Soft Condensed Matter: A perspective on the physics of food … Soft Condensed Matter: A perspective...

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 [email protected]

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


Greetings from my back yard showing state changes and water activity


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


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


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


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


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

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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


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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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


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


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

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/g to

tal)

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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


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


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


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

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b (g

H2O

/g to

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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


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


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


XRD @ 6 mo. @ 72% RH

Also did not brown because of local viscosity


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


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


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


Moisture loss relative to aw and Tg

S =3 @ ~ 14% moisture

Tg from Lin ~ 9% Moisture aw ~ 0.45


Influence of moisture loss on storage modulus

start

end


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%


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

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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


Crystal Collapse

Melt

> 210°C

Liquid stream

spin

Re-crystallize

Glass

cool

Rubber

humidify

W/H2O loss


Moisture as f (aw) water activity– Makower & Dye. J Ag. Food Chem 1956 4:72-77@ 35°C– BET monolayer ~ 4 g water/100g


General adsorption isotherm of sugar containing amorphous foods

one week

two weeks

water activity

moisture


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


Influence of increasing moisture or temperature


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


Crystallization of FD Sucrose by XRD @ 25°CPalmer et al 1956 J Ag Food Chem 4:77-81


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


XX--Ray Diffraction PrincipleRay Diffraction Principle

XX--RayRaySourceSource


.. ......

........

CrystalCrystal

Amorphous Amorphous MaterialMaterial

6500 counts/sec

6500 cps


XX--Ray Diffraction of fresh made Cotton CandyRay Diffraction of fresh made Cotton Candy

400 counts/sec

Amorphous Amorphous Fresh CCFresh CC


Halo pattern


X-RD Results

Stored at Stored at ~5 to 11 ~5 to 11 % RH for 5 years% RH for 5 years

400 counts/sec


Stored at 45% RH

1 hour 2 hours 5 hours

3000 counts/sec


Stored at 75% RH for 1 hourStored at 75% RH for 1 hour

3000 counts/sec


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%


Influence of increasing moisture on local viscosity ie diffusion


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)


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


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


Qa = 1000

Qa = 10,000


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


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


……………………………………………….……………………………………………….

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


Raffinosesuppresses

rate of sucrose crystallization, acting

as true a crystallizationinhibitor

Raffinose effect

Smythe 1967 Aust. J. Chem. 20: 1097-1114


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


Case study 3Soft cookies aw >0.55 starch not gelatinized

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b (g

H2O

/g to

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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


Microscopy - Fresh CookieStarch Granules - Maltese Crosses

92 X


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


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

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H2O

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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


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%


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


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


Soft Cookie24 hour


Cookie5 Days

Cookie 10 Days


Crystallization kineticsMicroscopy - 18 day Cookie

Starch Granules and Sucrose Crystals

Using first-order-red plate filter which enhances features of low birefringence.

230X


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


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


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


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


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


invertsuppresses

rate of sucrose crystallization but

Needs highconcentration

Invert sugar effect


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


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


Sucrose and HFCS (~ 2.5 :1 m/m)Starch

Fat

Water

Sucrose

Glucose and/or fructose


Sucrose Crystallizationinhibition by raffinose



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%


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%


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%


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


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

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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


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


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


Experimental designMeasure

Sensory

Tb - brittle-ductile

Tg - DMTA

moisture content (%)

m0


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)


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


The Other Ted Labuza Tb study


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


3 Point Bend


-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


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


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


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] )


Sensory Results: Moisture content 4

0

20

40

60

80

100

120

-10 10 30 50 70

Temperature (�

Sensory Results: Moisture content 4.95%


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


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.


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’


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


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


A overturned glass


Thank you for listening and enjoy your candy and cookies

Soft Condensed Matter: A perspective on the physics of food … Soft Condensed Matter: A perspective...

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