Depolymerization of sodium alginate under hydrothermal conditions

Article abstract of DOI:10.1016/j.carbpol.2009.11.032

The depolymerization of sodium alginate with hydrothermal treatment (180-240 °C) was studied to understand the selectivity of monosaccharide generation. Alginate depolymerized to oligosaccharides, monosaccharides and decomposition products that included lactic acid and glycolic acid. Alginate depolymerization under hydrothermal conditions occurred in a manner that initially released mannuronic acid (M) and then was followed by the release of guluronic acid (G). Monosaccharides were generated through the hydrolysis of the glycosidic bonds between the unit monomer with different selectivities among M-M, M-G and G-G units rather than random sites within alginate. Hydrothermal treatments shows promise as a method to modify the structure of alginate polymers. Crown Copyright

Full text of DOI:10.1016/j.carbpol.2009.11.032

Carbohydrate Polymers 80 (2010) 296–302
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Depolymerization of sodium alginate under hydrothermal conditions
a
b
a,b
Taku Michael Aida a, , Takuji Yamagata , Masaru Watanabe , Richard L. Smith Jr.
*
a Graduate School of Environmental Studies, Tohoku University, Sendai, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan
b Research Center of Supercritical Fluid Technology, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 October 2009
Received in revised form 13 November 2009
Accepted 18 November 2009
Available online 22 November 2009
The depolymerization of sodium alginate with hydrothermal treatment (180–240 °C) was studied to
understand the selectivity of monosaccharide generation. Alginate depolymerized to oligosaccharides,
monosaccharides and decomposition products that included lactic acid and glycolic acid. Alginate depo-
lymerization under hydrothermal conditions occurred in a manner that initially released mannuronic
acid (M) and then was followed by the release of guluronic acid (G). Monosaccharides were generated
through the hydrolysis of the glycosidic bonds between the unit monomer with different selectivities
among M–M, M–G and G–G units rather than random sites within alginate. Hydrothermal treatments
shows promise as a method to modify the structure of alginate polymers.
Keywords:
Alginate
Mannuronic acid
Guluronic acid
Polysaccharide
Monosaccharide
Decomposition
Hydrolysis
Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
Hydrothermal
Depolymerization
1. Introduction
the 1–4 glycosidic linkages split in a b-elimination pathway, result-
ing in unsaturated non reducing terminals. Acid (Chandia, Matsu-
Alginate is a linear hetero polysaccharide that consists of two-
unit monosaccharides, -mannuronic acid (M) and -guluronic acid
hiro, & Vasquez, 2001; Haug & Larsen, 1962; Haug et al., 1966)
and base (Haug et al., 1967a; Niemela & Sjostrom, 1985) methods
are fast, but require harsh chemicals.
D
L
(G) that occur in homo polymeric M blocks, homo polymeric G
blocks and hetero polymeric random MG blocks (Haug, Larsen, &
Smidsrod, 1967b). The physical and chemical properties of alginate
change with its molecular weight and M/G ratio that vary accord-
ing to its origin (Gacesa, 1988; Haug, Myklesta, Larsen, & Smidsrod,
1967c). In science, some of the main uses of alginate is in tissue
engineering (Augst, Kong, & Mooney, 2006), drug carrier studies
(Tonnesen & Karlsen, 2002) and materials synthesis (Lu, Gao, &
Komarneni, 2004). The design and tailoring of alginate polymers
with the suitable molecular weight and monomer distribution is
important in these applications (Draget, Smidsrod, & Skjak-Braek,
2002; Gacesa, 1988).
