TY - JOUR T1 - The Fractional Extraction and Quantitative Determination of Pectic Substances in Grapes and Musts JF - American Journal of Enology and Viticulture JO - Am J Enol Vitic. SP - 182 LP - 186 DO - 10.5344/ajev.1979.30.3.182 VL - 30 IS - 3 AU - Gordon L. Robertson Y1 - 1979/01/01 UR - http://www.ajevonline.org/content/30/3/182.abstract N2 - A sensitive and specific procedure is described for the fractional extraction and quantitative determination of pectic substances in grape berries and musts. The fractionation procedure involves the progressive extraction of the alcohol insoluble solids by water (when the high methoxyl pectins are extracted), ammonium oxalate (when the low methoxyl pectins are extracted) and cold alkali (which solubilizes the protopectin). The anhydrogalacturonic acid content of the three fractions is then determined quantitatively by heating the extract with concentrated sulfuric acid and sodium tetraborate and forming a chromogen with m-hydroxydiphenyl. The absorbance of the solutions is then compared to that obtained from standard solutions of galacturonic acid subjected to the same procedure.The advantages of this method over the commonly used carbazole method are demonstrated, and the reproducibility of both methods is presented. It is recommended that the procedure described herein be adopted for the routine determination of pectic substances in grapes. ER -