soft condensed matter: a perspective on the physics of food … soft condensed matter: a perspective...
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tplabuza © 2008 Slide # 1
Soft Condensed Matter: A perspective on the physics of food solid states and stability
Dr Ted P. Labuza
Department of Food Science and NutritionUniversity of Minnesota St Paul 55108 USA612-624-9701 fax 625-5272 tplabuza@umn.edu
Greetings from Minnesota, USA
We are 4.4 million
15,129 lakes
Two ocean going seaport ports
State bird is mosquito
Rated one of best places to live in USA but climate goes from -35°C to +37°C
tplabuza © 2008 Slide # 3
Greetings from my back yard showing state changes and water activity
tplabuza © 2008 Slide # 4
2005 -Physicists discover food physicsFoods are complex mixtures of water, small molecules and polymers ie “Soft Condensed Matter” eg a gel“ Food science and technology have started to profit from parallel developments made in SCM and nanotechnology”
Nature Materials (4) pp 731-740 2005
tplabuza © 2008 Slide # 5
Physicists discover food physicsState/phase diagrams for interparticle interactions such as phase separations, gelation, foams, emulsions and aggregation interactions etc. No mention of not-so-soft condensed matter or transition between NSS-SCM & SCM physical states as review was limited by editor
tplabuza © 2008 Slide # 6
A quick history to date of such physical phenomena
1981 What makes snack foods loose crispness ?– M. Katz and T Labuza JFS 46:403-409
Young’s modulus vs aw for cracker
tplabuza © 2008 Slide # 7
Effect of water activity on snack food crispness(Katz and Labuza, 1981)
Crispness Intensity Monolayer Values (g/100g)
Product aw mc aw moSaltine (baked) 0.39 7.0 0.22 4.8Potato Chip (deep fat fried) 0.51 5.7 0.21 2.9Corn Curl (extruded) 0.36 4.2 0.18 2.9Popcorn (puffed) 0.49 6.1 0.17 3.4
tplabuza © 2008 Slide # 8
Critical physical chemistry principlesIn relationship to the critical aw where crispness began to be lost Katz
and Labuza said “ These generally fell in the range 0.35 to 0.5 which is the same aw range where amorphous to crystalline transformations occur in simple sugar food systems and mobilization of solid food components begins”
00..000000
00..005500
00..110000
00..115500
00..220000
00..225500
00..330000
00..335500
00..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Mobility begins @ mo
mx
tplabuza © 2008 Slide # 9
A quick history to date1981 What make snack Foods loose crispness?
– M. Katz and T Labuza JFS
1988-89 Slade and Levine (and Franks) introduce glass transition (Tg ) concept theorizing that the water activity principle is all wet. Ted Labuza sells boat and stops fishing and decides to take the challenge.
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tplabuza © 2008 Slide # 10
1983 What make snack Foods loose crispness – M. Katz and T Labuza JFS
1988-89 Slade and Levine (and Franks) introduce Tg concept theorizing that the water activity principle is all wet1989 I get $50K Marcel Loncin Prize from IFT1991 1st International Meeting on Glass Transition Nottingham England attended by > 100 scientists1991 Roos & Karel - introduce the food physics state diagram. Roos and Karel Food Tech 45(12): 66 19911992 I purchase a DMTA and DSC and begin work on crispnessMany labs now begin to correlate crispness with Tg1995 Roos authors book “Phase Transitions in Foods “ Academic Press2002 My children begin to build physical foundation for state changes on simple food systems2008 Wageningen “Crispy Crack’s Symposium2008 I am here to tell the story
A quick Tg history to date
tplabuza © 2008 Slide # 11
Early 1948 Quote
“Glasslike low molecular weight substances comprisean important group of materials. In the broad standing, physical properties of common glassy materials such as brittleness, natural resins, stiff pitchesand hard candies are included.”
