Phytic acid decrease along hydrothermal treatment of bambara groundnuts: a deep assessment of the mechanisms involved

The decrease of phytic acid, an anti-nutrient involved in the reduction of mineral bioavailability is particularly important when eating foods made from Fabacea seeds, especially in Africa where people suffer from mineral deficiencies. Soaking bambara groundnuts in water at 55 °C was found efficient to reduce phytic acid. As this reduction may be due to diffusion or hydrolysis through phytase activation at elevated temperature, a diffusion-reaction numerical model was undertaken to help the analysis of the involved mechanisms and study the impact of the seed structure. This model allowed to evaluate part of initial phytic acid content released by diffusion (24 %), or due to phytase hydrolysis (40 %) or remaining in bambara seeds (36 %) after 24h of soaking and evaluate its apparent diffusivity (0.7 × 10 −11 m 2 /s). Comparison with cowpea seeds sharing similar structure but smaller size and higher hardness led to a lower decrease of phytic acid whereas comparison with results from ground or dehulled bambara revealed that the latter was the most interesting. Indeed, the molar ratio between phytic acid and the iron and zinc minerals in soaked dehulled bambara decreased by a factor of three, a required condition to increase the mineral bioavailability. • Hot soaking of bambara seeds efficiently reduces phytic acid at 55 °C. • Curve modelling of phytic acid reduction allows to describe involved mechanisms. • Apparent diffusivities of water, phytic acid and free phosphate were determined. • Seed composition and structure impact water diffusion and phytic acid decrease. • Removing bambara seed coat before soaking improves mineral bioavailability.