Pulses And Legumes AsFunctional Foods

B.S. Narasinga Rao

Legumes and pulses have longbeen a part of traditional diets inAsia, Africa and South America, whichinclude most of the world's develop­ing countries. More than 1,000 spe­cies of legumes are known to begrown1. Of these, only 20 or so havebeen cultivated for use as food. Theyhave been consumed as a rich sourceof protein supplementing the cereal- or tuber-based diets and have animportant role in human nutrition2•3.Some legumes such as ground nutand soybean are also good sourcesof oil.

In India, from time immemorial,many legumes and pulses (Table 1)have been consumed as part of aprimarily cereal-based diet. They areconsumed as whole gram or as splitpulses (dhals). Pulses are the mainsource of protein in the primarily veg­etarian Indian diet. Besides proteins,pulses are also good sources of vita­mins, minerals, (),)-3 fatty acids anddietary fibre or non-starch polysac­charides (NSP). Charaka4, the physi­cian of ancient India, has identified anumber of pulses as important di­etary components in disease man­agement. In recent years, pulses andlegumes have also been recognisedas part of functional foods5.

Several legumes contain non­nutrient bioactive phytochemicals6,7that have health-promoting and dis­ease-preventing properties. The im­portant health promoting 'non-nutri­ent' compounds present in pulsesand legumes include non-starchpolysaccharides (NSP), phytosterols,saponins, isoflavones, a class of

phytoestrogens, phenolic compoundsand antioxidants such as tocopherolsand flavonoids.

NSP IN PULSES AND LEGUMES

Pulses and legumes are a richsource of NSp8.9. The NSP compo­nent of some of the commonly con­sumed pulses10 is as shown in Table2. The NSP content of pulses andlegumes is 13 to 15 g of NSP per 100 g.Thus, they contribute significantly tothe total NSP intake of habitual Indiandiets. The NSP in pulses consists ofsoluble and insoluble non-cellulosicfibres. The average content per 100 gof water-soluble fibre is 4 to 7 g andthat of insoluble fibre is 5 to 7 g. TheNSP content of pulses is similar tothat of cereals and millets (8-20 g/100 g). A combination of cereals andpulses in a diet provides 50-85 g ofNSP depending on the quantity andthe type of cereal (or millet) and pulseused (Table 2).

Epidemiological observations anda number of human and animal stud­ies have shown that the NSP in pulseshave a role in protecting against de­generative diseases such as diabe­tes, cardiovascular disease and can­cer. NSP protects against chronicdiseases such as diabetes by control­ling blood glucose levels. Their hypo­cholesterolemic property protectsagainst cardiovascular disease. Theyalso help prevent bowel cancer bybinding carcinogens and toxins11,12.The disease-preventing potential ofNSP depends upon the proportion ofvarious fractions of NSP and their actual

content in a given food11. Some le­gumes such as fenugreek, which con­tains 40 per cent gum, can exert theexpected beneficial effect on a dailyintake of about 50 g13.

The NSP components exert theirbeneficial preventive effects throughseveral mechanisms. One ofthe mecha­nisms is through their swelling proper­ties, consequently reducing the transittime in the small intestine and reduc­ing the rate of release and their ab­sorption of glucone from dietary car­bohydrates and of cholesterol and fat.The second mechanism is through thebinding of carbohydrate carcinogensand toxins in the intestinal tract by theinsoluble NSP. This prevents or slowsdown the absorption of the carcino­gens and toxins. The NSP can alsobind bile acids and thereby promotethe excretion of cholesterol from theliver through bile. It must be remem­bered that through this binding prop­erty, NSP can also have some adverseeffects on the availability of dietarycalcium, magnesium, zinc and iron.

