TgApplications - Presentación

Dr Ted Labuza University of Minnesota Department of Food Science and Nutrition St Paul MN 55108voice 612-624-9701 fax 651-483-3302 [email protected]

Tg

tplabuza © 1998

Physical Chemistry of AmorphousPhase/State Transitions in Foods:

Dr Ted Labuza Department of Food Science and NutritionUniversity of MinnesotaSt Paul MN 55108

Tg

tplabuza © 1998

Water relations

uThermodynamics

uDynamics

uStructure

☞

☞

Tg

tplabuza © 1998

Concept of aw and Tg

DoesnÕt require a rocket scientistbut it helps


Tg

tplabuza © 1998

uThe voice had become so rigid that it cracked.

uThatÕs how molecules behave today, and thatÕs how

u they behaved back then, though in those days nobody

u blamed molecules for brittleness any more than they

ucredited them for plasticity.

uFrom Jitterbug Perfume by Tom Robbins

Tg

tplabuza © 1998

textural changes

uloss of crispness > BET

uloss of bowl life >0.5

uhardening of cookies ~0.4

ubread staling

ucaking of powders @ ~ 0.4

water activity or molecular mobility ?

Tg

tplabuza © 1998

Polymer Science Approachfree volume theory for diffusion

Diffusion and reaction function of:temperature above glass temperatureamount of plasticizer present (water)size of molecule diffusing


Tg

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Amorphous SolidPhases

solids (%)

Tg

rubbery

glassy

temperature

0% 100%

Tg

tplabuza © 1998

Early 1948 Quote

ÒGlasslike low molecular weight substances comprisean importance group of materials. In the broad standing,physical properties of common glassy materials such asbrittleness, natural resins, stiff pitchesand hard candies are included.Ó

Principles of High Polymer Theory and PracticeA. Schmidt and C. MairlesMcGraw Hill 1948 page 191

Tg

tplabuza © 1998

Crystal Collapse

Melt

> 210¡C

Liquidstream

spin

recrystallize

Glass

cool

Rubber

humidify


Tg

tplabuza © 1998

uspecific heat change (DTA, DSC, DDSC)

u thermal mechanical (caking, DMA, DMTA)

u thermal expansion (TGA)

uBrittle-ductile

udiffusional (ESR)

umolecular relaxation (NMR)

uother

Tg measurement Techniques

Tg

tplabuza © 1998

Method

heat at some constant rate (scanning rate)

1. DTA: single heater - measure DT as heat2. DSC: two heaters - measure energy input to keeptemperature the same (more sensitive)3 DDSC: DSC with sine wave T oscillation

sample blank

Heater

need to calibrate with indium for T meltneed constant baselineneed to clean pans of oil deposit

thermocouples

Tg

tplabuza © 1998

Theoretical differential scanning calorimetrythermogram -- thermal property change

free volume increase causes drop in Cp above glass transition

en

do

the

rmic

Temperature

Tg

Tm

cT


Tg

tplabuza © 1998

soluble coffee @ aw 0.75

use derivative function to get midpoint

Tg

tplabuza © 1998

Mechanical properties ofMaterials

u YoungÕs modulus

E= σσσσ / εεεε (σσσσ = stress, εεεε = strain)

u Shear stress

G = f / s

u Complex YoungÕs modulus

E* = E« + i E««

E« = storage modulus

E««= loss modulus

i = square root of -1

u tan ¶ = E«« / E«

Tg

tplabuza © 1998

Manufacturers

uRheometrics

uPolymer labs DMTA

uPerkin Elmer DMA

Computerand transducer

sample

Probe

scan at single frequencies eg 1 Hz = 1 cycle/secscan at multiple frequencies

temperaturecontrolled


Tg

tplabuza © 1998

DMTA

OscillatingProbe

Sample

Stable fixture

From Rheometrics Website

DMTA in lab

Tg

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Dynamic Mechanical ThermalAnalysis - mechanical property change

log E« (Pa)

temperature

low temperature

transition

drop in E«

slope

Tan¶ peak

Tan ¶

Elastic modulus drops significantly at glass transition

Tg

tplabuza © 1998

5

5.5

6

6.5

7

7.5

8

8.5

-30 20 70 120

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Lo

g M

od

ulu

s

(Pa

)

Ta

n δ

Temperature (¡C)

E«

E««

Tan δ

Tg results Nabisco Chocolate wafer


Tg

tplabuza © 1998

DMTA plot

Tg

tplabuza © 1998

Brittle-ductile transition Tb

uBrittle fractureÐ Òclean breakÓ

u Ductile fractureÐ no Òclean breakÓ

Ð sample deformed (yielding)

uAt constant strain and moisturecontent, the temperature at which thesystemÕs fracture changes from brittlefracture to ductile is the Tb.

