Horse chestnut (Aesculus hippocastanum L.) starch: Basic physico-chemical characteristics and use as thermoplastic material

Full text

Carbohydrate
Polymers
112
(2014)
677–685
Contents
lists
available
at
ScienceDirect
Carbohydrate
Polymers
j
ourna
l
ho
me
page:
www.elsevier.com/locate/carbpol
Horse
chestnut
(Aesculus
hippocastanum
L.)
starch:
Basic
physico-chemical
characteristics
and
use
as
thermoplastic
material
J.
Casta˜
noa,
S.
Rodríguez-Llamazaresb,∗,
K.
Contrerasb,
C.
Carrascoc,∗∗,
C.
Pozob,
R.
Bouzad,
C.M.L.
Francoe,
D.
Giraldof
aUnidad
de
Desarrollo
Tecnológico,
Universidad
de
Concepción,
Avda.
Cordillera
2634,
Coronel,
Chile
bCentro
de
Investigación
de
Polímeros
Avanzados
(CIPA),
Beltran
Mathiew
224,
Concepción,
Chile
cMaterials
Engineering
Department,
Universidad
de
Concepción,
Edmundo
Larenas
270,
Concepción,
Chile
dDepartamento
de
Física,
E.U.P.
Ferrol,
Universidad
de
A
Coru˜
na,
Avda.
19
de
Febrero,
s/n,
15405
Ferrol,
Spain
eDepartamento
de
Engenharia
e
Tecnologia
de
Alimentos,
Universidade
Estadual
Paulista,
R.
Cristóvão
Colombo,
2265
São
José
do
Rio
Preto,
SP,
Brazil
fDepartment
of
Metallurgical
and
Materials
Engineering,
Faculty
of
Engineering,
University
of
Antioquia
UdeA,
Calle
70
No.
52-21,
Medellín,
Colombia
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
29
March
2014
Received
in
revised
form
31
May
2014
Accepted
8
June
2014
Available
online
28
June
2014
Keywords:
Aesculus
hippocastanum
L.
Amylopectin
structure
Thermoplastic
starch
Non-edible
source
a
b
s
t
r
a
c
t
Starch
isolated
from
non-edible
Aesculus
hippocastanum
seeds
was
characterized
and
used
for
prepar-
ing
starch-based
materials.
The
apparent
amylose
content
of
the
isolated
starch
was
33.1%.
The
size
of
starch
granules
ranged
from
0.7
to
35
␮m,
and
correlated
with
the
shape
of
granules
(spherical,
oval
and
irregular).
The
chain
length
distribution
profile
of
amylopectin
showed
two
peaks,
at
polymeriza-
tion
degree
(DP)
of
12
and
41–43.
Around
53%
of
branch
unit
chains
had
DP
in
the
range
of
11–20.
A.
hippocastanum
starch
displayed
a
typical
C-type
pattern
and
the
maximum
decomposition
temperature
was
317 ◦C.
Thermoplastic
starch
(TPS)
prepared
from
A.
hippocastanum
with
glycerol
and
processed
by
melt
blending
exhibited
adequate
mechanical
and
thermal
properties.
In
contrast,
plasticized
TPS
with
glyc-
erol:malic
acid
(1:1)
showed
lower
thermal
stability
and
a
pasty
and
sticky
behavior,
indicating
that
malic
acid
accelerates
degradation
of
starch
during
processing.
©
2014
Elsevier
Ltd.
All
rights
reserved.
1.
Introduction
The
growing
accumulation
of
plastic
residues
in
landfills
and
oceans
and
the
strong
dependency
of
plastic
production
on
fossil
petroleum
resources
have
stimulated
research
on
bio-based
plas-
tic
alternatives.
Starch
is
a
renewable
and
inherently
biodegradable
raw
material
of
low-cost
that
can
be
transformed
into
bio-plastics
with
technologies
currently
used
for
manufacturing
synthetic
plastics.
The
worldwide
production
of
starch-based
plastics
is
esti-
mated
to
exceed
150,000
tons/year
(European
Bioplastic,
2014).1
Thermoplastic
starch
(TPS)
can
be
obtained
by
physical
mod-
ification
of
starch,
mixing
starch
with
a
plasticizer,
with
and
without
shear
stress,
at
temperatures
over
100 ◦C.
Water,
the
main
∗Corresponding
author.
Tel.:
+56
41
2661216;
fax:
+56
41
2751233.
∗∗ Corresponding
author.
Tel.:
+56
41
2207170;
fax:
+56
41
2203391.
E-mail
addresses:
s.rodriguez@cipachile.cl
(S.
Rodríguez-Llamazares),
ccarrascoc@udec.cl
(C.
Carrasco).
1Bioplastic
facts
and
figures.
European
Bioplastic
2013
(http://en.european-
bioplastics.org/multimedia/).
plasticizer
of
TPS,
is
used
together
with
other
plasticizers,
such
as
polyols
(sorbitol,
xylitol,
pentaerythritol
and
glycerol),
sugar
alco-
hols
and
non-ionic
and
anionic
surfactants
(Vieira,
da
Silva,
dos
Santos,
&
Beppu,
2011).
There
are
many
reports
of
starch
coming
from
different
botanical
sources
to
prepare
TPS.
In
most
studies
starch
comes
from
edible
fruits,
vegetables,
seeds
and
so
on
(van
Soest,
Benes,
de
Wit,
&
Vliegenthart,
1996;
Zullo
&
Iannace,
2009).
The
use
of
edible
sources
for
fabrication
of
plastics
is
controversial,
especially
in
developing
countries
with
a
deficit
of
arable
land
and
food.
Therefore,
non-edible
starch
has
gained
much
attraction
for
use
in
starch-based
materials
(Bharadwaj,
2010).
TPS
has
limited
use
in
the
plastic
industry
because
its
mechani-
cal
properties
depends
on
the
humidity
condition,
(Bertuzzi,
Castro
Vidaurre,
Armada,
&
Gottifredi,
2007;
Han,
2014,
chap.
9).
An
alternative
to
reduce
water
absorption
of
TPS
is
the
chemical
modification
of
starch
before
or
during
melt
blending.
When
the
modification
is
made
during
the
extrusion,
the
process
is
known
as
reactive
extrusion.