Principles of High Polymer Theory and PracticeA. Schmidt and C. MarlesMcGraw Hill 1948 page 191
tplabuza © 2008 Slide # 12
Critical physical physical chemistry principlesaw > ~ 0.2-0.3 - chemical reactions requiring water phase begin and increase in rate physical state changes also occur in real time and take place @ aw > monolayer
– mx at T = T ambient
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Mobility begins @ mo
mTg
tplabuza © 2008 Slide # 13
SCM Solid Food State MatrixHigh moisture true or colloidal solution, elastic gel or cell matrix with trapped water
Amorphous drying moist or
semi-moist
Crystallization of ice or small MW sugars Structured minimum free energy
Glassy or BrittleLow moisture
Rubbery or ductilemoderate moisture
Heat or humidify
Dry or cool
store
Hardening w/wo water loss
Cool or freeze or supersaturated
14Slide #tplabuza © 2008
Glass transition by m^ or T^
BE
Tem
pera
ture
Glassy/brittle/crispy
Rubber/ductile/soggyie loss of crispness
CD
Tg curve
Moisture 0
tplabuza © 2008 Slide # 15
0 °C
Te
Crystal melt line
Tm
Solution orColloidal amorphous matrix
freezing line
Boiling point line
vapor
-135 °C
Cg’
Tg’glass
rubber
Roos and Karel Food Tech 45(12): 66-71 1991Application of the state diagram in processing
Tgdry
Ice & super sat solution
ice & solute crystals
0% % solids 100%
100% % water 0%
glass
Critical line
T-room
100°C
Crisp dry food region at≥ T room
tplabuza © 2008 Slide # 16
Case study 1Marshmallows Loss of moisture causes hardening at mx, Why ?Is it Tg or aw or is it something else ?
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Initial state
mx
tplabuza © 2008 Slide # 17
Moisture loss induced hardening
Marshmallow Composition70-80% sugars (sucrose)2-5% gelatin15 to 28% water (so saturated)
Made by creating gelatin solution at >65°C adding in hot sugar solution (120 °C) and then whipping with air into a foam. All the sugar needs to dissolve first.Initial aw ~ 0.6 to 0.7
Process
tplabuza © 2008 Slide # 18
Marshmallows What causes them to get tough and leathery?NEB of sugars with gelatin if HFCS or high DE starchSucrose crystallization if above Tg
Collapse as water is lost increasing density as occurs in vegetable dryingMoisture loss crossing Tg at mTg thereby loosing plasticity because of loss of plasticizer volume
tplabuza © 2008 Slide # 19
XRD @ 6 mo. @ 72% RH
Also did not brown because of local viscosity
tplabuza © 2008 Slide # 20
Max initial ~ 0.225 N Un-packaged moisture loss @ 23°C
7 days @ 23 °CDark Green /Brown – Dry 14 N Black/Blue – 14 %RH 9 NLight Green/Red - 32%RH 11 NLight Blue/Pink – 42%RH 6 NDark Purple/Yellow – 72%RH 2 N
tplabuza © 2008 Slide # 21
Weight loss at ~42%RH y = -3E-06x 3 + 0.0012x 2 - 0.1714x + 21.81R2 = 0.9359
0.00
5.00
10.00
15.00
20.00
25.00
0 20 40 60 80 100 120 140 160 180
hours
moisturePoly. (moisture)
S=3
Weight loss at ~0.5 %RH y = -8E-06x 3 + 0.0027x 2 - 0.2883x + 21.715R2 = 0.9431
0.00
5.00
10.00
15.00
20.00
25.00
0 50 100 150 200hours
S=3
tplabuza © 2008 Slide # 22
Summary of results
%RelativeHumidity
Time toS=3 hours
Moisture contentg/100 g solids at S=3(% fraction loss)
Maximum ForceNewtons at S=3
YoungÕs ModulusNewtons at S=3
0 58 13.41 (38%) 9.5 0.9814 71 14.26 (35%) 8.6 0.8632 66 14.09 (35%) 10.9 1.0042 72 13.74(37%) 5.8 0.5172 NA NA (NA) NA NA
NA- not applicable
Average moisture @ S=3 = ~13.9 g water/100 g solids while mTg ~ 10
tplabuza © 2008 Slide # 23
Moisture loss relative to aw and Tg
S =3 @ ~ 14% moisture
Tg from Lin ~ 9% Moisture aw ~ 0.45
tplabuza © 2008 Slide # 24
Influence of moisture loss on storage modulus
start
end
tplabuza © 2008 Slide # 25
0 °C
Tmboiling line
glass
Tgdry
AB ED
C
rubber
leathery line
Drying out D--->E
Soft ---> leathery above mTg
Due solely to loss of plasticizer
A sugar solutionB gelatin solutionC mixed and heatedD cooled to RTE tough marshmallow
T = 23 C
-135 °C
0% % solids 100%
100% % water 0%
tplabuza © 2008 Slide # 26
tplabuza © 2008 Slide # 27
Case study 2Cotton candy Gets sticky, collapses and gets gritty at State Fairs
– high T and %RH
Is it Tg or is it aw?
