Localization and modeling of reaction and diffusion to explain folate behavior during soaking of cowpea

A first modeling approach was used to understand the behavior of folate in cowpea seeds during soaking at different temperatures (30 °C, 60 °C and 95 °C). Folic acid, 10-formylfolic acid, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate were quantified in both the seeds and the soaking water during the process. A 2D-axisymmetric seed soaking simulator was then built considering these 4 folate vitamers to simultaneously describe diffusion, oxidation and interconversion of the single vitamers. The model adjustments revealed the predominance of folate diffusion at 60 °C and 95 °C (apparent diffusivity 2–3 × 10−11 m2 s−1) whereas at 30 °C enzymatic interconversions of all vitamers into 5-methyltetrahydrofolate were observed (reaction rate of 8.0 × 10−5 s−1 for 5-formyltetrahydrofolate). The results of this study allow us to recommend a preliminary soaking step to retain folate in seeds and to improve the bioavailability of folates for human nutrition. •Our model describes the behavior of folates during soaking-cooking of cowpea.•The apparent diffusivity of folate increased with temperature.•Folate diffusion was confirmed by immunostaining of 5-CH3H4folate.•At 30 °C, all folate vitamers were interconverted into 5-CH3H4folate.•Our results allow us to recommend how to preserve folate during soaking-cooking.