state transitions and microstructure of food delivery

Yrjö H. Roos

State Transitions and Microstructure

of Food Delivery Systems Solids

Yrjö H. Roos

Food Technology

ESPCA/São Paulo School of Advanced Science

Advances in Molecular Structuring of Food Materials

2 April 2013

Faculty of Animal Science and Food Engineering (FZEA-USP)

April 1st to 5th, 2013

Yrjö H. Roos Food Technology

Contents

• Traditional approaches – Water activity and water sorption

• Food Polymer Science – Glass transition and water plasticization

– The state diagram

• Physical State – Single components

– Multiple components and immiscibility

• Crystallization and Stability – Nutrient stability

• Nutrient Delivery – Encapsulation and release

Augustin and Hemar, Chem Soc Rev 38, 902-912 (2009)


Traditional approach

• Water activity approach uses the chemical potential of water to explain stability. – Water available to support

microbial growth.

– Water as solvent and reaction medium.

• Reaction rates depend on water activity and temperature. – Desired reactions at high

temperature.

– Loss of nutrients and deterioration in storage.


Traditional Stability Map

Labuza, TP. J. Food Process. Preserv. 1: 167-190 (1977)

Labuza et al. Food Technol. 24: 543-550 (1970)

• Developed by Marcus Karel and Ted Labuza – Significant number of

studies on rates of non-enzymatic browning and lipid oxidation.

– Identifies BET monolayer value as an important stability point.

• No solvent water.

• Surfaces covered by water molecules.

Equilibrium: m(l ) = m(g)

aw

=p

p0

ww

w

m aKa

Ka

m

m

111


Food Polymer Science

• The Food Polymer Science

concept recognized the

noncrystalline (amorphous) or

partially crystalline (PC) state of

food solids and solids

plasticization by water.

– Developed by Harry Levine and

Louise Slade.

• Emphasized the applicability of

the Williams-Landel-Ferry (WLF)

relationship to describe free

volume changes and plasticization

above the glass transition.

“Fringed micelle” model of the crystalline-amorphous structure of PC polymers.

logh

hg

=-C1 T -Tg( )C2 + T -Tg( )

Slade and Levine,

Pure Appl. Chem.

60, 1841-1864 (1988)

Temperature dependence of relaxation times (viscosity) of glass forming materials.


The Physical State

Equilibrium

Solid

Non-equilibrium

Solid

Equilibrium

Liquid

Equilibrium

Liquid

Time-dependent

Phenomena SOLUTION

GLASS CRYSTAL

MELT

RUBBER Crystallization

Cooling

Co

olin

g

Heatin

g

(Pressure)

Non-equilibrium

Liquid

Roos and Karel (1991)

Food Technol. 45 (12): 66,68-71,107


Glass Formers in Foods

Milk Milk powder (lactose, proteins)

Ice cream mix Ice cream (sugars, proteins)

Coffee concentrate (sugars, proteins)

Dissolved solids

in water

Dehydrated solids

• low water foods

• food ingredients Freeze-concentrated solids

Freeze-dried coffee

Starch and proteins Cereals and snacks

Syrups Boiled candies

(carbohydr., proteins)

(sugars)

(carbohydr., proteins)

Food product Solids system (glassy components)


Water in Foods

• Solvent and reaction medium. – Effective water fraction (aw).

– Impact on reaction kinetics.

• Plasticizer. – Water content (m).

– Impact on physical state of solids.

– Impact on reaction kinetics.

• Supports life. – Effective water fraction (aw).

– Impact on biological functions (microbial

growth).

All water molecules are free (m) and exhibit high mobility, but their

colligative interactions may vary with effects on aw.

mw

= mw

0 +RT lnaw

aw

=p

p0

Tg

=w

1T

g1+ kw

2T

g2

w1+ kw

2

Chemical potential:

Water activity:

Plasticization (G-T):


The Noncrystalline State

Solid Liquid

Heat

Flo

w

Temperature

Cooling

Tg

Cooling

Heating

Onset

Cooling

Endset

End

oth

erm

al

He

at F

low

Heating

Heating

H V

S

Temperature

Crystalline solid state

Tm Tg

Noncrystalline liquid state

Noncrystalline

solid

states

Glass

transition

Equilibrium liquid state

• Structural relaxation times. – Indicate time-dependence.

– Affect free volume and microstructure.

– Fluidness around and above the glass transition.


One Component Systems

• Spray dried lactose

• Freeze-dried lactose – Retain the dissolved

state of molecules.