Tg

tplabuza © 1998

Three point bend


Tg

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Methods and MaterialsBrittle-ductile transition temperature (Tb)

Str

ess

Strain

At constantmoisture content

Yield (Maximum stress = yield strength)

Brittle Break (Maximum stress = brittle strength)

Tg

tplabuza © 1998

-4¡C

15¡C

Stress vs. Strain7.23% moisture content

-0.5

0

0.5

1

1.5

2

2.5

3

0 0.002 0.004 0.006 0.008

Strain

Str

ess (

MP

a)

Tb results

Tg

tplabuza © 1998

Methods and MaterialsBrittle-ductile transition temperature (Tb) at constant moisture

content

Str

en

gth

(M

Pa

)

Temperature (¡C)

σσσσb - brittle strength

σσσσy - yield strength

Tb Adapted fromVincent (1961)


Tg

tplabuza © 1998

Tb: 3.73% Moisture Content

0

0.5

1

1.5

2

2.5

-10 10 30 50

Temperature (¡C)

Str

en

gth

(M

Pa)

Tb

Tg

tplabuza © 1998

r2 = 0.98

Tb as a Function of Moisture Content

-20

-10

0

10

20

30

40

3 5 7 9

Moisture Content (g H2O/ 100 g solids)

Te

mp

era

ture

(¡C

)

Tg

tplabuza © 1998

0.40.30.20.10.0

-100

0

100

200

DE 5

DE 15DE 20DE 25DE 36

DE 10

Maltodextrins

moisture (g water/g solid)

Tem

pera

ture

(°C

)

Maltodextrin Tg values

Tg decreases with decreasing MW


Tg

tplabuza © 1998

Sugar Tg values

0.50.40.30.20.10.0-80

-55

-30

-5

20

45

70

95

120

lactose-Roos

sucrose-Roos

sucrose/amioca-Roos

maltose-Roos

glucose-Chan

maltose-Noel

moisture (g water/g solid)

Tem

pera

ture

(°C

)

Sugars

lactose

glucose

Tg

tplabuza © 1998

Tg of crackers by DMTA at a heating rate of 3oC/min

-200

20406080

100120140160180

0 0.05 0.1 0.15 0.2 0.25

E´ slopetan

T(oC)

water content (g water/ g solids)

¶

average 10¡C drop per 1% moistureTg = room temperature at 8-10% waterTg < 0¡C @ 30% moisture

Tg

tplabuza © 1998

Cracker & Bread vs cereal components

-40

-20

0

20

40

60

80

100

120

140

160

0 10 20 30 40

Cracker DMTAGliadin DMSGlutenin DMSGlutenin DSCAmylopectinDMTAGluten DMTABread(Modified TMA)

Tg (oC)

moisture (%)


Tg

tplabuza © 1998

Ingredient effects

usugars lower Tg curve

ustarch highest Tg line

uproteins lower than starch

uLower MW lower the Tg

u? of mixing Tg how to predictÐ Kauzman equation

Tg

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Texture Applications

u dynamics and structure

Tg

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Characteristics of the glassy and rubbery states.

Tg

solids (%)

rubbery

glassy

temperaturecrisp, brittlehigh viscosityreduced free volume

slow reaction rateshigh moduluslower heat capacity

softermore flexiblelower modulus

greater free volumelower viscosityfast reaction rates

sugar crystallization


Tg

tplabuza © 1998Thermodynamics with dynamics

0 ¡C Te

Tm

freezing line

ice

super sat solution

0% solids

100%

State Diagram

and

Roos and Karel Food Tech 45(12): 66 1991

Tg


0 ¡C Te

Crystal melt line

Tm

freezing line

ice

super sat solution

0% solids

100%

State Diagram

and


Tg


0 ¡C Te

Crystal melt line

Tm

Solution

freezing line

ice

super sat solution

0% solids

100%

State Diagram

and

boiling line

vapor



Tg


0 ¡C Te

Tg'

Glassy state

rubberystate

Crystal melt line

Tm

Solution

freezing line

ice

super sat solution

0% solids

100%

State Diagram

Tg dry

-135¡C

and

Cg'

boiling line

vapor


Tg

tplabuza © 1998

Tg

tplabuza © 1998

Potential Tg applications

u stickiness and caking

u staling of bread

u hardening of fruit pieces

u popcorn volume

u checking of pasta

u crispness change of snacks, cereal,pizza crust

u chocolate sugar bloom

u hardening of soft cookies

u volatile loss in drying,


Tg

tplabuza © 1998

Powder stability problems

uProcessingÐ Flow problems: powder sticking to equipment

walls and collecting zones.