Poly(carboxylic
acid)s
such
as
citric,
tartaric
and
malic
acids
have
been
used
as
cross-linking
agents
and
co-
plasticizers
to
elaborate
TPS.
Poly(carboxylic
acid)s
delay
water
uptake,
retrogradation
and
improve
mechanical
properties
of
TPS
http://dx.doi.org/10.1016/j.carbpol.2014.06.046
0144-8617/©
2014
Elsevier
Ltd.
All
rights
reserved.

678
J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
(Shi
et
al.,
2007)
and
are
also
non-toxic
and
of
low-cost.
Zuraida,
Yusliza,
Anuar,
and
Mohd
Khairul
Muhaimin
(2012)
reported
the
preparation
of
TPS
from
Malaysian
sago
and
different
ratios
of
citric
acid
and
glycerol.
TPS
prepared
with
glycerol:citric
acid
ratio
of
1:1
showed
higher
tensile
strength
than
those
prepared
only
with
glycerol.
Jiugao,
Ning,
and
Xiaofei
(2005)
showed
by
FTIR
spec-
troscopy
and
X-ray
diffractometry
that
citric
acid
reduced
hydrogen
bonding
between
starch
and
glycerol
during
storage,
inhibiting
the
formation
of
amylose–glycerol
inclusion
complexes
and
therefore
the
formation
of
V-type
structures
associated
with
re-crystallized
starch
(i.e.
retrogradation).
Citric,
malic
and
tartaric
acids
were
also
used
as
a
cross-linking
agent
of
starch/poly(butyene
adipate
co-terephthalate)
blends
to
improve
the
compatibility
of
the
poly-
meric
phase.
However,
these
organic
acids
promote
the
hydrolysis
of
starch,
degrading
them
to
dextrin
and
fragments
of
low
molecu-
lar
weight
(Olivato,
Grossmann,
Yamashita,
Eiras,
&
Pessan,
2012).
It
would
be
interesting
to
explore
the
effect
of
malic
acid
on
TPS
plasticized
by
glycerol,
because
of
its
lower
tendency
to
pro-
mote
chemical
modification
of
starch
(Olivato,
Grossmann,
Bilck,
&
Yamashita,
2012;
Olivato
et
al.,
2012b;
Ruxanda
&
Teac ´
ˆ
a,
2012).
An
attractive
source
of
non-edible
starch
is
the
seed
of
horse
chestnut
(Aesculus
hippocastanum
L.),
which
a
starch
content
over
35
wt.%
(ˇ
Cukanovi´
c
et
al.,
2011).
The
horse
chestnut
was
introduced
in
Chile
around
XVIII
century
with
arrival
of
European
immigrants,
and
due
to
its
exceptional
adaptability
has
spread
throughout
the
whole
country.
It
is
often
found
as
ornamental
trees
in
urban
communities
and
in
grassland
of
Chilean
fields.
Currently,
seeds
of
A.
hippocastanum
are
used
for
ornamental
purposes,
but
most
of
them
end
up
in
landfills.
Most
reports
related
to
seeds
of
A.
hippocastanum
are
focused
on
their
biochemical
composition
and
morphoanatomical
character;
however,
we
have
not
found
detailed
studies
about
the
chemical
and
physical
characteristics
of
A.
hip-
pocastanum
starch.
In
this
work,
A.
hippocastanum
starch
was
characterized
and
used
to
prepare
TPS
by
the
melt
blending
method.
We
studied
the
rheological,
mechanical
and
thermal
properties
of
this
TPS
and
the
effect
of
incorporating
malic
acid
as
co-plasticizer.
In
addi-
tion,
we
compared
the
morphological
and
mechanical
properties
of
TPS
from
A.
hippocastanum
starch
with
TPS
from
starch
of
Arau-
caria
araucana
seeds,
an
edible
source
with
C-type
semi-crystalline
structure
and
excellent
precursor
for
starch-based
materials
with
adequate
performance
(Casta˜
no,
Bouza,
Rodríguez-Llamazares,
Carrasco,
&
Vinicius,
2012).
2.
Experimental
2.1.
Materials
Starch
of
ripe
A.
hippocastanum
seeds,
collected
at
the
campus
of
the
University
of
Concepción,
Chile,
was
isolated
by
the
wet
milling
method.
The
plasticizers
used
were
glycerol
(99.5%
purity)
and
dl-
malic
acid
(99%
purity)
supplied
by
Oceanquímica
S.A.
(Valparaíso,
Chile)
and
Sigma
Aldrich
(Santiago,
Chile),
respectively.
2.2.
Characterization
of
A.
hippocastanum
starch
Physical–chemical
and
morphological
features
of
A.
hippocas-
tanum
starch
granules
are
summarized
in
Table
1.
Ash
and
moisture
content
were
determined
gravimetrically
in
triplicate
according
to
ASTM
D1102-56
and
Chilean
Standard
176/1
of
84,
respectively.
Nitrogen
content
was
assessed
by
using
Kjendhal
technique
(AOAC,
1990).
Swelling
power
(g/g
of
starch
on
dry
weight)
and
solubility
(g/g
of
starch
on
dry
weight)
were
determined
in
triplicate
using
the
method
reported
by
Singh,
McCarthy,
Singh,
Moughan,
and
Kaur
(2007).
In
short,
a
suspension
of
A.
hippocastanum
starch
was
Table
1
Physico-chemical
and
morphological
features
of
A.
hippocastanum
starch.
%
Small
granule
size
(0.5–10
␮m)a30.7
%
Medium
granule
size
(11–30
␮m)a67.6
%
Large
granule
size
(>31
␮m)a1.7
Moisture
contentb7.1
±
0.1
Ash
content
0.20
Apparent
amylose
content
(%)
33
Nitrogen
content
0.5
±
0.1
Phosphorus
content
(%)
0.0118
Calcium
content
(%) 0.0179
Sulfur
content
(%)
0.0033
Potassium
content
(%)
0.0465
Swelling
power
(g/g
of
starch
on
dry
weight)
6.5
±
0.2
Solubility
(g/g
of
starch
on
dry
weight)
3.1
±
0.1
Color
White
aDetermined
by
laser
diffraction
particle
size
analyzer.
bDeterminated
by
thermogravimetric
analyzer.
heated
at
60 ◦C
for
30
min
followed
by
centrifugation
at
4000
rpm
for
30
min.
