EFFECT OF WATER ACTIVITY AND

PHYSICAL STATE OF SUGARS AND

POLYOLS ON THEIR PROCESSABILITY

Mohamed MATHLOUTHI1 and Pierrick DUFLOT2 1MM FOOD CONSULTING, Reims, France

2Consultant, FITP, La Couture, France

10th EUROFOODWATER Conference on Water in Food – Prague, September 19-21, 2018

SURVEY Inroduction

- Sugars and Polyols in Food and Pharmaceutical Processes

- Impact of water activity on these processes

Characterization of sugars and polyols in the solid state

- Water vapor sorption isotherms of sugars and polyols

- Amorphous state properties

Stability of sugar and polyol powders

- Effect of the size and shape of crystals on caking

- Water vapor adsorption and deliquescence

- Amorphous state and the stability of powders

Crystallinity and Processability

- Sugar and polyol polymorphs and processability

- Amorphous sugars and polyols compression (tabletting)

- Crystallinity of sugars and polyols and food processes

Conclusion

INTRODUCTION

Sugars and polyols in Food Processing

INTRODUCTION Sugars and polyols in Pharmaceuticals

INTRODUCTION Impact of water activity on sugars used in processes

Characterization of sugars and

polyols in the solid state

Water vapor sorption isotherms of sugars and polyols

Water content

Hygroscopic or deliquescence point at aw = 0.83 for pure sucrose

Saturation

equilibrium

Crystal

Only the surface of crystal adsorbs

less than 0.01%

Critical aw aw

Last crystal dissolved

Adapted from A.G. Tereshchenko, J. Pharma Sci. 104:3639 – 3652, 2015

Notice the right angled change of slope

at the hygroscopic point

-10

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90 100

ERH

SUCROSE

Dextrose Monohydrate

Dextrose Anhydre

Maltitol

Mannitol

Sorbitol

Xylitol

Water vapor sorption isotherms of sugars and polyols

Hygroscopic point for pure sugars and polyols at right angled change of slope Water content

Effect of impurities on the Critical ERH of sucrose

Impurities and increase in Grain size dispersion reduce the

hygroscopic point and change the shape of water vapor sorption

Impurities I 0

83%

CRITICAL ERH OR HYGROSCOPIC POINT ON

THE ISOTHERMAL SORPTION CURVE OF FINE SUGAR

RH0

Critical ERH (RH0) of Dextrose Monohydrate

M. Allan and L. Mauer, Eurofoodwater, Leuven, 2016

IS O T H E R M E D E S O R P T IO N d u M A N N IT O L (20°C )

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

30 40 50 60 70 80 90 100

% HRE

g e

au

/ 1

00

g p

ro

du

it s

ec

Avec cristallisation

mal gérée

cristallisation bien

gérée

Effect of sorbitol impurity on Mannitol water vapor

adsorption

Sorption isotherms at 20°C

With traces of

sorbitol

No traces of

sorbitol

Water vapor adsorption isotherms of sorbitol polymorphs

-1

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50 60 70 80 90 100

% m

as

s v

ari

ati

on

Relative Humidity (%)

Dynamic Vapor Sorption at 20°C

Neosorb P 60W -650- Lot 493J

Sorbitol DEP Essai 09/004 Ech 854776 0.23 % H20 LRO

Neosorb P 20-60 DC Lot E055K

Neosorb P 300 DC Lot 18 N

b

Critical ERH the higher the more stable the sample:

g-sorbitol 600µm > g-sorbitol 300µm > g-sorbitol 20-60µm > b-sorbitol

RH0 of g

P. Duflot, Symposium AVH, 2008

RH0 of d

Characterization of the amorphous state

Amorphous state is not a fourth state of matter

-Amorphous means non crystalline. The term amorphous should be

used with an indication of the method of determination of structure.

i.e.: X-Ray amorphous or DSC amorphous…

- What appears to be non crystalline using XRD might be

crystalline if a shorter wavelength is used as is the case for neutron

diffraction or electron diffraction.

