Résumé:
The objective of this thesis is to study some conditions of manufacture of traditional couscous. To meet this objective, the study is organized around two main parts; a survey in the Northeast region of Algeria on the manufacture, preparation and consumption of artisanal couscous and the study of three practices identified during the survey (study of the effect of the addition of flour soft wheat with durum wheat semolina and barley flour, the addition of salt in the moist water of hydration and the agglomeration of gluten-free flours (corn, amaranth and buckwheat flours, quinoa and cassava)). Rheological properties during wet agglomeration were analyzed by the evolution of mean torque under water addition and shearing conditions using a Caleva® mixer torque rheometer. Mi-Pro® high shear granulator has been used to produce wet agglomerates, which were characterized by fraction distribution, water content, density, and agglomeration yield. After studying the granulability of gluten-free flours on the granulator scale, rolling tests of these flours were carried out according to the artisanal procedure. The data collected through the survey allowed us to design a traditional couscous-making diagram and several practices were listed as key operations that could greatly influence the quality of couscous. Among these practices, (i) the pre-cooking of the coarse semolina, (ii) the use of salted water as a hydration liquid, (iii) the addition of wheat flour or cornstarch during the finishing step, (iv) combined drying with shade and sun. The addition of wheat flour (WF) to wheat semolina (WS) and barley flour (FO) presents rheological profiles accentuating the cohesive-adhesive inter-granule effect. The optimum rate of the liquid (for maximum cohesion developed) depends on the studied effects: optimal ratio L/S tends to decrease with the salinity and to increase after addition of the FBT. The salinity of the hydration liquid decreases the inter-granular cohesion during solid-liquid mixing (effect on the liquid surface tension and the wettability of the solids) and results in the production of less dense agglomerates of large sizes. The granulation tests of gluten-free flours have demonstrated the technological feasibility of their transformation into couscous grains either at the laboratory scale or at the artisanal scale, except for cassava flour, which does not agglomerate under water addition and shearing conditions. Sensory analysis have shown that manufactured gluten-free couscous have acceptable scores for all organoleptic attributes except for amaranth couscous which has been ranked last due its very sticky nature and less firm texture.