The
supernatant
was
decanted
and
dried
over
night
at
70 ◦C
(soluble
solid).
The
solid
residue
of
centrifugation
was
weighed
for
swelling
power
measurement.
The
apparent
amylose
content
was
assessed
by
using
a
col-
orimetric
method
according
to
EN
ISO
6647
parts
I
and
II,
which
is
based
on
amylose–iodine
complex
formation.
The
absorbance
was
measured
at
620
nm
by
using
an
UV
spectrophotometer
(UV
mini
–
1240
Shimadzu,
Japan).
The
particle
size
distribution
was
determined
with
a
laser
diffraction
particle
size
analyzer
(Beck-
man
Coulter
LSTM 200,
Brea
CA,
USA).
At
least
three
measurements
were
done
to
obtain
the
average
particle
size
distribution
curves.
The
phosphorus,
sulfur,
calcium
and
potassium
content
were
quan-
tified
by
X-ray
fluorescence
spectrometry
(S4
Pioneer,
Bruker-AXS,
Germany).
5
g
of
powdered
starch
were
mounted
on
prolene
films,
and
analyzed
under
helium
atmosphere.
The
results
were
evaluated
by
SpectraPlus
v.1.6
spectrometer
software
(Socabim).
Thermal
stability
of
A.
hippocastanum
starch
was
evaluated
by
thermo-
gravimetric
analyses
(TGA).
Morphological
of
starch
granules
was
examined
with
scanning
electron
microscopy.
X-ray
diffraction
(XRD)
was
used
to
analyze
crystalline
structure
of
starch
granules.
A.
hippocastanum
starch
was
debranched
using
isoamylase
3U
(Megazyme
International,
Ireland)
enzyme
according
to
Wong
and
Jane
(1995).
The
branch
chain
length
distribution
of
amy-
lopectin
was
analyzed
according
to
Moraes,
Alves,
and
Franco
(2013)
using
high-performance
anion-exchange
chromatography
with
pulsed
amperometric
detector
(HPAEC-PAD)
system
(ICS
3000,
Dionex
Corporation,
Sunnyvale,
USA)
equipped
with
an
AS40
automatic
sampler.
Samples
were
filtered
(0.22
␮m
membrane)
and
injected
into
the
HPAEC-PAD
system
(20
␮L
sample
loop).
The
flow
rate
was
0.8
mL/min
at
40 ◦C.
The
standard
quadru-
ple
potential
(E)
waveform
was
employed
with
the
following
periods
and
pulse
potentials:
E1
=
0.10
V
(t1=
0.40
s);
E2
=
−2.00
V
(t2=
0.02
s);
E3
=
0.60
V
(t3=
0.01
s);
E4
=
−0.10
V
(t4=
0.06
s).
All
elu-
ents
were
prepared
with
ultrapure
water
(18
m
cm)
with
N2
sparging.
Eluent
A
was
150
mM
NaOH
and
eluent
B
was
500
mM
sodium
acetate
and
150
mM
NaOH.
The
branched
chains
of
amy-
lopectin
were
separated
using
a
Dionex
CarboPacTM
PA-100
guard
column
(4
×
50
mm)
and
a
Dionex
CarboPacTM
PA-100
column
(4
×
250
mm).
The
gradient
of
eluent
B
was
28%
at
0
min,
40%
at
15
min,
and
72%
at
105
min.
The
data
were
analyzed
using
the
Chromeleon
software,
version
6.8
(Dionex
Corporation,
USA).
The
analyses
were
performed
in
duplicate.
2.3.
Preparation
of
thermoplastic
starch
Before
melt-blending,
A.
hippocastanum
starch
and
plasticizers
were
premixed
by
hand
at
room
temperature.
A
Brabender
internal
mixer
(Plastograph®EC
plus,
Mixer
50EHT32,
Germany)
was
used

J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
679
Table
2
Composition,
rheological
and
tensile
properties
of
TPS.
Sample
code
A.
hippocas-
tanum
starch
(wt.%)
A.
araucana
starch
(wt.%)
Malic
acid
(wt.%)
Glycerol
(wt.%)
Torque
maximum
(N
m)
Plasticization
energy
(N
m/min)
Steady
state
(N
m)
Tensile
modulus
(MPa)
Tensile
strength
(MPa)
Elongation
at
break
(%)
CG-30
70
–
–
30
30.5
9.0
15.1
3.0
±
0.3a1.5
±
0.1
1.02
±
0.04
1.5
±
0.2b
0.3
±
0.2c
CG-MA-30
70
–
15
15
38.5
14.6
6.8
PG-30
–
70
–
30
22.8
8.8
17.4
4.0
±
0.5a2.4
±
0.2
1.14
±
0.07
2.0
±
0.3b
0.8
±
0.2c
PG-MA-30
–
70
15
15
31.5
10.9
4.4
a10%.
b30%.
c90%
at
unitary
deformation
of
strain.
to
prepare
TPS.
The
samples
were
blended
at
120 ◦C
and
60
rpm
for
15
min
and
torque
variation
as
a
function
of
time
was
recorded.
The
torque
values
of
maximum
peak
and
steady
state,
and
the
plasti-
cization
energy
were
determined
from
the
torque
rheometer
data
(see
Table
2).
The
integral
of
the
torque
curve,
from
time
zero
(when
all
the
components
were
in
the
mixing
chamber)
to
the
time
where
the
maximum
torque
is
reached,
was
reported
as
the
plasticization
energy
(Casta˜
no,
Rodríguez-Llamazares,
Carrasco,
&
Bouza,
2012).
Samples
were
labeled
specifying
the
type
of
starch
and
the
type
and
wt.%
of
the
plasticizer
agent.
For
example,
in
the
label
CG-MA-
30
C
corresponded
to
A.
hippocastanum
starch,
G
to
glycerol,
MA
to
malic
acid
and
30
to
the
wt.%
of
plasticizers
used
to
prepare
TPS,
i.e.
in
this
case
15
wt.%
of
glycerol
and
15
wt.%
of
malic
acid.
Table
2
summarizes
composition
of
thermoplastic
starch.