Ð Result: problems in clean upreduce efficiency

reduce product yield

reduce product quality

uStorage with timeÐ stickiness: powder sticks to walls of containers

Ð caking: clumping and collapse of powders

Ð crystallization of sugars: formation of hard mass

Tg

tplabuza © 1998

iso-viscosity (elasticity) lines

T ¡C

% solids

glass transition line

decreasingviscosity

about 102 drop per 10¡C

m

Tg

tplabuza © 1998

Caking

RUBBERY

GLASSY

¥ stickiness¥ caking¥ collapse

% solids

TemperatureA

C

B

Tg curve


Tg

tplabuza © 1998

T ¡C

% solids


sticky point + 10

caking Tg + 20

collapse & flow Tg +50

crystallization +20 to 30

Solid phase changes

Tg

tplabuza © 1998

phase change

¥ crystal state minimum free energy

aw= 0.2 aw=0.45

Saltmarch and Labuza JFS 45:1231; 1980

Tg

tplabuza © 1998

Applying the WLF model

2

l ogk

k=

- C 1( T - T )

C + ( T - T )

ref ref

ref

l ogk

ref

k

-1

=C 2

C 1(T - T ref )+

1

C1

Linear Regression method


Tg

tplabuza © 1998

WLF Kinetics*Effect of temperature above Tg

T- Tg Rate Increase Æ rate increase

3 107 10010 678 678 (0->10¡C)11 100020 74580 110 (10->20¡C)21 100,00030 261,030 3.5(20->30¡C)40 417,648 1.6(30->40¡C)

Òuniversal constants

Tg

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Lactose CrystallizationRoos & Karel JFS 57:775 Tg = 32¡C

T- Tg t seconds Q105 109.5 (100 yrs)

10 107 316

20 104.8 (~ 1day) 158

30 103 63

40 102 (< 2 min) 10

Tg

tplabuza © 1998

sugar crystallization rates

lactose>sucrose>glucose>fructose


Tg

tplabuza © 1998

Samples composition in %weight (dry basis)

Powder

Enfamil¨

(Mead Johnson)

Prosobee¨

(Mead Johnson)

Good Start¨

(Carnation)

Protein

12.15

16.39

12.97

Fat

30.94

28.96

27.57

Carbohydrate

56.91(lactose)

54.64(corn syrup solids)

59.46(lactose/maltodextrin)

Tg

tplabuza © 1998

Tsc as function of water activity

Enfamil¨

Good Start¨

Prosobee¨

1.00.80.60.40.20.0

20

40

60

80

100

120

140

160

storage water activity

Temperature(¡C)

Tg

tplabuza © 1998

Crystallization and Crispness

Soft Fresh BakedCookie

CrispCookie

Constant T, %RH no moisture change


Tg

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Sucrose Recrystallization (Makower & Dye. 1956)

uExperiment measured rate of sucrosecrystallization from a glass at differentrelative humidities

Ð At RH < 12%, no crystallization in 3 years

Ð At 33.6% RH, crystallization is rapid

uWater activity of soft cookie is 0.65

Tg

tplabuza © 1998

uMeasure changes from soft to firm

uInstrument Texture AnalyserTA.XT2

uPuncture Test

Tg

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Texture Analyzer - Fresh (1 hr) Cookie

uFresh soft cookie - flexible -probe makes a well


Tg

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Texture: 0ld (7 days) & Firm Cookie