Amorphous Lactose

Tg of a single, small molecular

weight component decreases

linearly with aw.

Critical aw

T ≈ 25°C

-100

-50

0

50

100

0.00 0.20 0.40 0.60 0.80 1.00

Te

mp

era

ture

(°C

)

Water Mole Fraction

-100

-50

0

50

100

0.00 0.05 0.10 0.15 0.20 0.25

Te

mp

era

ture

(°C

)

Water Mass Fraction

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Wate

r A

ctivity

Water Mole Fraction

-100

-50

0

50

100

0.00 0.20 0.40 0.60 0.80 1.00

Te

mpe

ratu

re (

°C)

Water Activity


Water Plasticization

100x M 100_Glucose - 20°C200 m 100x M 100_Glucose - 20°C200 m 100x M 100_Glucose - 20°C200 m



Thermal Plasticization

(enhanced mobility)

Water Plasticization

(enhanced mobility)

Free Volume

Mobility


The State Diagram

WEIGHT FRACTION OF LACTOSE

0.0 0.2 0.4 0.6 0.8 1.0 -150

-100

-50

0

50

100 Solubility

(equilibrium mixture

of a - and

b -lactose)

Supercooled

liquid

Glass

Ice and vitrified solute-unfrozen

water phase

Equilibrium freezing zone

Temperature range for maximum ice formation and freeze-drying

g T

g T

m

g T'

T'

g C'

TE

MP

ER

AT

UR

E (

°C) Glass transition

range

m T

Glass Transition

Melting

Peak integration gives latent heat

DSC analysis


Diversity of Components

logh

hg

=-C1 T - Tg( )C2 + T - Tg( )

- 140 - 120 - 100 - 80 - 60 - 40 - 20

0 20 40 60 80

0 0.2 0.4 0.6 0.8 1.0

1.4 0.016 Pa s

Tg + 80°C

Tg + 60°C

Tg + 40°C

0.002 Pa s

Tg + 20°C 7.1

4.4

1.4

2.6

2.7 0.0001 Pa s

Longinotti and Corti,

J. Phys. Chem. Ref. Data

37, 1502-1515 (2008)

3.8

0.4

2.4 0.9

0.32 Pa s

-8.6

-7.4

-5.6

-2.9

Tg + 10°C

Tg + 5°C

Tg + 2°C 11.3

10.5

Tg 12

9.2 0.15 s

2.9 s

22 s

100 s

WLF

log η

(Pa s)

log τ

(s)

TE

MP

ER

AT

UR

E (

°C)

SUCROSE

WEIGHT FRACTION

log η

(Pa s) τ (s)

Universal constants: C1 = 17.44

C2 = 51.6


Molecular Weight

-80

-40

0

40

80

120

160

200

100 1000 10000

Monosaccharides

Disaccharides

Maltodextrins

Te

mpe

ratu

re (

°C)

Molar Mass (g/mol)

Tg

=w

1T

g1+ kw

2T

g2

w1+ kw

2

Gordon-Taylor T

g= f lnM

w( )

Molecular size Water plasticization

Tg

Tm′

Tg′


Structural Relaxation Times

Dynamic Mechanical Analysis

Parallel plate electrodes

Dielectric Analysis


Structural Relaxation Times

RE

LA

XA

TIO

N T

IME

TEMPERATURE, WATER ACTIVITY OR WATER CONTENT

Glassy State Glass Transition Years

Months

Days

Hours Minutes Seconds

Flow

EX

TE

NT

OF

CH

AN

GE

IN P

RO

PE

RT

Y

Ha

rde

nin

g, C

rakin

g

Crisp

ne

ss

Stability Zone Critical Zone Mobility Zone

Str

uctu

ral T

ran

sfo

rma

tion

s

Incre

asin

g D

iffu

sio

n

Fermi’s Model

(M. Peleg)


Critical Water Plasticization

Time-dependent crystallization

0.0 0.2 0.4 0.6 0.8 1.0 0

10

20

30

40

50

WA

TE

R C

ON

TE

NT

(g

/10

0 g

of S

olid

s)

WATER ACTIVITY

Lactose

Anhyrous

a/b mixed crystals

a-lactose

monohydrate

crystals

Recrystallization

Extrapolated water sorption isotherm for non-crystalline lactose

-80

-60

-40

-20

0

20

40

60

80

100

120

0 10 20 30 40

WATER CONTENT (g/100g dry solids)

TE

MP

ER

AT

UR

E (

°C)

