Résumé
Pulses have important nutritional qualities, due to their high protein and starch contents. They contribute to a low carbon, healthy and affordable diet. During the processing of legumes by soaking and cooking operations, the behavior and final quality of legumes mainly depend on water transfers. These water transfers are governed by multiple thermal events related to starch (gelatinization, melting) and proteins (denaturations), which modify the affinity of water for these macromolecules. The objectives of this research are i) to better understand the physicochemical processes and the water transfers involved in the cooking of legumes ii) to identify some ways of improving the protein digestibility, which is considered to be much lower than that from animal proteins. Three legumes (green lentil, chickpea, navy bean) with distinct characteristics were selected. These legumes were milled to obtain flours and also turbo-separated to recover starch enriched flour (purity > 92 % db) and protein−fiber enriched flour (purity > 60 % db). These flours were equilibrated over a wide range of moisture content (0.2 to 4.0 kg/kg bs) and analyzed by differential scanning calorimetry (DSC). A Gaussian fitting of the DSC signal was developed. This desummation allowed to characterize the phase transitions of gelatinization and melting of starch and the denaturation of both vicilin and legumin. A modeling of the binary phase diagrams water/starch and water/protein−fiber was developed. This modeling revealed the starch melting even in excess of water. The binary water/starch phase diagrams from the three pulses are similar, unlike the water/protein−fiber phase diagrams. The aggregation of the phase diagrams (water/starch and water/protein−fiber) allowed to represent the behavior of the ternary system water/starch/protein−fiber and to propose a repartition of water between starch and protein−fiber. For example, for chickpea and bean, the amount of water attributed to starch increases from less than 10 % of total water to 35−45 % at the end of cooking. Measurements of in vitro protein digestibility under contrasting conditions revealed the low degree of freedom of the process (soaking, cooking) to increase protein digestibility by only 4 %. The results of this work were able to model the water/starch/protein−fiber equilibrium states and will facilitate the representation of dynamic model of water transfers in legumes during soaking and cooking.