CONTENTS• Pulses And Legumes As

Functional Foods1

- B.S. Narasinga Rao • Reviews and Comments:The Vitamin A Fiasco

5

- Dr C. Gopalan • Nutrition News

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• Reviews and Comments:Overweight/Obesity InAffluent School ChildrenIn Delhi

8

- Anshu Sharma• Foundation News

8

TABLE 1

Food LegumesBengal gram

(Cierarietinum)Adzuki bean(Phasedus angu/arus)

Black gram

(Phase a/us mu/ugo rorb)Lima bean(Phaseo/us /unatus)

Cowpea

(Vigna catana)Winged bean(Phosphocarpustetragonobo/us)Field bean

(Da/ichos lab lab)Bambera ground nut(Voandzeia

subtaerranea)Green gram

(Phase a/us aureus rorb)Jack bean(Canava/ia eusiforonis)

Horse gram

(Do/idios biflourus)Sword bean(Canava/ia g/adiata)

Lentil

(Lens escu/anta)Lablab bean(Lab lab purpureus)

Moth bean

(Phaseo/us aconitifo/iusRice bean(Rigna umbel/ata thunb)B Jacq)Peas

(Pisum sativus)Tepery bean(Haseo/us acutifo/is)

Rajmah

(Phaseo/us vulgaris)Groundnuta(Arachis hypogaea)

Red gram

(Cajanus cajan)Fenugreekb(Trigonel/a foemingraecum)Soyabeana

(G/ucine max merr)Kesari dhal(Lathyrus sativus)

a. b Source of oil and protein.

The third mechanism by whichNSP exert beneficial effects on chronicdiseases is through their fermenta­tion in the large intestine (colon)14.While soluble NSP are completelyfermented, the insoluble fibres arepartially fermented. As a result of thisfermentation, bacterial cell mass in­creases and reduces the transit timedue to increased bulk. Also as a re­sult of colon fermentation of NSP,short chain fatty acids such as bu­tyrates, propionates and acetates areproduced. Butyrates serve as a sourceof energy and thus help in rejuvena­tion of colon mucosal cells. They alsopromote differentiation and inhibitionof cell proliferation in human carci­noma cells and promote DNA repair.NSP, through the release offree fattyacid like butyrate on fermentation inthe colon, reduce the risk of coloncancer and inflammatory boweldisease.

The short chain fatty acids, par­ticularly propionates and acetates, enterinto splanchic circulation and are trans­ported to the liver where they exer­cise a direct inhibitory effect on therelease of glucose and synthesis ofcholesterol. Thus, they contribute in­directly to the hypoglycaemic andhypocholesterolemic effects of NSP.

ISOFLAVONES

(PHYTOESTROGENS)

Isoflavones are phytoestrogensthat exhibit weak oestrogen activityand are present in significant amounts

in pulses and legumes5.6. Isoflavonescan protect against hormone-depen­dent diseases such as breast cancerand cardiovascular disease6. Recentstudies have detected their antican­cer activity in a number of animalcarcinogenesis model experiments.Isoflavones also possess biologicalfunctions other than oestrogen-relatedactivity, for example, antioxidant ac­tivity. The important isoflavones aredaidzein, genistein, daidzin, genistin,biochinin A, protensin, formononetin,etc.

Sharma15.16 has studied theisoflavone content of common pulsesand legumes used as food in India;the values are given in (Table 3).There have been earlier reports onthe blood cholesterol lowering po­tential of chickpea (Bengal gram)'?and other legumes including soy­bean5.6. The hypocholesterolemicpotential of these legumes have beenattributed to their isoflavone content6.15.The isoflavone content of pulses isreported to increase after germina­tion. However, the potency ofisoflavones decreases after the le­gumes have been cooked16.

Recent studies on soy have sug­gested that a combination of soy pro­tein and isoflavones is necessary toproduce the greatest cholesterol-low­ering effect5.6. In addition to being ahigh-quality protein, soybean proteinis now thought to help prevent andtreat cardiovascular disease. There

were also earlier reports that Bengal

2

gram proteins also has a cholesterol­reducing property17. It is likely thatpulse proteins act in conjunction withtheir isoflavone contentto reduce bloodcholesterol. The oestrogenic activityof isoflavones are in the followingorder: biochinin A < daidzein <formononetin, and the isoflavone con­tent varies with the variety of legume.