Present methods for depolymerizing alginate are enzymatic
(Murata et al., 1993), acidic (Haug, Larsen, & Smidsrod, 1966; Haug
et al., 1967b; Yang, Li, & Guan, 2004), alkali (Haug, Larsen, & Smids-
rod, 1967a; Niemela & Sjostrom, 1985), and thermal treatment
(Holme, Lindmo, Kristiansen, & Smidsrod, 2003). Enzymatic assays
with alginate lyases, require long reaction times (ca. days) in which
Hydrothermal treatment, on the other hand, provides a method
that is rapid for modifying the polymer properties without using
harsh chemicals (Akiya & Savage, 2002; Brunner, 2009; Kruse,
2009). Hydrothermal treatment has been used for hydrolysis of
cellulose (Hayashi, Fujita, Irie, Sasaki, & Shibata, 2004; Sasaki, Fang,
Fukushima, Adschiri, & Arai, 2000), starch (Nagamori & Funazukuri,
2004), guar gum (Miyazawa & Funazukuri, 2006) and alginate
(Holme, Davidsen, Kristiansen, & Smidsrod, 2008; Matsushima
et al., 2005). In a previous study, Matsushima et al. (2005) studied
the decomposition of alginate in subcritical water and supercritical
water at temperatures from 250 to 375 °C with the goal to produce
homopolymers. Their work showed that they could obtain a homo-
polymer containing 98% guluronic acid at 250 °C in 88 ms reaction
time.
Since the reaction in supercritical water and subcritical water is
very fast, the depolymerization sequence undoubtedly occurs at
hydrothermal conditions and could allow the modification of
alginate molecular weight distributions. In this work, the objective
was to study the reaction of alginate under hydrothermal
conditions (180–250 °C) and to develop
a scheme for its
* Corresponding author. Fax: +81 795 5864.
depolymerization.
E-mail address: aida@scf.che.tohoku.ac.jp (T.M. Aida).
0144-8617/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbpol.2009.11.032

T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
297
7:3. The norharmane–acetonitrile solution was prepared by mixing
norharmane (10 mg) with acetonitrile (1 mL). Aliquots were placed
on a stainless steel sample plate and then ionized by nitrogen laser
pulses.
2. Experimental
2.1. Materials and methods
2.1.1. Materials
Sodium alginate (300–400 mPa s) was obtained from Wako
Pure Chemical Industries and was used as received. The character-
istics of the sodium alginate, which were determined by gel per-
meation chromatography (GPC), differential thermal gravitical
analyzer (TG) and 1H NMR, are shown in Table 1.
Pullulan standard P-82 with known molecular weight, from 5.9
to 404 kDa, was obtained from Showa Denko and was used for con-
structing the calibration curve for the GPC analysis. Mannuronic
and guluronic acid standards were prepared by procedures in the
literature (Konno & Oba, 2007) and analysis with HPLC chromatog-
raphy showed no other peaks. Distilled water was purified by a dis-
tillation apparatus (CPW-100, Advantec) and had a conductivity of
2.1.2.4. 1H NMR analysis. The ratio between mannuronic acid and
guluronic acid within the alginate was analyzed by an 1H NMR
technique given in the literature (Grasdalen, 1983; Grasdalen, Lar-
sen, & Smidsrod, 1979). The 1H NMR spectra were recorded with a
400 MHz spectrometer (Brunker Biospin DPX-400) at 80 °C and 80
scans. After the product was freeze-dried, the solid was dissolved
in 0.6 mL of D2O containing 0.1% acetonitrile as internal standard
(r
= 2.06 for the methyl group).
The G% and GG% of the alginate were calculated by a literature
method (Grasdalen, 1983; Grasdalen et al., 1979), and used three
peak areas, A, B, C, as defined next. The area of A was defined as
d = 4.95ꢀ5.17 (H-1 of guluronate), that of B was defined as
d = 4.55ꢀ4.82 (H-5 of guluronate and H-1 of mannuronate) and
that of C was defined as d = 4.40ꢀ4.50 (H-5 of guluronate), where
G% and GG% were calculated by the following equations:
5.5 lS/m.
