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Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Biopolymers in Solution
Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Biopolymers are ofsubstantial industrial interestNearly unlimited resourcesMore likely to be bio-compatible and biodegradableGood mechanical propertiesAlready Designed and Optimized by nature to fulfill a certain task Easy to make derivatives with desired property profiles“Natural” name on ingredient lists
2
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Application of Celluloseethers
* CM =carboxmethyl, HE = hydroxyethyl, HP = hydroxypropyl, M = methyl, SE = sulphoethyl, C = cellulose
thickeners, binding agents, stabilizers and emulsifiers
CMC, HPMC, MCFoodstuffs (sauces, milkshakes, bakery products)
thickeners, binding, emulsifying and stabilizing agents, film formation, tablet disintegrants
CMC, MC, HEC, HEMC, HPMCCosmetics (creams, lotions, shampoos), pharmaceuticals (ointments, gels, tablets, coated tablets)
friction reduction, water retention, enhanced ignition processes
MC, HPC, HPMCEngineering (extrusion, electrode construction, ceramic sintering)
anti-redeposition power, wetting ability, suspending and emulsifying agents
CMC, HEMC, HPMCDetergents
water retention, flow characteristics, surface activity
CMC, CMSEC, HEC, HPC, HPMCDrilling industry , mining (drilling fluids)
protective colloid, surface activityHEC, HPC, HPMCPolymerization
adhesive and film-forming properties, thickening, soil release)
CMC, MC, HPMC, CMSECTextile industry (sizes, textile printing dyes)
agents for binding and suspending, sizing aids and stabilizers
CMC, HEC, HEMC, HPMCPaper manufacture
stability of suspension, thickening, film formation, wetting
CMC, HEC, HEMC,HPMC, HEMCMCPaints
water retention capacity, stability under load, adhesive strength
MC, HEMC, HPMC, CMC, HEMCMCConstruction materials (plasters, filler, pastes)
FunctionCellulose derivative*Application
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Examples of Biopolymers in Solution
Xanthan:even distributionvisual impressionnatural pourabilityavoiding “sliminess“good “mouthfeeling”
HydroxyethylStarch:hypoallergenicenhanced osmotic pressurecontrolled diffusivity
Blood plasma volume expander
“Orbitz” Soft Drink
3
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Polysaccharides as Food Additives
Starch
GummiArabicum
Pektin
Alginates
Galactomannanes
Fermentation polymers
Celluloseether
Polymer Application
in Bakery Products and other Cereal Based Goods, Thickener for Soups and Sauces, Jams and Dessert Gels, etc.
Potatoe starchYellow maize starch Waxy rice starchWheat starch
Thickener for Ice Cream, Elasticity Enhancer in CandyE 414
Gelling agent for Gels, Preserved Food, Desserts,Thickener, Protective Colloid for Emulsions
E 440
Thyxotropic agent, Coating agent,Thickener in Ice Cream, Jams and Dessert GelsGelation agent in ready-to-use Preparations;Stabilizer for Ice Cream, Puddings, Dairy Products, Frozen Food and
Instant Meals, Emulsions und Suspensions as indigestible Starchsubstitute in Low-Energy-Food
Algin E 401Carrageenane(ι−,κ−, λ-) E 407Agar E 406
in Cheese for enhanced Water Retention, in Ice Cream for reducedSugar Crystalisation, in Salad Dressing for Emulsion Stability,
in Frozen Foods and Water Containing Instant Meals against Synärese,in Softdrinks for superior Mouthfeeling, as indigestible Starch Substitute in Low-energy-food
Guar E 412Locust BeanGum E 410
Stabilizer for Milk and Milk Products, Dressings and Canned Food, Thyxotropic Thickener in Ketchup und Sauces
Xanthan E 415
Emulsifier, Stabilizer and Thickener for Ice Cream, Milk and Fruit Juices, Soups and Sauces,
Binding Agents, Protecive Colloid
NaCMC E 466MCE 461HPC E 463HPMC E 464
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Biopolymers in “Natural “ Products
Are generally not considered to be dangerous because of longtime experience
Do not have to be explicitly mentioned on an ingredient list
Are they therefore boring and not worth investigation?