There have been extensive stud­ies on the health promoting anddisease preventing potential of soyisoflavones5•6. The two primaryisoflavones, daidzein and genistein,the latter exclusively present in soy­bean, are reported to be most bio­logically active phyto-estrogens.Daidzein, present in high concen­tration in soybeans, is known to modu­late hormone-related conditions suchas heart disease, osteoporosis, breastand prostatic cancers and meno­pausal symptoms5.6. There is cur­rently considerable interest in soyas a health food because of thesebiological functions. Isoflavones ex­tracted from soy are commerciallymarketed. Similarly, a combinationof 6.25 g of soy protein with 12.5 mgoftotal (extracted) isoflavones, equiva­lent to 25 g of soy alone, is marketedas a health food5.

Although a lot of work has goneon during the past decade on soyisoflavones, hardly any work, exceptfor a limited study by Sharma15.16,hasbeen done on the isoflavone contentof Indian pulses. Several commonlyconsumed pulses, particularly Ben­gal gram, contain high concentrationof isoflavones (152 mg/1 00 mg) 16.Greengram and black gram also contain 80­90 mg of isoflavones, made up ofmostly protensin and daidzein. Thereis, therefore, considerable scope forfuture research on the isoflavones of

Indian pulses, their content, structureand bioactivity to exploit isoflavone­rich pulses as health foods, in thesame way that soy has been exploited.These isoflavones with phenolic groupsin the molecule can also act as anti­oxidants along with other antioxidantssuch as tocopherols and flavonoidspresent in these pulses.

OTHER PHYTOCHEMICALS

Several other phytochemicalssuch as saponins, flavones, phenolicacids and precursors of mammalianlignan with anticarcinogenic poten­tial are reported to be present in soy­bean and their biological function have

been extensively studied6. Saponins,which are hypocholesterolemic agents,are reported to be present in soy athigh concentration. The presence andcontent of these phytochemicals inIndian pulses do not appear to havebeen studied to any significant ex­tent. These pulses, unlike soy, arewidely consumed in India. Occurrenceof these phytochemicals in Indianpulses, their identification, content,chemistry and their health benefitsrequire a systematic study. There isalso a need to study the bioavailabilityof isoflavones and other phytochemicalspresent in Indian pulses.

ANTIOXIDANT CONTENT

Pulses contain tocopherols, fla­vonoids and isoflavonoids, all of whichcan act as antioxidants. Although drypulses do not contain any ascorbicacid, the germinated pulses and im­mature green pulses do contain ascorbicacid which also has antioxidant activ­ity. The isoflavone content of pulseshas been shown to increase two tothree times after germination16. Thus,both dry legumes and green and ger­minated pulses are good sources ofantioxidants. Pulses contain about 3.5mg of vitamin E per 100 g as com­pared to 1.2 mg in cereals. On thebasis of total daily intake of 400 g ofcereals with 50 or 75 g of pulses, the

total antioxidant tocopherol intake worksout to 7.1-7.7 g. The flavonoids arereported to have four to five-fold anti­oxidant activity as compared to ascorbicacid. However, the exact levels of fla­vonoids and their antioxidant patencyhave not been studied in Indian pulses.Although pulses may not be a majorsource of antioxidants in a cereal­pulse-based diet, they can contributesignificantly to the total daily intake ofantioxidants on a diet based on cere­als, pulses, fruits and vegetables.

