Impact of soaking process on the microstructure of cowpea seeds in relation to solid losses and water absorption

A cytohistological investigation was performed to better understand the structural alterations of cowpea seeds in relation with soaking. Thin sections obtained from seeds soaked at 30 °C, 60 °C and 95 °C were treated to specifically visualize starch, proteins, cellulose and pectin. Micropyle behavior as well as water uptake and dry matter loss were also monitored. A Soaking at 30 °C induced slight alteration of parenchymatous cells of cotyledons, whereas drastic alterations were observed at 60 °C and intense alterations at 95 °C. All these structural modifications of cells could explain losses of nutrients and antinutritional factors at the highest soaking temperature (95 °C). The size of the apertures in the micropyle sections varied depending on both soaking temperature and time. At 30 °C and 60 °C, the micropyle aperture enabled notable water uptake by seeds. At 95 °C, water was entirely taken up through the testa. These results show that models describing nutrients losses and water uptake should account for these structure changes during soaking of legumes.