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Initial state
mx
tplabuza © 2008 Slide # 28
Crystal Collapse
Melt
> 210°C
Liquid stream
spin
Re-crystallize
Glass
cool
Rubber
humidify
W/H2O loss
tplabuza © 2008 Slide # 29
Moisture as f (aw) water activity– Makower & Dye. J Ag. Food Chem 1956 4:72-77@ 35°C– BET monolayer ~ 4 g water/100g
tplabuza © 2008 Slide # 30
General adsorption isotherm of sugar containing amorphous foods
one week
two weeks
water activity
moisture
tplabuza © 2008 Slide # 31
Crystal Formation
Nucleation requires local mobility enough to allow molecules to align Growth at specific faces requires longer distant mobilityBoth limited by diffusionDiffusion is affected by T, local viscosity(amount of plasticizer) and local free volumeAs occurs releases interacting solvent to change local mobility
tplabuza © 2008 Slide # 32
Influence of increasing moisture or temperature
tplabuza © 2008 Slide # 33
Recrystallization of freeze dried sucrose(Makower & Dye. 1956)
Experiment measured rate of sucrose crystallization from a glass at different relative humidities @ 23 °C
@ RH < 12%, no crystallization in 2 years ~ 2% water@ 16% RH took 200 days to occur@ 33.6% RH, crystallization ~ 3 days >3% water then falls
tplabuza © 2008 Slide # 34
Crystallization of FD Sucrose by XRD @ 25°CPalmer et al 1956 J Ag Food Chem 4:77-81
tplabuza © 2008 Slide # 35
Siemens D5005 X-ray Diffractometer
X-Ray
source
Sample cup rotates @ Θ/time
Detector rotates @ 2Θ/time
Slow scan with 0.04 step & 4 sec dwell times
tplabuza © 2008 Slide # 36
XX--Ray Diffraction PrincipleRay Diffraction Principle
XX--RayRaySourceSource
XX--RayRaySourceSource
.. ......
........
