Methods Of Analysis

Because of its complex composition, several methods are necessary to analyze for pectin (10). A few of the more important methods will be discussed here. Of the several col-orimetric methods developed to analyze for galacturonic l-»-2 Linkage l-»-2 Linkage

acid, the reaction of pectin with m-hydroxylbiphenyl in heated acids media to form a colored product is employed widely. Base titration before and after saponification is used for the simultaneous determination of DM and ga-lacturonic content. Also, DM is determined by saponifying methyl ester groups and analyzing for free methanol by gas chromatography or by oxidizing the methanol to formaldehyde, which is determined colorimetrically. Carboxyl and methylester groups also may be determined by infrared spectroscopy in deuterated water provided there is a prior calibration against known standards. Often, neutral sugars are analyzed by gas chromatography after hydrolysis and conversion to volatile derivatives. Various derivatives and stationary phases have been employed. In one method, sugars are converted to their alditol acetates and chromatographed on a high-performance capillary column. Acetyl esters are analyzed by conversion to acetic acid, separation by steam distillation, and titration of the acid. Fer-uloyl esters are hydrolyzed to ferulic acid, which is analyzed by the Folin-Ciocalteu reagent.

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