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

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

<figure><img src="image_1.png" /></figure>

## To cite this version:

Bettina Bellocq, Agnès Duri-Bechemilh, Bernard Cuq, Thierry Ruiz. The impact of the size distributions of the native wheat powders on their structuration behavior during wet agglomeration. 8. International Granulation Workshop, Jun 2017, Sheffield, United Kingdom. hal-01606480

HAL Id: hal-01606480

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Submitted on 2 Jun 2020

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# THE IMPACT OF THE SIZE DISTRIBUTIONS OF THE NATIVE WHEAT POWDERS ON THEIR STRUCTURATION BEHAVIOR DURING WET AGGLOMERATION

## Bettina Bellocq

Under the supervision of

Pr. Bernard CUQ, Dr. Thierry RUIZ and Dr. Agnès DURI

UMR IATE - INRA Montpellier - France

## 8th International Granulation Workshop

Sheffield (U.K.) - 28th June 2017

<figure><img src="image_1.png" /></figure>
# **13. IMPACT OF THE SIZE DISTRIBUTION OF SEMOLINA IN THE STRUCTURATION OF WHEAT POWDER BY WET AGGLOMERATION**

Bettina Bellocq, Agnès Duri, Bernard Cuq & Thierry Ruiz

UMR IATE 1208 CIRAD/INRA/Montpellier SupAgro/Université de Montpellier
2 Place Pierre Viala, 34060 Montpellier cedex 5, France.
E-mail: bellocq@supagro.inra.fr

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.
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
## 1.1. WET AGGLOMERATION OF FOOD POWDERS

**Agglomeration** is largely used to improve the powders **properties and behaviour**:

- Reduction in dust production.

- Enhancement in flowability.

- Increase in bulk density.

- Reduction in segregation.

During the agglomeration process... ...the **native small particles** are gathered to form **larger assemblies** with specific **porous structures**, called the **agglomerates**.

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

### Agglomerated food powders

- Cocoa beverage powders

- Instant soluble coffee

- Culinary powders

- Flavors powders

- Protein powders

- Infant formulas

- Couscous grains

- Dairy powders

- Milk powders

- Bakery mixes

- Starch
## 1.1. WET AGGLOMERATION OF FOOD POWDERS

Agglomeration is largely used to improve the powders properties and behaviour:

- Reduction in dust production.

- Enhancement in flowability.

- Increase in bulk density.

- Reduction in segregation.

During the agglomeration process... ...the native small particles are gathered to form larger assemblies with specific porous structures, called the agglomerates.

### Agglomerated food powders

- Cocoa beverage powders

- Instant soluble coffee

- Culinary powders

- Flavors powders

- Protein powders

- Infant formulas

### - Couscous grains

- Dairy powders

- Milk powders

- Bakery mixes

- Starch

<figure><img src="image_6.png" /></figure>
**1.1. WET AGGLOMERATION OF FOOD POWDERS**

Couscous grains are made by the succession of **3 unit operations**. The polydispersity of the size causes the high ratio of out of scope (up to 60%) of wet agglomerates.

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

Agglomeration is a **key unit operation** in the couscous production.

<figure><img src="image_8.png" /><figcaption>WET AGGLOMERATES OF COUSCOUS</figcaption></figure>
## 1.2. WET AGGLOMERATION - MECHANISMS

Wet agglomeration process is classically described as a combination of successive mechanisms at different rates :

- Wetting and nucleation.

- Growth and consolidation.

- Breakage, erosion, rupture

The cohesion forces generate interactions between particles, and promote granules growth.

<figure><img src="image_9.png" /></figure>
## 1.2. WET AGGLOMERATION - MECHANISMS

Wet agglomeration process is classically described as a combination of successive mechanisms at different rates :

- Wetting and nucleation.

- Growth and consolidation.

- **Breakage, erosion, rupture**

The **rupture forces** and **shearing** effects, lead to **breakage** and to reduce the granule size.

<figure><img src="image_10.png" /></figure>

The wet agglomeration process is a **balance between growth and breakage**
## 1.2. WET AGGLOMERATION - MECHANISMS

During the agglomeration process, a **liquid binder (water) is sprayed** over an agitated powder bed.

It generates **attractive interactions** and **links** between the native particles and...

... Promotes the **spatial arrangement of the native particles** with the binder.

The native particle characteristics, like the **particle size**, control the agglomeration **mechanisms** and the **end properties** of the products.

