Elaboration et comportement mécanique de matériaux composites amylo-protéiques

Starchy extruded foods are considered as solid foam and their texture is defined by their structure and the mechanical properties of the cell-wall, or constitutive material. This material is envisioned as dense composite of starch and proteins. In addition to composition, the mechanical properties of these composites depend on their morphology, created during extrusion. In this context, the aim of our study is to determine the relationship between morphological features and mechanical properties of legume based starch-protein composites in glassy state, using experimental and finite element modelling (FEM) approaches. In this purpose, dense pea composites having various starch-protein morphologies were obtained by twin-screw extrusion of pea flour and blends of pea starch and protein isolates (SP). Microscopy study of these samples revealed that their morphology displayed protein aggregates embedded in an amorphous starch matrix. This microstructure can be described by several features, such as the median size of protein aggregates, and a protein-starch interface index (Ii) derived from their total perimeter and area. These morphological features depended on the extent of starch destructuration and of protein aggregations, which are controlled by material composition and specific mechanical energy (100< SME<2000 kJ/kg) during extrusion. Pea flour composites exhibited a brittle mechanical behavior, whereas rupture of SP blend composites occurred in the plasticity domain at higher breaking stress and strain. The impact of morphological features, in particular of Ii, was explained by the poor interfacial adhesion between pea starch and pea protein aggregates. Nanoindentation study showed that the starch and protein phases, and the interphase of the composites exhibited significantly different values of modulus, depending on their composition and transformation. These results fed the FEM mechanical modelling study, which indicated that the elastic-plastic constitutive law following Voce scheme represented adequately the macroscopic and microscopic mechanical behaviors of pea composites. The implementation of these laws on the meshed microstructure of pea composites allowed predicting their mechanical behavior at macroscopic scale. This work provides a solid basis for further development of predictive models of the texture of legume based extruded foods.La texture des aliments amylacés extrudés, considérés comme des mousses solides, est définie par la structure et les propriétés mécaniques du matériau pariétal, ou constitutif. Ce matériau est envisagé comme un composite amylo-protéique dense. Outre sa composition, ses propriétés mécaniques dépendent de la morphologie créée lors de l'extrusion. Dans ce contexte, le but de notre étude est de déterminer la relation entre les caractéristiques morphologiques et les propriétés mécaniques des composites amylo-protéiques issus de protéagineux en utilisant une approche expérimentale et de modélisation par la méthode des éléments finis (MEF). Dans ce but, des composites denses, à base de farine de pois et de mélanges amidon-isolat de protéines de pois (AP), ont été obtenus par extrusion bi-vis. Leur morphologie, révélée par microscopie, présente des agrégats protéiques dispersés dans une matrice d'amidon amorphe. Cette morphologie peut être décrite par des caractéristiques, telles que la taille médiane des agrégats protéiques, et un indice d'interface (Ii) amidon/protéines défini à partir de leur périmètre et surface totale. Ces caractéristiques morphologiques varient avec le niveau de déstructuration de l'amidon et l'agrégation de protéines, modulées par la formulation et l'énergie mécanique spécifique (100<EMS<2000 kJ/kg) appliquée lors de l’extrusion. Les composites de farine de pois présentent un comportement fragile avec rupture dans le domaine élastique, tandis que les composites de mélanges AP présentent une rupture dans le domaine plastique, pour des contraintes et déformations plus élevées. L'impact des caractéristiques morphologiques, en particulier de Ii, sur le comportement mécanique s'explique en partie par la faible adhésion interfaciale entre l'amidon et les agrégats protéiques. Une étude par nanoindentation permet de déterminer les modules locaux des phases de l'amidon, de protéines et l'interphase, et de montrer que leurs valeurs varient avec la composition et la transformation des composites. Ces résultats alimentent un modèle mécanique (MEF), qui indique que la loi constitutive élastoplastique suivant le modèle de Voce représente bien le comportement mécanique des composites. L'implémentation de ces lois sur la microstructure maillée des composites a permis de prédire leur comportement mécanique à l'échelle macroscopique. Ce travail fournit une base solide pour le développement ultérieur de modèles prédictifs de la texture des aliments extrudés à base de protéagineux

Elaboration and mechanical behavior of starch-protein composites

Elaboration and mechanical behavior of starch-protein composites. 32nd EFFoST International Conference: Developing innovative food structures and functionalities through process and reformulation to satisfy consumer needs and expectation

Morphology and mechanical behaviour of pea-based starch-protein composites obtained by extrusion

International audienceStarch-legume protein composites were obtained by extrusion of pea flour and pea starch-protein blend at various specific mechanical energies (100-2000 kJ/kg) and a temperature low enough to avoid expansion. The morphology of these composites displayed protein aggregates dispersed in a starch matrix, revealed by microscopy. Image analysis was used to determine the median width of protein aggregates (D-50), their total perimeter and surface, from which a protein/starch interface index (I-i) was derived. The mechanical properties of composites were determined by a three-point bending test. The pea flour composites had a higher interface index I-i (1.8-3.1) with lower median particle width D-50 (8-18 mu m) and a more brittle behaviour than the blend composites that had a lower I-i (1-1.1) and higher D-50 (22-31 mu m). For both materials, rupture stress and strain were negatively correlated with I-i. This result suggested that there was a poor interfacial adhesion between the pea starch and proteins

Fava bean (Vicia faba L.) protein concentrate added to beef burgers improves the bioaccessibility of some free essential amino acids after in vitro oral and gastrointestinal digestion

International audienceThe influence of partial replacement of animal protein by plant-based ingredients on the protein digestibility of beef burgers was investigated. Beef burgers were supplemented with fava bean protein concentrate (FB) or a mixture of FB and flaxseed flour (FBFS), both processed by extrusion, at different levels: 0 (control), 10, 15, and 20 % (w/w). A pilot sensory analysis was conducted to select the percentage of flour inclusion for further assays: control, 10 % FB, and 10 % FBFS. Protein digestibility, amino acid profile, and protein secondary structure of these burgers after in vitro oral and gastrointestinal digestion were studied. In vitro boluses were prepared with the AM2 masticator, simulating normal mastication, and static in vitro digestion of boluses was performed according to the INFOGEST method. Inclusion of 10 % FB in beef burgers did not alter their flavour or tenderness compared to the control, whereas tenderness and juiciness scored slightly higher for the 10 % FBFS burgers compared to 15 % and 20 % FBFS ones. Poor lipid oxidative stability during storage was observed with 10 % FBFS burgers. Total protein content was significantly higher (p < 0.05) in 10 % FB burgers than in control burgers after in vitro oral digestion. Additionally, 10 % FB burgers presented higher amounts of free essential amino acids like isoleucine, leucine, phenylalanine, and valine at the end of digestion, as well as methionine, tyrosine, and histidine. Partial substitution of meat protein by 10 % FB improves the nutritional profile of beef burgers, without altering their sensory qualities