Glycosylation composition analysis

Fig. 1. Glycosyl composition analysis is achieved by conversion of the glycosyl residues of oligo- and polysaccharides into volatile alditol acetate derivatives. Experimental details...

Uronosyl residues of the polysaccharides offer the same problems for glycosyl linkage analysis as they do for glycosyl composition analysis. Before the linkages to the uronosyl residues can be ascertained, the uronosyl residues must be reduced by the carbodiimide method (124) to their corresponding deuterium-labeled alditols. 

Glycosyl-residue compositions were determined by GC-CIMS analysis of the per-O-trimethylsilylated methyl glycosides [23] separated on a fused-silicaDB-1 capillary column. The identity of each peak was confirmed by CIMS on a HP-5989 MS Engine (Hewlett-Packard). 

The glycosyl-residue compositions of the three purified fractions (Table 1) were very similar with a predominance of galacturonic acid, rhamnose and arabinose. The presence in the three purified fractions of the rare monosaccharides characteristic of RG-II (e.g. 2-( -methyl-L-fucose, 2-O-methyl-D-xylose, apiose, Kdo, Dha and aceric acid) was confirmed by GC-CIMS analysis. The molar ratios corresponded approximately to the known structure of the RG-II molecule (Figure 1) and to previously published data for RG-II from sycamore [26], rice [4], arabidospis leaves [8] and Pectinol [12]. 

Acid hydrolysates were added to a low aroma intensity white wine (ie the base wine), and the aroma properties of these samples were assessed by sensory descriptive analysis. In addition, the glycoside isolates from the Australian vineyards were subjected to glycoside hydrolase enzyme treatment, and duo-trio difference tests were performed on these hydrolysates added to a base wine. The volatile composition of each of the hydrolysates was investigated by GC/MS, and relationships between the two sets of data were determined. Finally, the glycoside concentration of each of the juices and skin extracts was determined by the glycosyl-glucose assay. 

---