Comparative evaluation of the effect of boiling and autoclaving of legume grains on tannin concentration

The study was designed to evaluate the effect of boiling and microwave treatment methods on reducing the concentration of tannins in Soy bean (Sb), Cowpea (Cp) and Pigeon pea (Pg) legume grains (LGs). The raw samples of LGs were roasted in a microwave oven for 3 and 6 minutes at 120 Three (3) LG seeds weighing 30 gms were boiled for 30 and 60 minutes in water at 100 oC. Meals of Raw, boiled and microwaved Sb, Pp and Cp LGs were subjected to proximate analysis for levels of tannins using the Folin-Ciocalteu assay technique. Absorbance for each sample as indicator of tannin concentration was read from UV-VSI spectrophotometer. Tannic acid levels in micrograms for the three (3) samples were read from the standard curve and the tannin content was calculated as on dry matter basis. Raw samples showed no significant (p<0.01) difference in tannin content in Sb, Cp and Pp. Boiling the LGs in water for 30 minutes resulted in the reduction of tannin up to 46.6% Sb, 53.5% Pp and 42.5% Cp. Boiling for 60 minutes resulted in the reduction of tannins to 62.5 % Sb, 72.9% Pp and 75% Cp respectively. Microwaving the LGs for 3 minutes resulted in 46.7% Sb, 54.2 % Pp and 37.5% Cp reduction of tannin levels respectively. Microwaving for 6 minutes reduced tannins by 71.1% in Sb, 65.1% in Pp and 65% in Cp. No tannin significant (p˂0.05) difference was observed for the effect of boiling and microwave treatment LGs.