2.1.2. Analytical methods
High performance liquid chromatography (HPLC) was used in
both qualitative and quantitative analyses of the monosaccharides,
mannuronic acid and guluronic acid. Gel permeation chromatogra-
phy (GPC) and matrix-assisted laser desorption/ionization time-of-
flight mass spectrometry (MALDI-TOF-MS) analyses were con-
ducted to follow changes in the molecular weight distribution of
the alginate. 1H NMR analysis was conducted to evaluate the
monomer sequence in the alginate polymer chain. Total organic
carbon (TOC) analyses were used to check the carbon balances.
area of A
ðarea of BÞ þ ðarea of CÞ
G%½%ꢁ ¼
ꢂ 100
ð1Þ
ð2Þ
area of C
ðarea of BÞ þ ðarea of CÞ
GG%½%ꢁ ¼
ꢂ 100
2.1.2.1. HPLC analysis. The HPLC analysis were used to quantify
mannuronic acid and guluronic acid. The HPLC system was
equipped with a refractive index (RI) detector (RI SE-61, SHODEX),
two RSpak KC-811 columns (Showa Denko) and H3PO4 aqueous
solution (5 mM) was used as mobile phase at a flow rate of
1.0 mL/min at 60 °C. The products mannuronic acid and guluronic
acid were quantified according to the calibration curve constructed
previously by the standards. Peaks corresponding to lactic acid and
glycolic acid were not quantified due to their small amounts.
2.1.2.5. TOC analysis. The total carbon concentration of the liquid
product was analyzed by TOC (Shimadzu, model TOC-5000A) and
the carbon recovery of the liquid phase was evaluated. The carbon
balances of the experiments conducted at 180 °C were approxi-
mately 96% for reaction times of 6 min and 59% at 14 min, 50% at
30 min. The decrease of carbon recovery indicated that hydrother-
mal treatment produced carbon products that were not soluble in
the liquid phase. It was observed that both solid and gas products
formed especially at the longer reaction times.
2.1.2.2. GPC analysis. The GPC system was equipped with an RI
detector (RI-1530, JASCO), an auto sampler (AS-2055plus, JASCO)
and column oven (CO-2065plus, JASCO). Asahipak GS-220HQ col-
umn and GS-520HQ column (Showa Denko) were used, and NaNO3
aqueous solution (0.3 M) was used as the mobile phase at a flow
rate of 1.0 mL/min at 60 °C. The calibration of the GPC was con-
ducted by using pullulan P-82 standards.
2.1.3. Procedure
An aqueous solution of sodium alginate with a concentration of
2.0 wt.% was prepared prior to the experiments. The alginate solu-
tion (3.0 g) was loaded into stainless steel tube (SUS316) batch
reactors that had an inner volume of 6.0 cm3. Before heating, each
reactor was purged with Ar gas to removal air and then sealed.
Heating of the reactor was initiated by immersion of the reactor
into a molten salt bath that was controlled at the desired reaction
temperature to within 3 °C. The reaction temperatures chosen for
study were 180, 200, 220 and 240 °C. The reaction was terminated
by transferring the reactor from the molten salt bath to a water
bath that was at room temperature. The reaction time was defined
as the time when the reactor was first placed into the molten salt
bath until the reactor was quenched in the water bath. The temper-
ature profile in the reactor was measured by using a batch reactor
having a thermocouple placed in the liquid phase of the solution.
The time required for the reactor to reach the reaction temperature
(200 °C) was 2 min, while the time for cooling to below 100 °C was
30 s. Experiments conducted at 2 min reaction time, therefore,
have higher uncertainty in the results. After the reactor was cool,
its content was washed with distilled water and the effluent ana-
lyzed. At least three experiments were conducted for each reaction
condition. The average and the deviation of the yields are shown as
data points and error bars in the graphs.
2.1.2.3. MALDI-TOF-MS analysis. Direct measurement of molecular
weights of the product compounds was confirmed with MALDI-
TOF-MS. The MALDI-TOF-MS spectra were recorded with an AXI-
MA-CFR Plus (AXIMA-CFR Plus, Shimadzu) in the reflectron and
the negative ion mode by collecting mass spectra with a nitrogen
laser at 337 nm. Samples for the analyses were prepared by mixing
0.5 lL of the product solution with 0.5 lL of the matrix solution.
