Soaking, boiling and antinutritional factors in pigeon peas (Cajanus cajan) and cowpeas (Vigna unguiculata)

The effects of soaking, boiling and combination of soaking and boiling at various treatment levels on the detoxification of trypsin inhibitor, cyanogenic glycoside, hemagglutinin, alkaloids and tannin in pigeon pea and vegetable cowpea were studied. Soaking was carried out for 6, 12 and 18 h while boiling was carried out for 40, 60 and 80 min. In combined soaking and boiling method, the beans were soaked for 12 h and then boiled for 40, 60 and 80 min. The results showed that the most effective method of detoxifying any of the toxicants was soaking for 12 h and boiling for 80 min. This method was able to reduce the trypsin inhibitor from 12.45 to 2.59 TUI/mg in pigeon pea and 25.60 to 3.20 TUI/mg in vegetable cowpea. The method also reduced the hemagglutinin content from 27.88 HU/mg to nil and 49.50 to 9.52 HU/mg; the cyanogenic glycoside from 40.50 mg/kg to nil and 83.81 to 5.06 mg/kg; alkaloids from 0.26 to 0.16% and 9.61 to 0.50%; and tannin from 1.60% to nil and from 3.42 to 1.28% in pigeon pea and vegetable cowpea, respectively. This method was found to be more potent in eliminating any of the toxicants rather than soaking or boiling alone.