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

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

manufacture of couscous grains

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

To cite this version:

Bettina Bellocq, Bernard Cuq, Agnès Duri-Bechemilh, Thierry Ruiz. Low shears wet granulation processes: application to the structuration of the durum wheat semolina for the manufacture of couscous grains. 8. International Granulation Workshop, Jun 2017, Sheffield, United Kingdom. 2017. �hal-01602687�

The variability of the raw materials associated with the differences between several apparatus induce a high degree of complexity in wet agglomeration. For the couscous production, the semolina is granulated using horizontal low shear mixer. The major aim of this work is to examine the effect of process conditions in low shear mixers and to propose the basis of a unique continuous description.

1. INTRODUCTION

5. CONCLUSION

Agglomerates of durum wheat semolina are saturated whatever the processes and operating conditions. The evolution of the size

distribution of the agglomerated structures with compactness shows a continuous growth process associated with the expansion of their

internal structure. These mechanisms deal with (i) classical growth of associated particles to nuclei, then nuclei to agglomerates, and

percolation to local paste state (dough pieces), and also (ii) fragmentation of dough pieces into a specific population of small saturated clusters, which are able to interact with nuclei. It is possible to link different processes under low shear conditions to generate agglomerates with

same specific functionalities.

3. RESULTS FOR THE 3 MIXERS

à

Description of the wet agglomeration

4 populations are presents in all the mixers (fragments,

nuclei, agglomerates and dough pieces). Small structures

and nuclei are less humid and more compact than larger structures.

à

Impact of the speed

A higher impeller speed leads to an increase of the breakage mechanisms, which help to improve the homogeneity in the bed by promoting consolidation and growth mechanisms. There is no impact of the speed on the water content and the compactness of the structures.

0.25 0.45 0.65 0.85 0.55 1.05 1.55 2.05 2.55 C omp ac tn es s (s ol id vol u me fr ac ti on ) Diameter (mm)

Vertical Horizontal Planetary

Evolution of compactness 0.25 0.45 0.65 0.55 1.05 1.55 2.05 2.55 W ate r c on te n t (g/ g d ry matte r) Diameter (mm)

Vertical Horizontal Planetary

Evolution of water content

0 0.1 0.2 0.3 0 0.5 1 1.5 2 M as s fr eq u en cy (%) Diameter (mm)

Vertical Horizontal Planetary

Evolution of size distribution

à

Impact of the water addition level

An increase of the water addition level leads to a decrease of the fragments and an increase of the nuclei, agglomerates and dough pieces. An increase of the water content and a decrease of the compactness are observed for all the structures.

²c

2. MATERIEL & METHODS

Liquid binder K rotative blade Planetary mixer Spray nozzle Horizontal mixer Liquid Binder Rotative blades Mixer Tank Spray nozzle Liquid binder Rotative blade Rotative bowl Vertical mixer Spray nozzle

Structuration mechanisms are analysed using the hydrotextural diagram. Mean values of water contents and compactness and their fluctuations around their respective means are taken into account to describe the impact of the process on agglomeration. Durum wheat semolina Water Wet agglomerates of couscous Characterized by: - size - water content - compactness

Water and mechanical energy

Impact of:

- mechanical mixers - impeller speeds

- water levels

Mechanical mixers

Low shears wet granulation processes: application to the structuration of

the durum wheat semolina for the manufacture of couscous grains

Bettina Bellocq, Bernard Cuq, Agnès Duri, & Thierry Ruiz

UMR IATE 1208 CIRAD/INRA/Montpellier SupAgro/Université Montpellier 2 Place Pierre Viala, 34060 Montpellier cedex 5, France

8th granulation workshop

!

!

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”

4. DISCUSSION

Water content (g/g dry matter)

ο Planetary mixer Horizontal mixer Δ Vertical mixer ο Planetary mixer Horizontal mixer Δ Vertical mixer -0.5 -0.3 -0.1 0.1 0.3 0.5 -0.5 -0.3 -0.1 0.1 0.3 0.5 C omp ac tn es s s tan d ar d d evi ati on (-)

Water content standard deviation (-)

Fluctuations of the water content and the compactness are correlated around their respective mean values. The growth of the agglomerates respects an association by the same hydro-textural categories.

Experiments show that all the structures are on the saturation curve, which indicates that they are all saturated in water whatever the mixers.

Evolution of the fluctuations Hydrotextural diagram

Increasi_{ng diame} ter

Increasi