PULSES- STRUCTURE, COMPOSITION AND PROCESSING

WHAT ARE PULSES?
Pulses are basically a fruit part of leguminous crops that are harvested solely for the seeds. Dried beans, lentils, and peas are the most common known and consumed pulses. Pulses do not include crops which are harvested green – these are the vegetable crops. Also excluded are those crops used mainly for oil extraction and leguminous crops that are exclusively used for sowing purposes.
Generally, all pulses have a similar structure, but differ in color, shape, size and thickness of the seed coat.
Mature seeds have three components – Seed Coat, Cotyledons and Embryo.
The seed coat or hull accounts for 7-15% of whole seed mass, cotyledons accounts for 85% of total seed and embryo for 1-4%.

STRUCTURE
The external structures of the seed are testa (i.e. seed coat), hilum, micropyle and raphe.
• The testa is the outer most part of the seed and covers almost all of the seed surface.
• The hilum is an oval scar on the seed coat where the seed was attached to the stalk.
• The micropyle is a small opening in the seed coat next to the hilum.
• The raphe is a ridge on the side of the hilum opposite to the micropyle.
When the seed coat is removed from the grain, the remaining part is the embryonic structure. The embryonic structure of the pulse consists of two cotyledons (or seed leaves) and a short axis above and below them These two cotyledons are not physically attach to each other except at the axis and a weak protection is provided by the seed coat to these cotyledons. Thus, the seed is usually vulnerable to breakage. The outermost layer of the seed coat is the cuticle, and it can be smooth or rough.
• Both the micropyle and the hilum are related to the permeability of the testa and to water absorption.

COMPOSITION
Carbohydrates – 55-65%
Proteins – 18-25%
Fat – 1-4%
Minerals – 1-3%
Fibers – 1-5%

PROCESSING OF PULSES

There are various steps involved in processing of pulses:

  1. SOAKING – Soaking in water is the first step in preparing pulses for consumption. It reduces the oligosaccharides of the raffinose family. It also reduces the amount of phytic acid in pulses.
  2. GERMINATION – It improves the nutritive value of food pulses. The ascorbic acid content of pulses increase manifold after 48 hours of germination. The germination process decreases or eliminates most of the anti nutritional and toxic factors in several pulses.
  3. DECORTICATION – It is a simple method 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 is removed by pounding and winnowing. Roasting also renders the husk easier to separate.
  4. COOKING – It destroys the enzyme inhibitors and thus improves the nutritional quality of food pulses. It also improves the palatability of the pulse.
  5. FERMENTATION – This process increases the pulse digestibility, palatability and nutritive value. It also improves the availability of essential amino acids and thus, the nutritional quality of protein of the blend.
  6. PULSE MILLING – The removal of the outer husk and splitting the grain into two equal halves is known as milling of pulses.