Anti-Nutritional Factors in Pulses

Pulses belong to family Fabaceae. It is Third Largest Plant Family and has 400 genera and 10,000 species. Pulses, whose history of cultivation dates back to earlier times, are essential for human and animal nutrition as well as crop rotation. Pulses are relatively a cheaper source of protein than milk, cheese, cashew, almond, meat and fish etc., hence valuable for developing countries.

The seeds of pulses are most commonly eaten can be economically stored well for future use. The food values of seeds of pulses is high, have about the some calorific value per unit weight as cereals and are fair sources of some vitamins and minerals. Their protein contents are generally about double that of most cereals. Consumption of pulses is highest in India as compared to other pulses growing countries due to low purchasing power and religious restrictions on non-vegetarian diet. Pulses contain about 18.0 to 32.0 % protein and about 1 to 5% fat. Pulses are considerably richer in calcium than most cereals and contain about 100 to 200 mg of calcium per 100 g of grain (Srivastava and Ali, 2004).They are also considerably rich in iron, thiamine, riboflavin and nicotinic acid as compared to cereals. Young sprouts of pulses like mungbean, mothbean and chickpea are popular foods in some places.

The fact that their grains contain 18-36 % protein, are sufficient in carbohydrates, consist of high amounts of phosphor, iron and calcium and are rich in vitamins (A, B, C, D) further adds to their significance. Since pulses contain high amounts of amino acids, they are consumed in developing countries together with low-protein and high calorie foods that are staple diets of those areas instead of animal proteins, which are both expensive and rare. Rice and bean or bean and bulgur in Turkey, corn and cowpea or rice and cowpea in African countries and corn and bean combinations (mixtures) complement each other in terms of their nutrient contents.

However, in addition to increasing consumption of pulses in diets, it is also important to know how sparing amounts of antinutrient substances that are inherent in them will be removed. It has been established that pulses contain various substances, some varieties of which can be toxic (though rare) or may cause indigestion.

Anti-Nutritional Factors

Anti-nutritional are natural or synthetic compounds that interfere with the absorption of nutrients. For maintaining the nutritional value of food, it is necessary that heating temperature and length of processing do not exceed the optimum temperature required to eliminate the effect of inhibitors. Pulses contain several anti-nutritional factors, such as trypsin and chymotrypsin inhibitors, lectins, polyphenols, flatulence factors, lathyrogens, saponins, antihistamines and allergens  (Abbas and  Ahmad ,2018).

Enzyme Inhibitor

Protease (trypsin, chymotrypsin) and Amylase Inhibitors: These protein inhibitors are found in many nutrients. Found in various forms, inhibitors are present in the tissues of animals and plants as well as in microorganisms. By virtue of their innumerable pharmacological properties, they also enjoy medical value. The rate of water-soluble non-glucose proteinase inhibitor in legume seeds is about 0.2-2 % of the total soluble protein. These substances reduce protein digestion. They decompose with heat. Therefore, when legumes are eaten raw or without being cooked properly, they upset digestive functions and cause diarrhea or excessive gas. Autoclave treatment or boiling also reduces the quantity of these substances.

About 10-20 % of the total active trypsin is found in human pancreatic juice. They bind proteases, which are resistant to digestion in the small intestine, and thus ensure their removal through excretion. This is why the availability of amino acids (methionine and cystine) consisting of sulphur in legume grains is low. Sulphur deficiency may occur in a diet that is dependent on legume grains. In addition to this information, it is also known that trypsin inhibitors also carry characteristics of an insecticide. Amylase inhibitors alter reactions to blood sugar and insulin by slowing down digestion and thus can be used for therapeutic purposes in diabetes (Osman, 2007).

Lectins (Hemagglutinins)

All of them are proteins or glycoproteins. Lectin activity has been determined in more than 800 varieties of the legume family, which consists of 600 genus. 2-10 % of the total protein legume seeds are lectins. One of their most important characteristics is that they prevent absorption of digestive end products in the small intestine. They enable the coagulation of red blood cells by affecting erythrocytes. Lectins possess some other interesting chemical and biological properties, some of which are as follows: they interact with specific blood groups; they perform various functions in mitotic division, demolish cancerous cells and have toxic effects in some animals. Since they bond with different sugar groups, their bonding with intestinal wall may exhibit variation depending on the type of sugar. If some types of beans are consumed raw, they may cause shock cramps. Besides these characteristics, lectins can easily disintegrate (Jindelet al., 1982).

