Impact of fluidized bed granulation on structure and functional properties of the agglomerates based on the durum wheat semolina

The granulation step determines the production yield and the final characteristics of the agglomerated couscous grains of durum wheat. The objective of the present work was to explore the capability of the fluidised bed technology to produce agglomerates of durum wheat semolina. The impacts of different processing conditions have been investigated on the structure and functional properties of the agglomerates. The size, shape, water content, compactness, and mechanical strength of the granules were measured. The fluidized bed agglomeration process has been found to produce agglomerates of durum wheat with different attributes compared to those produced by granulation using the low shear mixers. The results were discussed in regard to the hydro-textural approach, in order to get a better understanding of the mechanisms and relationships between process, structure, and properties. Two major agglomeration mechanisms contribute to the growth of the wet agglomerates: a fractal-structuring process followed by a phenomenon of densification. By studying the evolution of the compactness, diameter and water content, it was demonstrated that inter granular arrangements led to an expansion followed by a densification of the wet agglomerates. A relationship was proposed to describe the growth using a fluidized bed of the wet agglomerates of durum wheat semolina

European Young Cereal Scientists Gather in Bergamo, Italy

European Young Cereal Scientists Gather in Bergamo, Ital

Description of rolling as unit operation during the couscous process

Couscous agglomerates are made from durum wheat semolina by the succession of 4 unitoperations: agglomeration, rolling, cooking and drying. Rolling stage is conducted to give aspherical shape to the agglomerates and to separate them according to size criteria.Continuous rolling drum is used by industry, and for some of them it is composed of aninclined perforated cylinder rotating about its central axis. The rolling stage is one criticaloperation during the couscous grain processing, as rolling mainly determines the process yield,by generating significant mass flows of too small and too large agglomerates that could reachmore than 60% of the total mass flow. The objective of the present work is to investigate therolling stage as a unit operation, to determine the rolling process efficiency and itscontribution on the structuring mechanisms of the couscous agglomerates.We used specific rolling equipment at pilot scale. Two metal grids allow separatingthe agglomerates in three fractions: fine, medium, and large agglomerates. Durum wheatsemolina was used as raw materials to generate the wet agglomerates by a standard procedure.We investigated (i) the screening efficiency by assessing the three fractions yield, (ii) therolling efficiency by measuring the circularity of agglomerates after rolling; (iii) thesecondary agglomeration mechanisms by comparing the size distributions of the agglomeratesbefore and after rolling; and (iv) the impact of rolling conditions on the hydro-texturalcharacteristics of agglomerates.Results demonstrated that the rolling operation induces slight changes in the structureof the agglomerates and generates secondary agglomeration mechanisms. The change insetting conditions of the rolling operation has no significant impact on the screeningefficiency and on the hydro-textural characteristics of agglomerates (diameter, compactness,and water content). A physical approach was conducted to determine both the sieving andpassing speeds of agglomerates and showed that classification function of the rotating drumcan be greatly improved

Contribution of cooking and drying to the structure of couscous grains made from durum wheat semolina

Background and objectives: During the processing of couscous grains of durum wheat semolina, the steam cooking and the drying stage helps strengthen the structure and reaches the end-properties of the product. The objective of the present work was to investigate the physicochemical mechanisms generated during the steam cooking stage, under different water contents, and the drying stage, under different temperatures.Findings :The physicochemical characteristics of couscous grains (size, shape, compactness, water content, extent of starch gelatinization, microstructure, and texture) were measured during processing. These mechanisms are promoted by high temperatures during processing under different conditions of water contents and by water transfer. The mechanisms were discussed in regard to the state diagram of the wheat components and the hydrotextural diagram.Conclusions : During the steam cooking and the drying stages, the grains remain saturated by interstitial water, which means that the deformation mechanisms of the grains compensated the variations of the water content.Significance and novelty : An analytical drying model describes the kinetics of average water contents during the first part of the drying stage and allows modelling the changes in compactness and the subsequent changes in diameter for the agglomerates of couscous grains

The impact of the size distributions of the native wheat powders on their structuration behavior during wet agglomeration