uOld firm cookie - fractured &punctured

Tg

tplabuza © 1998

Texture Analyzer GraphsSlope is a function of the Modulus

8 hr cookie

slope = 43 g/mm5 day cookie

slope=594 g/mm

Tg

tplabuza © 1998

Texture Analysis

Cookie Texture Using Punch Test

Force (g) to Peak

0

150

300

450

600

750

900

0 2 4 6 8 10 12

Age of Cookie in Days


Tg

tplabuza © 1998

Texture Analysis

Cookie Texture Using Punch Test

Gradient or Slope (g/mm) to Peak

0

150

300

450

600

750

900

0 2 4 6 8 10 12

Age of Cookie in Days

Slo

pe

to

Pe

ak

g/m

m

Tg

tplabuza © 1998

Siemens D5005 X-ray Diffractometer

Tg

tplabuza © 1998

Powder X-ray Diffraction

uX-ray pattern unique for everycrystalline form - ÒfingerprintÓ

uTechnique well suited foridentification

uScattering phenomenonÐ X-rays hit crystalline solids - scatter in all

directionsÈ In some of these directions, the scattered beams are completely

in phase and reinforce one another to form the diffracted beams.


Tg

tplabuza © 1998

BraggÕs Law

nλλλλ ====2d sin θθθθ

u λλλλ is the wavelength of parallel monochromatic

x-ray beam (CuKαααα)))) λλλλ=1.54

u Incident on crystalline sample at an angle θθθθ

u d is the distance between the planes of thecrystal

u n is the order of reflection (an integer)

Tg

tplabuza © 1998

Sucrose Powder X-ray Pattern

10 12 14 16 18 20 22 24 262-Theta(¡)

x10^3

2.0

4.0

6.0

8.0

10.0

Inte

nsity(C

ou

nts

)

[P24-1977.dif] C12H22O11 - Sucrose, SCAN: 5.0/37.25/0.05/1(sec), Cu, I(max)=10000, 02/18/00 13:13

24-1977> C12H22O11 - Sucrose

Tg

tplabuza © 1998

X-ray Patterns for Other Ingredients:Flour, margarine, & Egg Solids

10 12 14 16 18 20 22 24 262-Theta(¡)

0

100

200

300

400

500

600

Other ingredientsgive background


Tg

tplabuza © 1998

Soft Cookie - 1 hour

10 12 14 16 18 20 22 24 26

2-Theta(¡)

0

250

500

750

1000

1250

Inte

nsity(C

ou

nts

)

[1HR#2.MDI] 1 hour cookie, SCAN: 10.0/27.0/0.05/1(sec), Cu, I(max)=384, 05/21/00 17:21

24-1977> C12H22O11 - Sucrose

If get rid of background,peaks are very small.

Tg

tplabuza © 1998

Cookie - 1 day - Peaks Grow

10 12 14 16 18 20 22 24 262-Theta(¡)

0

250

500

750

1000

1250

Inte

nsi

ty(C

ou

nts

)

[1DAY#5.MDI] 1day .91gram Cookie#3, SCAN: 10.0/27.0/0.05/1(sec), Cu, I(max)=489, 05/22/00 17:56

24-1977> C12H22O11 - Sucrose

Tg

tplabuza © 1998

Cookie - 5 days - Continue to Grow

10 12 14 16 18 20 22 24 262-Theta(¡)

0

250

500

750

1000

1250


Tg

tplabuza © 1998

Cookie - 10 Days

10 12 14 16 18 20 22 24 26

2-Theta(¡)

0

250

500

750

1000

1250

Inte

nsi

ty(C

ou

nts

)

[10DA#1.MDI] 10 day cookie, 0.98 g, SCAN: 10.0/27.0/0.04/1(sec), Cu, I(max)=1338, 05/31/00 22:02

24-1977> C12H22O11 - Sucrose

Tg

tplabuza © 1998

Overlay & Offset of Patterns

10 12 14 16 18 20 22 24 262-Theta(¡)

0

500

1000

1500

Inte

nsity(C

ou

nts

)

[1HR#2.MDI] 1 hour cookie, SCAN: 10.0/27.0/0.05/1(sec), Cu, I(max)=384, 05/21/00 17:21

[1DAY#5.MDI] 1day .91gram Cookie#3, SCAN: 10.0/27.0/0.05/1(sec), Cu, I(max)=489, 05/22/00 17:56[5DAY#2.MDI] Cookie made on 5/21 scanned on 5/26 - 1.03 grams, SCAN: 10.0/27.0/0.04/1(sec), Cu, I(max)=758, 05/26/00[10DA#1.MDI] 10 day cookie, 0.98 g, SCAN: 10.0/27.0/0.04/1(sec), Cu, I(max)=1338, 05/31/00 22:02

