kg and 88 - 194 g/kg, while lignin content was from 71 to 175 g/kg. In more detail ... as hydrolysate from the Klason lignin procedure by 72 % sulfuric acid and ...
Journal of the Japan Institute of Energy, 91,J.621-628 Jpn. Inst. (2012) Energy, Vol. 91, No. 7, 2012
621
Original Paper
Characterization of Lake Biwa Macrophytes in their Chemical Composition Harifara RABEMANOLONTSOA, and Shiro SAKA （Received December 2, 2011）
Macrophytes growing in Lake Biwa such as ofusa-mo (Myriophyllum aquaticum), sennin-mo (Potamogeton maackianus), okanada-mo (Egeria densa), kuro-mo (Hydrilla verticillata) and kokanada-mo (Elodea nuttallii) were characterized in their chemical composition in order to evaluate their potential as biorefinery feedstocks. As a result, cellulose and hemicellulose contents were found to be in a range, respectively, between 227 - 436 g/ kg and 88 - 194 g/kg, while lignin content was from 71 to 175 g/kg. In more detail, hemicelluloses were mostly composed of xylose, galactose, mannose and arabinose in relatively equal amounts, whereas lignin was composed of guaiacylpropane, syringylpropane and p -hydroxylphenylpropane moieties, while ash and protein were remarkably high to be 105-223 g/kg and 137-229 g/kg, respectively. Although inorganics as shown by ash might be a limitation in the utilization of the macrophytes as biorefinery feedstocks, cellulose, hemicellulose, lignin and protein are available as raw materials for the production of a wide range of valueadded biobased products. Key Words Myriophyllum aquaticum, Potamogeton maackianus, Egeria densa, Hydrilla verticillata, Elodea nuttallii, Lake Biwa, Chemical composition
1. Introduction
verticillata) as well as okanada-mo (Egeria densa) were also
Biorefinery from terrestrial biomass feedstocks en-
abundant in the basin 5). The large quantity of macrophytes
countered problems related to food price and land use. Land
especially in summer and early autumn engenders navi-
occupies only about 30% of the earth surface, while the
gation and odor issues so that the Shiga prefectural gov-
remaining 70% is covered with water and, particularly
ernment, Japan spent ¥ 70 million in FY 2007 to remove
freshwater ecosystems were demonstrated to be some of
2,800 t of the macrophytes in conjunction with other aquatic
1)
the most productive ones on earth . In place of terrestrial plants, aquatic plants are therefore investigated as new candidates for renewable resources.
plants and algae 6). The question then arises as to how to use efficiently those available biomass. Under such circumstances, the
Aquatic plants play important roles in physico-chem-
chemical composition of the macrophytes should serve as
istry of lakes and their ecology with significant impact on
a basis and an effective tool to define the most profitable
the food chain 2) 3). They also present several uses as
use of the biomass. Therefore, the aim of this study is to
biosorbent for water purification to extract nutrients, heavy
analyze the chemical composition of the major macrophytes
metals or other toxic chemicals 2) 3). In the case of Lake Biwa,
growing in the Lake Biwa in order to evaluate their poten-
most macrophyte species are invasive and their quantity
tial as biorefinery feedstocks.
seems to increase drastically over the years 4). The total biomass on dried weight basis of macro-
2. Materials and methods
phytes in the southern basin of the Lake Biwa was esti-
Fig. 1 shows the various species of the macrophytes
mated to be 10,735 ± 3,030 t in 2002 against 6,500 t in
collected in the Lake Biwa, whereas Table 1 shows their
2001 and 3,940 t in 1936. In 2002, sennin-mo (Potamogeton
taxonomical classification, their part studied, sampling time
maackianus) was the dominant species, and kuro-mo (Hydrilla
and sampling site in the Lake. The samples were rinsed
Department of Socio-Environmental Energy Science, Graduate School of Energy Science, Kyoto University Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan
with water, air-dried, milled with a Wiley mill (1029-C, Yoshida Seisakusho Co., Ltd.), and sieved to retain particles of 150-500 μm in size (30-100 mesh). For comparison, buna
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
622
or Japanese beech (Fagus crenata) as hardwood sample was
In brief, ash was determined after incineration of the oven-
also prepared in a similar way.
