Effects of processing methods on phytate and tannin content of black small common beans (<i>Phaseolus vulgaris</i> L.) cultivated in Mozambique

Antinutritional factors (ANFs) are the most found chemical in legumes, including beans. This study was done to evaluate the effects of processing techniques on the anti-nutritional factors of common beans. Soaking in water alone, and soaking in sodium bicarbonate (0.05 %) solutions (1:3 in both cases), germination for 24- and 48-hours (at 25 °C), and conventional and pressure cooking, were applied. The dried and ground processed beans were subjected to analysis for phytate and tannin (vanillin-HCl, Burns). The ANFs were significantly affected by each treatment (P < 0.05). Soaking the beans in water and sodium bicarbonate showed a reduction in phytate content of 17.79% and 27.32 %, respectively. The reduction in phytate content by 22.57% for germination of 24 hours and 34.95 % for 48 hours at 25 °C was achieved. The amount of phytate reduced by conventional cooking and pressure cooking was 33.29 % and 35.21 %, respectively. It was also illustrated that the soaking reduced the tannin content by 46.88 % for soaking in water and 54.76 % for soaking in sodium bicarbonate. Reductions in tannin content of 59.44% and 66.69% were obtained by 24-hour and 48-hour germination, respectively, while ordinary and pressure cooking showed tannin reductions of 69.81 % and 77.69 % respectively. Pressure cooking showed the highest reduction in the ANFs and greatly affected the phytate and tannin content, followed by ordinary cooking and germination for 48 hours. It was concluded that pressure cooking shows the highest reduction in phytate and tannin contents.