Dry fractionation fractionation of of wheat wheat bran for bran [PDF]

SLIDE 1

Dry Dry fractionation fractionation of

f wheat

wheat bran for bran for the the manufacture manufacture

f
f

functional ingredients 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.

SLIDE 2

Introduction

Structure of the wheat grain

Wheat = the most consumed cereal in Europe, with 112 kg/person/year (FAO, 2003). Wheat grain = complex structure, composed of several parts : Outer pericarp (3-4%) Testa (1%) Aleurone layer (6-8%) Starchy endosperm (80-85%) Germ (3%)

Embryonic axis Scutellum Cross cells Tube cells Hyaline layer Inner pericarp Outer layers + endosperm residues

= Bran

15-20%

f the grain

Outer layers

SLIDE 3

Introduction

Grain milling : production of wheat bran

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

f refined white flour (endosperm).

White flour Bran Human food

Wheat bran = important by-product :

! 6 million tons produced / year in Europe ! Under-valued, mostly used for animal feeding ! But interesting nutritional potential

SLIDE 4

Introduction

Structure and composition of wheat bran

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. Pericarp :

Insoluble dietary fibers
Antioxidants bound to cell walls

(phenolic acid oligomers) Microscopy analyses : VTT-Finland Alkylresorcinols

Testa :

Dietary fibers

(arabinoxylans, β β β β-glucans)

Bound antioxidants

(Ferulic acid monomers)

Aleurone cell wall :

Proteins & lipids
Antioxidants
Vitamin E & B vitamins
Minerals + Phytic acid

Intracellular contents (trapped in the cells):

SLIDE 5

Introduction

Production of ingredients from bran

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,

r 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.

! To be used as “health-promoting” food ingredients

SLIDE 6

Dissociation

Dry Fractionation :

Separation

Combination of several processing steps : dissociation step + separation steps

Introduction

Definition of bran fractionation

Fragmentation

“green technology” : no harmful solvents, no effluents
no drying steps, no denaturation of compounds, keeps matrix effect

SLIDE 7

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

Is it possible to fractionate more ?

from « histological fractionation » to « sub-cell fractionation »

Introduction

Wheat bran fractionation processes

Processes based on :

Traditional processes : grinding, sieving, air-classification
Innovative processes : electrostatic separation, but with low yields (≈5%)

SLIDE 8

Introduction

Wheat bran fractionation processes

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

Innovative processes for bran fractionation

SLIDE 9

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

1. Fragmentation / Dissociation

SLIDE 10

R 2 = 0,87

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

120
100
80
60
40
20

20 40

Temperature (° C) Mechanical Energy (J/mm3)

1. Fragmentation / Dissociation

Mechanical properties

R 2 = 0,98

500 1000 1500 2000 2500 3000

120
100
80
60
40
20

20 40

Temperature (° C) Young Modulus (N/mm²)

R 2 = 0,82

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0

120
100
80
60
40
20

20 40

Temperature (° C) Ultimate strain (%)

$ $ $ $ Rigidity % % % % Extensibility % % % % Energy to rupture

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.

Manual dissection of wheat grains

Tensile tests at controlled T°

SLIDE 11

Product feed Liquid Nitrogen flow Liquid Nitrogen recycling Impact grinding mill Cooling conveyor (screw with liquid N2) Powdered product

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.

SLIDE 12

1. Fragmentation / Dissociation

Bran grinding at pilot scale

Amb 1 step Amb 2 steps Amb 3 steps Cryo 1 step

" Ultrafine grinding amb & cryo : same D50 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.

Microscopy : VTT-Finland

Influence of the temperature on the fragmentation & dissociation of bran

D50 = 126 µm D50 = 96 µm D50 = 51 µm D50 = 54 µm D50 = 126 µm D50 = 96 µm D50 = 51 µm D50 = 126 µm D50 = 96 µm

SLIDE 13

39 52 53 20 40 60 80

10°

C

60°

C

100°

C

% of total particles volume < 50 µm

" Cryogenic grinding : most important changes in particle size reduction between -10° C and

60°

C.

1. Fragmentation / Dissociation

Bran grinding at pilot scale

Influence of the temperature on the fragmentation & dissociation of bran

% particles < 50 µm

" Cryogenic grinding : low T° $ $ $ $ bran brittleness ! ! ! ! faster particles size reduction. 2 cryogenic grinding steps $ $ $ $ proportion of fine particles.

