Changes in some antinutrients of cowpeas (Vigna unguiculata) processed with ‘kanwa’ alkaline salt

The effect on several anti-nutritional factors in cowpeas (Vigna unguiculata L. Walp) was investigated following treatment at 100°C or 121°C with solutions (0.1% w/v) of kanwa rock salt or NaHCO₃ in distilled water. The concentration of polyphenols, calculated as tannic acid, was reduced substantially up to 67% under the alkaline conditions employed, but the reduction appeared to be greater (69–79%) at higher temperature. The loss of phytic acid was greater (27–40%) when beans were cooked in NaHCO₃ than in kanwa (11–29%). The concentration of reducing sugars was decreased in all treatment groups especially under alkaline conditions. There was no evidence for the formation of lysinoalanine in any of the samples.