Читать книгу Polysaccharides - Группа авторов - Страница 105

The classical ‘freeze–thaw’ example of fractionating the agar is the oldest known fractionation method of agar. The gelling counterparts of polysaccharides (agarose) were broken up from their non gelling counterparts (agaropectin), purely by freezing, thawing and then pressing the agar gel. In 1979 Usov [14] and his team recognised this non-gelling counterpart as agaropectin. In old times, to exhibit the heterogeneity of agar and separate agarose (Polysaccharide fraction with highest gelling capacity) from agaropectin (the charged polysaccharide counterpart of poor or non-gelling quality), the differential solubility of agar polysaccharide was used. In 1946 Yanagawa [15] extracted polysaccharide fractions with sulfate content by mixing agar of G. amansii at 3, 50–55 and at 75–80 °C in water. As well as he acquired different yields of agar from Gloiopeltis, Gracilaria, Ceramium, Gelidium and Acanthopeltis species of agarophytes, simply by boiling them at 70, 60, 50% of alcohol. In 1970 Guiseley [16] developed a method to precipitate polysaccharides. Since methylated agar polysaccharide is soluble in hot ethanol, in 1970 Guiseley used this property of agar to precipitate polysaccharide. In 1986 Lahaye developed a procedure to extract agar. In this method water is added to the different boiling ethanol-water solutions at different temperatures to get a sequential solvent of agar. Izumi [17] and Yaphe’s group studied the differences in charges densities of agar polysaccharide by using anion exchange chromatographic techniques.