-Each method of preparation (freeze-drying, spray drying, milling,

quenched melt… leads to a different amorphous structure:

-amorphous sugar can be classified as a supercooled liquid

(quenched melt), or a microcrystalline solid (freeze-dried,…).

Characterization of the amorphous state

FTIR Spectra of :

V: sucrose quenched melt (Vitreous or glassy)

L: Lyophilized sucrose

C: Crystalline Sucrose

and aqueous solutions at 20°C:

22% (m/m) – dilute

66% (m/m) – saturated

70% (m/m) – supersaturated

Comparison of molecular organization

V – dilute state (no S-S association)

L – Saturated solution (S clustring)

C – supersaturated (pre-nucleation)

Mathlouthi M., Cholli A.L. et Koenig J.L. (1986), Carbohydr. Res., 147, 1-9

Characterization of the amorphous state

DTA Thermograms of sucrose crystalline (C), freeze-dried (FD) and quenched melt (QM)

Mathlouthi M., Cholli A.L. et Koenig J.L. (1986), Carbohydr. Res., 147, 1-9

Tg

Tm

Tr

WATER VAPOUR ADSORPTION KINETICS BY

FREEZE-DRIED SUCROSE

(X-ray amorphous = microcrystalline)

-2

-1

0

1

2

3

4

5

6

7

0 20 40 60 80 100 120

hours

water intake % 20 % r.h.

27 % r.h.

38 % r.h.

44 % r.h.

T = 20 °C

WATER VAPOUR

ADSORPTION KINETICS BY

AMORPHOUS SUGAR AT

DIFFERENT R.H.

WATER RELEASE AFTER

RECRYSTALLIZATION WHICH

TRIGGERS THE CAKING

PHENOMENON

M. Mathlouthi, in Sucrose Prperties and Applications, Blackie, London, 1994

Stability of sugar and polyol powders

Causes of instability of sugar and polyol powders

Powder caking or soft lumping is one of the most frequent instability

observed during storage and transport of bulk sugar and polyol crystals

Sugar caking is a spontaneous phenomenon of adhesion of particles which

change from free flowing behaviour to soft lumps in a first stage and then into

agglomerated non flowing (caked) solid.

The major factors affecting the caking phenomenon are:

Presence of amorphous (microcrystalline) particles, which act as lumping trigger

Quality of crystals (grain size distribution, surface defects, broken crystals,

inclusion of impurities, …)

Water content (total moisture, surface moisture, bound water)

Equilibrium Relative Humidity (or aw ) of sugar

Gradient of Temperature and R.H. in the bag or the silo

Schematic steps of lumping

a) Pendular step: 0 – 44%

b) funicular step: 44-75%

c) capillary step: 75 – 86%

d) drop step: > 86%

E

R

H

Effect of RH on the stability of sugar and polyol powders

DUST FORMATION DURING DRYING

Dust particles are composed of broken crystals (X-ray amorphous): short time high temperature drying is at the origin of dust formation. Also abrasion during screening.

Dust particles act as triggers of caking as RH increases

EFFECT OF CRYSTAL SIZE DISTRIBUTION

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0,3 0,4 0,5 0,6 0,7 0,8 0,9Aw

Wat

er c

onte

nt (g/

Kg

M.S

.)