0

0.2

0.4

0.6

0.8

WA

TE

R A

CT

IVIT

Y

Glass transition

GAB Isotherm

Glass Transition Region

(Critical Storage Parameters)

Crystallization

Critical water

content

Critical water

activity

Lactose crystallization

Spray dried lactose

Freeze-dried lactose

“Tomahawk”

“needles”

76% RH

Haque and Roos, Innov Food Sci Emerg Technol 7, 62-73 (2006)

m

mm

K' Caw

(1 Caw )[1 (K' 1)Caw ]

GAB Model


Critical Water Activity

1210864200

0.2

0.4

0.6

0.8

CR

ITIC

AL W

AT

ER

AC

TIV

ITY

Maltodextrins

DE4

DE10

DE20

DE36

DE25

Skim milk powder

Lactose

Horseradish roots

Strawberries

Skim milk powder with hydrolyzed lactose

CRITICAL WATER CONTENT (g/100 g of solids)

• Critical aw (glass transition) affects directly (glass former mobility):

– Stickiness and caking of powders.

– Collapse (viscous flow) of dehydrated foods.

– Crispness of snacks and cereals.

– Crystallization of food components.

• Critical aw may affect diffusion and reaction rates indirectly (reactant mobility):

– Enzymatic changes.

– Nonenzymatic browning.

– Oxidation.

• Glass transitions can be global or occur locally in food microstructure.

– Changes often occur below the global glass transition.

Glass transition vs. reactant mobility

Room temperature


Multicomponent Systems

Water – Extremely Mobile

Plasticiser Small Solute – Glass Transition-

Dependent Mobility Lipid – Phase

Separated


Plasticiser Miscible Components – Solute Mix

Glass Transition-

Dependent Mobility



Dependent Mobility

Protein – Phase

Separated



Dependent Mobility

Polymer – Partially Crystalline

Phase Separated

A

D C

B

Plasticization

and phase

separation

Plasticization


Microstructural Complexity

• Dispersed and phase separated components in dynamic conditions (solid/liquid/gaseous).

• Highly mobile gaseous components.

• Molecular assembly (surface and molecular interactions).

O2

H2O

Polymers

Dispersed

Phase


Miscibility vs. Phase Separation

SMP:MD (DE 17) -50

0

50

100

150

0 5 10 15 20

WATER CONTENT (g/100 g solids)

TE

MP

ER

AT

UR

E (

°C)

35:65

1:9

MD(DE17)

9:1

65:35

Lactose

0

20

40

60

80

100

120

0 20 40 60 80 100

MALTODEXTRIN CONTENT(%)

0.11 aw

0.23 aw

0.33 aw

0.44 aw

MD(DE17)

TE

MP

ER

AT

UR

E (

°C)

0

40

80

120

0 3 6 9 12

Lactose

Lactose-CAS (3:1)

Lactose-SPI (3:1)

0

40

80

120

0.0 0.1 0.2 0.3 0.4 0.5

Lactose

Lactose-CAS (3:1)

Lactose-SPI (3:1)

Water Content (g/100 g of Solids) Water Activity

Te

mp

era

ture

(°C

)

Te

mp

era

ture

(°C

)

Skim milk solids

with various levels

of maltodextrin

(miscible with

lactose).

MD Content

aw

aw

Lactose and lactose

with either Casein

(CAS) or Soy Protein

Isolate (SPI) (poorly

miscible with lactose). aw

Plasticization of

miscible

carbohydrates.

Plasticization of

phase separated

lactose.

Zhou Y and Roos YH,

J Food Sci 76 E368-E376 (2011)

Silalai N and Roos YH,

J Food Eng 106 306-317 (2011)

Tg of the sugar!

Tg of the mix!

Carbohydrates and Proteins


Glass Transition vs. Water Activity

Water activity and glass transition -

Water activity may vary locally in

food microstructure, although often

measured globally.

Food stability ‘map’ and the glass

transition – Glass transition may

be a local property of some

solids fractions and their water

plasticization.

Roos, Y.H. J. Food Sci. 52: 146-149 (1987)

Tg of small saccharides fraction!

Both aw and Tg can be misleading microstructural stability criteria!


Water Sorption of Components

0

5

10

15

20

25

0.0 0.2 0.4 0.6 0.8

Wa

ter

Co

nte

nt

(g/1

00

g o

f S

oli

ds

) Water Activity!