The control of the wet agglomeration processes of powders depends on the combined contribution of native powders characteristics, energy input, and wetting liquid binder. The objective of this work is to specifically investigate the contribution of the size distribution (d50 and span) of the native particles, on the dimensional and structural characteristics of the agglomerates. Experiments are performed with native semolina particles. The agglomeration process is conducted using water as liquid binder. Several fractions of native semolina with contrasted dimensional properties (d50 and span) are prepared by a sieving procedure. The wet granulation is processed under specific conditions using a low shear granulator at constant blade speed, product load, liquid spraying condition (constant dimensionless spray flux) and residence time. The agglomerates properties are evaluated by the distribution of the measured values of the size, water content and compactness. The mean values and their fluctuations are both taken into account to describe the agglomeration mechanisms.Whatever the size distribution of the native powder, the mechanisms involved in the agglomeration process are the same but with different importances especially the breakage of agglomerates. We observed specific effects of the span and the median diameter of native powders on the size distribution of the agglomerates. Using small native particles (d50 < 250 μm) improves the homogeneity of the size distribution of the agglomerate bed. Using slightly dispersed native particles (span < 1.0) leads to a better uniformity on the size distribution. We demonstrate that the conditions to obtain a population of agglomerates with a narrow size distribution depend on the ratio between the water droplet diameter (d50drop ~ 250 μm), and the median diameter of the native particles. This diameter ratio is considered as a process parameter. We propose to build a modified dimensionless spray flux number by incorporating this diameter ratio. The nucleation step is specifically described by this new dimensionless number

Impacts of the size distributions and protein contents of the native wheat powders in their structuration behaviour by wet agglomeration

Article soumisThe control of the wet agglomeration processes of powders depends on the contribution of the characteristics of the native powders. The objective of this work is to specifically investigate the contribution of the size distribution (d50 and span) and composition (the protein contents) of the native particles, on the dimensional and structural characteristics of the wet agglomerates. Different fractions of native semolina with contrasted size properties (d50 and span) and protein content are used as raw materials. The wet granulation is conducted using a low shear granulator and liquid spraying condition at constant dimensionless spray flux. The structure properties are evaluated by the distribution of the measured values of the size, water content and compactness. We observed specific effects of the span and the median diameter of native powders on the size distributions of the wet agglomerates. Using small native particles (d50 < 250 μm) improves the homogeneity of the size distributions. Using slightly dispersed native particles (span < 1.0) leads to a better uniformity on the size distributions. Using semolina with high protein content could lead to a narrow size distribution by limiting the process of fragmentation and the formation of fragments in the bed. We showed that the mechanisms involved in the agglomeration process are similar whatever the size distribution and the protein content of the native powders

Low shears wet granulation processes: application to the structuration of the durum wheat semolina for the manufacture of couscous grains

Low shears wet granulation processes: application to the structuration of the durum wheat semolina for the manufacture of couscous grains . 8. International Granulation Worksho

Les procédés d’agglomération par sollicitations mécaniques. Application à la structuration de la semoule de blé dur pour la fabrication du couscous

Les procédés d’agglomération par sollicitations mécaniques. Application à la structuration de la semoule de blé dur pour la fabrication du couscous. 16. Congrès de la société française de génie des procédés (SFGP 2017

Screening efficiency and rolling effects of a rotating screen drum used to process wet soft agglomerates

The rotating screen drums are largely used in most powder handling and processing industries. They are commonly used for size separation of granular materials. Objectives of the present work are to better understand both roles, screening efficiency and shaping effects and to investigate and model which process parameters are relevant when using an inclined rotating screen drum for processing wet couscous agglomerates. Durum wheat semolina was used as raw material to produce the wet agglomerates. The pilot rotating screen drum equipment was composed of two sieves to separate three fractions: fine, medium, and large agglomerates. The shaping effects of the rotating screen drum were evaluated from the measurements of the physico-chemical characteristics (size distribution, water content, compactness, and circularity) on wet soft agglomerates. To describe the screening efficiency parameters of a rotary screen drum, a specific method was developed by using a matrix analysis of the different measured weights of the collected products. The impacts of rotating screen drum parameters (angle of inclination, rotating speed, and product flow rate) on the sieving efficiency and on the shaping effects were investigated. The present results demonstrate high apparent screening efficiency of the rotating screen drum when used with wet agglomerates of durum wheat, ranging between 89 and 96% depending on the process conditions Finally, using dimensional analysis, two correlations were proposed on the circularity and the apparent screening efficiency whatever the operating conditions used (drum speed, angle of inclination and feed rate)