Biomedical Engineering Reference
In-Depth Information
(Brand & Morand, 1997) but as it will be stressed in the following part of the chapter, the
chemicals and polymers of this underexploited biomass along with their abundance,
biological properties and “renewability” represent a potential source to be explored.
2.1 Chemical-physical properties
2.1.1 Ulvan composition
Green algae such as Ulva sp. are known to contain high amounts of good-quality protein,
carbohydrate, vitamins and minerals (Taboada et al., 2010). Among these, polysaccharides
are gaining increasing attention as they possess unique physical and chemical properties
representing a versatile material platform for potential biological applications.
Ulvan represents a class of sulphated heteropolysaccharide extracted from the cell wall of
green seaweeds belonging to Ulva sp. whose composition has been extensively debated
(Lahaye & Robic, 2007; Robic et al., 2009; ) and showed to vary according to several factors
including the period of collection, the ecophysiological growth conditions, the taxonomic
origins and the post-collection treatment of the algal sources (Lahaye & Robic, 2007).
Four types of polysaccharides are reported to be contained in the biomass of Ulva sp. ,
including the water soluble Ulvan and insoluble cellulose as major one and an alkali-soluble
linear xyloglucan and glucuronan in minor amounts (Lahaye & Robic, 2007). Ulvan
represents the major biopolymeric fraction of the cell wall having the function of
maintaining the osmolar stability and protection of the cell (Paradossi et al., 2002). As
usually found in polysaccharides present into the cell walls, Ulvan is present in close
association with proteins and the conventional methods of extraction and purification
resulted not completely effective in the removal of the protein fraction even after a specific
deproteinization protocol (Alves et al., 2010).
Extraction is conventionally achieved by using warm water solution (80-90°C) containing
ammonium oxalate as divalent cation chelator and the recovery of Ulvan is generally
obtained by precipitation in ethanol. The yield of extraction usually ranges from 8% to 29%
of the algal dry weight depending on the applied purification procedure (Lahaye & Axelos,
1993; Lahaye et al., 1994).
The sugar composition of Ulvan is extremely variable but rhamnose, xylose, glucuronic and
iduronic acid and the presence of sulphate groups have been identified as the main
constituents of the polymer (Paradossi et al., 2002; Robic et al., 2009). These monomers are
arranged in an essentially linear fashion even though a slight degree of branching has been
found (Lahaye & Robic, 2007). The chemical heterogeneity of Ulvan is partially striken by a
“structural motif” found within the heteropolymer chain essentially given by the presence of
repeating dimeric sequences constituted by aldobiuronic acid disaccharides designated as type
A (glucurorhamnose 3-sulphate, A 3s ) and type B (iduronorhamnose 3-sulphate, B 3s ) (Figure 3).
Fig. 3 Structure of the main disaccharide repeating units in Ulvan.
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