The matrix solution was prepared by mixing a norharmane–aceto-
nitrile solution and trifluoroacetic acid (0.1 M) at a volume ratio of
Table 1
Characterization of sodium alginate used in this work: weight average molecular
weight (Mw), water content, mannuronic acid content (M), guluronic acid content (G)
and M/G ratio.
Mw (Da)
Water content (%)
14
M%
57
G%
43
M/G ratio (ꢃ)
1.3
4.2 ꢂ 105

298
T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
high hydrophilia and also its self-catalytic nature due to the car-
3. Results and discussion
boxylic acid in its chemical structure (Smidsrod, Haug, & Larsen,
1966) that promotes hydrolysis earlier than when polysaccharides
are treated under hydrothermal conditions. The conditions for dis-
solution of polysaccharides has noted to be important in hydro-
thermal decomposition reaction of cellulose (Ogihara, Smith,
Inomata, & Arai, 2005).
Fig. 2(a–d) shows the individual yields of mannuronic acid and
guluronic acid as a function of reaction time for each temperature.
Mannuronic acid gave higher yields than guluronic acid at low
reaction times, but its yield decreased to a value below that of
guluronic acid as reaction time increased. This means that the
decomposition of alginate under hydrothermal conditions proba-
bly occurred in a manner in which mannuronic acid was initially
released and was severed at the glycosidic bonds between mannu-
ronic–mannuronic (M–M) groups. The results show the possibility
for selective recovery of monosaccharides with hydrothermal
treatment.
3.1. General characteristics of hydrothermal treated samples
Reaction of a 2 wt.% solution of alginate at 180 °C for 6, 14 and
30 min gave product solutions that became progressively darker
(Figs. S1 and SI) which indicated rapid reaction of alginate. Some
general characteristics of the reacted solutions are noted here be-
fore discussing the results in detail. HPLC chromatograms of the
product solutions had identifiable peaks with a retention time cor-
responding to glycolic acid and lactic acid and also unidentifiable
peaks (Figs. S2 and SI). It was observed qualitatively that the re-
acted solutions had viscosities that were progressively lower
according to the reaction time, which suggests that the hydrother-
mal treatment caused the molecular weight of the alginate to de-
crease. The decrease in molecular weight is discussed later with
the obtained GPC chromatograms. The pH of the raw material in
solution was 7.1. After the reaction, the pH of the solutions were
4.8, 4.7 and 4.9 for 6, 14 and 30 min hydrothermal treated samples,
respectively. The decrease in pH for hydrothermal treated solu-
tions confirmed the formation of water soluble acids. In the exam-
ination of the reactor contents, gases were formed as well as solids,
especially at the larger reaction times (ca. 14 min), however, these
were not quantified.
3.3. Alginate decomposition pathway
In the previous section, it was shown that alginate monosac-
charides, mannuronic and guluronic acid, exhibited different reac-
tion times for peak (maximum) yields and also that those
compounds had different reactivities under hydrothermal condi-
tions. GPC, MALDI-TOF-MS and 1H NMR analyses were conducted
to study the decomposition pathway of alginate. The reaction
products at 180 °C were chosen to study in detail, since monosac-
charides yield were high and alginate decomposition were slow
enough to follow.
3.2. Generation of mannuronic acid and guluronic acid
Fig. 1 shows results for the combined yield of monosaccharides,
mannuronic and guluronic acid, as a function of reaction time over
the range of temperatures studied. The combined monosaccharide
yield as given by the peak in the data at each temperature tended
to increase and then decrease as reaction time progressed, which is
evidence that the initial monosaccharides formed subsequently
decomposed. The highest combined monosaccharide yield for each
temperature was shifted to shorter reaction times as the reaction
temperature became higher, which is similar to previous observa-
tions for monomeric species obtained from hydrothermal treat-
ment of cellulose (Hayashi et al., 2004), starch (Nagamori &
Funazukuri, 2004) and guar gum (Miyazawa & Funazukuri, 2006).
