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.
Highlights
The food that has been eaten and swallowed is mixed with saliva, gastric fluids and churned by peristaltic movements of the stomach into a creamy fluid called the chyme
A total of 38 P. vulgaris bean seed varieties were obtained from University of Nairobi, Kenya and multiplied at Sokoine University of Agriculture, Morogoro Tanzania to obtain enough beans to be subjected to cooking and laboratory analysis for tannins and phytates
The tannin and phytate levels in the P. vulgaris bean varieties are presented in Figures 1 and 2
Summary
The food that has been eaten and swallowed is mixed with saliva, gastric fluids and churned by peristaltic movements of the stomach into a creamy fluid called the chyme. The absorption of mineral elements is a very complicated system and several components in foods can form soluble and insoluble complexes with these elements under intestinal conditions (Gibson et al, 2010). Cereals and other plant related foods, which form the base of diets for most African communities, contain phytate (myo-inositol hexaphosphate and other inositol phosphates), a known inhibitor of iron and zinc absorption (Hurrell et al, 1992; Lönnerdal, 2000; Afify et al, 2011). Phytate-containing foods may be a strong contributing factor for poor iron and zinc status in population that consume these diets (Gibson et al, 2010). In a study in Malawi, a high intake of phytate was correlated with poor iron and zinc status in pre-school children (Gibson et al, 2010)
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