4
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Natural Product Beer
“Deutsches Reinheitsgebot aus dem Jahr 1516”
(German purity law of 1516)
beer may only consist of four ingredients:
o Watero Barley Malto Hopo Yeast
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Problems caused by Biopolymers during the Beer Brewing Process
• Improper malting and/or mashing results in high viscosity that lowers the extract yield and affects wortrun-off
• During storage periods a gelatinous precipitate is sometimes formed which
blocks filter media in the final filtrationforms “Fisheyes” in the final productthe gel consists to 99% of (1,3)(1,4)-β-D-Glucan
5
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
(1,3)(1,4)-β-D-GlucanLinear Polysaccharide consisting of β-Glucose monomers30% (1,3)-glycosidiclinkage70% (1,4)-glycosidiclinkageStatistical distribution of the linkagesOnly isolated (1,3)-glycosidic linkages
⇒Hot water soluble
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Sources of (1,3)(1,4)-β-D-Glucan• (1,3)(1,4)-β-D-Glucan
is a structure-polysaccharide in the cell walls of:
BarleyOatLichenan (Island Moss)Yeast
Schildchen Mehlkörper (Endosperm)
Blattkeim
Wurzelkeim
Aleuron- oder Kleberschicht
Spelze
Fruchtschale und Samen
Root Seed
Leaf Seed
Endosperm
Spelt
Alueron
Fruit Hull
Shield
• 70% (1,3)(1,4)-β-D-Glucan• 20% Arabinoxylan• 6% Protein• 2% Cellulose
Barley:
The Endosperm of Barley consists of:
6
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
The Beer Brewing Process
(1,3)(1,4)-β-D-glucan is enzymatically freed from the cell wall during soaking, germination and kiln drying processDuring the malting and mashing process the glucan is enzymatically degraded
Barley Malt Wort Beer
Water Hop Draff
1. Soaking2. Germination3. Kiln Drying
1. Grinding2. Mashing3. Refining
4. Wort Boiling
1. Fermenting3. Storing3. Filtering4. Bottling
YeastWater
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Isolation of β-Glucan• From beer: • precipitation from chilled
solutions• Forced gelation under shear
• From Draff: • coupled enzymatic and chemical
extraction
• From Barley Oat or Lichenan:
Gerste
Rohextrakt( -Glucan, Arabinoxylan, Proteine, Maltodextrine)β
β-Glucan
Mahlen
Kochen in 70 % EtOH
Zentrifugieren
Fällen in 50 % EtOH
Fällen mit 30 % (NH ) SO4 2 4
ProteineMaltodextrine
Arabinoxylan
Grinding
Barley
Boiling in 70 % EtOH
Centrifugation
Raw Extract
Precipitation in 50 % EtOH
Precipitation with 30 % (NH4)2SO4
7
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Polymer AnalysisCode Origin M w M n M w/M n [η ] kH
(103 g/m ol) (103 g/m ol) (cm 3/g) (g/m l)
Barley G lucan SEC/M ALLS/DRI Viscosim etry GG375 Chem ically isolated from Barley 374 236 1,6 509 0,855 GG300 Megazym e 298 206 1,5 458 0,832 GG275 Megazym e, St.* 274 179 1,5 444 0,762 GG200 Megazym e, St.* 202 140 1,4 333 0,772 GG165 Megazym e 166 86 1,9 255 0,621 GG140 Megazym e, St.* 140 90 1,6 256 0,726 GG100 Megazym e 103 74 1,4 211 0,632 GG70 Ultrasonically degraded GG100 72 47 1,5 172 0,637 GG50 Ultrasonically degraded GG165 43 33 1,3 115 0,565 GGBeergel Isolated from sheared Beer 56 36 1,6 n.b. --- GGFrost Isolated from frozen Beer 23 17 1,4 n.b. --- Oat G lucan HG220 Megazym e 218 152 1,43 335 0,747 HG40 U ltrasonically degraded HG220 40 32 1,25 n.b. --- Lichenan LN55 Megazym e 55 32 1.72 n.b. --- Glucan Code Glucose Xylose Other Sugars
Acid Hydrolysis and Borat-Complex-Anion Exchange-Chromatographie com. available barley glucane (Megazyme )
GG300 ... GG50 97,5 2,5 0*
Glucan isolated from barley GG375 95,9 3,8 0,3* Glucan from beer GGFrost 96,2 3,8 0* Glucan from beer gel GGBiergel 96,3 0 3,7* Oatglucan HG 220 99,7 0 0,3* Lichenan LN55 97,2 0 2,8*
Protein < 1,9% (KJELDAHL andCHN-Analysis)
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Definition of a GelCompositional Definition:
Colloidal System with at least 2 phases one of which forms a 3-dimensional network that acts like an elastic solid
Structural Definition:Highly ordered mesophase structures; covalent polymer networks; physical networks with ordered domains; disordered rodlike structures
Phenomenological Definition:Semi-soft, firm material made from two components (small solid concentration) that has a frequency independent storage modulus G’ and a loss modulus that is at least one decade lower
10-1 100 101 10210-1
100
101
102
103
104
105
G'
|η*|
G''
G''
G'|η*|
|η* |
/ [P
a·s]
ω / [rad·s-1]
10-2
10-1
100
101
102
103
104 Barley Glucan GG165Molar Mass: 165.000 g/mol6% (w/w) in H2O
Blue: freshly prepared SolutionRed: after 72h
G'
G'' /
[Pa]
8
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Time dependent Gelation of β−Glucan
• The gelation of β-glucan is thermo reversible (Tc = 349K - 355K)
• The solution stays in the sol state for an induction period before the onset of gelation
• Problem: How to find– Gelpoint– Speed of
Gelation
0 10 20 30 40 50 60100
101
102
103
104
|η* | /
[Pa·
s]
t / [h]
100
101
102
103
104
|η*|
G''
G'
G',
G''
/ [P
a]
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
tanδ = 1 as the Gelpoint?
• At tan δ = 1 (G’=G’’) the elastic properties become dominant over the viscous properties
• But the crossover of G’ and G’’ is not independent of the frequency
0 10 20 30 40 50 60
10033.3
103.3
1 0.33
0.01
0.1
1
10
100
tan δ
t (min) ω (rad/s)
40 min
29 min
Barley GlucanMolar Mass: 103.000 g/mol10% (w/w) in H2O
9
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Stress Relaxation Test • Shear Modulus in the linear
viscoelastic regime as measured for the onset of build up of a solid structure
• Good method to detect the buildup of a global network
• But every data point is a single experiment:
– Large amount of samples needed
– Time
0 20 40 60 80 1000
2
4
6
8
10
12
G(t)
(kP
a) a
t t =
45
s
t (min)
Gel Point
Barley Glucan GG100Molar Mass:100.000 g/mol10% (w/w) in H2O( ) ( )tG t
τγ
=
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
The Elasticity Increment• The Elasticity Increment
IE (the maximum slope of the storage modulus G’ ) is a measure of the gelation speed
• It also gives a gelation point
• IE is independent of the Frequency
• IE includes the induction period, the shape of the curves is the same for a certain polymer solvent system
0 10 20 30 40 50100
101
102
103
104
105
IE= 0,05 h-1
IE = 0,91 h-1
IE = 5,28 h-1 50.000 g/mol 103.000 g/mol 298.000 g/mol
10% (w/w) in H2O
G' /
[Pa]
t / [h]
maxE t
GlogI
∂
′∂=
10
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Speed of Gelation • Elasticity Increment IE:
increasing Concentration
increasing Molar Mass
increasing Polydispersity
4 5 6 7 8 9 1010-2
10-1
100
101
MW= 43.000 g/mol, MW/Mn = 1,25 MW= 72.000 g/mol, MW/Mn = 1,49 MW= 166.000 g/mol, MW/Mn = 1,93 MW= 103.000 g/mol, MW/Mn = 1,39 MW= 298.000 g/mol, MW/Mn = 1,45
I E / [h
-1]
c / [% w/w] ⇒ The spontaneous Gelation is determined by the low molar mass molcules
⇒ No spontaneous Gelation below a critical concentration
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Shear induced Gelation• Barley glucan (molar mass
298.000 g/mol) shows an induction period > 4h at a concentration of 10% (w/w)
• This induction time can be shortened by applying a shear rate of 2s-1 for 2 min and a rest period of 10 min (1 cycle)
• After 3 cycles (44 min) a global network has formed
0 2 4 60
40
80
120
100 %
73 %
35 %
26 %
Creep recovery
after 3. Cycle
after 2. Cycle
Creep test fresh
after 1. Cycle
γ / [%
]
t / [min]
11
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Shear induced Gelation in dilute Solutions
• A dilute solution of barley glucan (Mw = 165,000 g/mol, c = 0.025%), sheared for 10 min with an Ultraturrax (10.000 rpm) shows a precipitation of a gel-like sediment that contains 95% of the former dissolved glucan after 96 h.