CrystalCrystal
Amorphous Amorphous MaterialMaterial
6500 counts/sec
6500 cps
tplabuza © 2008 Slide # 37
XX--Ray Diffraction of fresh made Cotton CandyRay Diffraction of fresh made Cotton Candy
400 counts/sec
Amorphous Amorphous Fresh CCFresh CC
XX--RayRaySourceSource
Halo pattern
tplabuza © 2008 Slide # 38
X-RD Results
Stored at Stored at ~5 to 11 ~5 to 11 % RH for 5 years% RH for 5 years
400 counts/sec
tplabuza © 2008 Slide # 39
Stored at 45% RH
1 hour 2 hours 5 hours
3000 counts/sec
tplabuza © 2008 Slide # 40
Stored at 75% RH for 1 hourStored at 75% RH for 1 hour
3000 counts/sec
tplabuza © 2008 Slide # 41
JFPP 71; 2004 Cotton candy process
0 °C ice
boiling linevapor
glass
Tgdry
T = 23 C
S - initial crystalline CC - finished product - cotton candy
rubberSCC
Tm
Tg’Crystals as f(t)-135 °C
0% % solids 100%
100% % water 0%
tplabuza © 2008 Slide # 42
Influence of increasing moisture on local viscosity ie diffusion
tplabuza © 2008 Slide # 43
General Reaction Kinetics
A A ++ XX AXAX ** B B ++ XX
RateRate == dAdAdtdt
== ±± kkobsobs AA[[ ]]nn
kkobsobs==f(diffusion of solvent/molecule)f(diffusion of solvent/molecule)
AA== reactant / volume solventreactant / volume solventn n == order order (via curve fitting)(via curve fitting)
tplabuza © 2008 Slide # 44
Reaction ParametersEnough solvent to dissolve reactant AReactant mobility A+X->B– Local solvent phase viscosity– Polymer matrix allowing mobility
Solvent effects e.g. dielectric, ionic strength, pH
tplabuza © 2008 Slide # 45
Influence of water content on rate
aw
Solids ---->
<------ aw
Tg5 4 3 2 1
Log τ
5
2
34
1
678Water activity
effect at constant T
tplabuza © 2008 Slide # 46
Qa = 1000
Qa = 10,000
tplabuza © 2008 Slide # 47
Makower & Dye 1965Sucrose crystallization kinetics
aw g water/100gsucrose
days tocrystallization
0.046 1 >700
0.086 1.6 >700
0.1180.162
2.22.9
>700~200
0.242 4 ~ 30
0.2820.34
5 ~5<3
tplabuza © 2008 Slide # 48
Model for Makower and Dye results
Shows may occur even below Tg
Projected > 700 days
measured ~ 200 days
P Labuza measured~3 days at Tg = 23°C
tplabuza © 2008 Slide # 49
……………………………………………….……………………………………………….
75% RH 1 hour75% RH 1 hour
45% RH45% RH5 hour5 hour
33% RH33% RH-- 3 days3 days ~0.1% RH~0.1% RH
11% 11% RHRH
Glass Transition Diagram of SucroseGlass Transition Diagram of Sucrose
Solutions: good package & low T in distribution
Makower and Dye
16% RH 200 days @ 25
Biophysical Jr. 70:1769-76
Initial CC
tplabuza © 2008 Slide # 50
Raffinosesuppresses
rate of sucrose crystallization, acting
as true a crystallizationinhibitor
Raffinose effect
Smythe 1967 Aust. J. Chem. 20: 1097-1114
tplabuza © 2008 Slide # 51
XRD of CC (5% raffinose/95% sucrose) @ 23°C
32% RH
72 hr
11% RH
5 weeks
32% RH
37 days vs 3 days
43% RH
48 hr vs 5 hr43% RH
24 hr
Kelly Lienen Chemical Eng Undergrad UROP project
tplabuza © 2008 Slide # 52
Case study 3Soft cookies aw >0.55 starch not gelatinized
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Initial state
monolayer
tplabuza © 2008 Slide # 53
Microscopy - Fresh CookieStarch Granules - Maltese Crosses
92 X
tplabuza © 2008 Slide # 54
DSC for Cookie Dough and Baked Cookies
Baked 2hr old: Onset 118°C, Peak 123 °C lower moisture
Baked 5 Day Old: Onset 120°C, Peak 130°Clowest moisture
Dough : Onset 110°C, Peak 118°C higher moisture
tplabuza © 2008 Slide # 55
Case study 3Soft cookies aw >0.55 starch not gelatinizedCookies harden (dry and crumbly texture) over time without loosing moisture Is it Tg or is it aw?
