The polysaccharide was hydrolyzed to monomeric units
and transformed to the corresponding alditol acetates. A sample
(0.1 g) of crude product was mixed with 1.25 mL of 72%
sulfuric acid and incubated for 60 min at 30 °C. The mixture
was diluted with 13.5 mL of distilled water and incubated in
boiling water bath for 4 h. After incubation, the mixtures
were cooled and 3.1 mL of 32% of NaOH (W/V) was added.
At the end of the hydrolysis, a 0.2 mL of sample was taken
separately and 2 mL of 2% sodium borohydride in dimethyl
sulfoxide was added. The mixtures were then shaken well at
40 °C for 90 min after which 0.2 mL of glacial acetic acid
was added to decompose the excess sodium borohydride.
After cooling, 4 mL of acetic anhydride and 0.4 mL of
1-methylimidazole were added to the solution. The mixtures
were then incubated for 10 min at room temperature, and
then 20 mL of distilled water was added to decompose excess
acetic anhydride. After cooling, 8 mL of dichloromethane
was added and the mixture was shaken vigorously to achieve
total alditol acetate extraction. The upper layer was removed
and the lower phase was washed three times with 20 mL of
distilled water. The dichloromethane was evaporated at 40 °C
under vacuum and the final alditol acetate residues were dissolved
in 1 mL of dichloromethane and stored at –20 °C.
Alditol acetates were separated on a 30 m × 0.25 mm ID ×
0.25 μm film thickness column DB 5 ms (Agilent Technologies)
attached to the GC-2010 (GCM-QP 2010) Shimadzu
chromatograph equipped with a flame-ionization detector and
a split injector. High purity hydrogen was used as the carrier