24-1977> C12H22O11 - Sucrose

Tg

tplabuza © 1998

Sucrose

Fructose

Dual Texture Cookieglass transition solution

Tg sucrose > Tg fructose

hard

soft center


Tg

tplabuza © 1998

Ingredients (in descending order)Used to Make Soft Cookies

uKeebler - Soft Batch Chocolate ChipÐ Sugar, HFCS, modified food starch

uKeebler - Soft Ôn ChewyÐ Sugar, HFCS, modified food starch, date paste, molasses,

invert sugar

uNabisco - Chewy Chips Ahoy(microwaveÕem)

Ð HFCS, sugar, dextrose, lactose, corn starch, molasses

uPepperidge Farm - Soft Baked ChocolateChunk

Ð Raison paste, sugar, fructose, brown sugar, invert sugar

uArchway - Chocolate ChipÐ Sugar, HFCS, corn syrup, corn starch modified

Tg

tplabuza © 1998

Soft Cookies

desire long life withsoft texture

make fresh like

problemhardens with age

Tg

tplabuza © 1998

Dual Texture Cookiesoft center/crispy outer layer

% solids

dough

10070

inner layer

outer layer

T ¡C

frying orbaking

sucrosebased

fructose based


Tg

tplabuza © 1998

Bread staling

long shelf life military bread

Tg

tplabuza © 1998

TGAState Diagram for Bread

LeMeste et al. (1992)

10090807060

0

40

80

120

160

% solidsOmnitherm Model 500 Polymer Labs

Tg = -12¡C @ 32% moisture

Tg

tplabuza © 1998

White bread Tg = -11¡C m =25%

Ra

te

Temperature

GrowthNucleation

37°C0°C 4°C-20°C

maximum staling at 4¡C stopped in freezer at -15¡C


Tg

tplabuza © 1998

Effect of water activity on snack food crispness(Katz and Labuza, 1981)

Crispness Intensity Monolayer Values critical

Product aw mc aw mo g H2O/100 g g H2O/100g

Saltine 0.39 7.0 0.22 4.8Potato Chip 0.51 5.7 0.21 2.9Corn Curl 0.36 4.2 0.18 2.9Popcorn 0.49 6.1 0.17 3.4

Tg

tplabuza © 1998

Perceived crispness Corn flakes

Sauvegeot and Blond 1991 J Texture Studies 22:423

0

2

4

6

8

10

Sen

so

ry S

co

re

0 0.2 0.4 0.6 0.8 1water activity

Tg

tplabuza © 1998

Tg Studies of Cereals

u LeMeste et. al . , 1992. White pan bread. ModifiedThermomechanical Analysis.

u Kalichevsky et. al. , 1993. Wheat gluten. DMTA.

u Kalichevsky et. al. , 1993. Amorphous amylopectin. DMTA.

u Cocero and Kokini, 1991. Glutenin. Dynamic MechanicalSpectrometry and DSC.

u De Graaf et. al. , 1993. Gliadin. Dynamic MechanicalSpectrometry.

u Wang and Jane 1994 Starch retrogradation

u Labuza and Nikoladis 1996 J. Food Sci, J Thermal Analysiscracker and itÕs dough

u Hyman PhD Thesis U of Minn 2000


Tg

tplabuza © 1998

Effect of moisture gain oncrispness loss

temperature

Tg

solids (%)

rubbery

glassy

T room

finishedcrispcrackermoisture gain

? where is crispnesslost

0% 100%

Tg

tplabuza © 1998

T ¡C

% solids


sensory crispness Tg + ? ¡C

Solid phase changes

Tg

tplabuza © 1998

Improved crispness of dry snack food

temperature

T room

20 40 60 80 100

% solids

frying,

extrusion or

puffing

dough or

raw food

reformulatedcurve

normal curve

crispsoggy


Tg

tplabuza © 1998

Te

mp

era

ture

Moisture

glass

rubber

Crispy

Less Crispy

25¡C

Moisture content at which the crispnessintensity begins to decreases sharply atroom temperature

Tg curve for gluten

Gluten (Attenburrow et al. 1992 & Nicholls et al. 1995)

Tg

tplabuza © 1998

Te

mp

era

ture

Moisture

glass

rubber

Crispy

Less Crispy

25¡C


Tg curve for starch

Starch (Attenburrow et al. 1992 & Nicholls et al. 1995)

Tg

tplabuza © 1998

Te

mp

era

ture

Moisture

glass

rubber

Crispy

Less Crispy

25¡C


Tg curve

Crispy bread (Roudaut et al. 1998)