The highest combined monosaccharide yield of alginate is much
lower than that which can be obtained for other polysaccharides
(Hayashi et al., 2004; Miyazawa & Funazukuri, 2006; Nagamori &
Funazukuri, 2004). Alginate monosaccharides, mannuronic and
guluronic acid, are much more reactive than cellulose and its olig-
omers. The lower decomposition temperatures of alginate com-
pared with cellulose, starch or guar gum, can be explained by its
Fig. 3 shows a GPC chromatogram of alginate treated under
hydrothermal conditions for various reaction times. The raw algi-
nate solution had
a weight average molecular weight of
4.2 ꢂ 105 Da. Product molecular weight distribution shifted to-
wards lower values as reaction time increased. At 6 min (Fig. 3),
alginate decomposed into monosaccharides as designated by the
arrow that marks the monosaccharide peak (mannuronic acid
and guluronic acid). From the GPC results (Fig. 3), it can be seen
that compounds having molecular weights that were lower than
the monosaccharides were formed. As the reaction time increased
to 10 min (Fig. 3), the molecular weight distribution shifted to-
wards smaller values, which indicates an increase in monosaccha-
rides and decomposition products. At 20 min reaction time (Fig. 3),
the intensity of the monosaccharide peak decreased compared
with results for 10 min reaction time and the peak representing
the decomposition products increased. Acids and low molecular
weight products were most likely formed through the decomposi-
tion of the monosaccharides, however, they could have also been
formed as alginate undergoes depolymerization. In an attempt to
distinguish between these possible pathways, MALDI-TOF-MS of
the product solutions was measured as discussed next.
20
180oC
200oC
Fig. 4 shows a representative MALDI-TOF-MS chart of the prod-
uct solution obtained from treating alginate under hydrothermal
conditions at 180 °C for 10 min. High intensity readings were ob-
served at 723, 795, 898, 1072, 1246, 1418 m/z where 795 m/z is
the peak for the matrix used (Fig. 4). These results show that oligo-
saccharides were produced during the hydrothermal treatment of
alginate. The molecular weight of the unit monosaccharides of algi-
nate (mannuronic acid or guluronic acid) is 176, which was practi-
cally equal to the mass difference observed between neighboring
peaks in the spectra. The consistent differences between the peaks
are evidence that the decomposition of alginate under hydrother-
mal conditions proceeds through the hydrolysis of the glycosidic
bonds between the unit monomer and not through random sites
within alginate. If random decomposition of the alginate occurred,
the MALDI-TOF-MS spectrum should give a broad molecular distri-
15
220oC
240oC
10
5
0
0
5
10
15
20
30
Reaction time [min]
Fig. 1. Combined yield of mannuronic and guluronic acid as a function of reaction
time obtained from treating alginate under hydrothermal conditions at 180, 200,
220 and 240 °C.

T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
299
a
b
15
15
10
Mannuronic acid
Guluronic acid
Mannuronic acid
Guluronic acid
10
5
0
5
0
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Reaction time [min]
Reaction time [min]
6
6
c
d
Mannuronic acid
Guluronic acid
Mannuronic acid
Guluronic acid
4
2
0
4
2
0
0
2
4
6
8
10
0
2
4
6
8
10
Reaction time [min]
Reaction time [min]
Fig. 2. Yield of mannuronic and guluronic acid as a function of reaction time obtained from treating alginate under hydrothermal conditions at (a) 180 °C, (b) 200 °C, (c)
220 °C and (d) 240 °C.
bution that does not have a characteristic difference of 176 be-
tween the neighboring peaks. Therefore, the decomposition prod-
ucts that were observed at 180 °C for 6 min in Fig. 3 were most
likely generated from monosaccharides rather than from alginate
directly. Under hydrothermal conditions, it can be concluded that
the decomposition of monosaccharides to small molecular weight
compounds readily occurs.