< 250 µm 400-500 µm 500-800 µm > 800 µm

< 250 m

Fraction 250-400 m

> 800 m

EFFECT OF CRYSTAL SIZE DISTRIBUTION ON WATER

VAPOR ADSORPTION ISOTHERM OF GRANULATED

SUGAR

DELIQUESCENCE

1st Order transformation

Crystaline solid dissolution occurs when the RH is greater

than the deliquescence point RH0

RH0 decreases with increasing Temperature

M. Allan and L. Mauer, 9th Eurofoodwater, Leuven, 2016

Sugar and polyol polymorphs

processability

Dextrose Monohydrate – Anhydrous transition

Dextrose Monohydrate

needles

Dextrose Anhydrous

prisms

Dextrose Anhydrous – Monohydrate transition

Dextrose Monohydrate

needles Anhydrous Dextrose

prisms

Lamellar shape

Dextrose Monohydrate – Anhydrous transition

-Hydrate/anhydrate transition mainly depends on T°

-Transition occurs at T > 50°C with no amorphization

-A zero order kinetics is observed

-Anhydrous/monohydrate transition seems to be

water activity dependent at T < 50°C

-No dissolution or amorphization observed

- Zero order kinetics

Anhydrous a-D -Glucose - Monohydrate transition

pictures

Evolution of crystals during hydration at ERH = 75%

No melting or amorphization observed

Dextrose polymorphs and compressibility

An increase in the moisture content of anhydrous

dextrose produced a corresponding increase in tensile

strength of tablets up to the 8.9% moisture level, possibly

due to a recrystallizing effect.

any further increase in moisture content beyond this

point produced a marked reduction in both tablet tensile

strength and tablet toughness.

The yield forces and percentage porosity obtained

under compression for anhydrous dextrose were

observed to decrease with increasing moisture

content up to a level of 9.20%. For dextrose monohydrate, any increase in moisture

content obtained by exposure to elevated humidity led to

a reduction in both tensile strength and toughness.

Armstrong et al., Drug Development & Industrial Pharmacy, Vol. 12 , Iss. 11-13,1986

To optimize Mannitol crystallization it is needed to:

- determine solubility in pure and technical solutions (with sorbitol)

- determine the MSZW (metastable zone width)

- measure the crystallization rate

- determine the optimal quantity of seed slurry

Mannitol Crystallization

COURBES SOLUBILITE MELANGE

MANNITOL/SORBITOL (g/100g)

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

TEMPERATURES (°c)

G%

GEA

U

75 - 25 50 - 50 35 - 65 Mannitol

Solubility of mannitol in mixtures

Mannitol/sorbitol (g/100g)

Crystal shape

Mannitol Crystallization

Kinetics of water adsorption by mannitol polymorphs

Adsorption of water at 97% R.H. by b - Mannitol (a) and d – Mannitol (b)

The less stable polymorph adsorbs more water more rapidly

Yoshinari et al. , Int J. Pharmaceutics, 247(2002) 69_77

Polymorphic transition and the compressibility

of mannitol

Mannitol is a commonly used non-hygroscopic tabletting excipient

with application in both direct compression and wet-granulation

methods.

water vapour at high relative humidity (97% RH) is sufficient to bring

about b - d polymorphic transition with a consequent increase in

surface area and improved compaction properties.

It is possible to improve the compaction and compression properties

of mannitol by utilising a polymorphic transition induced by moisture

on granulation.

Yoshinari et al. International Journal of Pharmaceutics 258 (2003) 121–131

Crystallization of sorbitol

Molten sorbitol

High speed granulator

Seeding

Maturation

Grinding

Sifting

sorbitol seed fine particles

Crystallization of Sorbitol: DSC of g polymorph

Sorbitol polymorphs change over time to reach the stable g form with Tm = 100°C

P. Duflot, Symposium AVH, 2008

Kinetics of water vapor adsorption of b- and g-

sorbitol

0 5 10 15 20 25 30 35

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

Time (h)

[1]:sorbitol beta

[2] : sorbitol gamma

The most stable polymorph adsorbs less water vapor

Application of Sorbitol polymorphs

Pharmaceutical applications g-Sorbitol needles

g -Sorbitol agglomerates after

milling and sifting

Food applications

P. Duflot, Symposium AVH, 2008

Amorphous sugars and polyols compression (tabletting)

Tabletting conditions

J. BERGGREN, Ph D Thesis, Uppsala, 2003

Amorphous sugars and tabletting

- The tabletting properties of a material may be changed and

the compactability improved if it is made amorphous.

