Effects of cooking duration on nutrient composition and levels of some antinutritional factors of lablab (Lablab purpureus C.V. Rongai) seeds

This study investigated the effects of varying the duration of cooking on the nutrient composition and levels of some antinutritional factors in lablab seeds. Raw lablab seeds were subjected to four durations of cooking, viz: 15, 30, 45 or 60 minutes respectively, in a drum of boiling water. The samples were dried and assayed for their proximate compositions, mineral contents, presence and levels of trypsin inhibitors (TIA), phytic acid, tannin and hydrocyanic acid (HCN). The raw lablab seeds contained 94.03% dry matter (DM), 26.12% crude protein (CP), 7.86% crude fibre (CF), 2.02% ether extract (EE), 4.43% ash and 59.57% nitrogen free extract (NFE). The proximate composition was not significantly (P>0.05) affected by duration of cooking. Potassium (15.66g/Kg DM) and iron (245.17g/Kg DM) were the most abundant macro and micro mineral elements, respectively in the raw lablab seeds while sodium (0.06g/Kg DM) and copper (53.62 mg/kg DM) were the least for macro and micro minerals, respectively. Except for calcium and sodium, all the minerals assayed were leached significantly (P<0.05) during cooking. Cooking lablab seeds at 1000C for forty-five minutes decreased trypsin inhibitor activity (TIA) from 593.87 mg/100g to 132.00 mg/100g; phytic acid from 5.65 mg/100g to 0.10 mg/100g; tannin from 0.22 mg/100g to 0.10 mg/100g and hydrocyanic acid (HCN) from 1.58 mg/100g to 0.45 mg/100g, respectively. These values correspond to 77.77, 78.93, 54.55 and 71.52 percent reductions in TIA, phytic acid, tannin and hydrocyanic acid, respectively. Cooking lablab seeds for 45 minutes appear to be the optimum for elimination of these antinutrients from lablab seeds.Keywords: Lablab seeds, cooking time, toxic factors, proximate compositions, minerals