GAB Lactose-MD23 (70:30)

Cal. Lactose-MD23 (70:30)

Exp. Lactose-MD23 (70:30)

GAB-amorphous Lactose

Cal. amorphous lactose (MD23)

Exp. Lactose

Exp. MD23

GAB MD23

Non-crystalline lactose

Non-crystalline lactose-MD23 (70:30)

MD23

Cal. data

0

5

10

15

20

25

0.0 0.2 0.4 0.6 0.8

Wa

ter

Co

nte

nt

(g/1

00

g o

f S

oli

ds

)

Water Activity!

GAB Lactose-MD9 (70:30)

Cal. Lactose-MD9 (70:30)

Exp. Lactose-MD9 (70:30)

GAB-amorphous Lactose

Cal. amorphous lactose (MD9)

Exp. Lactose

Exp. MD9

GAB MD9

Non-crystalline lactose

Non-crystalline lactose-MD9 (70:30)

MD9

mL = mtotal – mMD

Water sorption by non-crystalline lactose, mL (at each aw up to 0.76 aw)

Data from mixtures

Data from mixtures

Potes et al., Carbohydr Polym 89, 1050-1059 (2012)


Glass Transitions of Components


Similar plasticization of

component mixtures, but very

different diffusion of individual

molecules: - Plasticization changes free

volume and local mobility.

- Diffusion contributes to reactions and crystallization (collisions).

-80

-20

40

100

160

0 5 10 15 20

Tg (°C

)

Water Content (g/100 g of Solids)

-80

-20

40

100

160

0 0.2 0.4 0.6 0.8

Tg (

°C

)

aw

Lactose

Lactose-MD9 (90:10)

Lactose-MD9 (70:30)

MD9

-80

-20

40

100

160

0 5 10 15 20

Tg (°C

)

Water Content (g/100 g of Solids)

-80

-20

40

100

160

0 0.2 0.4 0.6 0.8

Tg (°C

)

aw

Lactose

Lactose-MD23 (90:10)


MD23

Reaction rates?

Crystallization rates?


Sucrose Crystallization

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 200 400 600 800 1000 1200 1400 1600

cm -1

Ra

ma

n in

ten

sity

36 °C 64 °C

54 °C 68 °C

Sucrose

Crystallization of

amorphous sucrose

followed by Raman

spectoscopy


Crystallization

• Glass transition temperature close to that of lactose.

– Rate of lactose crystallisation above Tg is dependent on composition.

Lactose-MD23

65.6% RH

100:0 (k1 = -1.4721)

0

1

2

3

0 5 10 15 20 25

90:10 (k1 = -0.1878)

70:30 (k1 = -0.0299)

40:60 (k1 = 0.0003)

0

1

2

3

0 5 10 15 20 25 Time (Days)

100:0 (k1 = -0.7868)

90:10 (k1 = -0.2013)

70:30 (k1 = -0. 0623)

40:60 (k1 = -0. 0218)

Lactose-MD23

76.1% RH

Lactose-MD9

0

1

2

3

0 5 10 15 20 25

ln W

ate

r C

onte

nt (g

/10

0 g

of S

olid

s)

40:60 (k1 = 0.0005)

70:30 (k1 = -0.0361)

100:0 (k1 = -1.4721)

90:10 (k1 = -0.3952)

65.6% RH

Time (Days)

0

1

2

3

0 5 10 15 20 25

100:0 (k1 = -0.7868)

90:10 (k1 = -0.2011)

70:30 (k1 = -0.0986)

40:60 (k1 = -0.0353)

76.1% RH

Lactose-MD9

ln W

ate

r C

onte

nt (g

/10

0 g

of S

olid

s)



Mobility and Crystallization

-4

-2

0

2

4

6

8

-4

-2

0

2

4

6

8

0 10 20 30 40 50

log

tcr (

s)

log

t (

s)

T - Tg

2 months

2 weeks

2 days

2 hours 20 min

10 min 2 min

3 s

1 s 0.5 s

10 ms 3 ms

1 ms 0.3 ms

Time to complete crystallization

Structural relaxation time DSC heat of

crystallisation

Ra

te C

on

sta

nt

(k1)

(Da

y-1

)

- 1 . 6

- 1 . 2

- 0 . 8

- 0 . 4

0

0 . 4

0 20 40 60 80 100 Concentration of Lactose (%)

0.66 aw

Lactose-MD 9

Lactose-MD 23

-0.8

-0.4

0

0.4

0 20 40 60 80 100

Concentration (% Lactose)

K

MD9_0.76aw

MD23_0.76aw

Lactose-MD 9

Lactose-MD 23

20 40 60 80 100

Concentration of Lactose (%)

