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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