- Crystalline sugars and polyols may be rendered amorphous as

an effect of the size reduction operations.

- Loss of crystallinity after grinding depends on the packing of

molecules (mannitol poor glass former – sorbitol easily amorphized).

- The presence of fine particles increases the points of inter-particle

contact and therefore strengthens cohesion potential of the tablet.

- Sugar crystals contain dislocations, along which chemical bonds

can be broken, for high pressures; After breakage, particles are

reunited, which reinforces the hardness of tablet

INFLUENCE OF FINE PARTICLES RATIO

ON TABLET STABILITY

J.C.. Guyot et al., AVH Symposium, 1997

B: Optimum ratio:

increased inter-

particle contacts

Dispersion Fines/Large particles

Continuous network Dispersion Large/Fine particles

* Patents WO2017013338A1 and WO2010001063A1

By B. Boit, P. Lefèvre, D. Passe (Roquette Frères, 04/07/2008)

Comparison of tabletting processability Lactose vs. Mannitol

Crystallinity of sugars and polyols and

food processes

Effect of sugar grain size on the thickness of biscuit dough

Thickness (mm)

Liquid icing granulated coarse sugar

Hard biscuit dough

Shortbread dough

J.F. Tharault, Colloque A7 CEDUS, Nov. 1994

Effect of sugar grain size on biscuit dough length

Liquid icing granulated coarse sugar

Hard biscuit dough

Shortbread dough

Length (cm)

J.F. Tharault, Colloque A7 CEDUS, Nov. 1994

Crystallinity of sugars and polyols and

food processes

Sugar panning

Core

Sugar

coating

Microcrystals +

concentrated

amorphous solution

In hard panning, there is formation of successive layers of

sucrose microcrystals bonded to each other in a

concentrated amorphous solution.

.water content around 1 to 3%

- size of crystals < 30 microns.

M. Mathlouthi and B. Goguelet, Colloque A7 CEDUS, Nov. 1997

Undesired crystallinity: sugar bloom in frozen icing

Formation of sucrose hydrates at the suface of frozen icing:

- hydrated sucrose clusters (hexamers) organised

tridimensionally in concentrated amorphous solution (CAS).

- short range order; short lifetime; no recent XRD

characterization.

- very low melting points (Tm = 45.7°C for hydrate II (S,

2.5H2O) and 27.8°C for hydrate I (S,3.5H2O).

- High instability of hydrates in concentrated amorphous

solution (CAS)

- slight perturbation (thermal, mechanical, …) leads to

melting or dissolution of hydrates.

CONCLUSIONS

WHAT TO REMEMBER?

Water vapor sorption of pure sugars and polyols exhibit

a right angled change of slope at the hygroscopic point RH0.

RH0 is lowered by the presence of impurities and fine

particles (change in the shape of sorption isotherm).

Amorphous Sugars and polyols are either supercooled

liquids (Quenched melt or concentrated amorphous

solutions –CAS-) or microcrystalline solids (freeze-dried…)

It is recommended to add the technique of detection of

amorphous state (i.e. amorphous to XRD).

Above RH0, flowability decreases, deliquescence, lumping

and caking may occur, in presence of fine particles.

Sugar and Polyol Polymorphs have different processability

properties (Dextrose anhydrous vs. Dextrose Monohydrate;

Mannitol d and b; sorbitol polymorphs)

Tabletting properties improved if crystalline sugars or polyols

are made amorphous (to XRD) by size reduction.

Fine particles have increased inter-particle contacts and

stronger cohesion potential of pharmaceutical tablets.

Polymers (PVP, CMC, …) needed for the stabilization of tablets

and prevention of crystallization of amorphous sugars.

In hard panning, crystallinity of sucrose controlled to obtain

size of 30µm in a concentrated amorphous solution (CAS).

Sucrose Grain size impacts biscuit dough length and

thickness.

Sugar bloom in frozen icing fondant reveals undesired

crystallinity of sucrose hydrates.

CONCLUSIONS