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RESEARCH PRODUCT

Study of the biochemical composition and physico-chemistry of a protein-based food model of Parkia biglobosa

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In West Africa, the seed of the cowpea (Parkia biglobosa) is used in traditional pharmacopoeia and especially in human food as a condiment. This legume is very rich in proteins and lipids and remains a poorly exploited source of protein. Our thesis focuses on the valorization of Néré seeds for the development of new protein-rich products of plant origin as an alternative to the use of soybean as a basic ingredient. The objectives were : (i)biochemical and physicochemical characterization of protein isolates from Néré seed flour according to the extraction process, (ii) selection of proteolytic lactic acid bacteria capable of fermenting Néré juice, reducing anti-nutritional factors in order to increase nutrient bioavailability, (iii) obtaining a protein-rich food model.From Nere seed meal, protein extraction yields by aqueous solution extraction were determined as a function of pH, ionic strength and the presence of fat. The isolated proteins showed maximum solubility at low pH 2-3 and high pH 8-10. The protein profile by SDS-PAGE is similar to that of other seed legumes: albumins, globulins and their subunits.The effects of the use of Lactobacillus plantarum strains on the reduction of anti-nutritional factors and the improvement of protein digestibility in raw and fermented Nerea seed juice were studied. Heat treatment considerably reduces anti-nutritional factors such as phytates, tannins, trypsin inhibitors. All strains of Lactobacillus plantarum used improved protein digestibility (in vitro) and contributed, in a variable way, to the reduction of anti-nutritional factors contents.The thermal gelability of the protein isolates of albumins and globulins of cowpea was determined as a function of pH. At pH 7, the minimum concentration for thermal gel formation is between 100-120g/l. It appears that the development of a food model from protein isolates is not well suited to West Africa, as it seems preferable to limit protein losses in a long separation/purification process of protein fractions. Thus, a model was developed to maximize the use of the proteins available in the Néré seed. Based on the soybean tofu technique, Nere and soybean juices were heat treated in the presence of bivalent salts (MgCl2 and CaCl2) at different concentrations. Tofu samples prepared with 20 and 40 mM concentrations of MgCl2 and CaCl2, respectively, showed significant coagulum and resulted in a "firm" type of tofu. Uni-axial compression analysis revealed that the hardness and cohesion of the samples were a function of the nature and concentration of divalent salts, while adhesion was not significantly affected. The rheology at imposed stress allowed to observe a predominance of the elastic character over the viscous character. The best combination resulted in a Néré tofu with a dry matter content of 30.9% and protein contents of 13% and 7.2%.The work of this thesis shows a way to valorize the nutritional potential of this tropical legume and to develop food products such as beverages and tofu for human consumption in Africa.