The decomposition of alginate under hydrothermal conditions
seems to occur through an acid hydrolysis pathway and not
through the base hydrolysis b-elimination pathway. In a previous
study (Haug, Smidsrod, & Larsen, 1963) it was reported the rate
of base hydrolysis of alginate is significantly lower than the acid
hydrolysis at conditions of pH below 5. We acknowledge that the
pH of the hydrothermal treated samples were in the range of
4.7–4.9.
Mannuronic and Guluronic acid
In Fig. 2, it was shown that mannuronic acid was initially
formed and then guluronic acid was subsequently formed for all
of the temperatures that were studied. This indicates that a selec-
tive hydrolysis occurred between the four types of glycosidic bonds
(M–M, M–G, G–M and G–G) in some sequence as depolymerization
proceeded.
(a)
(b)
To understand the hydrolysis pathway between these different
glycosidic bonds, we conducted 1H NMR analysis and evaluated the
monomer sequence in the alginate polymer chain. Fig. 5 shows a
typical 1H NMR spectrum of alginate solution that was treated un-
der hydrothermal conditions. Table 2 shows the monomer compo-
sition and sequence of the alginate before and after hydrothermal
treatment. The monomer composition in the alginate decreased for
mannuronic acid and increased for guluronic acid after hydrother-
mal treatment. Selective hydrolysis of mannuronic acid seem to oc-
cur, which is consistent with the HPLC analyses in Fig. 2. The
results also showed that as the GG sequence increased, MM de-
creased and MG did not show any change, which indicates that
selective hydrolysis occurs at the M–M glycosidic bonds rather
than at the G–G glycosidic bonds.
(c)
(d)
6
8
10
12
14
16
18
Retention time [min]
Fig. 3. Gel permeation chromatograms of product solutions obtained from treat-
ment of a 2 wt.% alginate solution under hydrothermal conditions at 180 °C with RI
detector. (Reaction times: (a) raw material, (b) 6 min, (c) 10 min and (d) 20 min).

300
T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
matrix
795.30
5
4
898.86
723.92
6
1072.87
789.31
7
930.21
1246.04
899.83
777.60
805.19
1073.86
724.92
725.22
8
952.25
1126.01
1064.59
924.24
1247.03
1248.03
1418
796.30
861.05
1073.21
918.29
996.15
700
800
900
1000
1100
1200
1300
1400
Mass / Charge
Fig. 4. Number of monosaccharide units of product (bold numerals) after treatment under hydrothermal conditions determined from MALDI-TOF-MS. Conditions: 2 wt.%
alginate concentration, hydrothermal treatment at 180 °C and 6 min reaction.
Fig. 5. 1H NMR spectrum of a 2 wt.% alginate solution treated under hydrothermal conditions (180 °C and 6 min reaction time).
Table 2
perature changed the order of the kinetic rates of the hydrolysis of
Mannuronic acid (M) and guluronic acid (G) composition of sodium alginate before
and after hydrothermal treatment according to 1H NMR analysis. Conditions: 2 wt.%
these three (M–G, M–M, G–G) glycosidic bonds. A study on the
decomposition kinetics of alginate using a flow apparatus, having
better control of reaction time and temperatures, might provide
better understanding to these kinetic effects.
sodium alginate in water and reaction temperature of 180 °C.
M%
G%
GG%
MG%
MM%
Raw material
6 min
10 min
57
51
17
43
49
83
18
24
42
25
25
n.p.
32
26
n.p.
Based on the results obtained in this work, a reaction path-
way can be proposed for the decomposition of alginate under
hydrothermal conditions (Scheme 1). In the proposed pathway,
the decomposition of alginate occurs by hydrolysis at the glyco-
sidic bonds with different selectivities. We consider that this is a
result from the difference in the kinetics of hydrolysis of the
three types of glycosidic bonds in the order of M–M, M–G and
G–G. Initially mannuronic acid is produced from alginate and
then guluronic acid forms from a G-rich alginate oligomer. After
mannuronic acid forms, it decomposed rapidly to water soluble
acids, solids and gas.
n.p., not present.