CURRENT PRODUCTION OFPULSES AND LEGUMES IN INDIA

Considering the nutritional im­portance of legumes and pulses inIndian diets, their production and percapita availability is rather depress­ing20. While cereal production hasdramatically increased to self-suffi­ciency since Independence, pulse pro­duction and per capita availability hasactually gone down since 1950. Percapita availability of pulses has de­creased from 60 g in 1950 to 38 g in1990, a reduction of nearly 40 percent. On the other hand, the per capitaavailability of cereal and millets hasincreased from 330 g to 470 g in spiteof a four-fold increase in population.The cereal-to-pulse ratio, which shouldbe ideally 8:1, has risen from 6:1 to12:1. There is an urgent need to im-

prove pulse production in the countryto yield at least 60 g of pulses percapita per day. In order to provideadequate protein in the cereal-basedIndian diets, the intake of pulses hasto be 50-75 g per day and it should behigher (75 g) in diets based on riceand millets (ragi), with protein con­tent of 6-7 per cent, than in dietsbased on wheat and other millets with10-12 per cent proteins (50 g). On thisbasis, the production of all pulsesand legumes should increase fromthe current 14 million tonnes to atleast 27 million tonnes. This can per­haps be achieved by growing pulsesin irrigated areas, after the rice orwheat crop, using better variety ofseeds and exploiting less commonlyused and unfamiliar legumes. The pro­duction of groundnuts and soy, whichare also important sources of edibleoil, should be taken into account whileconsidering per capita availability ofproteins from legumes. In the presentagricultural policy on food produc­tion, the emphasis should shift fromcereals to pulses.

There is also a need to cultivateminor legume seeds such as rice bean,moth bean, goa bean and tropicallima bean after establishing their nu­tritional quality and safety. Several ofthese unfamiliar legume pulses havein fact been investigated at NIN for

TABLE 2Dietary Fibre in Pulses and Legume Foods (g/100 g)

Foods

TotalNon-cellulose polysaccharidesCelluloseLignin

Legumes with husk

TotalWaterWatersoluble

insoluble

Bengal gram

26.010.13.76.413.42.5

Soya bean

20.89.93.46,58.22.7

Winged bean

35.217.09.77.313.34.9

Kesari dhal

18.66.42.63.89.13.1

Dhals Red gram

13.410.3--2.11.0

Black gram

13.69.5--2.90.9

Bengal gram

13.47.1--5.51.2

Green gram

13.28.6--3.71.0

Rice

8.34.1--2.71.6

Wheat

17.210.6--5.51.2

400 g rice + 75 g blackgram dhal

43.423.5--13.07.1

400 g wheat + 50 g blackgram dhal

75.649.2--23.55.3,

3

TABLE 3

Isoflavone Content of Pulses and Legumes(mg/100 g fresh weight)Isoflavones

Soya beanBengal gramGreengramBlack gramRed gram

Daidzein

2.7 (49)'5.180.7 (81)88.0 (98.0)85"

Protensin

4.8 12

Formononetin

44.1

Biochinin A

98.6

Genistin

95.4

Genistein

2.4

Daidzin

40.6

Total

67.8 - 388.6152.680.788.897

"Content on sprouting

their chemical and nutritional qualityand safety. More studies on their usein Indian cooking and their functionalcomponents require to be initiated.The possible use of lathyrus seeds asa pulse with daily intake not exceed­ing 25 g with low toxin content ob­tained by growing low-toxin variet­ies21 or by the removal of toxin9 can beexplored.

SOY AS A LEGUME FOOD IN INDIA

The production of soy bean hasincreased significantly in recent de­cades in India. Currently, it occupiesa prominent place among pulses andlegumes grown in India, current pro­duction being 6.52 million tonnes.

The soy bean grown in India isexclusively used as a source of oiland the meal as a protein source inanimal feeds. There is an urgent needto promote soy bean as a legumegrain for human use in India, not onlyto meet our shortage in pulses butalso to use it as a functional food.However, several problems need tobe overcome before soy bean can beused as a legume food in India, whereit is completely unfamiliar, unlike incountries of East and South East Asia.

