Abstract
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.
- Received November 1978.
- Revision received January 1979.
- Accepted January 1979.
- Published online January 1979
- Copyright 1979 by the American Society for Enology and Viticulture
Sign in for ASEV members
ASEV Members, please sign in at ASEV to access the journal online.
Sign in for Institutional and Non-member Subscribers
Log in using your username and password
Pay Per Article - You may access this article (from the computer you are currently using) for 2 day for US$10.00
Regain Access - You can regain access to a recent Pay per Article purchase if your access period has not yet expired.