• The gel formed at early gelation stages consists mainly of the high molar mass parts
20 24 28 32Eluate Volume / [ml]
SolutionGel
Barley glucan 165.000 g/mol
Eluation Spectrum of the Size-Exclusion-Chromatography (SEC) after 48 h and 96 hours:
The shear induced gelation is caused by the high molar mass molecules
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Sol State of β-Glucan
10-2 10-1 100 101 102 103 10410-3
10-2
10-1
100
101
102
Mw= 224, 3,0% Mw= 166, 3,0% Mw= 166, 2,0% Mw= 166, 1,0% Mw= 166, 0,5%
Mw / 103 [g/mol] Mw= 285, 6,0% Mw= 285, 4,0% Mw= 285, 3,0% Mw= 285, 2,0% Mw= 285, 1,7% Mw= 285, 1,0% Mw= 285, 0,5% Mw= 285,0,25% Mw= 285, 0,1%
η / [
Pa⋅s
]
g / [s-1]10-2 10-1 100 101 102 103
10-2
10-1
100
101
102
103
104
G' G'' Mw / 103 [g/mol] 6% Mw= 285, 6,0% 4% Mw= 285, 4,0% 3% Mw= 285, 3,0% 2% Mw= 285, 2,0% 1% Mw= 285, 1,0%
G',
G''
/ [Pa
⋅s]
ω [rad/s]
• During the induction period, the glucan solution behaves as a typical viscoelastic fluid, no evidence of aggregates
12
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Birefringence in Polymer solutions
d'n2'0λ∆π
=δ
Phase-difference
Field Vector E'0
Field Vector E'1
d'n2'0λ
=δ
δ’
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Stress-Optical Rule• In the scope of the stress-
optical rule, it is found that, independent from the shear velocity:
• - the mean orientation of the segments and the first principal tensor τI take up the same angle in relation to the shear direction ( φ = χ )
• - the birefringence ∆n‘ (= n‘I -n‘II) is proportional to the first principal tensor difference ∆τ(= τI - τII )
principal tension ellipsoid
segment orientation
τI
τII
τI
τII
n'I
n'I
n'II
n'II
∆n‘ = C ⋅ ∆τ
13
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Flow Birefringence of β-Glucan
10-2 10-1 100 101 102 10310-9
10-8
10-7
10-6
10-5
10-4
3,0% 2,0% 1,0% 0,5%
∆n' /
[-]
g / [s ]10-2 10-1 100 101 102 103
10-10
10-9
10-8
10-7
10-6
10-5
10-4
Mw / 103 [g/mol] Mw= 285, 6,0% Mw= 285, 4,0% Mw= 285, 3,0% Mw= 285, 2,0% Mw= 285, 1,7% Mw= 285, 1,0% Mw= 285, 0,5% Mw= 285,0,25% Mw= 285, 0,1%
∆n' /
[-]
g / [s ] • The Flow Birefringence shows deviation from the expected linear dependence on the shear rate in the Newtonian regime
Mw=166,000 g/mol
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Stress Optical Coefficient
21
221 N4 +τ⋅=τ∆
φ⋅′∆⋅⋅
=τ 2sinnC2
121
100 101 102 103 104100
101
102
103
104
τ21 N1 6,0% 4,0% 3,0% 2,0%
τ 21, N
1 / [P
a]
g / [s-1]
10-1 100 101 102 1030
2x10-8
4x10-8
6x10-8
8x10-8
6,0% 4,0% 3,0% 2,0%
∆n'/∆
τ / [
Pa-1]
g / [s-1]
• The Stress-Optical Coefficient C can be calculated from the birefringence and shear experiments
• The Stress-Optical Rule is valid only for high shear rates
Mw=285,000 g/mol
14
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
c(x)
x
c(x)
x
c(x)
x
mäßig konzentrierteNetzwerklösung
mäßig konzentriertePartikellösung
mäßig konzentrierteNetzwerklösungmit Aggregaten
∆ ∆ << c/ x 1∆ ∆ >> c/ x 1
Form Birefringence
τ⋅⋅
⋅
∂∂
+τ⋅=+Tk
Ncn
ncCnn
B
2
fiForm birefringence is only detectible
• if
• and if there is a “form”:
2n 0c
∂ ≠ ∂
c 1x
∆ ∆
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Intrinsic vs. Form Birefringence
In the case of finite expandable or shear instable aggregates the form birefringence(aggregates) is overcompensated by the intrinsic birefringence (polymer segments) above a critical shear rate.