28 36 53 53 69 20 40 60 80

1 amb 2 amb 3 amb 1 cryo 2 cryo

% of total particles volume < 50 µm

% particles < 50 µm

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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

SLIDE 15

2. Particles separation

Electrostatic properties of materials

" 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.

Tribo-charging of particles : definition

Air flow Air flow

+

+ + + + + + +

Walls of the charging pipe

SLIDE 16

5.9 7.2 3.0 5.4 5.8 5.7

2 4 6 8

Medium Fine Medium Fine Medium Fine Entire wheat bran Aleurone fraction Pericarp fraction Charge / mass (µC/g)

2. Particles separation

Electrostatic properties of materials

Tribo-charging of particles

Intact

" 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

f the aleurone and bran particles .

SLIDE 17

Air flow Air flow Feeder Tribo-charger Collecting bins Electrode plate Electrode plate

pericarp aleurone

2. Particles separation

Electrostatic separation at pilot scale

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 (D50 ≈ 50 µm).

SLIDE 18

Microscopy analyses : VTT-Finland F3B+ F3B- F3A- F3A+

D50 = 93 µm D50 = 50 µm D50 = 49 µm D50 = 38 µm

2. Particles separation

Electrostatic separation at pilot scale

Negatively charged fractions Positively charged fractions F2A+ F2B- F2A- F2B+ F1A- F1B+ Initial bran Rich in aleurone cell walls Rich in pericarp material

Good separation of the particles depending on their composition. Production of fractions of contrasted composition, at good yields. 13% 9% 7% 34%

D50 = 51 µm

SLIDE 19

Outer pericarp 7% Intermediate layer 21% Starchy endosperm 17% Aleurone cell contents 21% Aleurone cell walls 34%

Production of fractions of contrasted composition, with good yields

Aleurone cell walls 26% Aleurone cell contents 6% Starchy endosperm 1% Intermediate layer 18% Outer pericarp 49%

Pericarp typology Aleurone typology Initial ground bran

Outer pericarp 20% Intermediate layer 26% Starchy endosperm 12% Aleurone cell contents 24% Aleurone cell walls 18%

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

2. Particles separation

Electrostatic separation at pilot scale

SLIDE 20

3. Properties of the fractions

Breadmaking tests

Production of wheat fractions & breads

Wheat grains (cv. Tiger, 2006)

Wholemeal flour
White flour

Wheat bran Wheat flours

white bread
whole bread
bran breads

= whole bread, same ferulic acid and ash content Grinding at ambient Tº

Bran Ambient medium
Bran Ambient fine
Bran Ambient ultra-fine

Cryogenic grinding

Bran Cryogenic ultra-fine

Electrostatic separation

Fraction +
Middle fraction
Fraction -

SLIDE 21

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, Tº, enzyme secretions & peristaltic movements.
Dialysate samples (= contain all the bioaccessible compounds) collected every hour.
Phenolic acids quantification.

Tiny-TIM

Gastric compartment Intestinal compartment Enzyme secretions Dialysis membrane Dialysate samples

SLIDE 22

R 2 = 0,86

10 20 30 40 10 20 30 40

% particles < 20 µm

Bioaccessible FA (µg/g br. DM)

R 2 = 0,79

5 10 15 20 5 10 15 20 25 30

% particles < 10 µm

Bioaccessible SA (µg/g br. DM)

Ferulic acid Sinapic acid

3,3 18,1 12,2 13,8 15,4 6,4 22,7 21,7 26,2 30,7

5 10 15 20 25 30 35 40

White bread Whole bread BAT medium BAT fine BAT ultrafine Bioaccessible compounds (µg/g DM )

sinapic acid ferulic acid

In bran-rich breads : The bioaccessibility of phenolic acids depends

n 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)

3. Properties of the fractions

Bioaccessibility of bioactives

SLIDE 23

The bioaccessibility of phenolic acids depends on the composition of fractions

11,7 16,7 9,8 22,7 26,7 31,8 23,0 32,1 starting bran Tribo-separated bran positive middle negative 3,3 18,1 6,4 22,7

5 10 15 20 25 30 35 40

White bread Whole bread Bioaccessible compounds (µg /g DM )

sinapic acid ferulic acid

Breads made with ground bran fractions (coll M. Noort team TNO, NL) TIM experiments with bran breads (coll R. Havenaar team, TNO, NL)

3. Properties of the fractions

Bioaccessibility of bioactives

SLIDE 24

" 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

Conclusion

SLIDE 25