Structural elucidation of hemicelluloses from Vetiver grass
Introduction
The majority of plant materials are constructed from three major polymeric components: cellulose, hemicelluloses and lignin. The hemicelluloses are estimated to account for one third of all components available in plants. Structures of the hemicelluloses vary significantly in different plants and have been topics of great academic interest. The hemicelluloses from cell wall of the Gramineae family plants such as cereal plants and grasses mainly consist of a chain backbone of (1→4)-linked β-d-xylopyranosyl residues to which α-l-arabinofuranose units are linked as side branches (Izydorczyk and Biloaderis, 1995, Xiao et al., 2001, Sun and Sun, 2002). The manner of attachment of arabinose units to the xylan backbone has been a matter of continuous research. The linkages of Araf to C(O)3 and to C(O)2,3 of xylose residues have been reported (Ebringerova et al., 1990). More recently, the presence of another linkage type, namely Araf linked to C(O)2 of Xylp residues, has been verified for arabinoxylans (Izydorczyk & Biloaderis, 1995). A small proportion of oligomeric side-chains consisting of two or more arabinosyl residues linked via 1→2, 1→3 and 1→5 linkages has been reported although most arabinofuranosyl residues in arabinoxylans are found as monomeric substituents. Terminal galactosyl and glucosyl residues can be present but are usually quantitatively minor and might originate from contaminant polysaccharides (Ebringerova et al., 1990, Izydorczyk and Biloaderis, 1995, Ebringerova and Heinze, 2000, Xiao et al., 2001). Glucuronopyranosyl (and 4-methyl ether) residues were found and attached directly to the C-2 position of xylose from barley straw (Sun & Sun, 2002), rice and rye straws (Izydorczyk and Biloaderis, 1995, Xiao et al., 2001).
Although arabinoxylans from various cereals and/or various plant tissues share the same basic chemical structure, they differ in the manner of substitution of the xylan backbone. The main differences are found in the ratio of arabinose to xylose (Ara/Xyl), in the relative proportions and sequence of the various linkages between these two sugars, and in the presence of other substituents. The ratio of Ara/Xyl in arabinoxylans from wheat endosperm may vary from 0.50 to 0.71 but it is usually lower than that found in bran (1.02–1.07). Similarly, rye bran endosperm arabinoxylans are less substituted (0.48–0.55) than rye bran counterparts (0.78) (Izydorczyk & Biloaderis, 1995). In general, arabinoxylans from rice (Shibuya & Iwasaki, 1985) and sorghum (Woolard, Rathbone, & Novellie, 1976) seem to consist of more highly branched xylan backbones than those from wheat, rye, and barley, and they may contain galactose and glucuronic acid substituents, in addition to the pentose sugars.
According to His Majesty's Initiative, the principal utilisation of the Vetiver grass in Thailand is for preventing soil erosion and conserving soil moisture due to its deep thick root system like on underground curtain. Similar to other undervalued agricultural residues, leaves of the Vetiver grass which has been normally cut every few months are not used as industrial raw materials and are burnt in field or on the side of the road. The main purpose of the work, being presented here just a part, is to assess the possibility of preparing wound dressing materials or other chemicals based on hemicelluloses extracted from the Vetiver grass. Therefore, elucidation of the molecular structure of the Vetiver grass hemicelluloses was of our particular interest.
Section snippets
Sample preparation
Vetiver grass (V. zizanioides, ecotype Songkhla 3), age of about 9 months, was kindly supplied by Land Development Department (Nakornrachasima, Thailand). The ground leaves were dried in an oven at 60 °C for 16 h before use. The principal composition (%w/w) of the Vetiver grass is 34.46% cellulose, 39.40% hemicelluloses, 7.87% lignin, 3.66% ash and 3.97% protein. The isolation of hemicelluloses was performed in the same manner as described in previous work (Methacanon, Chaikumpollert,
Monosaccharide identification
The extracted hemicelluloses consisted of two fractions: water-soluble and water-insoluble fractions. Their monosaccharide compositions were identified and quantified as shown in Table 1. The major monosaccharide in both soluble and insoluble fractions is xylose (ca. 46 and 63%, respectively) followed by arabinose (ca. 16 and 10%, respectively). This result suggested that the hemicelluloses from the Vetiver grass are mainly composed of arabinoxylan. The Ara/Xyl ratio of water-soluble and
Conclusions
It is concluded that the hemicellulose samples from the Vetiver grass is an arabinoxylan mainly consisting of a backbone of 1,4-linked xylopyranosyl units (Fig. 4). The (1→4)-xylopyranose backbone is substituted on O-2 and/or O-3 by single residue or short chains. These branches may be single arabinose residue, single glucuronic acid residue or a short chain of sugar residues containing arabinose, xylose and galactose. In addition, the (1→4)-linked β-d-xylopyranosyl residues in the backbone may
References (21)
- et al.
A simple and rapid preparation of alditol acetates for monosaccharide analysis
Carbohydrate Research
(1983) - et al.
Determination of the structures of trisaccharides by 13C-NMR spectroscopy
Carbohydrate Research
(1984) - et al.
A simple and rapid method for the permethylation of carbohydrates
Carbohydrate Research
(1984) - et al.
Hemi-celluloses polymers from the cell walls of beeswing wheat bran: part I, polymer solubilised by alkali at 2o
Carbohydrate Research
(1987) - et al.
Structural features of a water-soluble l-arabino-d-xylan from rye bran
Carbohydrate Research
(1990) - et al.
Cereal arabinoxylans: advances in structure and physico-chemical properties
Carbohydrate Polymers
(1995) - et al.
Hemicellulosic polymer from Vetiver grass and its physicochemical properties
Carbohydrate Polymers
(2003) - et al.
Linkage of p-coumaroyl and feruloyl groups to cell-wall polysaccharides of barley straw
Phytochemistry
(1985) - et al.
Isolation and characterization of hemicellulose B and cellulose from pressure refined wheat straw
Industrial Crops and Products
(1998) - et al.
Fractional and structural characterization of hemicellulose isolated by alkali and alkaline peroxide from barley straw
Carbohydrate Polymers
(2002)
Cited by (120)
From waste to a resource? Hemicelluloses enhance the dissolution and stability of the amorphous state of carbamazepine
2024, Sustainable Chemistry and PharmacyHemicellulose: Structure, chemical modification, and application
2023, Progress in Polymer ScienceAdvances in extraction, purification, structural characteristics and biological activities of hemicelluloses: A review
2023, International Journal of Biological MacromoleculesNarrow-leafed lupin (Lupinus angustifolius L.): Characterization of emulsification and fibre properties
2022, Future FoodsCitation Excerpt :The intensity of these bands decreased from the full fat sample to the dietary fibre, indicating protein removal from the sample. The band at 1245 cm−1, due to the CO stretching and the sharp band at 1055 cm−1, due to CO, CC stretching or COH bending in monosaccharide units was also identified (Chaikumpollert et al., 2004; Xu et al., 2010), confirming the structure of the polysaccharide. The band at 896 cm−1 is attributed to β-glycosidic linkages between the various monosaccharides identified in the pectin structure and other polysaccharide moieties such as xylan, mannan, and cellulose (Gupta et al., 1987; Yang & Zhang, 2009).
Coupling between acid precipitation and resin adsorption for purifying alkaline extracted hemicellulose from sugarcane bagasse
2022, Journal of Cleaner Production