Influence of Dry- and Wet-milling of Maize and Wheat ...

Influence of Dry- and Wet-milling ofMaize and Wheat Starches

on their Structure and Properties

Claudia Niemann, Birgit Sadler, Friedrich Meuser, Technical University Berlin

Peter Kilz, Polymer Standard Service, Mainz

27/04/2006 Dry and Wet Milling of Starch 2TUB-GV

1. Purpose of Starch Particle Size Reduction2. Dry-milling of Maize and Wheat Starches

3.1. Morphology, CWB, CWS3.2. Gel formation, gel stability, freeze-thaw stability3.3. Target parameters of milling

4. Wet-milling of Maize and Wheat Starches4.1. Systems analytical model – Specific Mechanical Energy4.2. Product properties

5. Comparison of structure and properties of the products5.1. Rheological properties5.2. Molar mass

6. Similarities and differences: Process and Products

1698/06


Purpose of Starch Particle Size ReductionTexturizers – Stabilizers – Fat mimetics

1. Instant TexturizersInstant swelling in cold water

Provide “body” and viscosity

Thermo-reversible gel formation

2. Instant StabilizersNo need to heatNo need to heat

Avoid EAvoid E--NumbersNumbers

3. Fat mimetics

1699/06


Demands on Milled StarchesTexturizers – Stabilizers – Fat mimetics

1. Spontaneous gel formation with few dry matter

High Cold Water Binding Capacity (CWB)

2. Visco- stable Gels

Low Cold Water Solubility (CWS)

3. Freeze-thaw Stability

No Syneresis4. Smooth Mouthfeel

Small particles or high swelling capacity

1700/06


Examples:

Maize starch and Wheat starch

1701/06


Maize starchCWB = 0.7 g/g d.m.

CWS = 1.1 %

Wheat starchCWB = 0.9 g/g d.m.

CWS = 1.3 %

SEM (x 700)

Dry-milling of Maize and Wheat StarchesNative Starches – Scanning Electron Microscopy

1703/06


Maize starch CWB = 5.7 g/g d.m.

CWS = 25.4 %


CWS = 25.4 %Milling time: 6h, pre-drying: 130°C, 15min

Water content < 5%

Dry-milling of Maize and Wheat StarchesMorphological Features - SEM

1704/06


Maize starchGel formation: good

Gel stability: very goodFreeze-thaw-stab.: very good

Mouth feel: almost smooth

Wheat starchGel formation: good


Mouth feel: smooth

Dry-milling of Maize and Wheat StarchesGels 25% Starch d.m. -- Light Microscopy

(x 100)1705/06


Dry-milling of Maize and Wheat Starches25% Gel Wheat starch - SEM

1706/06


Dry-milling of Maize and Wheat StarchesResults

Optimized conditions result inoptimum target parameters

CWB ≥ 3 g/g starch d.m.

10% TS ≤ CWS ≤ 25% d.m.Crushing of starch granules and their

deformation by pressure/shear is necessary

Wet-milling in aqueous suspension

1707/06

27/04/2006 Dry and Wet Milling of Starch 11TUB-GV1 Meuser and van Lengerich, 1984

Materials and MethodsWet-milling

Systems Analytical Model1

Definition of

1. Process parameters X :Milling conditions

2. System parameter Y :Specific Mechanical Energy (Input)

3. Structure parameter S :Starch structure

4. Target parameters Z :Functional properties (CWB, etc.)

1708/06


CoBall® Mill

Process-Parameters X

Bead fillRotor speed (r.p.m.)

Mass flowStarch concentration

At 3 different levels

Materials and MethodsWet-milling - Composition of factorial design

1709/06


Wet-milling of Maize and Wheat StarchesResults - Wheat starch

Specific Mechanical Energy InputMaximum Rotor Speed

Deg

ree

of b

ead

fill[

%]

Dry matter [%]Mass

flow [kgh-

1 ]

N = 2600 min-1

r2 = 0.916

1713/06


Maize starch

CWB = 0.4 ln SME + 0.11

Wheat starch

CWB = 0.3 ln SME + 0.93Logarithmic relationship !

Wet-milling of Maize and Wheat StarchesRelationship SME - CWB

Logarithmic or linear relationship ?

Prob>F 0.0001

CW

B [g

/g s

td.m

.

Prob>F 0.0001CW

B [g

/g s

td.m

.

