EFFECT OF PROCESSING ON THE NUTRIENTS AND ANTINUTRIENTS OF SOME SELECTED LEGUMES

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ABSTRACT

Ten different legumes (Cajanus cajan (CC), Prosopis Africana (PA), Sphenostylis sternocarpa (SS), Mucuna pruriens (MP), Vigna unguiculata (VU), Glycine max (GM), Vigna radiata (VR), Vigna sublobata (VAS), Vigna subterrena (VS), Vigna sp. (VSp)) were obtained from obtained from Ogige market in Nsukka. The seeds of each type of legume were divided into two groups. The legume seeds of the first group were de-stoned and dry-milled to obtain fine legume flours. The seeds of the second group were also de-stoned and boiled separately in round-mouthed beakers fitted with condensers, in a seed to water ratio of 1:5 (w/v) at 1000C for 60 minutes. The seeds were boiled till they became tender. They were then hand-milled. The ground legumes were then stored in refrigerators in air-tight containers prior to and during the analysis. The proximate, vitamin, mineral and antinutrients compositions of the raw and boiled legumes were determined. The protein contents of the raw legumes ranged from 14 % to 36 %, boiled legumes- 7% to 17%; carbohydrate- 10% to 63% for raw legumes and 18% to 36% for boiled legumes; fat- 1% to 22% for raw legumes and 1% to 3% for boiled legumes; fibre – 2 % to 6 % for raw legumes and 1% to 2% for boiled legumes; moisture increased from 8% to 24% in raw legumes to 46% to 69% in boiled legumes while Ash dropped from 2% to 4 % in raw legumes to 2% to 3% in boiled legumes. There was a general reduction in these proximate composition parameters except for moisture which was increased due to imbibition of water during boiling. The vitamin B1 levels in raw legumes dropped from 0.39 – 0.55 mg/100 g to 0.26 to 0.37 mg/100 g in the boiled legumes; the vitamin B6 for raw legumes which was in the range of  0.21 to 0.25 mg/100 g dropped to 0.14 to 0.22 mg/100 g for boiled legumes; vitamin E in raw legumes was lowered from 0.53 – 0.76 mg/ 100g to 0.48 -0.66 mg/100 g in the boiled legumes; vitamin B9 of raw legumes which ranged from 0.53 to 0.76 mg/100 g dropped to 0.17 to 0.22 mg/100 g in boiled legumes; vitamin A of the raw legumes which ranged from 0.60 – 7.25 mg/100 g went down to 0.19 to 4.56 mg/100 g in the boiled legumes. The minerals determined in the legumes were sodium (Na), calcium (Ca), potassium (K), phosphorus (P), iron (Fe), zinc (Zn) and magnesium (Mg). The values were as follows: sodium- 0.14 to 0.76 mg/100 g in the raw but dropped to 0.13 to 0.30 mg/100 g in boiled legumes; calcium- 0.28 to 0.59 mg / 100 g in raw legumes went up to 0.25 to 0.89 mg/100 g in boiled legumes; potassium- to 0.89 mg/100 g in raw legumes but dropped to 0.12 to 0.26 mg/100 g in the boiled legumes, phosphorus- 0.44 to 0.61 mg / 100 g in raw legumes but was reduced to 0.15 to 0.97mg/100g in the boiled legumes, zinc- 0.87 to 3.34 mg / 100 g in the raw legumes but dropped to 0.93 to 1.12 mg / 100 g in the boiled legumes and iron moved down from 1.14 to 1.65 mg/100 g in raw legumes to 1.13 to 1.43 mg/100 g in the boiled legumes. The phytate, oxalate, saponin and tannin contents of the legumes were examined. The values were as follows:  phytate- 0.98 to 2.26 g/100 g in the  legumes but was reduced to 0.62 to 1.75mg/100g in the boiled legumes; tannin- 418.92 to 578.85 mg/100 g but 410.24 to 497.95 mg/100 g in the boiled legumes; oxalate- 0.87 to 1.33 mg/100 g in the raw legumes but dropped to 0.23 to 0.59 mg/100 g in the boiled legumes. The findings in this study show that processing of food by boiling causes the loss of both nutrients and antinutrients constituents of legumes.