CG-30
and
PG-30
samples
for
tension
tests
were
injection-
molded
by
using
a
Minijet
II
(Haake
Thermo
Scientific,
Waltham,
USA),
under
the
following
conditions:
130 ◦C
of
cylinder
tempera-
ture,
55 ◦C
of
mold
temperature,
and
300
bar
of
injection
pressure.
To
compare
mechanical
and
morphological
properties
of
TPS
from
A.
hippocastanum
and
from
A.
araucana,
the
latter
was
prepared
using
the
same
condition
as
described
above.
2.4.
Characterization
of
thermoplastic
starch
2.4.1.
Scanning
electron
microscopy
(SEM)
Morphology
of
A.
hippocastanum
starch
granules
and
of
cryo-
genically
fractured
surface
of
the
mechanical
test
specimens
of
TPS
obtained
by
injection
molding
(sputtered
with
a
gold
coating
of
ca.
50
nm)
were
observed
at
200×,
600×
and
1000×
magnifications
with
a
field
emission
scanning
electron
microscope
(JEOL
JSM
6380
LV,
Tokyo,
Japan)
operated
at
15
kV.
2.4.2.
Thermogravimetric
analysis
(TGA)
Thermal
stability
of
A.
hippocastanum
starch
and
TPS
was
eval-
uated
using
a
thermogravimetric
analyzer
NETZSCH
209
F3
TGA
(Tarsus,
Selb,
Germany).
TGA
tests
were
carried
out
at
10 ◦C/min
under
nitrogen
atmosphere
(20
mL/min),
from
30
to
900 ◦C
for
A.
hippocastanum
starch
and
from
30
to
600 ◦C
for
TPS.
2.4.3.
X-ray
diffraction
(XRD)
X-ray
diffraction
analysis
of
A.
hippocastanum
starch
and
TPS
was
performed
using
a
Bruker
Endeavour
diffractometer
(model
D4/max-B,
Germany)
with
Cu
K␣
radiation
(40
kV
and
20
mA).
The
spectra
were
recorded
over
a
2
range
of
4–35◦at
steps
of
0.02◦
and
time
per
step
of
0.02◦/s.
Peak
fitting
analysis
was
done
using
a
Gaussian
distribution
function.
Degree
of
crystallinity
was
cal-
culated
using
the
method
reported
by
Frost,
Kaminski,
Kirwan,
Lascaris,
and
Shanks
(2009).
2.4.4.
Fourier
transform
infrared
spectroscopy
(FTIR)
The
FTIR
spectra
of
A.
hippocastanum
starch
and
TPS
were
recorded
in
triplicate
at
room
temperature
with
a
Jasco
FTIR
4100
spectrophotometer
(USA)
in
the
range
of
4000–600
cm−1at
2
cm−1
resolution.
The
background
and
sample
spectra
were
scanned
64
times
in
transmittance
mode.
About
5
mg
of
finely
ground
solid
sample
was
ground
with
90
mg
of
dry
potassium
bromide
and
a
7
mm
pellet
was
formed
under
high
pressure.
Data
was
analyzed
with
spectral
manager
Version
2.
The
data
preprocessing
consisted
of
smoothing
and
manual
baseline
correction.
For
comparison,
the
spectra
were
normalized
by
using
the
band
at
1459
cm−1,
related
to
the
symmetric
deformation
of
CH2of
starch
(Cael,
Koenig,
&
Blackwell,
1975),
which
does
not
change
with
treatment
(Morán,
Vázquez,
&
Cyras,
2013).
2.4.5.
Tensile
properties
Tensile
tests
were
performed
according
to
ASTM
D638
standard
on
a
Karg
Industrietechnik
universal
testing
machine
(Krailling,
Germany)
using
a
type
V
dumbbell
specimen.
The
crosshead
speed
was
set
at
5
mm/min.
Tensile
strength,
percent
of
elongation
at
break
and
Young’s
modulus
at
10%,
30%
and
90%
of
strain
were
calculated
from
the
stress–strain
curves.
At
least
7
individual
mea-
surements
were
carried
out
for
each
formulation.
3.
Results
and
discussion
3.1.
Characterization
of
A.
hippocastanum
starch
Starch
granules
of
A.
hippocastanum
seed
accumulate
funda-
mentally
in
parenchyma
cells
of
cotyledons.
The
size
of
oval
parenchyma
cells
found
was
around
86
␮m,
considering
only
the
large
part
of
the
cells
(see
complementary
information,
Fig.
A1).
This
value
is
similar
to
the
value
reported
by
Musatenko,
Generalova,
Martyn,
Vedenicheva,
and
Vasyuk
(2003)
for
parenchyma
cells
of
mature
A.
hippocastanum
seeds
collected
in
Kiev,
Ukraine.
Inside
cells,
a
fiber
network
associated
to
cytoskeletal
elements
was
also
observed.
Fig.
1
shows
a
SEM
image
and
the
size
distribution
of
starch
gran-
ules
isolated
from
A.
hippocastanum.
Starch
granules
in
parenchyma
cells
are
of
diverse
shape
and
size.
The
size
of
granules
is
linked
to
their
shape,
thus,
small
granules
(0.7–9.5
␮m)
are
spherical,
the
medium
(10–17
␮m)
are
oval
and
the
larger
size
(18–35
␮m)
are
irregular
(for
620
granules
counted).
The
granule
surface
is
smooth
without
pores
and
erosion.
A
typical
bimodal
size
distribution
of
A.
hippocastanum
starch
granules
is
shown
in
Fig.
1B.
Around
10%
of
granules
have
sizes
between
0.4
and
3.5
␮m
(first
interval)
and
the
remainder
granules
ranged
from
3.6
to
37
␮m
(second
interval).
Only
5%
of
granules
are
over
30
␮m
in
size.

680
J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
Fig.
1.
(A)
SEM
micrograph
and
(B)
particle-size
distribution
of
A.
hippocastanum
starch.
The
apparent
amylose
content
of
isolated
A.
hippocastanum
starch
was
(33.1
±
0.1%),
considerably
higher
than
the
14.2%
and
13.8%
of
coarse
granules
and
fine
granules,
respectively,
of
A.
hippocastanum
starches
from
Bratislava,
Slovak
reported
by
Hricovíniová
and
Babor
(1992).
