Assessment of cyanogenic potential,nitrate and nitrite contents,and trypsin inhibitor activity of some Nigerian legumes

Edible seeds of seven varieties of legumes commonly consumed by Nigerians in large quantities were evaluated for total protein, cyanogens, nitrate and nitrite contents, and trypsin inhibitor activity using chemical, biochemical, enzymatic, and spectrophotometric methods. All analyzed samples contained cyanogen and nitrate with levels ranging from 5.88 +/- 0.26 to 28.55 +/- 1.32 mg/100 g of DM and from 49.64 +/- 4.60 to 239.42 +/- 7.20 mg/100 g of DM, respectively. Only three of the varieties contained detectable levels of nitrite, which varied from 0.54 +/- 0.01 to 3.19 +/- 0.2 mg/100 g of DM. Trypsin inhibitor activity was detected in all of the samples, ranging from 7.75 to 100.75 micromol/min/mg of protein. Total protein content of the legumes ranged from 17.8 to 28% on a dry weight basis. There was a positive correlation (r = 0.71) between the cyanogenic potential and the nitrate content of the dry seeds. Processing reduced about 78.6-88.8% and 71.0-89.5% of total cyanogen and nitrate contents of the seeds, respectively. Following administration of 5.0-15 mg of NO3 to rats by stomach intubation, analysis of their 24, 48, and 72 h urine showed that only 40% of the administered nitrate appeared in the urine unmetabolized. Processing was shown to drastically reduce these antinutritional factors to very low levels. The health implications of these findings are discussed.