# Dry fractionation of wheat bran for the manufacture of functional ingredients

Youna Hemery, Joel Abecassis, Cecile Barron, Marc Chaurand, Agnès Duri-Bechemilh, Valerie Lullien-Pellerin, Frederic Mabille, Milena dos Reis Martelli, Abdelkrim Sadoudi, Marie-Francoise Samson, et al.

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## ► To cite this version:

Youna Hemery, Joel Abecassis, Cecile Barron, Marc Chaurand, Agnès Duri-Bechemilh, et al. Dry fractionation of wheat bran for the manufacture of functional ingredients. 17. International Conference of IGV GmbH - Grains are functional, May 2009, Bergholz-Rehbrücke, Germany. hal-01603365

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Submitted on 4 Jun 2020

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Dry fractionation of wheat bran for the
manufacture
of
functional ingredients

Y. Hemery,

J.Abécassis, C. Barron, M. Chaurand, A. Duri, V. Lullien-Pellerin, F. Mabille, M. Martelli, A. Sadoudi, M-F Samson

and

Xavier Rouau

INRA, UMR 1208 "Agropolymer Engineering and Emerging Technologies"

INRA-CIRAD-UMII-Supagro, F-34000 Montpellier, France.

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HEALTHGRAIN

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INRA

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UMR

iAte

ingénierie des Agropolymères
& technologies émergentes
# Dry fractionation of wheat bran for the manufacture of functional ingredients

Y. Hemery, J.Abécassis, C. Barron, M. Chaurand, A. Duri, V. Lullien-Pellerin, F. Mabille, M. Martelli, A. Sadoudi, M-F Samson and Xavier Rouau

INRA, UMR 1208 "Agropolymers Engineering and Emerging Technologies"
INRA-CIRAD-UMII-Supagro, F-34000 Montpellier, France.

The current wheat milling process aims at recovering white flour (starchy endosperm) and discarding bran and germ. Wheat bran is thus a by-product used for animal feeding, even if due to its high nutritional potential, it could be used as food ingredients to increase the nutritional quality of human foods. Dry fractionation processes can be developed in order to make better use of all the different parts of wheat grain, and aim at recovering separately the different layers of the bran, to produce fractions rich in the different bran tissues, like pericarp-rich fractions (rich in fibers) or aleurone-rich fractions (rich in vitamins, minerals, antioxidants). A study on the different steps of wheat bran fractionation has been carried out. A methodology based on biochemical markers of the different bran tissues has been developed in order to track the different parts of the grain and their behaviour upon processing. The potential of two processes was studied in particular : ultra-fine grinding and electrostatic separation. First, the mechanical properties of the different bran layers were studied, to define the conditions in which these bran layers were the most brittle. Grinding tests were then carried out at small scale, to evaluate the effect of low temperatures on particles size reduction. As very fine particles where obtained, ultra-fine grinding was tested at larger scale to compare cryogenic and ambient grindings, and to produce ultra-fine bran with a median particles diameter inferior to 50µm. In these ultra-fine fractions, most of the bran layers and cellular structures were found to be dissociated. In a second time, the sorting of bran particles according to their origin (aleurone, pericarp...) was studied, using electrostatic separation. Therefore, the electrostatic properties (like the ability of particles to get charged by triboelectrification and to keep an acquired charge) were studied for whole bran and for pericarp-rich and aleurone-rich fractions. As these different types of particles were found to exhibit contrasted properties, the electrostatic separation of ultra-fine bran was carried out at pilot scale, and allowed to obtain bran fractions that were found to exhibit different biochemical compositions and to contain different bran tissues proportions (one richer in pericarp particles, and one richer in aleurone particles). The different fractions obtained by ultra-fine grinding and electrostatic separation were incorporated into white flour to prepare pseudo whole breads. These breads then underwent an *in vitro* digestion, so the influence of the bran fractions on the bioaccessibility of bioactive compounds was measured. This study showed that wheat bran and bran fractions have a good potential as food ingredients.
Wheat = the most consumed cereal in Europe, with 112 kg/person/year (FAO, 2003).

Wheat grain = complex structure, composed of several parts :

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Introduction

Grain milling : production of wheat bran

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Aim of the current milling process :

→ To separate the starchy endosperm from the wheat germ and the outer layers.

→ Most of European cereal food products : made of refined white flour (endosperm).