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Initial state
monolayer
tplabuza © 2008 Slide # 56
Freezing point line
boiling line
glass
Tgdry
A Brubber
C
A initial formulaB Soft cookie C sugar snap
Tm
T = 23 C0 °C
Tg’ B’
-135 °C
0% % solids 100%
100% % water 0%
tplabuza © 2008 Slide # 57
Cookies in the Market
Nabisco - Chewy Chips Ahoy - Soft- 6 months Shelf Life
– HFCS, sugar, dextrose, lactose, molasses– Moisture: 9.4% and aw : 0..59– X-ray pattern: Some crystalline sucrose
10 12 14 16 18 20 22 24 262-Theta(°)
0
500
1000
1500
2000
Inte
nsity
(Cou
nts)
[CHWYCAHY.MDI] Chewy Chips Ahoy by Nabisco, SCAN: 10.0/27.0/0.04/4(sec), Cu, I(max)=1961, 09/18/00 19:29
tplabuza © 2008 Slide # 58
Control CookieWater Activity Changes with Time
0.425
0.475
0.525
0.575
0.625
0.675
0.725
0 2 4 6 8 10 12 14 16 18 20
Wat
er A
ctiv
ity
Cookie Middle
Outer Edge
Time in Days
tplabuza © 2008 Slide # 59
Soft Cookie24 hour
tplabuza © 2008 Slide # 60
Cookie5 Days
Cookie 10 Days
tplabuza © 2008 Slide # 61
Crystallization kineticsMicroscopy - 18 day Cookie
Starch Granules and Sucrose Crystals
Using first-order-red plate filter which enhances features of low birefringence.
230X
62Slide #tplabuza © 2008
Fit of the First Order Model - f= C exp (kt)-
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10 12 14 16 18 20 22
Time in Days
Frac
tion
of c
ryst
alliz
ed s
ucro
sef
5% Less Sucrose
Control
5% More Sucrose
tplabuza © 2008 Slide # 63
Texture TestInstrument parameters– Probe to cookie diameter at least 1:3– Probe to hole diameter ~ 1:1 1/2
Slide # 64
21 days
8 days
3 days
1 hr
Age of Control
Texture Analysis
Increase in max peak force and modulus with cookie age and no moisture change
65Slide #tplabuza © 2008
Cookie Firmness as affected by HFC
0200400600800
100012001400
0 3 6 9 12 15 18 21Time in Days
5% Less
Control
5% More
5% Lessw/5%HFCSSControlw/5%HFCSS
66Slide #tplabuza © 2008
Correlation of Texture and Sucrose
y = 43.072x - 159.72R2 = 0.8812
-10 0
0
100
200
300
400
500
600
700
800
Text
ure
-Gra
dien
tCrystallized in Control Cookie
2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
g crystallized sucrose in 100 g of cookie
67Slide #tplabuza © 2008
Correlation Between Firmness and Sucrose Crystallized
5% Less Sucrosey = 116.89x +
31.904R2 = 0.9565
5% More Sucrosey = 35.384x - 337.4
R2 = 0.9091
Control Sucrosey = 43.072x -
159.72R2 = 0.8812
0
200
400
600
800
1000
0 5 10 15 20 25
g Crystallized Sucrose per 100 g Cookie
tplabuza © 2008 Slide # 68
invertsuppresses
rate of sucrose crystallization but
Needs highconcentration
Invert sugar effect
Smythe 1967 Aust. J. Chem. 20: 1097-1114
Change in Cookie Firmness with Tim
0200400600800
100012001400
0 3 6 9 12 15 18 21Time in Days
5% Less
Control
5% More
5% Lessw/5%HFCSSControlw/5%HFCSS
tplabuza © 2008 Slide # 70
Cookies with HFCSSCorrelation Between Firmness & Crystallized Sucrose
Control & 5% HFCSSy = 35.278x - 195.59
R2 = 0.7157
5% Less & 5% HFCSSy = 39.664x + 67.834
R2 = 0.9141
-200-100
0