Oligosaccharides                                                                                                

They are gas generating factors in legumes. Legume seeds, which produce digestive gases in humans and animals, contain oligosaccharides of raffinose, stachyose and verbascose. As the duration of cooking increases, a decrease is observed in oligosaccharide content. Moreover, a decrease in oligosaccharide content also occurs when soaking water is poured, seeds are washed a second time or seeds are germinated. It is known that flatulent substances, which belong to the indigestible fibers group, reduce the risk of intestinal cancer, fortifies the immune system, increases excretion frequency and weight as well as HDL cholesterol level (Gupta and Wagle, 1980)

Phenol Compounds

They constitute plants’ protection mechanisms against external factors. It is known that there is a relationship between flower color and boll color and tannin compositions. They are found in fruit and vegetables and in some cereals. They cause plants to have a pungent taste. They reduce bioavailability of some minerals. Tannins of this group are usually stable when confronted with heat, and they may negatively affect pH mechanism, reduce protein digestion, and cause nitrogen mechanism. They can be discharged with excrement (Jain and Kumaret al., 2009).

Table 1.  Anti-nutrients and their concentrations in different food sources

Saponins

They are glycoside derivatives that are found in many plants. Their general characteristics can be cited as follows: they give a bitter taste, foam when they are treated with various solutions and cause hemolysis in red blood cells. Since they reduce the surface tension of blood in cold-blooded animals, they have an extremely toxic effect. On the other hand, due to their cholesterol-reducing effect, legumes are the most important sources of saponins. The fact that saponins can bond with cholesterol and therefore reduce absorption and that legumes contain saponins points to their importance for health. Studies on medical uses of saponins continue (Sharma and Sehgal, 1992).

Phytic Acid AndPhytoids

Phytoid phosphor accounts for almost 80 % of the total phosphor in many legume seeds. Most of them are found on the outer layer of the aleurone or endosperm . Phytic acid causes the bioavailability of essential minerals to decrease and turn into insoluble compounds whose absorption and digestion is less in the small intestine. Pulses are sources of dietary phytoid . When phytoid phosphor is not made use of, it is discharged with excretion. A way of preventing this is through the hydrolysis of phytoid phosphor; for this purpose, besides methods such as soaking, germinating, using food rich in vegetable endogen phytosis enzyme and storing, methods like cooking and performing autoclave where phytoid phosphor is demolished in the presence of heat can also be used.

The studies that have been conducted demonstrated that phytoids reduce cholesterol level and protect against intestinal cancer of iron origin. Besides, phytoids exhibit characteristics of natural antioxidants thanks to their benefits such as reducing lipid peroxidation. Moreover, pulses are important sources of calcium, copper, iron, magnesium, phosphor, potassium and zinc. The content of these minerals and their bio-availability depend, to a large extent, on the degree of the processing (cooking) process and their absorption is affected by the phytoid level found in the plant. 50-80 % of the endogen phytoids in broad beans can be discharged through soaking and cooking

(Alonso et al., 2000).

Toxic Amino Acids

There are certain amino acids in legume plants that are not of protein nature and reduce nutritious value and cause toxic effects. These substances are commonly found in Lathyrus and broad beans. Dihydroxyphenyl alanine (DOPA) is the most common toxic amino acid found in legumes. Although these amino acids do not display a direct toxic effect, the plant firstly takes on a black color due to these substances, and then withers. Moreover, the nutritional value of plants that contain such amino acids (broad beans, Lathyrus) decreases substantially.Toxic amino acids are believed to combine causes of metabolic favism. Despite all these, these substances can not do any kind of harm because they need to be in large quantities in the plant to pose a risk.In addition to this group of toxic substances, some legumes may contain sparing amounts of antivitamin substances and estrogen factors.

