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Protein crops are an excellent source of starch (40-55% dry base), protein (20-30%) and fibre (10-30%). Compared to cereals, protein proteins in protein crops are relatively rich in lysine and low in sulphur amino acids: cysteine, methionine and tryptophan. The combination of protein and cereal foods provides an adequate nutritional protein profile.

The formulation of extruded gluten-free and GMO-free snacks, entirely based on protein crops, is an interesting way to introduce legumes to young people. These new snacks have a texture that depends on their density, honeycomb structure and the intrinsic properties of the constituent material, called parietal material.

To be able to predict the texture of snacks, it is essential to understand the organization of the constituent phases (starch, protein), which is called starch-protein morphology, and the mechanical properties of the parietal material, and then to integrate them into a numerical prediction model.

The parietal material has a morphology with a starch matrix embedded in protein aggregates. The size of the aggregates varies according to the type of raw material (pea flour, mixtures of starch (A) and pea protein (P) with a ratio A/P = 2/1 in dry base) and the intensity of the thermomechanical treatment by extrusion. Voids are observed at the interface of starch and proteins indicating low interfacial resistance. The materials produced exhibit brittle behaviour with a break in the elastic domain for pea flour extrudates and a break in the plastic domain for extrudates of AP mixtures. The starch-protein interface index defined by the ratio of the total perimeter of protein aggregates to the square root of their total surface area governs the variation in mechanical properties. The increase in the interface index, with low adhesion between the proteins and the starch matrix, weakens the material. These results show that it is possible to modulate the mechanical properties of the extruded products according to their morphology, which is itself controlled by the extrusion conditions.

In perspective, the images obtained by confocal laser scanning microscopy (CLSM) will be integrated into a digital model to predict the mechanical behaviour of pea composites and subsequently extruded cellular foods.