The
differences
in
amylose
content
can
be
attributed
to
their
different
source
and
cultivar
zone,
the
starch
isolation
procedure,
and
the
analytical
methods
used.
They
used
dimethyl
sulfoxide
in
the
isolation
procedure
and
the
amylose
content
was
determined
biamperometrically
by
sorption
of
iodine.
In
Fig.
2
a
normalized
HPAEC-PAD
chromatogram
shows
the
branch
chain
length
distribution
of
amylopectin
from
A.
hippocas-
tanum
starch.
There
are
two
peaks,
the
first
one
at
DP
=
12
(the
most
abundant
branch
unit
chain)
and
the
second
one
at
DP
41–43.
A
shoulder
at
DP
18–22
is
also
observed.
Average
DP
of
branch
chains
of
amylopectin
was
18.89
±
0.05.
The
proportion
of
amylopectin
unit
chains
of
DP
6–12,
13–24,
25–36
and
≥37
were
31.51%,
48.08%,
10.85%
and
9.56%,
respectively.
Previous
work
showed
correlations
among
chain
length
distribution
of
amylopectin
and
crystalline
structure
of
starch,
granule
size,
swelling
power
or
gelatinization
temperature.
Singh
et
al.
(2012)
found
that
low
size
granules
of
10–30
␮m
from
different
rice
bean
lines
contained
higher
amount
of
DP
11–20
branch
unit
chains
of
amylopectin
than
large
size
granules
of
30–105
␮m.
Around
53%
of
branch
unit
chains
of
A.
hip-
pocastanum
starch
showed
a
DP
of
11–20,
characteristic
of
small
size
granules.
The
type
of
semi-crystalline
structure
of
starch
granules
depends
on
the
DP
of
external
branch
chains
of
amylopectin
(Jane,
2009,
chap.
6).
A-type
starches
have
a
larger
proportion
of
short
B1-
and
A-chains,
which
are
located,
with
their
ends
free
and
Fig.
2.
Profile
of
amylopectin
branch
chain
length
distribution
of
A.
hippocastanum
starch
analyzed
by
HPAEC-PAD.
unrestricted,
in
one
cluster.
B-type
starches
have
longer
B-chains
(B2-,
B3-
and
B4-chains)
that
may
extend
through
multiple
clusters
and
are
restricted
in
their
movements.
Jane
et
al.
(1999)
analyzed
branch
chain-length
of
amylopectin
of
starch
isolated
from
differ-
ent
botanical
sources
and
found
some
trends
of
branch
chain-length
distribution
for
starches
with
the
same
crystalline
type.
A-type
starches
had
15.6–27.4%
of
short
chains
(DP
6–12)
and
6.6–26.7%
of
long
chains
(DP
>
37),
in
contrast
to
B-type
starches
that
had
8.5–12.3%
and
26.1–29.5%
of
short
and
long
chains,
respectively.
Similar
results
were
reported
by
Srichuwong,
Sunarti,
Mishima,
Isono,
and
Hisamatsu
(2005a),
but
with
26.4–36.3%
(narrower
range)
of
branch
chains
with
DP
9–12
for
A-type
starches.
A.
hip-
pocastanum
starch
displayed
substantial
amounts
of
short
chains
of
DP
6–12
(31.5%)
and
very
few
long
chains
(9.6%),
showing
a
diffrac-
tion
pattern
characteristic
of
semi-crystalline
structure
of
type
C,
as
will
be
discussed
later.
Each
starch
displays
its
own
chain-length
distribution
profile
of
amylopectin,
and
therefore
it
is
not
surpris-
ing
that
A.
hippocastanum
starch
is
not
following
the
trend
found
by
Jane
et
al.
(1999).
The
proportion
of
each
branch
chain
and
aver-
age
chain
length
of
A.
hippocastanum
starch
was
within
the
range
reported
for
other
C-type
starches
(Chung
&
Liu,
2012).
The
values
of
swelling
power
and
solubility
of
A.
hippocastanum
starch
are
shown
in
Table
1.
The
ability
of
starch
to
swell
in
excess
water,
as
well
as
its
solubility,
is
mainly
related
to
variations
in
chain
branch
length
distribution
of
amylopectin
and
phospho-
rus
content.
Srichuwong,
Sunarti,
Mishima,
Isono,
and
Hisamatsu
(2005b)
proposed
that
swelling
power
is
associated
with
the
unit-
chain
ratio
(APC)
of
amylopectin,
i.e.
the
ratio
of
relative
molar
distribution
of
amylopectin
unit-chains
with
DP
6–12
to
that
of
DP
6–24.
A
larger
proportion
of
short
chains
increased
the
swelling
power
of
starch
granules,
due
to
short
chains
forming
short
and
weak
double
helices,
decreasing
the
stability
of
crystalline
packag-
ing.
The
APC
ratio
of
A.
hippocastanum
starch
was
0.396,
similar
to
starch
granules
of
lesser
yam,
which
had
C-type
structure
and
its
swelling
power
at
70 ◦C
was
around
8
g/g.
The
difference
in
swelling
properties
among
starches
is
also
attributed
to
phosphorus
compounds,
such
as
phospholipids
and
phosphate
monoesters.
Phospholipids
form
water
insoluble
com-
plexes
with
amylose
during
heating,
retarding
starch
granule
swelling,
while
phosphate
monoesters
on
long-branch
chains
of
amylopectin
decrease
the
interaction
between
double
helices,
facil-
itating
water
penetration
and
therefore
granular
swelling.
The

J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
681
Fig.
3.
X-ray
diffraction
pattern
of
A.
hippocastanum
starch.
average
total
phosphorus
content
of
starch
from
A.
hippocastanum
was
0.0118%.
This
value
was
higher
than
that
reported
for
starch
from
Aesculus
assamica
(0.0016%)
cultivated
in
India
(Soni,
Sharma,
&
Bisen,
1989),
both
belonging
to
the
same
genus.
It
is
interesting
to
observe
that
the
swelling
power
of
A.
hippocastanum
starch
is
twice
of
that
of
A.
assamica
starch,
which
tentatively
can
be
attributed
to
the
lower
P
content
of
the
latter.