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

http://www.cjtech.co.kr/Process%20Principles%20Agglomeration%20Granulation.htm
## 1.3. HYDROTEXTURAL APPROACH

Hydrotextural approach is used to describe agglomeration mechanisms based on changes in compactness and diameter of the agglomerates as a function to the water content.

Hydrotextural diagram is limited by the **saturation curve** until which agglomerates are completely filled by water.

<figure><img src="image_13.png" /><figcaption>Schema of the hydrotextural diagram (Ruiz et al., 2005)</figcaption></figure>

Agglomerates were analysed by measuring :

<table><tr><td>Size</td><td>= Median diameter</td></tr><tr><td>Water content</td><td>= Mass of water / Mass of dry product</td></tr><tr><td>Compactness</td><td>= Volume of solid / Total Volume</td></tr><tr><td>Saturation degree</td><td>= Volume of liquid / Volume of void</td></tr></table>
## 1.4. OBJECTIVES

No study on the impact of the particle size of native semolina during the agglomeration in the process of the couscous grain has been conducted yet.

AGGLOMERATION

ROLLING

COOKING

DRYING

<figure><img src="image_14.png" /><figcaption>Durum wheat semolina</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Wet agglomerates</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Cooked agglomerates</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Couscous grains</figcaption></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>
**1.4. OBJECTIVES**

No study on the impact of the particle size of native semolina during the agglomeration in the process of the couscous grain has been conducted yet.

<figure><img src="image_20.png" /></figure>

AGGLOMERATION

<figure><img src="image_21.png" /></figure>

ROLLING

<figure><img src="image_22.png" /></figure>

COOKING

<figure><img src="image_23.png" /></figure>

DRYING

<figure><img src="image_24.png" /><figcaption>Durum wheat semolina</figcaption></figure>

<figure><img src="image_25.png" /><figcaption>Wet agglomerates</figcaption></figure>

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /><figcaption>Cooked agglomerates</figcaption></figure>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /><figcaption>Couscous grains</figcaption></figure>

<figure><img src="image_30.png" /></figure>

**OUR OBJECTIVES WERE :**

→ To describe the agglomeration operation of the couscous grains by analysing experimental investigations.

→ To understand how the particle size distribution of semolina impact the agglomeration operation of the couscous grains.
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
## 2.1. NATIVE WHEAT POWDERS

Durum wheat semolina of industrial quality was used as "standard semolina".

<figure><img src="image_31.png" /></figure>

4 fractions of semolina with different particle size distributions were obtained by sieving the standard semolina.
## 2.1. NATIVE WHEAT POWDERS

The selected semolina allow studying the effect of particle size distributions: $d_{50}$ and span, with **almost similar values of the physico-chemical properties**.

<table><thead><tr><th></th><th>Standard</th><th>Small</th><th>Low span</th><th>Coarse</th><th>Very coarse</th><th>Methods</th></tr></thead><tbody><tr><td>d<sub>50</sub> (μm)</td><td>287</td><td>129</td><td>282</td><td>339</td><td>393</td><td>Laser granulometry</td></tr><tr><td>Particle size span (-)</td><td>1.51</td><td>1.58</td><td>0.92</td><td>1.02</td><td>0.77</td><td>Laser granulometry</td></tr><tr><td>Water content (%)</td><td>17.30</td><td>15.70</td><td>16.00</td><td>13.90</td><td>16.10</td><td>Method 44-15A AACC</td></tr><tr><td>Protein content(%)</td><td>12.4</td><td>13.02</td><td>12.66</td><td>12.39</td><td>12.35</td><td>Method 050 (AFNOR</td></tr><tr><td>True density ρ<sub>s</sub> * (g/cm<sup>3</sup>)</td><td>1.42</td><td>1.46</td><td>1.45</td><td>1.45</td><td>1.45</td><td>Helium pycnometry</td></tr></tbody></table>
## 2.2. DIRECT WET AGGLOMERATION PROCESSES

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

### Horizontal mixer

- Low shear conditions

- Two horizontal shaft axes

- Laboratory scale

- Constant mixing rate (100 rpm-15min)

### Single fluid nozzle

- $d_g = 240 \ \mu m \rightarrow$ Change in the ratio $d_{50}/d_g$

- Flow rate = 2 g.sec⁻¹

- Final water content = 0.45 g/g dry matter

- Constant final mass = 1000 g (semolina + water)

<figure><img src="image_34.png" /></figure>
**2.3. AGGLOMERATES CHARACTERISTICS**

To describe the agglomeration mechanisms and the product characteristics, we evaluated
the size distribution and the agglomerates characteristics **on each sieve**.