Substances of this kind may be activated with heat and cause serious harm. Extensive studies are reported in the relevant literature on the elimination of these substances in order to reduce their harmful effects on plants . When it is taken into account that pulses are sources of the highest quality vegetable proteins, the importance of studies on the toxicity mechanisms of toxic amino acids that have an unfavorable effect on the quality of this protein and the degree of their potential harm become obvious (Jain and Kumaret al., 2009).

Goitrogens

Soybean, a kind of oil seed, contain glycosides called goitrogens. Consisting of sulphur, these glycosides cause the thyroid gland to grow by inhibiting the iodine intake of the thyroid gland. This toxic effect can be reduced with the addition of iodine to the diet (Jain and Kumaret al., 2009).

Cyanogens Glycosides (Hcn)

Many members of the plant kingdom contain cyanide. The cyanide contents of some legumes have been investigated for long years. Cyanogen compounds of tall plants are of two types: cyanogens glycosides and cyanogen lipids. Both groups contain cyanohydrins and free carbonyl. Since glycosides, which consist of HCN (hydrocyanohydric acid), can come out as a result of hydrolysis, they are potentially toxic. Cyanide cannot be disintegrated with heat and since it separates from legumes during cooking or washing, it will be beneficial to pour soaking water. It is known that broad beans and Lima beans are potential sources of cyanide. ( Jain and Kumaret al., 2009).

Vicine And Convicine (Favism Factors)

Favism is a hemolytic disease that is found in sensitive individuals with consumption of broad beans. It is more widely found in people living in the Mediterranean countries. It is known to be of genetic source. The structure of hemoglobin, which is the primary carrier of oxygen, is upset. Dizziness, vomiting, feeling of tiredness and dark orange urine, which is the first symptom of blood transfusion, are symptoms of this disease. The disease disappears soon but incidences of death may be encountered when the disease is prolonged. This disease of hemolytic anemia is caused by favogens.  Favism also causes high fever and jaundice

( Jain and Kumaret al., 2009)

Physical Process For Removing ANF’S In Pulses

However, it has been observed that the effects of these factors disappear or decrease when legumes are properly prepared. Among appropriate techniques of preparing legumes are germination, peeling, soaking, cooking, treating with various chemicals, fermenting, adding enzymes, roasting and frying. However, heat treatment applied to remove antinutritious substances should be performed carefully because this can lead to a decrease in essential amino acids. The most important factor that affected the amount of the ingredients in a grain is genetic constitution. Pulses contain proteins, oils, vitamins, mineral substances, carbohydrates and dietary fibers, which positively affect nutritional value as well as antinutrients that negatively affect diets (Srivastava and Srivastava, 2002).

Conclusion                               

Pulses are generally subjected to various processing before their consumption. These include dehulling, milling, soaking, germination, fermentation and cooking. Such processing has several nutritional advantages. Heat treatment has been well established to destroy proteinous antinutrients, such as protease inhibitor and lectins, but this treatment may also destroy some of the amino acids and vitamins. For maintaining the nutritional value of food, it is necessary to ensure the heating temperature required to eliminate the effect of inhibitors. Proteins in pulses are known to interact with lipids, tannins, phytates, flavour compounds and pigments. These interactions occur when pulses are processed and converted into various products and decrease the bioavailability of proteins.

Similarly, tannins and phytates interact with minerals and vitamins resulting in low bioavailability of minerals and vitamins. Thus, bioavailability of nutrients depends not only on content of the seed, but also on the interaction of nutrients under various  processing conditions and these processes produce edible product having a reduced level of anti and toxic compounds. Therefore, soaking, cooking of presoaked beans and germinating hold a good potential for improving the nutritional value of lablab bean by reduction in antinutritional factors such trypsin inhibitors and phytic acid and thereby enhancing its utilization. Elimination of antinutrients or toxic compounds depends on type of pulses and the processing technique. Research efforts should be made in the direction to reduce these antinutrients and success can be expected in future.

REFERENCES

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Author details

Jyotsna Setty^1*, Aakash¹, Astha Pandey¹, Akshita Maheshwari²

1. Ph.D. Scholar, Institute of Agricultural Sciences, B.H.U, Varanasi-221005

2.  Research Scholar, CBSH, GBPUA&T, Pantnagar, Uttarakhand-263145

Corresponding Author - Jyotsna Setty

*Corresponding author e-mail:  settyjyotsna@gmail.com