Unfortunately,
we
found
no
reports
about
branch
chain
length
distribution
of
amylopectin
iso-
lated
from
A.
assamica.
The
X-ray
diffraction
pattern
of
A.
hippocastanum
starch
is
shown
in
Fig.
2.
A.
hippocastanum
starch
displays
a
characteris-
tic
C-type
pattern
with
diffraction
peaks
at
2
=
5.7◦,
15.4◦,
17.2◦,
22.0◦and
22.7◦.
The
C-type
pattern
is
not
characteristic
of
all
starches
from
the
seed
of
genus
Aesculus.
For
example,
starch
from
Aesculus
indica
shows
an
A-type
pattern
(Wani
et
al.,
2014).
The
degree
of
crystallinity
of
A.
hippocastanum
starch
was
calculated
using
a
simple,
quick
and
objective
method
(Frost
et
al.,
2009).
Amorphous
background
scattering
was
estimated
using
an
iterative
smoothing
algorithm.
The
value
of
degree
of
crystallinity
found
was
10.7%,
which
is
lower
than
that
of
starch
from
A.
Araucana
(15.1%)
(Casta˜
noet
al.,
2012a).
Both
starches
have
a
C-type
structure
and
the
degree
of
crystallinity
was
calculated
using
the
same
values
of
polynomial
order,
number
of
iteration
and
point
of
window.
Thermal
stability
of
native
A.
hippocastanum
starch
was
analyzed
by
TGA.
Fig.
3
shows
the
TGA
and
derivative
of
the
TG
curves
(DTG)
of
starch
in
the
temperature
range
of
20–900 ◦C.
The
TGA/DTG
curves
revealed
three-steps
of
decomposition.
The
small
weight
loss
(around
7%)
between
30
and
140 ◦C
was
attributed
to
the
evap-
oration
of
water
from
starch
granules.
The
percentage
of
weight
loss
in
this
step
was
similar
to
the
moisture
content
of
A.
hippocastanum
starch
determined
gravimetrically.
After
240 ◦C
the
weight
loss
rate
quickly
increased
and
two
degradation
steps
were
distinguished
at
249
and
317 ◦C
with
a
weight
loss
of
5.5%
and
38.4%,
respectively.
The
third
degradation
step
between
289
and
400 ◦C
was
attributed
to
intermolecular
dehydration
to
levoglucosan
and
some
volatile
products,
such
as
carbon
dioxide,
lower
aldehydes,
methylfuranes,
and
ketones.
The
residue
at
900 ◦C
of
around
10%,
probably
belongs
to
char
of
oxidized
organic
matter
and
inorganic
substances,
such
as
calcium,
sulfur
and
potassium,
detected
by
X-ray
fluorescence
spectrometry.
FTIR
spectrum
of
A.
hippocastanum
starch
in
the
2000–800
cm−1
region
is
shown
in
Fig.
5.
Starches
from
different
botanical
sources
have
similar
FTIR
spectra
and
the
absorption
bands
have
been
assigned
in
many
previous
reports
(Cael
et
al.,
1975;
Santha,
Sudha,
Vijayakumari,
Nayar,
&
Moorthy,
1990).
The
broad
band
at
3416
cm−1was
assigned
to
O–H
stretching
vibration
and
the
sharp
band
at
2930
cm−1to
C–H
bond
stretching
of
methine
group
of
glucose
rings.
The
band
at
1646
cm−1was
attributed
to
ı(O–H)
bending
vibration
of
water.
The
bands
at
1459
and
1419
cm−1were
assigned
to
the
bending
vibrations
of
methylene
group
and
the
band
at
1369
cm−1was
ascribed
to
C–H
symmetric
bending
vibration
of
methyl
group.
The
stretching
vibration
bands
of
C–C
and
C–O
appears
in
the
region
at
1300–800
cm−1.
Their
intensity
has
been
related
to
amorphous
and
crystalline
phases
of
starch.
In
particu-
lar,
the
intensity
of
band
at
1019
cm−1decreases
with
increasing
of
amorphous
state
(van
Soest,
Tournois,
de
Wit,
&
Vliegenthart,
1995).
3.2.
Characterization
of
TPS
from
A.
hippocastanum
starch
3.2.1.
Evaluation
of
processability
by
torque
rheometry
The
torque-rheometer
plots
as
a
function
of
time
showed
three
steps
for
TPS:
an
increasing
torque
from
the
beginning
until
a
maximum
value
is
reached,
attributed
to
a
plasticization
pro-
cess,
followed
by
a
stage
of
continuously
decreasing
values,
and
finally
the
steady
state.
The
torque
values
of
maximum
peak
and
steady
state,
and
the
plasticization
energy
are
summarized
in
Table
2.
TPS
prepared
from
A.
hippocastanum
starch
had
higher
plastifi-
cation
energies
and
maximum
torques
than
those
from
A.
araucana
starch.
The
type
of
plasticizer
employed
in
the
preparation
of
TPS
also
affected
the
values
of
plasticization
energy
and
torque
in
steady
state;
plasticization
energy
was
higher
for
glycerol:malic
acid
plasticized
TPS
than
for
glycerol
plasticized.
TPS
with
malic
acid
presented
the
higher
viscosity
(first
and
second
step)
due
to
the
reduction
of
mobility
of
the
polymeric
chains
as
a
result
of
chemical
modification
of
starch
by
malic
acid.
Olivato
et
al.
(2012a)
reported
that
multifunctional
organic
acids,
such
as
malic
acid,
were
able
to
interact
with
the
hydroxyl
groups
of
starch;
carboxyl
and
ester
groups
were
formed
during
reactive
extrusion,
promoting
esterifi-
cation
and
trans-esterification
reactions
of
starch.
Once
starch
granules
were
destructurized,
the
torque
decreased
until
reaching
a
steady
state.
CG-MA-30
and
PG-MA-30
samples
showed
the
lowest
torques
in
steady
state
(see
Table
2),
because
multifunctional
organic
acids
also
promote
the
acid
hydrolysis
of
the
glycosidic
linkages
of
starch,
decreasing
the
molecular
weight
of
amylose
and
amylopectin,
as
well
as
the
degree
of
polymerization
of
the
amylopectin
molecules
(Da
Róz,
Zambon,
Curvelo,
&
Carvalho,
2011).
