Anti-nutritional profile of tannins, polyphenols and phytic acid of Phaseolus beans from Togo

Abstract

Phaseolus beans are important sources of protein, fibre, minerals, and bioactive compounds in West Africa, although their nutritional quality may be affected by antinutritional compounds such as phytic acid and tannins. This study evaluated the variability of antinutritional compounds in Phaseolus spp. beans cultivated in Togo and identified nutritionally relevant biochemical profiles. A total of 47 bean samples collected through a nationwide ethnobotanical survey and cultivated under field conditions were analysed. Phytic acid, tannins, soluble polyphenols, and total polyphenols were quantified using standard colorimetric methods, and the data were subjected to ANOVA, correlation analysis, and hierarchical clustering. Significant differences (p < 0.05) were observed among samples for all measured compounds. Phytic acid contents ranged from 6.53 to 22.64 mg/g, tannins from 1.77 to 60.71 mg/g, soluble polyphenols from 0.27 to 5.08 mg GAE/g, and total polyphenols from 1.60 to 7.11 mg GAE/g. Samples TOKV6, AVEV21, PALV13, and YOKV27 exhibited the highest levels of antioxidant-related compounds, whereas OKPL29, KOYV43, and P206 × 2 showed the lowest antinutritional contents. Seed coat colour significantly influenced biochemical composition. Brown seeds with black spots showed the highest phytic acid (22.26 mg/g) and soluble polyphenol contents (4.11 mg GAE/g), whereas white seeds had the lowest tannin (8.7 mg/g) and soluble polyphenol levels (1.22 mg GAE/g). Positive correlations were observed among compounds, particularly between tannins and soluble polyphenols (r = 0.67). These findings highlight the nutritional diversity of local Phaseolus germplasm and support the selection of bean varieties with improved nutritional quality.