10-2 10-1 100 101 102 10310-10
10-9
10-8
10-7
10-6
10-5
∆n'i (Intrinsic Part)
∆n'f (Form Part)
∆n' /
[-]
g / [s ]
10-2 10-1 100 101 102 10310-10
10-9
10-8
10-7
10-6
10-5
∆n'i (Intrinsic Part)
∆n'f (Form Part)
∆n' /
[-]
g / [s ]
10-2 10-1 100 101 102 10305
1015202530354045
(Intrinsic φi Part)
φf (Form Part)
φ / [
°]
g / [s-1]10-2 10-1 100 101 102 10305
1015202530354045
(Intrinsic φi Part)
(Form Part) φf
φ / [
°]
g / [s-1]
Only the Orientation of the dominating part of the birefringence can be seen, creating typical tilted s-curves
15
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Orientation of the Birefringence
10-6 10-510-4 10-3 10-210-1 100 101 10205
1015202530354045
6,0% 4,0% 3,0% 2,0% 1,7% 1,0% 0,5% 0,2% 0,1%φ
/ [°]
g/gcrit / [-]
Barley GlucanMolar Mass:285.000 g/mol( )[ ]
ϕλ⋅γ
+
λ⋅γ+⋅
γ⋅λ=φ
bn2
b0
bn
b0
0
1
11arctan21
• Orientation of the intrinsic flow birefringence in the vincinity of the stress optical rule, dependinging on empirical parameters:
0γ ⋅λ
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Reduced Birefringence
0.01 0.1 1 10 100 100010-9
10-8
10-7
10-6
10-5
10-4
6,0% 4,0% 3,0% 2,0% 1,7% 1,0% 0,5% 0,2% 0,1%
∆n'/η
0 / [P
a-1⋅s
-1]
g / [s-1]
( )[ ] ( )bn4
b02
0bn2
b00 11C2n
⋅⋅
ϕλ⋅γ
+⋅λ⋅γ+λ⋅γ+⋅γ⋅η⋅⋅=′∆
Barley GlucanMolar Mass:285.000 g/mol
Flow Birefringence in the vicinity of the stress optical rule, depending on empirical parameters:
• The high shear rates are dominated by the intrinsic birefringence and do not allow a detection of the aggregate behavior• Below a concentration of 1% a change in the flow behavior of the aggregates can be seen
γ⋅η⋅⋅=′∆γ<<γ
0C2nkrit
16
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Dichroism of Aggregates in Solution
Loss of Intensity
Field Vector E''0 Field Vector E''1
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Form Dichroism• Dichroism is only caused by
form partsOnly deformation behavior of Aggregates visible, no contribution of the single polymer chain
10-2 10-1 100 101 102 10310-10
10-9
10-8
10-7
6,0% 4,0% 3,0% 2,0% 1,7% 1,0% 0,5% 0,2% 0,1%
∆n''
/ [-]
g / [s-1]
• Plateau region is formed either by:Finite deformable Aggregates orEquilibrium between Aggregate breakdown and shear force
Barley GlucanMolar Mass:285.000 g/mol
17
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Orientation of Aggregates in the flow field
• The rise of the Orientation angle to more statistic orientations at higher shear rates indicates an aggregate breakdown
10-1 100 101 102 10305
1015202530354045
6,0% 4,0% 3,0% 2,0% 1,7% 1,0% 0,5% 0,2% 0,1%
θ [°
]
g [s-1]
Statistic Orientation
Total Orientation
Barley GlucanMolar Mass:285.000 g/mol
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Plateau regions of Flow Dichroism
• The reduced Dichroism ∆n’’/c in the plateau regions represents the sum of absolute Deformability of an aggregate and its concentration in Solution
• Below a concentration of 1%, ∆n’’/c reaches a new plateau value, indicating a change in the aggregate structure
10-1 100 101 102 10310-7
10-6
10-5
6,0% 4,0% 3,0% 2,0% 1,7%
∆n''/
c [m
l⋅g-1]
g [s-1]100 101 102 103
10-7
10-6
10-5
∆n
''/c
[ml⋅g
-1]
1,0% 0,5% 0,2% 0,1%
g [s-1]
Barley GlucanMolar Mass:285.000 g/mol
18
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Aggregate Size Depending on Concentration• At concentrations higher than