Similar
behavior
of
rheological
properties
was
reported
by
Jiugao
et
al.
(2005)
for
glycerol
plasticized
starch
modified
with
citric
acid.
On
the
other
hand,
the
time
required
to
reach
steady
state
depended
on
the
type
of
plasticizer
and
type
of
starch
(see
Fig.
A2).
The
time
was
around
4
min
for
samples
without
malic
acid,
8
min,
for
the
CG-MA-30
sample,
and
11
min
for
the
PG-MA-30
sam-
ple.
Glycerol:malic
acid
plasticized
TPS
showed
a
slight
downward
trend
with
time
in
steady
state,
indicating
a
continuous
but
small
change
in
viscosity
of
these
samples.
The
reduction
of
viscosity
of
TPS
with
malic
acid
is
attributed
not
only
to
the
decrease
of
molec-
ular
weight
of
starch,
but
also
to
less
branch
chains
of
amylopectin
participating
in
the
formation
of
entanglements
structures
with
the
outer
chains
of
other
amylopectin,
or
with
amylose
(van
Soest
et
al.,
1996).
3.2.2.
Scanning
electron
microscopy
SEM
images
of
the
fractured
surfaces
(Fig.
6)
displayed
continu-
ous
phases.
However,
some
broken
starch
granules
were
detected
in
the
rough
fractured
surface
of
the
CG-30
sample
(Fig.
6A).
The
broken
granules
were
completely
embedded
in
the
TPS
matrix.
No
signs
of
granule
pullout
and
pits
on
the
surface,
and
no
obvious

682
J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
Fig.
4.
TGA
and
DTG
curves
of
(A)
A.
hippocastanum
starch
and
(B)
TPS.
gaps
at
the
irregular
interfaces
between
the
broken
granule
and
the
matrix
were
observed.
Thus,
the
addition
of
30
wt.%
of
glycerol
in
the
CG-30
sample
was
not
enough
for
achieving
complete
plasti-
cization
of
TPS
under
used
processing
conditions.
Similar
results
were
reported
by
Qiao,
Tang,
and
Sun
(2011)
and
Mao,
Imam,
Gordon,
Cinelli,
and
Chiellini
(2000).
As
reported
previously
the
PG-30
sample
exhibited
a
rough
and
homogenous
surface
without
granules
(Casta˜
no
et
al.,
2012b).
CG-MA-30
and
PG-MA-30
samples
presented
smooth
and
homogenous
fractured
surfaces
with
some
randomly
distributed
holes.
Ma,
Chang,
Yu,
and
Stumborg
(2009)
reported
that
pits
found
in
fractured
surface
of
glycerol:citric
acid
plasticized
TPS
were
due
to
exfoliation
of
non-destructured
starch
granules.
However,
frag-
ments
or
entire
granules
were
not
observed
at
the
surface
of
these
samples,
as
expected
for
concentrations
of
organic
acids
higher
than
1
wt.%,
which
promote
the
disruption
and
dissolution
of
starch
granules
(Jiugao
et
al.,
2005).
3.2.3.
Thermal
stability
TGA
curves
of
TPS
exhibited
similar
behavior
with
three
steps
of
decomposition
(Fig.
4B).
Loss
weight
varied
slowly
from
room
tem-
perature
up
to
100 ◦C,
with
a
weight
loss
of
about
2%.
The
maximum
decomposition
temperature
(Tmax)
and
associated
weight
loss
at
each
decomposition
step
depended
on
starch
source
and
plasticizer
used.
Glycerol:malic
acid
plasticized
TPS
exhibited
lower
thermal
stability
than
TPS
prepared
with
glycerol
alone,
due
to
a
reduction
of
molecular
weight
of
starch
chains
by
acid
hydrolysis
(Jiugao
et
al.,
2005).
Thermal
degradation
at
the
first
step
of
decomposition
was
asso-
ciated
to
loss
of
low
molecular
weight
substances
such
as
water
and
glycerol.
Tmax of
first
step
of
CG-30
sample
(176.9 ◦C)
was
higher
than
that
of
PG-30
(156.9 ◦C)
due
to
the
lower
water
content
of
A.
hippocastanum
(7.0
wt.%)
compared
to
A.
araucana
(8.1
wt.%).
With
decreasing
water
content
of
TPS
the
boiling
point
of
glycerol–water
mixture
increases.
This
behavior
is
more
pronounced
at
weight
fraction
of
water
lower
than
10
wt.%
in
water/glycerol
mix-
tures
(Chen
&
Thompson,
1970).
The
second
decomposition
peak
appeared
in
the
range
of
277–282 ◦C
for
TPS
prepared
with
glycerol
and
in
the
range
of
257–262 ◦C
for
glycerol:malic
acid
plasticized
TPS,
and
was
mainly
associated
to
evaporation
of
glycerol.
Note
that
weight
loss
at
Tmax of
second
peak
was
one-third
less
in
glycerol:malic
acid
plasticized
TPS.
After
300 ◦C
the
weight
loss
cor-
responds
to
dehydration
and
decomposition
of
starch
(Liu,
Xie,
Yu,
Chen,
&
Li,
2009).
As
expected,
the
values
of
Tmax of
the
third
step
only
depended
on
starch
source,
being
301.9
and
306.9 ◦C
for
TPS
prepared
with
A.
hippocastanum
starch
and
with
A.
araucana
starch,
respectively.
The
residual
weight
percentage
of
TPS
prepared
with
glyc-
erol:malic
acid
was
higher
than
those
prepared
with
glycerol.
Similar
results
were
reported
by
Shi
et
al.
(2007).
They
attributed
the
increasing
of
residual
weight
to
the
tendency
of
char
formation
of
esterified
starch.
3.2.4.
FTIR
analysis
The
changes
in
FTIR
spectra
between
2000
and
800
cm−1of
A.
hippocastanum
starch
plasticized
with
glycerol
alone
and
with
glyc-
erol:malic
acid
by
melt
blending
are
shown
in
Fig.
4.
The
intensity
of
bands
between
1200
and
950
cm−1decreased
in
TPS,
due
to
the
destructuration
and
decreasing
crystallinity
of
starch
(van
Soest
et
al.,
1995).