Previous studies on decomposition of alginate under acidic con-
ditions suggest that the selective hydrolysis occur at the MG glyco-
sidic bonds (Haug & Larsen, 1963). These studies have been
conducted at lower temperatures (100 °C) than used in this work.
According to the results in this work, increasing the reaction tem-

T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
301
Scheme 1. Depolymerization pathway of sodium alginate under hydrothermal conditions.
4. Conclusions
Appendix A. Supplementary data
The reaction of alginate under hydrothermal conditions was
studied. Alginate depolymerizes under hydrothermal conditions
to monosaccharides, in a manner that initially releases mannu-
ronic acid and then is followed by the release of guluronic acid.
The decomposition reaction of alginate is promoted by increas-
ing temperature, however, the monosaccharide yields decrease
with increasing temperature. As the reaction proceeds, monosac-
charide decomposition occurs. The decomposition of alginate oc-
curs by hydrolysis at the glycosidic bonds, however, different
selectivities exist between M–M, M–G and G–G units. Selective
production of MM, MG or GG oligomers or of monosaccharides,
mannuronic acid and guluronic acid, may be possible by using
the kinetic differences of hydrolysis with hydrothermal treat-
ment. Experiments are in progress on studying the molecular
weight modification with a flow apparatus and will be reported
in the future.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carbpol.2009.11.032.
References
Akiya, N., & Savage, P. E. (2002). Roles of water for chemical reactions in high-
temperature water. Chemical Reviews, 102, 2725–2750.
Augst, A. D., Kong, H. J., & Mooney, D. J. (2006). Alginate hydrogels as biomaterials.
Macromolecular Bioscience, 6, 623–633.
Brunner, G. (2009). Near critical and supercritical water. Part I. Hydrolytic and
hydrothermal processes. Journal of Supercritical Fluids, 47, 373–381.
Chandia, N. P., Matsuhiro, B., & Vasquez, A. E. (2001). Alginic acids in Lessonia
trabeculata: Characterization by formic acid hydrolysis and FT-IR spectroscopy.
Carbohydrate Polymers, 46, 81–87.
Draget, K. I., Smidsrod, O., & Skjak-Braek, G. (2002). Biopolymers. In A. Steinbuchel
(Ed.). Polysaccharides II: Polysaccharides from Eukaryotes (Vol. 6, pp. 215–245).
Weinheim: Wiley-VCH Verlag GmbH.
Gacesa, P. (1988). Alginates. Carbohydrate Polymers, 8, 161–182.
Grasdalen, H. (1983). High-field, 1H NMR spectroscopy of alginate – Sequential
structure and linkage conformations. Carbohydrate Research, 118, 255–260.
Grasdalen, H., Larsen, B., & Smidsrod, O. (1979). P.M.R. study of the composition and
sequence of uronate residues in alginates. Carbohydrate Research, 68, 23–31.
Haug, A., & Larsen, B. (1962). Quantitative determination of uronic acid composition
of alginates. Acta Chemica Scandinavica, 16, 1908–1918.
Acknowledgments
We thank Dr. Masao Konno, Riken Shokuhin Co. Ltd. (Japan,
Miyagi), for providing the monosaccharides standards. We thank
Mr. Hiroaki Saito (Tohoku University, Japan) for the NMR analysis,
Ms. Aya Haneda (Tohoku University, Japan) for the MALDI-TOF-MS
analysis. Financial support from Global COE (Tohoku University) is
gratefully acknowledged.
Haug, A.,
& Larsen, B. (1963). Solubility of alginate at low pH. Acta Chemica
Scandinavica, 17, 1653–1662.
Haug, A., Larsen, B., & Smidsrod, O. (1966). A study of constitution of alginic acid by
partial acid hydrolysis. Acta Chemica Scandinavica, 20, 183–190.
Haug, A., Larsen, B., & Smidsrod, O. (1967a). Alkaline degradation of alginate. Acta
Chemica Scandinavica, 21, 2859–2870.

