GALACTURONATE IN PECTIC SUBSTANCES FROM FRUITS AND VEGETABLES - COMPARISON OF ANION-EXCHANGE HPLC WITH PULSED AMPEROMETRIC DETECTION TO STANDARD COLORIMETRIC PROCEDURE

A HPLC method was developed to identify and quantify galacturonate; results were compared with those from a standard colorimetric procedure. HPLC was also used to determine neutral monosaccharide profile of isolated pectic substances (PS). The PS, isolated with ammonium oxalate from the total dietary fiber of apple, cucumber, celery, grapefruit and radish, were analyzed. Mean PS on original dry matter basis ranged from 6.0 +/- 0.51% for apple to 18.5 +/- 0.1% for celery. Galacturonate of isolated PS determined using anion exchange chromatography coupled with pulsed amperometric detection was not significantly different (P > .2) from that determined colorimetrically. Major monosaccharides in PS of all substrates were arabinose and galactose. Rhamnose, xylose and glucose also were detected in certain sources in much lower amounts. This HPLC method allows precise quantification of galacturonate and will be a useful tool for study of chemical composition of pectin.