Tg

tplabuza © 1998

Te

mp

era

ture

Moisture

glass

rubber

Crispy

Less Crispy

25¡C


Tg curve

Extruded Model system (Roos et al. 1998)

Tg

tplabuza © 1998

Tg curveTe

mp

era

ture

Moisture

glass/crispy

rubber/soggy

Crispy

Less Crispy

25¡C Tci

Tg

tplabuza © 1998

Tg curveTe

mp

era

ture

Moisture

glass/crispy

rubber/soggy

Crispy

Less Crispy

25¡C

Tci curve


Tg

tplabuza © 1998

Prinzenrolle (GBB Report 1996)

R2 = 0.89

R2 = 0.94

R2 = 0.87

-60

-40

-20

0

20

40

60

80

100

0 5 10 15 20

Moisture Content(g H2O/ 100 g solids)

Te

mp

era

ture

(¡C

)

E' onset DMTAE' onset DMALinear (E' onset DMTA)Poly. (E' onset DMA)Linear (E' onset DMA)

Tg

tplabuza © 1998

-40

-30

-20

-10

0

10

20

30

40

50

60

3 5 7 9

Moisture (g H2O/ 100 g solids)

Te

mp

era

ture

(¡C

)

Sensory Tci

E' onset DMTA

E' onset DMA

Tb

Nabisco Chocolate Wafers

Tg

tplabuza © 1998

Economic $$$ Decisions

¥ Formulation Change

¥ ? how far above Tg issensory perception change

¥ Packaging Change

¥ lower WVTR

¥ Processing

¥ lower moisture content


Tg

tplabuza © 1998

popcorn collapse and flow

500

1000

1500

2000

2500

3000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

water activity

Tg

tplabuza © 1998

Flavor Encapsulation

A Tg song

ÒDoes your chewing gum loose its flavoron the bed post over night ?Ó

Lonnie Donegan and his Stiffle band1951 Top Ten Hit

Tg

tplabuza © 1998

Reaction kinetics

uDo reactions stop below the Tg line ?

uIs GAB/BET monolayer important ?

uImpact on shelf life prediction ?


Tg

tplabuza © 1998

20% Loss of ChlorophyllFreeze dried spinach 37¡C

0 . 80 . 70 . 60 . 50 . 40 . 30 . 21

10

100

1000

water activity

Tim

e fo

r 20

% c

hlor

ophy

l los

s at

37

°C 9 months 4 g water/100 g solids

2 days

16 g water/100 g

Moisture 4 x increase rate 140 x increase

Tg

tplabuza © 1998

Relative Stability Map

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.0

water activity

Lipid oxidation

moisture

vitamin

NEB

Enzymeactivity

Mold yeast Bacteria

Tg

tplabuza © 1998

lysine/ xylose Karmas et al1992

Temperature range Relative rate increase Relative rate increase pred ic ted observed Tg → Tg + 10°C 6 7 8 21 .8Tg + 10°C → Tg + 20°C 1 1 0 7 .39Tg + 20°C → Tg + 30°C 3 . 5 4 .06Tg + 30°C → Tg + 40°C 1 .58 2 .82

Universal constants are ÒNOTÓ


Tg

tplabuza © 1998

NEB Karmas et al 1992

0.00330.00320.00310.00300.00290.00280.0027-10

-8

-6

-4

-2

0

2

1/T (K-1)

ln(k

)

rubbery

glassy

Tg

Ea = 45.1 kcal/mol

Ea = 20.8 kcal/mol

Tg

tplabuza © 1998

Ascorbic Acid Resultsmoisture = 0.085 g H2O/g solid

8060402000.0

0.1

0.2

0.3

Temperature (¡C)

Tg= 46.5¡C

Tg

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r

Break in Arrhenius plot

Rubbery : E a =12.5 kcal/mole2

=0.87

Glassy: = 20.8 kcal/mole=0.98

All: E a =19.4 kcal/mole =0.98

3.8e-33.6e-33.4e-33.2e-33.0e-32.8e-3

-8

-6

-4

-2

0

1/T (K-1)

Tg

= 46.5¡C

Ascorbic acid degradation, Maltodextrin DE15 matrix


Tg

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Conclusions

uwater activity important todescribe driving force forequilibria and chemical shelflife

uglass transition describesdynamics and structurefunctions

uboth are critical

Tg

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AACC BOOK

Tg

tplabuza © 1998

A overturned glass

water activity or a glass transition

TgApplications - Presentación

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