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

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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.. Investi-gation 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�

Investigation of the production of wet agglomerates of durum wheat

semolina using a fluidized bed granulator

Results

Water content impact:

- Larger diameters

- Higher values of water contents - Lower values of compactness - No impact on the sphericity 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.

Introduction & Objectives

0.2 0.3 0.4 0.5 0.6 0 0.5 1 1.5 2 2.5 3 C omp ac tn es s (s ol id vol u me fr ac ti on ) Diameter (mm) 0.2 0.3 0.4 0.5 0.6 0 0.5 1 1.5 2 2.5 3 M eas u re d w ate r c on te n t (g/ g d ry matte r) Diameter (mm) 0 0.2 0.4 0.6 0.8 1 0 0.5 1 1.5 2 2.5 3 S p h er ic ity (-) Diameter (mm)

Hydrotextural analysis

Mechanisms of durum wheat semolina

agglomeration in a fluidized bed

A large range in the diameter values is observed on the size distribution

curve (d₅₀ = 650 µm). The water content of the wet agglomerates is

positively correlated with their diameter. The increase of the d₅₀ 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 (d₅₀

≤ 1600 µm), followed by some phenomena of densification for the larger

structures (d₅₀ ≥ 1600 µm) .

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.

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.

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.

Bettina Bellocq

_{, Bernard Cuq}

_{, Thierry Ruiz}

_,

_{Agnès Duri}

_{, Kevin Cronin}

_{, Denis Ring}

_{UMR IATE 1208 CIRAD/INRA/Montpellier SupAgro/Université Montpellier.}

2

_{Department of Process & Chemical Engineering, University College, Cork, Ireland.}

!

!

! ! = 1

1 + !_!∗!(1 − !!!!!_! !)

Semolina size impact:

- Larger diameters

- Lower values of water contents - Lower values of compactness - Slight decrease of the sphericity

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.

(a) (b)

Microstructure of the agglomerates based on of durum wheat semolina prepared with the fluidized bed (a) and commercial couscous grains (b) at different magnifica<ons.

a) b)

Fluid Bed experiments

Acknowledgments - The authors would like to thank the

Agence Nationale de la Recherche (ANR ALID 2013) for its financial support through the program “Dur Dur”

8th granulation workshop Size distribu<on Evolu<on of the compactness Evolu<on of the water content Evolu<on of the sphericity 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 C omp ac tn es s (s ol id vol u me fr ac ti on )

Water content (g/g dry matter)

0.19 0.21 0.31 0.37 0.48 Hydrotextural diagram Increasing d_iameter COOKING Steam cooker 100°C DRYING Oven 50°C Characteristics measured: -  Size -  Shape -  Water content -  Compactness -  Strength -  Microstructure

Wet agglomerates characteristics ?

Atomising nozzle air

Air outlet Air W at er Filters Air Heating system Air flow Temperature probe Nozzle Peristaltic pump Distributor place Balance

Semolina sizes tested:

d₅₀=280 µm

d₅₀=619 µm

Water amounts tested: -24 g

-48 g -72 g -100 g -130 g

Dried agglomerates characteristics ?

Vs the traditional couscous grains ?

WET AGGLOMERATION

Fluidized bed granulator

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

0 10 20 30 40 50 0 1 2 3 4 M as s fr ac ti on (%) Diameter (mm)