c*, the competition between possible aggregation points leads to smaller aggregates
• The formation of bigger aggregates below the critical concentration leads to a greater distance between the single aggregatesthe buildup of a global network between free polymer chains and aggregates is not possible below c* . It can only be induced, for example by a shear force that enhances the random contacts between the single aggregates
c < c* c > c*
T > 353K
T = 298K
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Comparison of different glucansGlucan Mn
[g/mol]
Gelation Speed
IE / [h-1]
Transmission
T(sol) / T(gel)
lichenan 32 000 >50 64 barley glucan 33 000 5,3 31 oat glucan 32 000 0,86 24
20 40 60 80 100102
103
104
105
lichenan barley glucan oat glucan
65° C62 °C
73 °C
G' /
[Pa⋅
s]
T / [°C]
• The speed of the gelation shows differences between the different glucans, though their number average molar mass is nearly the same
• The transmission quotient as well as the gel softening temperature indicate the biggest cluster size for lichenan, followed by barley and oat glucan
• The cluster size coincides with the gelation speed
c = 6%
19
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
(1,3)-(1,4) Linkage Ratio
110 105 100 95 90 85 80 75 70 65 60 55
ppm
Haferglucan
Gerstenglucan
Lichenan
C-1
1,3- 1,4-Verknüpfung
17 18 19 20 21 22 23
1,3,5-Tri-O-acetyl-2,4,6-tri-O-methyl-D-glucitol
1,4,5-Tri-O-acetyl-2,3,6-tri-O-methyl-D-glucitol
Gerstenglucanbarley glucan
barley glucan
oat glucan
lichenan
linkage
13C-NMR Spectroscopie:
GC-Spectrum of methylated, hydrolised, reduced and acetylated barley glucan:
t / [min]
Polysaccharid Linkage Ration (1,3) : (1,4)
Methylation 13C-NMR
Lichenan - 27 : 73 Barley glucan 28:72 28 : 72 Oat glucan 29:71 29 : 70
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
5 10 15 20 25
Inte
nsitä
t
Zeit (min)
P = 3 6 7 8 954
Lichenan
Gerste
Hafer
(1,3)-(1,4) Linkage Distribution
t / [min]
(1 4)→(1 4)→
(1 4)→(1 3)→
Intensity
Oat
Barley
Lichenan
glucane P=3 : P=4 : P=5
Lichenan 23 : 1: 2,5 Barley glucan 2,5 : 1 : 0,12 Oat glucan 1,9 : 1 : 0,08
• specific enzymatic cutting of the (1,3)(1,4)-β-glucan chain with Lichenase (E.C. 3.2.1.73) only at (1,4) positions after a (1,3) linkage
•oligomer analysis with anion exchange chromatography shows that lichenan has the most regular distribution of cellotriose units and oat glucan the most irregular distribution
20
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
New Aggregation Mechanism
Old Mechanism:Association via
hydrogen bonds of long cellulose-like sequences ((1,4)-linkages)
β-(1,3)
{Cellotriose- Einheit
celluloseartigeSequenz
a) b)
cellulose-likesequence
cellotrioseunit
New Mechanism:Association via
hydrogen bonds of of regularly distributed sequences of cellotriose units
Biopolymers in Solution – Rheo-mechanical and Rheo-optical Detection of Gels in Beer
Conclusions and ways to optimizethe beer brewing process
• Addition of enzymes to degrade (1,3)(1,4)-β-D-glucanNot allowed for German beer
• Temperature control during the mashing processMostly optimized
• Avoiding high shear rates during pump-, transportation and filtration process
Slower output and therefore higher costs• Degradation of high molar mass (1,3)(1,4)-β-D-glucan with mechanical
methods to avoid shear induced aggregation• Selection and breeding of new barley with irregular distribution of
cellotriose units