1715/06



CWS = 16.6 %

Wet-milling of Maize and Wheat StarchesSpray-dried starches – Morphological features

SME = 752.4 Wh/kg

Optimum CWB and CWS at

Maximum SME under the chosen

conditons

1717/06


Maize starchGel formation: good


Mouth feel: spongy

Wheat starchGel formation: good


Mouth feel: smooth(x 200)

Wet-milling of Maize and Wheat StarchesGels 25% Starch d.m. - Light Microscopy

1718/06


Wet-milling Maize and Wheat StarchesResults

1. Process can be described by a Systems Analytical Model

2. Maize starch absorbed more SME than Wheat starch

3. CWB and CWS are related to ln SME (Rotor speed, degree of bead fill, starch mass flow)

4. Wheat starch gels exhibit improved sensory properties and freeze-thaw-stability compared to maize starch gels

5. Properties of optimum wet-milled starches are different from properties of optimum dry-milled starches (morphology, CWS, sensorial properties)

Structure - Function Relationships ?

1719/06


Dry- and Wet-milled Maize starchRheology

Starch Conc. Yield Stress

d.m. [%] τ [Pa] γ [s-1] ηo [Pa.s] Maize dry-milled

25

90.0

6.1 x10-03

1.5 x104

Maize wet-milled

20

12.0

1.0 x10-03

1.2 x104

Yield Stress of particle gels from dry- and wet-milled Maize starch

Temperature 25°C1720/06


Starch c Stress - Ramp Area

[%TS] ηstart [Pa.s]

ηstartplat [Pa.s]

ηendplat [Pa.s]

ηend [Pa.s]

τ / γ [Pa.s]

Maize dry-milled

25

1.5x104

210

67

1.3x104

3.4x102

Maize wet- milled

20

1.2x104

1

1

4.4x101

1.4x104

Gels from dry and wet-milled Maize starch

Stress ramp 0-300 Pa, 240s, stress plateau 60 s, stress ramp 300-0 Pa, 240 s

Dry- and Wet-milled Maize StarchRheology - Thixotropy

1 4

1721/06


Particle size or Molecular size1?

Particle size: Counted in dry state

80% of all particles < 5 μm(dry- and wet-milled starches)

Molecules:

Size Exclusion Chromatography1 Augustat et al., 1962

Milled Maize and Wheat StarchesSize Exclusion Chromatography

High molar massconstituents(Amylopectin)

Low molar mass constituents(Amylose)

Elution volume [ml]

Mas

s fr

actio

n[%

]

“Intermediatefraction”

1722/06


Elutionsvolumen [ml]

Mas

s fr

actio

n[%

]

Native and Porous

Dry-milled

Turquois: 3hPink: 6h

Elution volume [ml]

Mas

s fr

actio

n[%

]

Milled Maize and Wheat StarchesSEC - Dry-milled Maize starch

Differential mass distribution of native and dry-milled Maize starch1723/06


Milled Maize and Wheat StarchesSEC/MALLS - Wet-milled Maize starch

RI and LS signals of native and wet-milled Maize starch

Elution volume [ml]

Native Wet-milled underoptimum conditions

5.0 10.0 15.0 25.0 30.020.0

RI S

igna

l Int

ensi

ty

LLS

Sign

al In

tens

ity

Injection Peak

1724/06

LS signal native LS signal milled

Elution volume [ml]


Milled Maize and Wheat StarchesWeight Average Molar Mass (SEC/MALLS)

Starch Mw [x 10-6gmol-1]Maize native 31.2

Maize dry-milled 6.5

Maize wet-milled 8.4

Wheat native 29.1Wheat dry-milled 13.5

Wheat wet-milled 22.2

Differences observed in SME:Maize starch was more affected than Wheat starch

1727/06


Dry-MillingConsiderable decrease in Molar Mass

Free molecule aggregates strengthen gel matrix (Network + Nanoparticles?)

Wet-MillingDecrease in Molar Mass observed (esp. Maize)

Gel matrix mainly from Amylose (weak network formation)

Longer recovery time - Irreversible structuredestruction during rheological analysis

Milled Maize and Wheat StarchesDry- and Wet-milling – Structure and Properties

1728/06


Differences in Structure and Function

Destruction of superstructure of the starch granule and of molecular structures

Dry-millingMechanical Degradation (Impact)

Wet-MillingMechanical Pasting and Degradation (Shear)

Milled Maize and Wheat StarchesDry- and Wet-milling – Structure and Properties

1729/06


Similarities - Differences

Wet-millingDeformation (Shear, scission)

Tear to pieces (Shear)

Good CWB, CWS, F-T-S

Energy necessary 0.6 kWh/kg0.6 kWh/kg

Dry-MillingDeformation (Impact, shear)

Crushing (Impact, pressure)

Very good CWB, CWS, F-T-S

Energy necessary 84 kWh/kg84 kWh/kg

++++ Sensory++ Rheostable

- - - Energy balance

+++Sensory+/- Rheostable

+++ Energy balance

Milled Maize and Wheat StarchesDry- and Wet-milling – Process and Products

1730/06

Influence of Dry- and Wet-milling of Maize and Wheat ...

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