**Size distribution** by sieving: d50, span, yield per sieves

<figure><img src="image_35.png" /></figure>

**Distribution of water content** by weighing
after oven drying at 105°C for 24h

**Distribution of compactness** hydrostatic
balance (Precisa serie 321 LX 120+ density kit)

<figure><img src="image_36.png" /><figcaption>Hydrostatic balance</figcaption></figure>
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
**3.1. AGGLOMERATION OF STANDARD SEMOLINA**

**Large dispersion** in size was observed. Specific shape and hydrotextural characteristics allow distinguishing **5 types of structures** according to their diameter:

- **Small** (0.3 – 0.5 mm) = native particles of semolina

- **Fragments** (0.5 – 0.6 mm) = mechanical erosion of larger structures

- **Nuclei** (0.6 – 1.0 mm) = primary association of semolina particles

- **Agglomerates** (1.0 – 2.0 mm) = association of fragments and/or nuclei

- **Dough pieces** (>2.0 mm) = association of agglomerates which passes the percolation state

<figure><img src="image_37.png" /></figure>
## 3.1. AGGLOMERATION OF STANDARD SEMOLINA

Agglomeration growth of semolina to produce couscous grains leads to:

- Increasing water content

- Decreasing compactness

according to an **increase in the median diameter** of the structures.

Evolution of the size distribution of the agglomerated structures with compactness shows a **continuous growth process** associated with the expansion of their internal structure.

Mechanisms deal with (i) a **classical growth** and (ii) a **fragmentation of dough pieces**.

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>
## 3.2. IMPACT OF THE DIAMETER

5 types of structures are present in the mixer after the agglomeration. Ratio of each structure is different with a change in the $d_{50}$ of the size distributions of semolina.

<figure><img src="image_40.png" /></figure>

The median diameter of the native semolina strongly impact the agglomeration yield
## 3.2. IMPACT OF THE DIAMETER

An increase of the d50 of the semolina leads to:

→ **increasing the dough pieces, the small and the fragments.**

<table><thead><tr><th></th><th>d50<br>(µm)</th><th>Small<br>(%)</th><th>Fragments<br>(%)</th><th>Nuclei<br>(%)</th><th>Agglomerates<br>(%)</th><th>Dough pieces<br>(%)</th></tr></thead><tbody><tr><td>Low span semolina</td><td>282</td><td>3.7</td><td>1.7</td><td>41.0</td><td>27.6</td><td>17.0</td></tr><tr><td>Coarse semolina</td><td>339</td><td>13.9</td><td>12.6</td><td>12.2</td><td>27.9</td><td>22.1</td></tr><tr><td>Very coarse semolina</td><td>393</td><td>28.0</td><td>18.1</td><td>7.4</td><td>18.8</td><td>20.6</td></tr></tbody></table>
## 3.2. IMPACT OF THE DIAMETER

An increase of the d50 of the semolina leads to:

* increasing the dough pieces, the small and the fragments.

* decreasing the nuclei and the agglomerates.

<table><thead><tr><th></th><th>d50<br>(µm)</th><th>Small<br>(%)</th><th>Fragments<br>(%)</th><th>Nuclei<br>(%)</th><th>Agglomerates<br>(%)</th><th>Dough pieces<br>(%)</th></tr></thead><tbody><tr><td>Low span semolina</td><td>282</td><td>3.7</td><td>1.7</td><td>41.0</td><td>27.6</td><td>17.0</td></tr><tr><td>Coarse semolina</td><td>339</td><td>13.9</td><td>12.6</td><td>12.2</td><td>27.9</td><td>22.1</td></tr><tr><td>Very coarse semolina</td><td>393</td><td>28.0</td><td>18.1</td><td>7.4</td><td>18.8</td><td>20.6</td></tr></tbody></table>
**3.3. IMPACT OF THE SPAN**

**5 types of structures** are presents in the mixer after the agglomeration. Ratio of each structure is different with a change in the span of the size distribution of semolina.

