# Investigation of the production of wet agglomerates of couscous grains using a fluidized bed granulator

Bettina Bellocq, Bernard Cuq, Thierry Ruiz, Agnès Duri-Bechemilh, Kevin

Cronin, Denis Ring

► To cite this version:

Bettina Bellocq, Bernard Cuq, Thierry Ruiz, Agnès Duri-Bechemilh, Kevin Cronin, et al. Investigation of the production of wet agglomerates of couscous grains using a fluidized bed granulator. 8. International Granulation Workshop, Jun 2017, Sheffield, United Kingdom. 2017. [hal-01605172](https://hal.science/hal-01605172)

HAL Id: hal-01605172

https://hal.science/hal-01605172

Submitted on 2 Jun 2020

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>
# 148. INVESTIGATION OF THE PRODUCTION OF WET AGGLOMERATES OF DURUM WHEAT SEMOLINA USING A FLUIDIZED BED GRANULATOR

Bettina Bellocq¹, Thierry Ruiz¹, Bernard Cuq¹, Agnès Duri¹, Kevin Cronin² & Denis Ring²

1 UMR IATE 1208 CIRAD/INRA/Montpellier SupAgro/Université Montpellier
2 Department of Process & Chemical Engineering, University College, Cork, Ireland
E-mail: bettina.bellocq@supagro.inra.fr

Mastering the industrial processes in which wheat powders are used to produce couscous is still partly based on practical industrial experience and empirical knowledge. Wet agglomeration, rolling, cooking, drying and screening are the main unit operations which are sequentially involved in the couscous grain production. Granulation is the main step that determines the production yield and the final size and shape of the couscous grain. Control of granule size distribution after the wet granulation stage is a very important quality constraint. The objective of this work is to explore whether the novel technique of fluidised bed granulation can produce agglomerates of durum wheat semolina and to investigate if this method could prove a successful alternative to the conventional method using low shear mixer technology to produce the couscous grains.

The couscous agglomerates were produced in a batch fluidised bed granulator with water as the binding medium (top spray). The size, shape, hydrotextural properties (moisture content and compactness) and strength of the granules were measured. Fluidised bed granulation provided a more controlled size distribution than is achievable with the corresponding low shear granulation approach. The agglomerates have specific hydrotextural properties, with different values of their functional attributes that allow us to think to a new ways of texturing durum wheat semolina agglomerates. The final grains size, shape and moisture content were similar to the values measured for commercially available samples. Nevertheless granule compactness was lower. The strength of the granules increased with an increase in the size and the compactness of the final couscous grain.
<figure><img src="image_2.png" /></figure>

The
University
Of
Sheffield.

# Investigation of the production of wet agglomerates of durum wheat semolina using a fluidized bed granulator

8th granulation workshop

Bettina Bellocq¹, Bernard Cuq¹, Thierry Ruiz¹, Agnès Duri¹, Kevin Cronin², Denis Ring²

¹UMR IATE 1208 CIRAD/INRA/Montpellier SupAgro/Université Montpellier.

²Department of Process & Chemical Engineering, University College, Cork, Ireland.

## Introduction & Objectives

Agglomeration is a key operation in the elaboration of couscous grains of durum wheat semolina (made by successive operations: wet agglomeration, cooking and drying). It is usually conducted in mechanical mixers and determines the production yield, the final size, shape and functionalities of couscous. The main objective of this work is to **explore the capability of the fluidised bed technology to produce agglomerates of durum wheat semolina**.

## Results

### Mechanisms of durum wheat semolina agglomeration in a fluidized bed

A large range in the diameter values is observed on the size distribution curve ($d_{50}$ = 650 µm). The water content of the wet agglomerates is positively correlated with their diameter. The increase of the $d_{50}$ of the wet agglomerates is also associated to a decrease of their compactness. Large agglomerates are more spherical. **Mechanism for the wet agglomeration can be considered as fractal morphogenesis** for the smaller structures ($d_{50} \le 1600$ µm), followed by some **phenomena of densification** for the larger structures ($d_{50} \ge 1600$ µm).

<figure><img src="image_3.png" /><figcaption>Size distribution</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Evolution of the compactness</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Evolution of the water content</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Evolution of the sphericity</figcaption></figure>

## Fluid Bed experiments

<figure><img src="image_7.png" /></figure>

### Water content impact:

- Larger diameters

- Higher values of water contents

- Lower values of compactness

- No impact on the sphericity

### Semolina size impact:

- Larger diameters

- Lower values of water contents

- Lower values of compactness

- Slight decrease of the sphericity

### Characteristics of the dried agglomerates in fluidized bed

Dried agglomerates of durum wheat semolina are characterized by **irregular shape, with very rough surfaces**. They appeared as semi discrete particles glued to each other. **The strength to compress the granules was significantly lower** than those measured for the classical couscous grains.

<figure><img src="image_8.png" /><figcaption>a) Microstructure of the agglomerates based on durum wheat semolina prepared with the fluidized bed (a) and commercial couscous grains (b) at different magnifications.</figcaption></figure>

### Characteristics of the traditional couscous grains in low shear mixer

The classical couscous grains were characterized by **spherical shape with regular surfaces**. The native semolina particles were poorly visible in the grains. The **classical couscous grains were more compact** and consolidated by complete starch gelatinisation during the cooking stage.

## Hydrotextural analysis

On the hydrotextural diagram, the structures become closer to the saturation curve with an increase in their size. Mechanisms of agglomeration in a fluidized bed show a **first stage of expansion**, which is induced by an addition of water. The saturation degree slightly increases. During the **second stage**, the structures continue to grow up but with **densification mechanisms** due to the capillarity influence.

$$ \phi(w) = \frac{1}{1 + d_s^* w \left(1 - e^{-\frac{w - w_m}{d}}\right)} $$

A relationship describes the variation of the compactness (link to the size of the structure) by using only the water content. Where $d_s^*$ is the real density of the semolina particle, w is the water content, $w_m$ is the water content at S=50% and d is the reverse slope of the central quasi-linear section of the sigmoidal curve

<figure><img src="image_9.png" /><figcaption>Hydrotextural diagram</figcaption></figure>

## Conclusion

Agglomeration in fluidized bed of durum wheat semolina is characterized by a **higher amount of agglomerates** with diameter between 1 and 2 mm (considering as a better yield for the production of couscous). Agglomerates of durum wheat are **less compact** than the classical couscous grains. Agglomeration is driven by a **fractal formation process** followed and by **densification mechanisms** for the large agglomerates. **Specific model is used to describe the interparticle arrangements.**