dried samples at 600 ℃ for 4 h. For additional analyses,
The samples were then oven-dried and the summative
the samples were extracted with acetone until it was clear
chemical composition was determined according to the
of any color. On the extractives-free samples, holocellulose
7)
method by Rabemanolontsoa et. al as summarized in Fig. 2.
and lignin were, respectively, determined by modified Wise method 8) and Klason method 9) . Both were then ash- and protein-corrected by subtracting ash and protein contents of the residues from the total residues yielded. Cellulose content was determined as α -cellulose by extraction with 17.5 % aqueous sodium hydroxide of the holocellulose powder 10) and hemicellulose content was evaluated by the difference between holocellulose and cellulose contents. Crystallinity of the α-cellulose samples were analyzed with an X-ray diffractometry (RINT 2200V, Rigaku Denki). The operating voltage and current were 40 V and 30 mA, respectively. Additionally, monosaccharides composition was determined by a combined method 11). Glucose was quantified as hydrolysate from the Klason lignin procedure by 72 % sulfuric acid and analyzed with high-performance anionexchange chromatography (HPEAC, Dionex ICS-3000
Fig. 1 Various species of the selected macrophytes alive in the Lake Biwa
system) equipped with CarboPac PA-1 column (4mm × 250mm), whereas the other neutral sugars and the uronic
Table 1 Taxonomical classification of the selected macrophytes, their part studied, sampling time and site in the Lake Biwa
Classification Angiosperm Dicotyledon Monocotyledon
Vernacular name
Ofusa-mo Sennin-mo
Scientific name
Part studied
Myriophyllum aquaticum Potamogeton maackianus
Entire plant
Okanada-mo
Egeria densa
Kuro-mo
Hydrilla verticillata
Kokanada-mo
Elodea nuttallii
Stem together with leaves Stem together with leaves Stem together with leaves Stem together with leaves
Sampling time
04/2010 07/2010 07/2010 07/2010 07/2010
Sampling site Moriyama, Shiga, Japan 35°2’41.65”N 135°55’3.24”E Otsu, Shiga, Japan 35°3’16.29”N 135°52’40.72”E Otsu, Shiga, Japan 35°3’16.29”N 135°52’40.72"E Moriyama, Shiga, Japan 35°1’37.91”N 135°54’54.93”E Moriyama, Shiga, Japan 35°1’37.91”N 135°54’54.93”E
Fig. 2 Analytical method applied to the selected samples to quantify their chemical composition 7)
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
acids by acid methanolysis 12) using Hitachi G-7000M and
623
rophytes.
M-9000 gas chromatograph-mass spectrophotometer (GC-
Acid-soluble lignin from ofusa-mo, a dicotyledonous
MS) equipped with 30 m × 0.25 mm i.d., 0.25 μm CP-Sil 8
macrophyte was, thus, higher than that of the monocoty-
CB-Low Bleed/MS capillary column. As for xylose, the high-
ledonous ones studied.
est value among the 2 procedures was taken. Acetyl group
In addition to holocellulose and lignin, the macrophytes
was quantified from the acetic acid obtained after the 72 %
contained protein in a range from 137 to 229 g/kg. These
sulfuric acid hydrolysis 9). Aminex HPX-87H column (Bio-
values agree well with data from literature reported in
Rad) was used with a refractive index detector and the tem-
various macrophytes to be from 98 to 228 g/kg 16). These
perature of the column oven was set at 85 ℃. Distilled wa-
lines of evidence confirm that aquatic macrophytes are rich
ter was utilized as the mobile phase at a flow-rate of
in protein.
0.6 ml/min.
On the content of inorganic constituents as shown by
Furthermore, alkaline nitrobenzene oxidation was per-
ash, it varied greatly with species. Kuro-mo, okanada-mo
formed on the extractives-free samples according to Iiyama 13)
and kokanada-mo presented the highest ash content to be
with slight modifications. The oxidized products were,
respectively 223, 201 and 158 g/kg, followed by ofusa-mo
silylated using trimethylchlorosilane (TMCS), bis
to be 112 g/kg and sennin-mo to be 105 g/kg. Ash content
(trimethylsilyl)trifluoroacetamide (BSTFA) and pyridine in
of the aquatic macrophytes was generally high as compared
a volumetric ratio of 2:1:7 and analyzed by gas chroma-
to wood. This is probably due to the high capacity of the
tography with veratraldehyde as an internal standard.
