Some pulses used in food contain chemical constituents having toxic properties.
Trypsin inhibitors: Trypsin inhibators are proteins that inhibit the activity of trypsin in the gut and interfere with digestability of dietary proteins and reduce their utilisation. Pancreas enlargement and growth retardation occur in animals that consume diet containing trypsin inhibators. They are generally heat labile and moist heat treatment like pressure cooking destroys them. Autoclaving at 120o C for 15-30 minutes inactivates almost all trypsin inhibators. These inhibitors prevent degradation of storage proteins during seed maturation.
Lathyrogens: Lathryism is a nervous disease that cripples man. The disease now known to result from an excessive consumption of the pulse Lathyrus sativus. It affects young men between the age of 15 to 45 yrs. Lathryus is known by the common name “Khesari Dal”. The dehusked seeds resemble Bengal gram dal or red gram dal. Hence, sometimes kesari dhal is used as an adulterant in other dals. The symptoms of lathyrism are muscular rigidity, weakness, paralysis of the leg muscle.
Stages of Lathyrism
First stage: It is characterised by a practical manner of walking with short steps and jerky movements and a kind of scissors or crossed gait. This is non0stick stage. The patient may remain in this condition for the rest of his life, or he may pass on to the next stage.
Second stage: The muscular stiffness is increased and this makes it necessary to perform all walking by titling the pelvis to such a degree that a stick is necessary to maintain balance. This is called one-stick stage.
Third stage: The muscular rigidity is so great that the patient needs two sticks for support and there is marked titling of the pelvis sideways to maintain balance. This is called two-stick stage.
Figure: One-stick stage of lathyrism
Final Stage: By this time, the patient is unable to walk upright on account of considerable bending of the knees and extreme stiffness of the lower limbs. The patient is then reduced to crawling by taking his weight on his hands. The neurotoxin responsible for lathyrism is β-N-Oxalyl-L-α,β diamino propionic acid. Toxin can be removed by steeping or parboiling.
Steeping Process
Four times the quantity of seeds is first brought to a boil.
Seeds are soaked in hot water for two hours.
Water is drained off.
The seeds are washed with cold fresh water and sun dried.
Eighty to ninety percent of the toxin is removed by this method.
Eighty to ninety percent of toxin leach out by this process.
To prevent lathyrism, the following aspects are to be educated in endemic areas:
The cause of the disease.
The fact that lathyrus pulse can safely form not more than a quarter of the total amount of cereals and pulses eaten per day.
Inherent danger of paying wages in terms of lathyrus sativus.
Recognition of early symptoms like muscle spasm and immediate withdrawl of the pulse from the diet.
The need for growing alternative crops in place of lathyrus sativus.
Favism: Favism is a disease characterised by haemolytic anaemia that occurs when individuals who are deficient in glucose – 6 - phosphate dehydrogenase consume faba beans or broad beans. Three different compounds present in faba beans have been implicated as playing a causative role in the disease. Two of these are glycosides known as vicine and covicine and the third is an amino acid derivative known as dihydroxy phenyl alanine, DOPA. Germinating and boiling reduce these toxic substances.
Haemagglutinins: These are proteins in nature and sometimes referred to as phyto agglutinins or lectins. Haemagglutinins reduce the food intake resulting in poor growth. Haemagglutinins are isolated from soya bean, field bean, white bean, double bean and horse gram. Haemagglutinins are heat labile.
Goitrogens: These substances interfere with iodine uptake by thyroid gland. Thiocyanate, isothicyanates and their derivatives are present in soyabean groundnuts and lentils. Excessive intake of these foods in the face of marginal intake of iodine from foods and water may lead to precipitation of goitre.
Tannins: Tannins are condensed polyphenolic compounds. They are present in high amounts in seed coat of most legumes. Tannins bind with iron irreversibly and interface with iron absorption. Tannins also bind proteins are reduced their availability. Removal of seed coat of legumes reduces the tannin content. Removal of husk lowers tannin content and thus improve the appearance, texture, cooking quality, palatability, digestability of the grain and bioavailability of nutrients.
Pulse cookery: The cooking quality of pulses is a function of the cooking time, that is, the time of boiling during which they attain desirable softness. In addition the cooking quality is also a function of an increases in volume after cooking, higher dispersibility of solids into cooking media and improved texture. Pulse foods which are too hard, sticky or slimy in texture are unattractive. Cooking time influences the nutritive value and overall utilisation of pulses.
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