<figure><img src="image_41.png" /></figure>

The span of the native semolina strongly impact the agglomeration yield
## 3.3. IMPACT OF THE SPAN

An increase of the span of the semolina leads to:

→ **increasing the small and the fragments.**

<table><thead><tr><th></th><th>Span</th><th>Small<br>(%)</th><th>Fragments<br>(%)</th><th>Nuclei<br>(%)</th><th>Agglomerates<br>(%)</th><th>Dough pieces<br>(%)</th></tr></thead><tbody><tr><td>Low span semolina</td><td>0.92</td><td>3.7</td><td>1.7</td><td>41.0</td><td>27.6</td><td>17.0</td></tr><tr><td>Standard semolina</td><td>1.51</td><td>22.7</td><td>12.5</td><td>10.9</td><td>27.2</td><td>19.3</td></tr></tbody></table>
## 3.3. IMPACT OF THE SPAN

An increase of the span of the semolina leads to:

* increasing the small and the fragments.

* decreasing the nuclei.

<table><thead><tr><th></th><th>Span</th><th>Small<br>(%)</th><th>Fragments<br>(%)</th><th>Nuclei<br>(%)</th><th>Agglomerates<br>(%)</th><th>Dough pieces<br>(%)</th></tr></thead><tbody><tr><td>Low span semolina</td><td>0.92</td><td>3.7</td><td>1.7</td><td>41.0</td><td>27.6</td><td>17.0</td></tr><tr><td>Standard semolina</td><td>1.51</td><td>22.7</td><td>12.5</td><td>10.9</td><td>27.2</td><td>19.3</td></tr></tbody></table>
## 3.4. AGGLOMERATES CHARACTERISTICS

Same trends were observed concerning the evolution of water content and compactness according to the diameter of the structure...

...The median diameter and the span do not impact the compactness and the water content of each structure according to their median diameters.

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
**4.1. HYDROTEXTURAL ANALYSIS**

We have represented on the diagram **the values** of **water content** and **compactness** of the **different structures** for the standard semolina.

<figure><img src="image_44.png" /></figure>

The structures on each sieve follow the saturation curve.
**4.1. HYDROTEXTURAL ANALYSIS**

We have represented on the diagram **the values** of **water content** and **compactness** of the **different structures** for the standard semolina.

<figure><img src="image_45.png" /></figure>

The structures on each sieve follow the saturation curve.
**4.1. HYDROTEXTURAL ANALYSIS**

We have represented on the diagram **the mean values** of **water content** and **compactness** of the structures for all the **different size distributions** of semolina.

<figure><img src="image_46.png" /></figure>

The size distributions of semolina do not change the hydrotextural properties of the structure: they are **all saturated by water.**
**4.1. HYDROTEXTURAL ANALYSIS**

**Fluctuations** of the water content and the compactness are **correlated** around their respective mean values for all the different size distributions of semolina.

<figure><img src="image_47.png" /></figure>

The growth of the agglomerates respects an **association by the same hydro-textural categories.**
## 4.2. AGGLOMERATION MECHANISMS

Agglomeration mechanisms was studied regarding the ratio of the median diameter of the semolina particles on the median diameter of the droplets of water ($d_{50}/d_g$):

<figure><img src="image_48.png" /></figure>

$d_{50}/d_g \le 1$ or lower span → Mechanism of **nucleation/growth** is favoured.
## 4.2. AGGLOMERATION MECHANISMS

Agglomeration mechanisms was studied regarding the ratio of the median diameter of the semolina particles on the median diameter of the droplets of water ($d_{50}/d_g$):

<figure><img src="image_49.png" /></figure>

$d_{50}/d_g \ge 1$ or higher span → Mechanism of **paste/fragmentation** is favoured.
PLAN

1 INTRODUCTION - WET AGGLOMERATION

2 NATIVE WHEAT POWDERS AND METHODS

3 RESULTS - IMPACT OF DIAMETER AND SPAN

4 DISCUSSION - AGGLOMERATION MECHANISMS

5 CONCLUSION
CONCLUSION

* The **size distributions** ($d_{50}$ and span) of the semolina particles has a **significant influence** on the yield of the agglomeration.

* Continuous growth process is associated with the **expansion of the 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)

(ii) **Fragmentation of dough pieces** into a specific population of small saturated clusters, which are able to interact with nuclei.

<figure><img src="image_50.png" /></figure>

* As a function to **the ratio of $d_{50}/d_g$** one **major mode is favoured:**

$d_{50}/d_g \le 1$ the nucleation/growing is favoured.

$d_{50}/d_g \ge 1$ the paste/fragmentation is favoured.
QUESTIONS ?

Bettina Bellocq

Under the supervision of
**Pr. Bernard CUQ, Dr. Thierry RUIZ and Dr. Agnès DURI**

UMR IATE - INRA Montpellier - France

8th International Granulation Workshop

Sheffield (U.K.) - 28th June 2017

<figure><img src="image_51.png" /></figure>