powders formed during scouring and
simultaneous dehusking and splitting
operations.

20. • Modern CFTRI Method of Pulses Milling
• CFTRI method of “dhal” milling is described as follows.
 Cleaning
• Cleaning is done in rotary reel cleaners to remove all impurities from
pulses and separate them according to size.
 Preconditioning
• The cleaned pulses are conditioned in two passes in a dryer (LSU type)
using hot air at about 120°C for a certain period of time.
• After each pass, the hot pulses are tempered in the tempering bins for
about 6 h. The preconditioning of pulses helps in loosening husk
significantly.

21.  Dehusking
• The preconditioned pulses are conveyed to the pearler or dehusker where
almost all pulses are dehusked in a single operation. The dehusked whole
pulses “gota” are separated from split pulses and mixture of husk, brokens,
etc. (chuni-bhusi), and are received in a screw conveyor where water is
added at a controlled rate.
• The moistened, “gota” is then collected on the floor and allowed to remain
as such for about an hour.
• Lump Breaking
• Some of the moistened “gota” form into lumps of varying sizes. These
lumps are fed to the lump breaker to break them.

22. • Conditioning and Splitting
• After lump breaking, the gota is conveyed to LSU type
of dryer where it is exposed to hot air for a few hours.
The “gota” is thus dried to the proper moisture level
for splitting.
• The hot conditioned and dried dehusked whole pulses
are split in the emery roller.
• All of them are not split in one pass. The mixture is
graded into grade I pulses, dehusked whole pulses, and
small brokens.
• The unsplit dehusked pulses are again fed to the
conditioner for subsequent splitting.

23. Parching of pulses
• Legumes such as bengal gram and peas are
parched to give highly acceptable products.
• Bengal gram is tied in moist cloth and kept
overnight before it is parched.
• Peas are soaked in water for 5 min, dried partially
in the sun for 15 min and then parched.
• Salt and turmeric powder are sometimes added
to the steeping water or grains smeared with the
paste of the same before they are parched.

24. • Parching is done in hot iron vessel containing
sand at 190-200⁰C for 60-80 seconds.
• Parched bengal gram has been successfully
used in treatment of Protein calorie
malnutrition in children.