Wheat bran = important by-product :

→ 6 million tons produced / year in Europe

→ Under-valued, mostly used for animal feeding

→ But interesting nutritional potential
## Wheat bran :

* Contains most of the vitamins, minerals, antioxidants & interesting phytochemicals.

* Can contribute to increase the nutritional quality of foods, if included in flours during milling, or **used as food ingredients**.

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Microscopy analyses : VTT-Finland

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iAte
ingénierie des Agrupolymères
& technologies émergentes

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INRA
### Fractionation of wheat bran : why ?

**To remove detrimental compounds**

* Mycotoxins, heavy metals & pesticide residues, concentrated in the outer pericarp (Aureli and D'Egidio, 2007; Fleurat-Lessard et al., 2007; Laca et al., 2006).

* Phenolic compounds responsible for bitter taste (Heinio, 2008).

* Anti-nutritional factors like phytates, or other compounds that are detrimental for breadmaking (enzymes, thiols...)

**To concentrate interesting compounds**

* To produce ingredients enriched in aleurone, known for its high nutritional potential (Amrein, 2003; Bach Knudsen, 1995; Buri, 2004; Fenech, 1999).

* Or ingredients rich in dietary fibres and/or rich in antioxidant compounds.

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→ **To be used as “health-promoting” food ingredients**
### Dry Fractionation :

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Combination of several processing steps : dissociation step + separation steps

* "green technology" : no harmful solvents, no effluents

* no drying steps, no denaturation of compounds, keeps matrix effect
Several processes already exist (patents)
---

focused on aleurone layer or aleurone cell purification :

* Stone & Minifie (1988) : separation of aleurone

* Goodman Fielder (1995) : aleurone rich flour

* Bühler (2003) : separation of aleurone cells
  → clusters of ± intact cells

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Processes based on :

* Traditional processes : grinding, sieving, air-classification

* Innovative processes : electrostatic separation, but with low yields (≈5%)

Is it possible to fractionate more ?

from « histological fractionation » to « sub-cell fractionation »
Innovative processes for bran fractionation

Ultra-fine grinding of bran :

• Separation of cell walls / cell contents : more specific ingredients

• Increase of the bio-accessibility of the nutrients ?

Cryogenic grinding of bran :

• Widespread in drug industry and for spices processing

• A way to obtain very fine particles

• Allow the preservation of biological activities (no heating during processing)

Electrostatic separation :

• Good method for sorting powders

• Charging of the particles & separation of the particles in an electric field
# 1. Fragmentation / Dissociation

1st step of fractionation processes → tissues fragmentation & dissociation

Cryogenic grinding : very low T° → study of mechanical properties at low T°

Mechanical properties of the different isolated bran layers :

* Tensile tests at various temperatures (-100 to 25°C)

* On whole outer layers

Grinding tests of bran at pilot scale :

* Influence of the composition of bran layers

* Influence of the grinding temperature
## Manual dissection of wheat grains

<figure><img src="image_13.png" /><figcaption>Tensile tests at controlled T°</figcaption></figure>

## Mechanical properties of whole bran layers

☞ T°: greatly influences the mechanical properties of whole bran layers

* Increase in rigidity, Decrease in extensibility

* Loss of plasticity (ductile → brittle) & mechanical energy to rupture.

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# 1. Fragmentation / Dissociation

Process : ultrafine grinding

## Ultrafine grinding of bran : influence of the temperature

* At pilot scale : on several kg using a high speed impact mill with a screw feeder

* Grinding at ambient temperature and under cryogenic conditions (liquid nitrogen).

* Particles' characterization : particle's size & microscopy.

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### Influence of the temperature on the fragmentation & dissociation of bran

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Amb 1 step

$D_{50}$ = 126 µm

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Amb 2 steps

$D_{50}$ = 96 µm

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Amb 3 steps

$D_{50}$ = 51 µm

* Ultrafine grinding amb & cryo : same $D_{50}$ but ≠ dissociation.

* Successive grinding steps at ambient T° → dissociation of the different bran tissues (different tissues extensibilities).

* Cryogenic grinding: low temperature = ↗ brittleness and ↘ extensibility of all the tissues → composite particles.

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### Influence of the temperature on the fragmentation & dissociation of bran

* Cryogenic grinding : most important changes in particle size reduction between -10℃ and -60℃.