In
particular,
the
band
at
1019
cm−1,
associated
to
C–O
bond
of
C–O–C
in
starch
(Jiugao
et
al.,
2005),
was
not
observed
in
CG-30
and
CG-MA-30
spectra.
However,
the
band
at
1052
cm−1
(shoulder
in
FTIR
spectrum
of
A.
hippocastanum
starch)
was
shifted
to
a
lower
wave
numbers
in
CG-30
(1039
cm−1)
and
CG-MA-30
(1035
cm−1)
samples.
The
shift
of
band
at
1052
cm−1to
lower
wave
numbers
(around
13
cm−1)
in
TPS
prepared
with
glycerol
could
be
due
to
the
formation
of
hydrogen
bonds
among
C–O–H
and
C–O–C
groups
of
starch
and
OH
of
glycerol.
In
glycerol:malic
acid
plasti-
cized
TPS
this
shift
was
higher
(around
17
cm−1),
probably
due
to
hydroxyl
and
carboxyl
groups
of
poly(carboxylic
acid)
interacting
stronger
with
C–O–H
and
C–O–C
groups
in
starch
than
with
glyc-
erol.
A
new
strong
band
appeared
at
1739
cm−1on
FTIR
spectrum
of
CG-MA-30
sample,
which
corresponds
to
C
O
ester
carbonyl
group
stretching.
The
peak
at
1739
cm−1is
associated
to
the
ester
bond
in
esterified
starch
(Diop,
Li,
Xie,
&
Shi,
2011;
Ma
et
al.,
2009).
3.2.5.
Tensile
properties
The
effect
of
starch
source
(A.
hippocastanum
and
A.
araucana)
on
the
tensile
properties
of
glycerol
plasticized
TPS
is
shown
in
Table
2,
where
tensile
modulus,
tensile
strength
and
elongation
at
break
of
TPS
are
summarized.
Note
that
tensile
modulus,
i.e.
tan-
gent
modulus,
was
calculated
at
10%,
30%
y
90%
of
strain,
because
the
samples
did
not
present
Hookean
behavior.
PG-30
compared
with
CG-30
exhibited
higher
values
of
tensile
properties.
Tensile
strength
was
60%
and
tensile
modulus
at
high
deformation
of
strain
was
almost
200%
higher;
the
rigidity
and
higher
strength
of
PG-30
was
associated
to
the
absence
of
residual
starch
granules
at
frac-
tured
surfaces
(Fig.
6B)
and
the
higher
apparent
amylose
content
of
A.
araucana
starch.
Chaudhary,
Torley,
Halley,
McCaffery,
and
Chaudhary
(2009)
studied
the
effect
of
amylose
content
on
tensile
properties
of
TPS
from
maize
obtained
by
melt
blending,
and
con-
cluded
that
high
amylose
TPS
tend
to
be
tougher
due
to
the
higher

J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
683
Fig.
5.
FTIR
spectrum
of
A.
hippocastanum
starch
and
TPS.
Fig.
6.
SEM
micrographs
of
fracture
surfaces
of
molded
TPS
specimens:
(A)
CG-30;
(B)
PG-30;
(C)
CG-MA-30
and
(D)
PG-MA-30.
degree
of
interactions
among
the
double
helix
structure
of
amylose
and
the
outer
chains
of
amylopectin.
The
entanglement
between
amylose
and
amylopectin
gave
a
TPS
material
with
a
denser
poly-
mer
network.
Glycerol:malic
acid
plasticized
TPS
prepared
exhibited
a
sticky
behavior,
making
it
impossible
to
remove
the
specimens
from
the
mold
without
plastic
deformation.
The
sticky
behavior
was
attributed
to
the
fact
that
malic
acid
(15
wt.%)
promoted
acid
hydrolysis
of
the
glycosidic
linkages
in
starch.
Da
Róz
et
al.
(2011)
correlated
the
reduction
of
viscosity
and
the
stickiness
of
TPS
pre-
pared
with
glycerol:water:poly(carboxylic
acid)
with
the
decrease
of
molecular
weight
in
starch.
4.
Conclusion
A.
hippocastanum
L.
seed
is
an
attractive
source
of
non-edible
starch
for
the
production
of
starch-based
materials.
This
seed
is
easily
collected
and
presently
ends
up
in
landfills.
Starch
isolated
from
A.
hippocastanum
seed
shows
a
bimodal
size
distribution
with
characteristic
shapes
for
each
mode.
A.
hippocastanum
starch
dis-
played
a
typical
C-type
diffraction
pattern.
The
high
swelling
power
of
this
starch
is
due
to
the
proportion
of
short
branch
chains
of
amylopectin
(APC
ratio
=
0.396)
and
phosphorous
content
(0.012%).
Glycerol
plasticized
TPS
from
A.
hippocastanum
and
from
A.
aura-
cana
starch
showed
similar
rheological
and
thermal
properties.

684
J.
Casta˜
no
et
al.
/
Carbohydrate
Polymers
112
(2014)
677–685
Tensile
strength
and
young
modulus
were
lower
for
TPS
from
A.
hip-
pocastanum.
The
fractured
surface
of
glycerol
plasticized
TPS
from
A.
hippocastanum
starch
displayed
residual
starch
granules.
The
use
of
malic
acid
at
15
wt.%
as
co-plasticizer
adversely
affected
thermal
and
mechanical
properties
of
TPS
plasticized
by
glycerol.
Glycerol:malic
acid
plasticized
TPS
exhibited
pasty
and
sticky
behavior,
which
can
be
attributed
to
increasing
depolymer-
ization
of
starch
molecules
by
acid
hydrolysis
promoted
by
malic
acid.
Acknowledgments
This
work
has
been
financed
by
CONICYT-REGIONAL
R08C1002
and
Programa
de
Financiamiento
Basal
para
Centros
Científicos
y
Tecnológicos
de
Excelencia
PFB-27,
Projects
InnovaChile
13IDL2-
23120
and
Fondef
D09I1195.
Appendix
A.
See
Figs.
A1
and
A2.
Fig.
A1.
Storage
parenchyma
cells
from
cotyledon
of
mature
A.
hippocastanum
seed.
Fig.
A2.
Torque
variation
as
a
function
of
time
for
TPS.
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