100200300400
500600700
0 2 4 6 8 10 12 14 16 18 20
g crystallized sucrose per 100 g of cookie
Tex
ture
- G
radi
ent i
n g/
mm Control
71Slide #tplabuza © 2008
Sucrose and HFCS (~ 2.5 :1 m/m)Starch
Fat
Water
Sucrose
Glucose and/or fructose
tplabuza © 2008 Slide # 72
Sucrose Crystallizationinhibition by raffinose
Smythe 1967 Aust. J. Chem. 20: 1097-1114
tplabuza © 2008 Slide # 73
Freezing point line
boiling line
-135 °C
Tg’glass
Tgdry
A BB’
crystalsrubberC
A initial formulaB Soft cookie,C sugar snap
Tm
T = 23 C0 °C
0% % solids 100%
100% % water 0%
74Slide #tplabuza © 2008
Sucrose Crystallization In cookies w/wo raffinoseBelcourt and Labuza JFS
Grams of Recrystallized Sucrose Control and Raffinose Variables
y = 0.3567x + 8.469R2 = 0.8158
y = 0.2278x + 6.2109R2 = 0.8166
0
2
4
6
8
10
12
14
16
18
20
0 5 10 15 20 25Age (days)
Gra
ms
Rec
ryst
alliz
ed S
ucro
se
/100
gram
s of
Coo
kie
Control 2Raffinose 2Linear (Control 2)Linear (Raffinose 2)
Control
Raffinose
Inhibition ratio = 63%
75Slide #tplabuza © 2008
Texture Peak Force Averages
y = 35.451x + 343.28R2 = 0.8822
y = 65.246x + 390.82R2 = 0.9167
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 5 10 15 20Time (days)
Peak
For
ce (g
)
ControlRaffinose
Inhibition ratio = 54%
tplabuza © 2008 Slide # 76
Mechanism
•
• sugar crystallizes during storage
•water activity increases in storage
•Loose plasticizer volume
•Water migrates to un-gelatinized starch granules
•Causes firming & crumbly - not grainy like Cotton candy
•Adding HFCS reduces crystallization rate (local viscosity & diffusion) as incresases plasticizer volume and lowers Tg
•Raffinose directly inhibits crystal growth
tplabuza © 2008 Slide # 77
Case study 4 The start of the storyCrispy foods loose crispness as pick up moisture
– sugar cookies, fried extruded and baked snacks, cereal, pizza crust– Initial aw >0.3 so brittle
Is it Tg or is it aw?
00..00000000..00550000..11000000..11550000..22000000..22550000..33000000..33550000..440000
aaww
moi
stur
e w
b (g
H2O
/g to
tal)
moi
stur
e w
b (g
H2O
/g to
tal)
00..00 00..11 00..22 00..33 00..44 00..55 00..66 00..77 00..88 00..99 11..00
Initial crisp state
Non-crisp state
tplabuza © 2008 Slide # 78
Sugar Snap cookie
– Famous™ Chocolate Wafers (Nabisco)Composition:
Enriched Wheat Flour, Sugar, Vegetable Shortening, Cocoa, High Fructose Corn Syrup, Coconut, Chocolate, Whey, Baking Soda, Salt, Eggs, Soy Lecithin, Dextrose, Artificial Flavor
tplabuza © 2008 Slide # 79
BrittleBrittle--Ductile TransitionDuctile TransitionTe
mpe
ratu
re
Moisture
Soft Ductile StateSoft Ductile State
Hard Brittle StateHard Brittle State
B A
Tb curve similar to Tg
tplabuza © 2008 Slide # 80
Experimental designMeasure
Sensory
Tb - brittle-ductile
Tg - DMTA
moisture content (%)
m0
tplabuza © 2008 Slide # 81
5
5.5
6
6.5
7
7.5
8
8.5
-30 20 70 1200
0.1
0.2
0.3
0.4
0.5
0.6
0.7Lo
g M
odul
us (
Pa)
E´
E´´
Tan δ
Tg results
Tan δ
Temperature (°C)
tplabuza © 2008 Slide # 82
DMTA
r2 = 0.77
r2 = 0.75
r2 = 0.87-20-10