* Cryogenic grinding : low T° ↗ bran brittleness → faster particles size reduction.
2 cryogenic grinding steps ↗ proportion of fine particles.

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## 2. Particles separation

**2nd step of fractionation processes → sorting of the dissociated particles**

The conventional separation methods (sieving, air-classification) are not adapted to the separation of ultrafine particles : inefficiency and re-agglomeration phenomena

→ Use of electrostatic separation, based on the particles' ability to get charged

**Study of the electrostatic properties of particles, at small scale :**

* Tribo-charging of different bran materials

**Study of the separation after tribo-charging at pilot scale :**

* Influence of the composition of particles
## 2. Particles separation

### Tribo-charging of particles : definition

* Particles charged by rubbing against each other & the charging device walls.

* Materials : electron donor / electron acceptor → Behavior highly influenced by the surface properties of the particles (composition, water content).

* The particles are then separated depending on the sign of their acquired charge.

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## 2. Particles separation

### Tribo-charging of particles

* Intact aleurone cells & pericarp particles display different tribo-charging behavior → due to differences in cell walls compositions.

* The particles of these materials may be separated by electrostatic separation.

* Effect of the breakage of aleurone cells during grinding : the release of intracellular compounds modifies the particles surface composition → modifies the charging behavior of the aleurone and bran particles.

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### Use of tribo-charging for the separation of bran particles

* Electrostatic separation **tested at pilot scale**, after tribo-charging.

* Particles separated in an electric field, depending on their acquired charges.

* The dissociation of the different bran layers = important parameter

* High % of composite particles in bran : much lower purity of fractions.

* 3 successive separation steps.
  Starting material : ultrafine ground bran (D$_{50}$ ≈ 50 µm).

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## 2. Particles separation

### Electrostatic separation at pilot scale

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Microscopy analyses : VTT-Finland

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## 2. Particles separation

### Electrostatic separation at pilot scale

#### Production of fractions of contrasted composition, with good yields

**Yield**: 1/3 of the initial bran

**Composed**: at 1/3 of aleurone cell walls material

**Contains** (of the initial bran)
* 2/3 aleurone cell walls
* 2/3 p-coumaric acid
* 2/3 ferulic acid

**Initial ground bran**

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**Pericarp typology**

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**Aleurone typology**

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# 3. Properties of the fractions

## Production of wheat fractions & breads

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# 3. Properties of the fractions

# Bioaccessibility of bioactives

## Nutritional potential of bran fractions : in vitro digestions

* 30g of fresh bread → Tiny-TIM digestion (TNO Intestinal Model, NL), during 6 hours.

* Stomach + small intestine compartments.

* Controlled pH, T°, enzyme secretions & peristaltic movements.

* Dialysate samples (= contain all the bioaccessible compounds) collected every hour.

* Phenolic acids quantification.

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iAte

ingénierie des Agrupolymères & technologies émergentes

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INRA
## 3. Properties of the fractions

### Bioaccessibility of bioactives

#### In bran-rich breads :

##### The bioaccessibility of phenolic acids depends on bran particle size

Breads made with ground bran fractions (coll M. Noort team, TNO, NL)

TIM experiments with bran breads (coll R. Havenaar team, TNO, NL)

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iAte

ingénierie des Agrupolymères & technologies émergentes

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

INRA
The bioaccessibility of phenolic acids depends on
the composition of fractions

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Conclusion

* Possible to produce food ingredients from bran bry dry processing

* Possible to improve the bioaccessibility of important compounds

• in reducing the particle size

• in selecting the tissues and sub-structure of interest

* Question : the techno-functional impact of the peripheral layers of the grain

• more work is needed to fully understand and overcome the problem

* Need to evaluate the investment and energy costs of innovative processes

→ transfert to industry
# Acknowledgements

HEALTHGRAIN
FP6 european project

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VTT (FI)

-Ulla Holopainen (microscopy)

TNO (NL)

-Martijn Noort (breadmaking)

-Rob Havenaar (TIM exp)

-Nuria Mateo (TIM exp)

BARILLA (IT)

BUHLER (CH)

Uppsala University (SW)

Helsinki University (FI)

INRA
CEPIA division

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Région Languedoc-Roussillon

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Ate

ingénierie des Agronomies
téchnologies émergentes

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INRA