There are several limitationsfor the use of soy bean as a foodlegume in Indian diets. These are theanti nutritional factors (trypsin inhibi­tors) which are not destroyed on ordi­nary cooking used for pulses, theunfamiliar organoleptic factors suchas flavour and odour, and the pres­ence of flatulence factors. Specialprocesses are available to eliminateor at least reduce these factors to amore acceptable level20. These prob-

lems with soya have been overcomein other Asian countries through fer­mentation to convert it to temphe orsoya sauce which is widely used inJapanese and Chinese cuisine.

Simple processing such as ger­mination or the use of green imma­ture pods can also help in utilisingsoy as a food legume or as a veg­etable. In India, soya can, however,be introduced as processed flour, which,through appropriate nutrition educa­tion, can be successfully incorporatedinto various familiar dishes that usedhal flours.

Dr B.S. Narasinga Rao is the President of the

Nutrition Society of India and Former Director ofNIN.

References

1. Tropical Legumes - Resources for the Future;

National Academy of Sciences

2. Rockland, L.B., Nishik, K.: Tropical grain le­gumes in tropical foods. Chemistry and Nutrition;

(Eds) G.E. Inglett and G. Charlambous, Vo12: 547­572, Academic Press, New York, 1979.

3. Patwardhan, V.N.: Pulses and beans in humannutrition. Amer J Clin Nutr; 11: 12-29, 1962.

4. Charaka: Regime of diet and dietetics.Charaka Samhita (English translation); (Ed) GulabKunverba, Vol 1: 179-211, Ayurvedic Society,Jamnagar, 1949.

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b) Wiseman, H.: Phytochemicals: epidemio­logical factors. Encyclopaedia of Human Nutrition;

(Ed) M.S. Sadler, Vol 3: 1549-1561, AcademicPress, New York, 1999.

4

7. Rao, B.S. Narasinga: Bioactive phytochemicalsin Indian foods. NFl Bull; 16(1), 1995.

8. Taranath, R.N., Muralikrishna, G., Salimath, P.V.,Rao, M.R. Raghavendra: Plant carbohydrates: Anoverview. Proc Indian Acad Sci (Plant Sci); 97: 81­155,1987.

9. Fehily, A.: Legume types and nutritionalvalue. Encyclopaedia of Human Nutrition; (Ed) M.J.Sadler, Vol 2: 1161-1188, Academic Press, NewYork, 1999.

10. Sharma, R.D.: Dietary fibre profile of selectedpulses. Ind J Nutr Dietet; 23: 330-332, 1986.

11. Eastwood, M.A.: The physiological effect ofdietary fibre: An update. Ann Rev Biochem; 12: 19­35, 1992.

12. Rao, B.S. Narasinga: Dietary fibre in Indiandiets and its nutritional significance. NFl Bull; 9(4):1-5, 1988.

13. Sharma, R.D., Raghuram, T.C.: Hypoglycaemiceffect of fenugreek seeds in non-insulin dependentdiabetic subjects. Nutr Res; 10(7): 31-739,1990.

14. O'Dea, K.: Factors influencing carbohydratedigestion: Acute and long-term consequences. DibNutr Metab; 3: 251-258, 1990.

15. Sharma, R.D.: Isoflavones and hypo­cholesterolemia in rats. Lipids; 14: 535-540, 1979.

16. Sharma, R.D.: Isoflavone content of Bengalgram at various stages of germination. J PlantFoods; 3: 259-264, 1981.

17. Mathur, K.S.: Hypocholesterolemic property ofBengal gram. Proceedings of Symposium on Nutri­tion and Heart Disease; 17-23, ICMR, 1971.

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Foods; 3: 259-264, 1981.

19. Mathur, K.S.: Hypocholesterolemic property ofBengal gram. Proceedings of Symposium on Nutri­tion and Heart Disease; ICMR, 17-23, 1971.

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Impetus Needed. Hindu survey of Indian agricul­ture; 61-65, 1999.

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