302
T.M. Aida et al. / Carbohydrate Polymers 80 (2010) 296–302
Haug, A., Larsen, B., & Smidsrod, O. (1967b). Studies on sequence of uronic acid
residues in alginic acid. Acta Chemica Scandinavica, 21, 691–704.
Haug, A., Myklesta, S., Larsen, B., & Smidsrod, O. (1967c). Correlation between
chemical structure and physical properties of alginates. Acta Chemica
Scandinavica, 21, 768–778.
subcritical and supercritical water. Industrial & Engineering Chemistry Research,
44, 9626–9630.
Miyazawa, T., & Funazukuri, T. (2006). Noncatalytic hydrolysis of guar gum under
hydrothermal conditions. Carbohydrate Research, 341, 870–877.
Murata, K., Inose, T., Hisano, T., Abe, S., Yonemoto, Y., Yamashita, T., et al. (1993).
Bacterial alginate lyase – Enzymology, genetics and application. Journal of
Fermentation and Bioengineering, 76, 427–437.
Haug, A., Smidsrod, O., & Larsen, B. (1963). Degradation of alginates at different pH
values. Acta Chemica Scandinavica, 17, 1466–1468.
Hayashi, N., Fujita, S., Irie, G., Sasaki, M., & Shibata, M. (2004). Reaction kinetics of
cellulose decomposition in hot compressed water. Journal of the Japan Institute
of Energy, 83, 805–814.
Nagamori, M., & Funazukuri, T. (2004). Glucose production by hydrolysis of starch
under hydrothermal conditions. Journal of Chemical Technology and
Biotechnology, 79, 229–233.
Holme, H. K., Davidsen, L., Kristiansen, A., & Smidsrod, O. (2008). Kinetics and
mechanisms of depolymerization of alginate and chitosan in aqueous solution.
Carbohydrate Polymers, 73, 656–664.
Niemela, K., & Sjostrom, E. (1985). Alkaline-degradation of alginates to carboxylic-
acids. Carbohydrate Research, 144, 241–249.
Ogihara, Y., Smith, R. L., Inomata, H., & Arai, K. (2005). Direct observation of cellulose
dissolution in subcritical and supercritical water over a wide range of water
densities (550–1000 kg/m3). Cellulose, 12, 595–606.
Holme, H. K., Lindmo, K., Kristiansen, A.,
& Smidsrod, O. (2003). Thermal
depolymerization of alginate in the solid state. Carbohydrate Polymers, 54,
431–438.
Sasaki, M., Fang, Z., Fukushima, Y., Adschiri, T., & Arai, K. (2000). Dissolution and
Konno, M., & Oba, T. (2007). Production method of
L
-guluronic acid metal salt of
D-
hydrolysis of cellulose in subcritical and supercritical water. Industrial
Engineering Chemistry Research, 39, 2883–2890.
&
mannuronic acid metal salt. Japan Patent Office, Pat. No. JP2007-230902.
Kruse, A. (2009). Hydrothermal biomass gasification. Journal of Supercritical Fluids,
47, 391–399.
Lu, Q. Y., Gao, F., & Komarneni, S. (2004). Biomolecule-assisted reduction in the
synthesis of single-crystalline tellurium nanowires. Advanced Materials, 16,
1629–1632.
Smidsrod, O., Haug, A., & Larsen, B. (1966). The Influence of pH on the rate of
hydrolysis of acidic polysaccharides. Acta Chemica Scandinavica, 20, 1026–1034.
Tonnesen, H. H., & Karlsen, J. (2002). Alginate in drug delivery systems. Drug
Development and Industrial Pharmacy, 28, 621–630.
Yang, Z., Li, J. P.,
& Guan, H. S. (2004). Preparation and characterization of
Matsushima, K., Minoshima, H., Kawanami, H., Ikushima, Y., Nishizawa, M.,
Kawamukai, A., et al. (2005). Decomposition reaction of alginic acid using
oligomannuronates from alginate degraded by hydrogen peroxide.
Carbohydrate Polymers, 58, 115–121.