Structure de l'amidon de maïs et principaux phénomènes impliqués dans sa modification thermique

Structures and phenomena occurring during the heat treatment of cornstarch. The structure of cornstarch and the modifications induced during the heat treatments are presented in this review. Current knowledge indicate that the starch granules are semi-crystalline entities composed mainly by amylose and amylopectin, undergoing deep reorganizations during the heat treatments. Gelatinization, glass transitions, relaxation phenomena, retrogradation and the formation of amylose-lipids complexes are the major phenomena involved in these reorganisations, and are the basis of changes of the techno-functional properties of cornstarch-based products during their heat treatment. La rhizosphère est le volume du sol situé au voisinage immédiat des racines des plantes et qui se caractérise par la présence d'exsudats racinaires (rhizodépôts). Ces exsudats sont utilisés par la microflore endémique en tant que signaux chimiques en plus d'être un substrat nutritif disponible pour la croissance et le développement de ces microorganismes dans la rhizosphère. Certaines de ces bactéries du sol, appelées PGPRs (Plant Growth Promoting Rhizobacteria), sont capables de coloniser les racines ou bien encore la rhizosphère, mais à la différence des autres bactéries rhizosphériques elles ont, en retour, un effet bénéfique sur la plante. Cet effet bénéfique peut être direct, ou indirect. La promotion directe de la croissance est le résultat du pouvoir d'acquisition des nutriments ou de la stimulation des hormones de la plante. D'autres mécanismes indirects, mais le plus souvent liés à la croissance des plantes, sont impliqués dans la réduction/suppression des pathogènes des plantes. Cet article décrit les différents mécanismes mis en jeu par les PGPRs dans leur environnement naturel pour influencer favorablement la croissance et la santé des plantes

Comparaison d'un modèle empirique et d'un modèle physique de séchage de grains de maïs en lit fluidisé

Comparison of two drying models applied to corn drying in fluidized bed. In this article, two predictive models of the temperature and water content of corn grains during their drying in a fluidized bed are compared. The first model is a simplified one, where the physical phenomena implied in the process are not described. It can be solved using freewares available on Internet. The second is a more complex model, based on the basic physical laws governing the phenomena of heat and mass transfer within the product. It requires the use of commercial finite element software to solve it. The two models are parameterized with four dryings where the temperature remains constant during the process, then validated on dryings with variable temperature and an intermittent drying. The two models are able to describe with an acceptable precision the evolutions of water content during continuous dryings, and to predict the evolutions of water content during dryings with variable temperature and the intermittent drying. The dynamic model is however not able to describe the evolution of the grains temperature during dryings at variable temperature with a precision lower than one degree Celsius. If this precision is sufficient, the use of the dynamic model will reduce considerably the costs in time and license of software for the modeling of the corn drying in a fluidized bed

Irvingia gabonensis seed fat as hard stock to formulate blends for trans free margarines

In order to formulate trans-free margarines, Irvingia gabonensis seed fat (IGF) was blended with a liquid oil which was either rapeseed oil (RO), groundnut oil (GNO), palm super olein (PSO) or Dacryodes edulis pulp oil (DPO). All the binary fat blends were evaluated in terms of melting behavior by Differential Scanning Calorimetry and p-NMR. Based on their melting behaviors by p-NMR, four blends (IGF/RO 30:70, IGF/GNO 30:70, IGF/GNO 20:80 and IGF/RO 20:80) were selected as having melting profiles closed to those of fat extracted from commercial margarines and literature data. Some physical properties of the selected fat blends such as solid fat content, hardness (by penetration) test, microstructure using an optical microscope and polymorphism using X-Ray Diffraction were evaluated. Those four trans-free fat blends showed similar hardness and solid fat content (SFC) than fats extracted from commercial bakery margarine, baking margarine and table margarine during storage experiments. All those four fat blends showed β’ crystals as stable polymorphic form, which is desirable for margarines. Therefore, those four fat blends are suitable to formulate trans-free margarines with desirable textural properties. © 2018 Elsevier Lt