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Nutrients and some anti-nutrients in horsegram (Macrotyloma uniflorum (Lam.) Verdc.)

N. Sudha, J. Mushtari Begum, K. G. Shambulingappa, and C. K. Babu

Abstract

Proximate nutrients, calcium, and some anti-nutrients in 16 varieties of whole horsegram and their dehulled seeds were estimated The protein, fat, and carbohydrate contents were higher in the dehulled samples than in the corresponding whole horsegram However, the moisture, fibre, ash, and calcium contents of the dehulled samples were lower. A significant portion of the anti-nutrients studied were removed by dehulling.

Introduction

Horsegram (Macrotyloma uniflorum (Lam.) Verdc.) is a pulse crop native to the south-east Asian subcontinent and tropical Africa. It is extensively cultivated, especially in dry areas of Australia, Burma, India, and Sri Lanka [1]. The use of dry seeds of horsegram is limited due to their poor cooking quality. However, it is consumed as sprouts in many parts of India. Recently, the US National Academy of Sciences identified this legume as a potential food source for the future [2].

Horsegram is relatively high in iron, but the availability of the iron is reduced by the phytates, tannins, and oxalic acid it contains. Horsegram is also a good source of protein [3] and appears to be a fairly good source of calcium. However, a study of 27 cultivars showed that the oxalic acid content averaged about 318 mg/100 g [4]; oxalic acid combines with calcium and iron to form an insoluble salt, rendering that calcium and iron unavailable for absorption. Germination is a simple method of food processing that results in increased nutritive value. It decreases the phytin phosphorus level and increases the availability of iron and calcium. Thus, the presence of anti-nutritional factors in horsegram is a matter of concern.

The present study was conducted to analyse proximate nutrients and also anti-nutritional factors in horsegram and dehulled samples.

Materials and methods

Sixteen samples of horsegram were procured from the All India Coordinated Research Project on Pulses, University of Agricultural Sciences, GKVK, Bangalore, India. A bulk sample for comparison purposes was obtained from Dryland Farm, University of Agricultural Sciences, GKVK, Bangalore.

Horsegram samples were cleaned, soaked overnight, germinated for 24 hours, and dried at 45°C until the moisture content was 12%. Dried samples were automatically dehulled using the Tamil Nadu Agricultural University dehulling mill. The dehulled seeds obtained accounted for 67% of the total seed weight. The whole horsegram and dehulled samples were powdered and sifted through an 80-mesh sieve and stored in airtight containers for analysis.

Proximate analysis was conducted according to official AOAC methods, with carbohydrates determined by difference [5]. A factor of 6.25 was used to convert nitrogen to protein. Calcium was estimated following the AOAC method [5]. Tannin was determined calorimetrically on the basis of the measurement of blue colour formed by the reduction of phosphotungstomolybdic acid in alkali solution following the AOAC method [5]. Oxalic acid was determined titrimetrically by being precipitated as calcium oxalate and titrated against standard potassium permanganate [5].

Results and discussion

The proximate nutrients and calcium content of the whole and dehulled horsegram are shown in table 1.

TABLE 1. Proximate composition and calcium content of whole and dehulled horsegram cultivars

W = whole; D = dehulled.

The protein contents of the whole and dehulled seeds were 22.1% and 22.4% respectively, similar to reported values [6]. Dehulling had very little effect on the fat content. However, the fat content of CODB-6, PHG-20, and PHG-62 was higher than that of the other varieties. The crude fibre content of the whole seeds was 5%, which is similar to reported levels [7]; the fibre content of the dehulled seeds was less than 2%, which can be attributed to the removal of the husk (12%) during processing. The carbohydrate content of the whole horsegram was 56.3%, slightly lower than the reported 66% [8]. In the dehulled seeds ash content levels (2.92%) were lower than in the corresponding whole samples (3.32%); however, both values were much lower than the 5% reported elsewhere for horsegram [9]. The calcium levels in the whole seed in this study are similar to those reported earlier [10]. Dehulling marginally reduced the content of calcium, from 236 to 223 mg/100 g. Horsegram appears to be a fairly good source of calcium. Prior information on the proximate analysis of dehulled horsegram is not available, although the results reported here are within the range reported for the other legumes [8]. Statistically significant differences among the varieties of horsegram and dehulled seeds were observed.

The anti-nutrient contents of the whole and dehulled seeds are shown in table 2. Oxalic acid content was higher in the whole horsegram than in the dehulled seeds, the means being 508 and 315 ma/ 100 g respectively. The variety HPK-2 had the highest oxalic acid content in whole (610 mg%) and also in dehulled seeds (406 mg%). The lowest oxalic acid content was in the dehulled seeds of variety K-42 (197 mg%). The tannin content of whole and corresponding dehulled seeds was 817 and 290 mg% respectively. Tannins were highest in the whole horsegram variety PHG-62 (896 mg%) and lowest in the dehulled seeds of variety CODB-6 (215 mg%). These findings indicate that dehulling could remove a large portion of oxalic acid and tannins. Similar findings have been reported by other workers [11, 12]. Oxalic acid and tannins decrease iron absorption, and the total amounts in horsegram were much higher than those found in other legumes studied. Data on phytate content should also be obtained, because it too decreases the bioavailability of iron.

TABLE 2. Anti-nutrients in whole and dehulled horsegram (mg/100 g)

References

1. Duke JA, Reed CF. Macrotyloma uniflorum (Lam.) Verdc. In: Duke JA, ed. Handbook of legumes of world economic importance. New York: Plenum Press, 1981.

2. National Academy of Sciences. Mothbean in tropical legumes: resources for the future. Washington, DC: National Academy of Sciences, 1978.

3. Borhade VP, Kadam SS, Salunke DK. Solubilization and functional properties of mothbean (Vigna aconitifolia marechal) and horsegram (Macrotyloma uniflorum L. Verdc.). J Food Biochem 1984;8:229-35.

4. Pore MS. Mineral composition and oxalic acid in horsegram. Indian J Agric Sci 1979;49:712-14.

5. AOAC. Official methods of analysis. 14th ed. Washington, DC: Association of Official Analytical Chemists, 1984.

6. Mushtari Begum J. Priyadarshini S. Shanta Hiremath R. Varietal difference in protein of horsegram (Dolichos biforus Linn.) Mysore J Agric Sci 1977;11:521-4.

7. Ray PK. Nutritive value of horsegram (Dolichos biflorus): Part I. Effect of feeding raw and treated seed flour on the growth of rats. Indian J Nutr Dietet 1969; 6:329-34.

8. Gopalan C, Ramashastri BV, Balasubramanyan SC. Nutritive value of Indian foods. Hyderabad, India: National Institute of Nutrition, ICMR, 1989.

9. Khader V, Rao SV. Limiting amino acids in horsegram (Dolichos biflorus). Indian J Nutr Dietet 1986;23:158-64.

10. Subba Rao A, Sampath SR. Chemical composition and nutritive value of horsegram (Dolichos biflorus). Mysore J Agric Sci 1979;13:198-205.

11. Gad SS, El-Zalaki ME, Mohamed MS, Mohaseeb SZ. Oxalate content of some leafy vegetables and dry legumes consumed widely in Egypt. Food Chem 1982;8: 169-77

12. Narasinga Rao BS, Prabhavathi T. Tannin content in foods commonly consumed in India and its influence on ionisable iron. J Sci Food Agric 1982;33:89-96.

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