macrophytes to uptake inorganics and heavy metals from
In addition, starch and protein determinations from extractives-free samples were, respectively, completed by perchloric acid method
14)
the water 17). Acetone extractives in the macrophytes were also stud-
and Kjeldahl nitrogen method by
ied. They mostly represent the extracellular components
using a nitrogen factor of 6.25 15), whereas lipid was deter-
that are not a part of the cell wall structure, being varied
mined by Soxhlet extraction with hexane.
from 26 to 67 g/kg in the macrophytes. They are therefore considered as minor constituents. However, they might
3. Results and discussion 3.1 Quantitative assay for chemical composition of the macrophytes
influence the quality of the biobased products to be derived from the macrophytes. Other minor components present in the macrophytes
The quantitative assay for chemical composition of the
were starch and lipid. Those compounds represent the en-
various macrophytes growing in the Lake Biwa was made
ergy storage in the plants. Ofusa-mo recorded the highest
in this study, and the obtained results are shown in Table
lipid content as 28 g/kg with the lowest starch content to
2. Instead of expressing the chemical composition as wt %
be 2 g/kg. The other macrophytes had their lipid fraction
of the original oven-dried samples, g/kg was used as it is
lower than 20 g/kg and starch varying from 16 to 23 g/
recently considered more adequate internationally for fur-
kg as reported in Table 2.
ther applications of the data for its quantification.
The individual analysis is based on a quantitative ba-
The obtained cellulose and hemicellulose contents of
sis for the total biomass, thus the obtained total must be
these macrophytes were found to be ranged, respectively,
theoretically 1000 g/kg. Since the summative results for
from 227 to 436 g/kg and 88 to 194 g/kg. On the results
the constituents independently analyzed of the macro-
of cellulose, they were slightly similar to the ones reported
phytes were in a range between 985 and 998 g/kg, the
by Boyd
16)
on different aquatic plants to be in a range from
188 to 356 g/kg, although in this study, the highest cellu-
results of all analyses must be valid, and most components have been evaluated.
lose content was found in kokanada-mo to be 436 g/kg. Lignin as a sum of Klason lignin and acid-soluble lig-
3.2 Holocellulose composition of the macrophytes
nin was the highest in ofusa-mo (175 g/kg), followed by
Holocellulose is composed of cellulose and hemicellu-
sennin-mo (149 g/kg). The three other species presented
lose which further comprises hexosan and pentosan such
similar results ranging from 71 to 79 g/kg. Thus, the total
as glucomannan and xylan, respectively.
lignin content of ofusa-mo, one of the dicotyledonous mac-
Therefore, composition of the neutral sugars, uronic
rophytes was higher than that of the monocotyledonous
acids and acetyl group of the macrophytes was studied and
ones studied. Similarly, spectral evaluation by UV spectros-
the obtained results are shown in Table 3. Holocellulose
copy resulted in 29 g/kg of acid-soluble lignin for ofusa-
(1) was determined by the sodium chlorite procedure, in
mo, against 15 to 18 g/kg for the monocotyledonous mac-
which the residual ash, lignin and protein were all corrected,
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
624
Table 2 Chemical composition of the macrophytes studied (g/kg of the original oven-dried biomass basis)
Biomass Vernacular name Ofusa-mo Sennin-mo Okanada-mo Kuro-mo Kokanada-mo
Buna a c
Scientific name Myriophyllum aquaticum Potamogeton maackianus Egeria densa Hydrilla verticillata Elodea nuttallii Fagus crenata
Lignin Cellulose a Hemicellulose b Klason c Acid- Protein Extractives soluble
Starch
Lipid
Ash
Total
263
194
146
29
162
53
2
28
112
989
347
88
131
18
229
40
20
19
105
997
262
181
54
17
226
26
16
15
201
998
227
141
64
15
228
