Effect of cooking on tannin and phytate content in different bean (Phaseolus vulgaris) varieties grown in Tanzania

Abstract

Phytates and tannins are present in varying proportions in legume based foods. Investigation on the effect of cooking on tannins and phytates was carried out on thirty eight raw and cooked bean (Phaseolus vulgaris) varieties. Tannins were assayed by vanillin-hydrochloric acid method, while phytates were determined by a method developed by Haugh and Lantzsch. There was a very high significant difference (P≤0.00001) in the tannin concentrations between the raw and cooked bean samples. The mean tannin content for the raw and cooked samples was 1.168±0.81 and 0.563±0.503%CE, respectively. Reduction of tannins after cooking ranged from 20%CE in M’mafutala to 81%CE in GLP 2 with an average reduction of 56.3%CE. Equally, there was a very high significant difference (P≤0.0001) in the phytate concentrations between the raw and cooked bean samples. The mean phytate content for the raw and cooked samples were 0.0219±002 and 0.0122±003 µg/mL, respectively. Cooking reduced the anti-nutritional factors significantly (p≤0.0001). The extent of anti-nutritional factors reduction varied between bean varieties. Cooking is therefore important for mineral absorption during digestion process in humans as it makes the minerals less bound and hence physiologically available.   Key words: Beans, phytates, tannins, minerals, raw, cooking, bioavailability.