**6. Monosaccharide composition**

334 Chromatography – The Most Versatile Method of Chemical Analysis

extraction [39].

HPSEC-MALLS/RI was used to compare the molar mass distribution of pectins obtained from the dried pomace of eleven apple cultivars [41]. Although the pectins were obtained under the same extraction conditions, some differences were identified among the fractions. According to the results, pectins from different variety of apple can display differences in their molar mass profiles as depicted in Figure 4 (for clarity only RI detector is shown).

**Figure 3.** Cumulative molar mass distribution for a polysaccharide obtained after 15 min and 48 h of

**Figure 4.** HPSEC elution profiles of pectins obtained from the dried pomace of eleven apple cultivars (columns: Waters Ultrahydrogel 2000/500/250/120 connected in series; eluent: 0.1M NaNO2 solution,

containing NaN3 (0.5 g/l); flow: 1.5 mg/ml) [41].

Information on the composition of pectins can be obtained by different chromatographic methods. Regardless of the method used to determine the monosaccharide composition, the pectin under study needs to be previously hydrolyzed in order to release its monomeric units. It is well known that the glycosidic linkages with acidic monosaccharides are more resistant to hydrolysis. For pectins, the different sensitivities to acid hydrolysis are: GalA-GalA > GalA-Rha > Rha-GalA > neutral sugar-neutral sugar 42. The chosen conditions must be a compromise between maximum hydrolysis with minimal degradation.

Although the more simple chromatographic methods, such as paper chromatography (PC) and thin layer chromatography (TLC), can give only qualitative information about the composition of pectins, they can be useful to check the adequacy of the conditions of hydrolysis.