-0.4

0

0.4

0.76 aw

-0.8 0

Roos and Karel, J. Food Sci. 57: 775-777 (1992)



Lactose in Milk Solids

Auty M (2013)


Relaxation time vs. Crystallization

0.02

0.04

0.06

0.08

0.10

0.12

-8

-6

-4

-2

0

2

0.00 0.20 0.40 0.60 0.80 1.00

log t

(s)

k (

firs

t ord

er

da

y-1

)

Water Activity

(Each aw corresponds to ∼same T - Tg)

Lactose

Lactose-MD9 (70:30)


WLF

Potesetal.Carbohydr.Polym.89,1050-1059(2012)

(Universal Constants)

Tg Tg+10K

Tg+15K


Oxidation and Free Volume

An increase in average free volume with increasing molecular

weight of the carbohydrate blend showed that small changes

in free volume affected oxygen diffusivity and autoxidation of

encapsulated oil in glassy carbohydrate matrices.

Note: Water contents, Tg and dissolved O2 varied!


FD Maltodextrin DE10-Sugar (1:1)

• Degradation of entrapped particles in

glassy membranes – O2 diffusion.

• Highest stability at 1 mol H2O/4 mol

monosaccharide units.

• Decreased relaxation times showed

increased rate constants and liquid flow.

-0.05

-0.04

-0.03

-0.02

-0.01

-6

-5

-4

-3

-2

-1

0

1

2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Glucose

Sucrose

log

t (

s)

Water Activity

Ra

te C

on

sta

nt (ln

%/d

ay)

Rate Constant

log Relaxation Time

Viscous Flow and Collapse -6 < log t < -3

Fructose

Encapsulated crystalline b-carotene Encapsulated non-crystalline b-carotene

• Oil-dissolved β-carotene showed

higher stability than crystalline β-

carotene particles.

• β-carotene in oil droplets require

oxygen diffusion to oil.

• Collapse at T>Tg improved stability.

Harnkarnsujarit et al, J Food Sci 77, E313-E320 (2012) Harnkarnsujarit et al, J Agric Food Chem 60, 9711-9718


Water Soluble Vitamins

Water Activity (aw)

log

t (

s)

Ra

te C

on

sta

nt (×

10

-2 Day

-1) 0

10

20

30

40

50

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

0.00 0.20 0.40 0.60 0.80 1.00

Lactose (DMA) Ascorbic Acid

Thiamine

Rate of Lactose Crystallization

Glass

Zhou and Roos, J Agric. Food Chem. 60:1075-1083, 2012


Emulsion Particle Size

• Formulation – Lactose or Lactose:Sucrose (70:30) 23.9%

– Sodium caseinate 4.6%

– Sunflower oil 11.5% (b-carotene 0.025%)

– Ascorbic acid 0.25%

• Heat treated at 100 ºC for 30 s.

• Homogenization (60 ºC). – Control emulsion (homogenized at 17 MPa).

– Nanoemulsion (microfluidised at 100 MPa).

• Spray dried at 185 ºC (inlet) 80 or 90 ºC (outlet). Cryo-SEM

Confocal Laser Microscopy

Oil

CHO Protein


Active Components

• Formulation and microstructural engineering for protection of sensitive components. – Often includes an

encapsulation process.

• Phase and state transitions. – Solid vs. liquid structures.

– Amorphous vs. crystalline structures.

– Native vs. denaturated states.

Matalanis et al, Food Hydrocoll 25, 1865-1880 (2011)

Stabilization

Release


Microencapsulation Processes

Drusch, S. (2013)

Short Shelf-life Long Shelf-life

Interface Engineering

Glass Formation (Solid Continuous Phase)


Particle Size

100nm 200nm 1000nm 2000nm

810008000 1n

d

Area 14100400

Volume 11/81/10001/8000

LaplaceDP(H2O,20°C)30bar 15bar 3bar 1.5bar

2bar 1bar 0.2bar 0.1bar


Targeted Delivery

Lunasin is a bioactive peptide in soybeans,

barley, wheat and rye.

• Cholesterol lowering

• Cancer preventing

• Cardiovascular disease preventing

Release ≠ Bioavailability


Summary

• Water activity is an important stability and safety parameter.

• Glass transition and water plasticization data are needed for matrix formation.

• The glass formers contribute to kinetics of microstructural transformations.

• The glass formers may be used to stabilize and release active components.

• Microstructural engineering is required for nutrient delivery.

state transitions and microstructure of food delivery

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