01020304050607080
3 5 7 9 11
Moisture Content (gH2O/100g solids)
Tem
pera
ture
(°C
)E' onset (°C)onset tan delta (°C)peak tan delta (°C)
Tem
pera
ture
°C
tplabuza © 2008 Slide # 83
The Other Ted Labuza Tb study
tplabuza © 2008 Slide # 84
Experimental MethodsStorage Study Preparation
Create six humidity chambersSpecific saturated salt solutionsRange from ~0 to 75% RHStore 5-6 wafers in open plastic jars in the RH chambers for 4 weeks
tplabuza © 2008 Slide # 85
3 Point Bend
tplabuza © 2008 Slide # 86
-4°C
15°C
Stress vs. Strain7.23% moisture content
-0.50
0.51
1.52
2.53
0 0.002 0.004 0.006 0.008
Strain
Stre
ss (M
Pa)
Tb resultsSt
ress
MPa
tplabuza © 2008 Slide # 87
Stored at Stored at ~0~0% RH % RH for 4 weeksfor 4 weeks
Stress/Strain @ RT as f(%RH)
Stored at Stored at 7575% RH % RH for 4 weeks 25X for 4 weeks 25X less hardless hard
tplabuza © 2008 Slide # 88
Tb: 3.73% Moisture Content
0
0.5
1
1.5
2
2.5
-10 10 30 50
Temperature (°C)
Stre
ngth
(MPa
)
TbStre
ss M
Pa
tplabuza © 2008 Slide # 89
Crispness Intensity
Sensory Panel– 3 sessions 46 samples were served each session to 10 judges in a
completely randomized order– The actual temperatures of the samples were determined using the IR
gun in a simulated panel– samples equilibrated to water activities of 0.17, 0.33, 0.44, 0.54, 0.59 – packaged– �equilibrated to desired temperatures (-15, 5, 15, 25, 35, 45, 55, 65,
75°C)– Modeled with Fermi Equation onset of crispness loss
Y(T) = Ys/(1 + exp[(T-Tc)/b] )
tplabuza © 2008 Slide # 90
Sensory Results: Moisture content 4
0
20
40
60
80
100
120
-10 10 30 50 70
Temperature (�
Sensory Results: Moisture content 4.95%
tplabuza © 2008 Slide # 91
Sensory Crispness plot as f(T) at constant moisture (Cami Hyman PhD)
0
25
50
75
100
125
-10 0 10 20 30 40 50 60 70Temperature (�C)
Cris
pnes
s Int
ensi
ty
Tci
tplabuza © 2008 Slide # 92
r2 = 0.79
Tci as a function of moisture content
-10
0
10
20
30
40
50
3 5 7 9
Moisture content (g H2O/ 100 g solids)
Tem
pera
ture
(°C
)T e
mp e
ratu
re °C
Initiation moisture for sensory loss as f(T)
R2 = 0.89 Payne & Labuza 2004 J.Drying Tech.
tplabuza © 2008 Slide # 93
Sensory Crispness line, Tg and Tb as f(m) after drying (baking)
-30
-20
-10
0
10
20
30
40
50
60
3 4 5 6 7 8 9 10
Temperature (�C)
Moisture g water/100g soilds Tb
sensory
Tg by G’
tplabuza © 2008 Slide # 94
0 °C
Tm
mTb
boiling line
brittle
Tci dry
T = 23 CAB
0% % solids 100%
100% % water 0%
BC
ductile
Sensory Loss of crispness
Getting moist B--->C
Brittle ---> Soft > mTb
Due to gain of water
A cookie doughB hard cookieC loss of brittleness
-135 °C
tplabuza © 2008 Slide # 95
conclusions
Material science principles are very applicable to physical state changes of amorphous foods (SCM)
Integration of aw and Tg or Tb concepts
Physical changes understood with a state diagram
tplabuza © 2008 Slide # 96
A overturned glass
tplabuza © 2008 Slide # 97
Thank you for listening and enjoy your candy and cookies
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