67
18
9
223
992
436
93
61
15
137
52
23
10
158
985
439
284
210
30
6
19
5
-
6
999
(Cellulose ) = (α -Cellulose) b (Hemicellulose) = (Holocellulose (1) in Table 3) - (α -Cellulose) (Klason lignin) = (Acid-insoluble material after Klason lignin procedure) - (ash in the residue) - (protein in the residue) Table 3 Monosaccharides and acetyl group composition of the macrophytes as compared to the one of Buna
Yield (g/kg of the original oven-dried biomass basis) c Biomass Vernacular name Ofusa-mo Sennin-mo Okanada-mo
Scientific name Myriophyllum aquaticum Potamogeton maackianus Egeria densa
Hydrilla verticillata Elodea Kokanada-mo nuttallii Kuro-mo
Buna
Fagus crenata
Hexoses Holocellulose Holocellulose (2) b (1) a Glc Man Gal Rha Fru
Pentoses Xyl
Ara
Acid sugars
Acetyl Glc-A Gal-A group c
457
434
289
41
24
13
22
32
37
3
13
9
435
426
343
6
5
8
3
58
26
2
17
6
443
413
267
19
59
16
1
51
16
8
16
6
368
333
241
1
44
12
1
29
24
1
10
7
529
501
422
31
26
8
0
25
14
5
21
5
723
687
417
14
36
23
0
213
9
3
17
32
a
Holocellulose (1) = Residue after sodium chlorite procedure − lignin in the residue − ash in the residue − protein in the residue Holocellulose (2) = 162/180 ∑ Hexoses ＋ 132/150 ∑ Pentoses ＋ 176/194 ∑ Acid sugars + 42/60 Acetic acid c Acetyl group = 42/60 Acetic acid d Glc : Glucose, Man : Mannose, Rha : Rhamnose, Xyl : Xylose, Ara : Arabinose, Glc-A : Glucuronic acid, Gal-A: Galacturonic acid b
whereas holocellulose (2) was estimated, based on the data
as compared to woods. However, not only the availability
of the contents of neutral sugars, uronic acids and acetyl
and abundance of the macrophytes but also the possible
group. The obtained results of holocelluloses (1) and (2) are
use of the other components might justify their utilization
in good agreement with each other to be comparable, in
as feedstocks for integrated biobased production.
spite of the different methods used.
The detailed monosaccharides composition of the
According to these results, kokanada-mo had the high-
holocellulose in Table 3 shows that glucose is evidently
est holocellulose content, slightly over 500 g/kg for both
the dominant sugar component, most probably coming from
holocelluloses (1) and (2), whereas ofusa-mo, sennin-mo and
the cellulosic portion of the samples.
okanada-mo had holocellulose (1) between 435 and 457 g/
X-ray diffractometry of the α-celluloses from the mac-
kg. Only kuro-mo had its holocelluloses (1) and (2) below
rophytes as compared to the one from buna were under-
400 g/kg. On the whole, the holocellulose content of the
taken and the diffraction patterns of the different species
macrophytes, varying from 368 to 529 g/kg is quite low
are shown in Fig. 3. The degree of crystallinity was calcu-
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
625
galactose and xylose in rather equal amounts to be 26 and 25 g/kg, respectively, in Table 3. As acid sugars, uronic acids such as glucuronic and galacturonic acids of the macrophytes were similar among species in their contents. However, galacturonic acid was higher than glucuronic acid in all the analyzed macrophytes. Table 4 shows hexosan and pentosan composition of the macrophytes as compared to the one of hardwoods buna (Fagus crenata). It is apparent that although slightly higher, hexosan content of hardwood is comparable to those of the Fig. 3 X-ray diffraction patterns of α -celluloses from the macrophytes as compared to the one from buna (F. crenata)
macrophytes, except for kuro-mo which presented hexosan below 300 g/kg. However, pentosan content in the macrophytes ranged between 34 and 74 g/kg. These values are
lated according to Segal et. al 18). While buna and kokanada-
remarkably low compared to 195 g/kg for buna, one of the
mo had comparable cellulose contents, respectively, 439 and
hardwoods.
436 g/kg, the degree of crystallinity for buna to be 71 % was much higher than the one of kokanada-mo to be 41 %.
3.3 Aromatic compounds from lignin
The other samples showed even lower degree of crystal-
The aromatic compounds produced from the extrac-
linity with 34% for sennin-mo, 32 % for ofusa-mo and 29 %
tives-free macrophytes by alkaline nitrobenzene oxidation
for both okanada-mo and kuro-mo. That finding suggests
are presented in Table 5.
that as compared to buna hardwood, the macrophytes pre-
The presence of p -hydroxybenzaldehyde, syring-
sented more amorphous cellulose which would be much
aldehyde and vanillin as the aldehydes of p -
prone to the milder hydrolysis than crystalline ones.
hydroxyphenylpropane (P), syringylpropane (S) and
The non-cellulosic monosaccharides including the
guaiacylpropane (G) units appears to indicate that the
uronic acids and a minor part of glucose are considered as
aquatic macrophytes have independently or associated to-
the hemicellulosic part of the samples. As opposed to hard-
gether with P, G and S types of lignin, characteristics of
wood which comprises xylose-rich hemicellulose, ofusa-mo,
monocotyledonous species such as rice and wheat etc. It is
one of dicotyledonous species, had its hemicellulose com-
interesting to note that, although ofusa-mo was a dicotyle-
posed of mannose, xylose, arabinose and galactose in a
donous species, its lignin seemed also to consist of P, G
relatively equivalent amount, implying that hemicellulose
and S moieties. The alkaline nitrobenzene oxidation results,
of ofusa-mo had the typical characteristics of its family
therefore, suggest that lignin structure of the macrophytes
(Myrtales) containing specifically arabinogalactan 19), in ad-
could be similar to those of herbaceous monocotyledonous
dition to xylan. Okanada-mo and kuro-mo, monocotyledon-
species.
ous species, had a noticeable amount of galactose, respec-
However, it was reported for herbaceous samples that
tively, 59 and 44 g/kg as compared to their other monosac-
a large proportion of p-hydroxybenzaldehyde and vanillin
charides. Kokanada-mo had mannose as its predominant
produced after the alkaline nitrobenzene oxidation could
hemicellulosic monosaccharide to be 31 g/kg, followed by
be formed respectively from p-coumaric acid and ferulic
Table 4 Hexosan and pentosan composition of the macrophytes as compared to that of buna (g/kg of the original oven-dried biomass basis)
Vernacular name Ofusa-mo Sennin-mo Okanada-mo Kuro-mo Kokanada-mo Buna a b
Biomass Scientific name Myriophyllum aquaticum Potamogeton maackianus Egeria densa Hydrilla verticillata Elodea nuttallii Fagus crenata
Hexosan = 162/180 ∑ Hexoses Pentosan = 132/150 ∑ Pentoses
Total
Hexosan a
Pentosan b
411 403 385 316 472 636
350 329 326 269 438 441
61 74 59 47 34 195
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
626
Table 5 Aromatic compounds produced from extractives-free macrophytes by alkaline nitrobenzene oxidation (g/kg of original ovendried sample)
Aromatic compounds Guaiacyl moiety Vanillin Vanillic acid Coniferyl aldehyde Acetovanillin Ferulic acid Syringyl moiety Syringaldehyde Syringic acid p-Hydroxyphenyl moiety p-hydroxybenzaldehyde p-hydroxybenzoic acid Coumaric acid
Ofusa-mo Myriophyllum aquaticum
Sennin-mo Potamogeton maackianus
Okanada-mo Egeria densa
Kuro-mo Hydrilla verticillata
Kokanada-mo Elodea nuttallii
Buna Fagus crenata
0.21 0.18 0.90 0.25 0.29
2.69 0.35 1.54 2.76 0.65
0.15 0.00 3.11 0.83 2.71
0.29 1.45 10.43 1.10 1.75
0.07 0.25 1.91 0.22 0.00
7.84 -
0.25 0.00
1.87 0.28
0.13 0.68
0.23 1.06
0.10 0.17
15.69 -
0.22 0.19 0.25
0.73 0.42 0.38
0.05 0.56 0.18
0.11 0.66 1.66
0.05 0.00 0.00
-
260. Such absorbance is due to the simultaneous presence of guaiacyl and syringyl moieties of lignin 21) 22). Typical UV spectra of guaiacyl, syringyl and p-hydroxyphenyl model compounds were respectively presented by Aulin-Erdtman 23), Pew 24) and Lang 25). Both syringyl and guaiacyl model compounds showed a minimum absorbance at 250 to 260 nm with maximum at 270 to 280 nm, while p-hydroxyphenyl model compound gave a strong peak at 260 nm with minimum absorbance in wavelengths lower than 240 nm. Musha and Goring 22) stated that if some p-hydroxybenzoic residues are associated with syringyl residues, the peak at 280 nm should flatten because of the strong abFig. 4 UV spectra of the acid-soluble lignins from different macrophytes and Japanese beech (Fagus crenata) for comparison
sorbance at low wavelength of the p-hydroxybenzoic acid group and that the minimum absorbance at 250-260 nm is likely to shift to the lower wavelength. Those facts can be
acid esterified or etherified with lignin, and not from P
observed in the difference between the UV absorbances
and G moieties in the lignin polymer itself 13) 20). Since a large
of buna and the macrophytes, confirming the statement
amount of p-coumaric acid and ferulic acid were found in
above as the studied macrophytes contained p -
the samples as accounted in Table 5, it is possible that a
hydroxybenzoic residues. This conclusion is in good agree-
major part or all the p-hydroxybenzaldehyde and vanillin
ment with the results obtained from the alkaline nitroben-
recovered was originated from p-coumaric acid and feru-
zene oxidation results.
lic acid.
Apart from the lignin phenylpropane units, phenolic
Therefore, in order to confirm the lignin structures,
acids, for instance, ferulic acid and coumaric acid were also
UV spectra of the acid-soluble lignins from the macrophytes
detected as shown in Table 5. They might represent the
were studied in Fig. 4 and compared with that from buna.
phenolic compounds linking lignin with polysaccharides,
Spectra for ofusa-mo and kuro-mo are not shown but they
which may play an important role in reinforcing the me-
were similar to those of the other macrophytes shown in
chanical strength of the plant cell walls as demonstrated
Fig. 4.
in grass species 26).
The spectrum found for buna is typical of hardwood lignin showing a maximum absorbance at a wavelength between 270 and 280 nm, with minimum between 250 and
J. Jpn. Inst. Energy, Vol. 91, No. 7, 2012
3.4 Lake Biwa macrophytes as potential biorefinery feed-
627
lower as compared to the ones of buna, a hardwood. The detailed monosaccharides study revealed that the
stocks
A macrophyte is an aquatic plant that grows in or near
macrophytes contained glucose in a range between 241 and
water and is either emergent, submergent or floating 27),
422 g/kg, while the xylose contents were low as compared
being classified into both dicotyledons and monocotyledons
to hardwood buna. Accordingly, the contents of pentosan
in angiosperms. To clarify its chemical composition, vari-
in the macrophytes were rather small.
ous macrophytes growing in Lake Biwa were selected and
Although cellulose and hexosan contents of buna and
studied. Consequently, holocellulose composed of cellulose
kokanada-mo were comparable, the degree of crystallinity
and hemicellulose was rather low in about 450 g/kg on
of α -celluloses from kokanada-mo and the other studied
average. In addition, lignin as the sum of Klason lignin and
macrophytes were much lower than the one from buna.
acid-soluble lignin was also low in content varying from
Additionally, alkaline nitrobenzene oxidation on the
71 to 175 g/kg. On the other hand, protein and ash con-
macrophytes suggested that their lignin consisted of P, G
tents were found to be rather high in a range between 137-
and S moieties. Such result was further confirmed by UV
229 g/kg and 105-223 g/kg, respectively. Furthermore,
spectrophotometry on the acid-soluble lignin of the macro-
extractives, starch and lipid were found in total to be 57-
phytes.
94 g/kg. Therefore, it might be concluded that the macro-
Characterization of the Lake Biwa macrophytes in their
phytes are composed of various chemical constituents. This
chemical composition revealed that those species had low
finding suggests that the macrophytes can be of high po-
potential for the traditional ethanol production. However,
tential to various applications for biorefinery. However,
cellulose, hemicellulose, protein, lignin, starch and ash are
those macrophytes are not good candidates as raw materi-
available materials for the production of extensive variet-
als for the traditional bioethanol production, in spite of the
ies of biobased products.
claiming that the macrophytes in Lake Biwa can be good raw materials for ethanol production 28).
Acknowledgement
In more details on the saccharides content, hemicellu-
This work was accomplished under financial support
loses in the macrophytes were essentially composed of
from Kyoto University Global Center of Excellence (GCOE)
xylose, mannose, galactose and arabinose in relatively equal
Energy Science Program by the Ministry of Education,
amounts, thus not rich in pentosan (34-74 g/kg), while lig-
Culture, Sports, Sciences, and Technology, Japan (MEXT).
nin was characterized by the presence of p -hydroxy-
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