Determination of pectic substances in the presence of dextrins

Abstract

The determination of pectins in the presence of dextrins in canned fruit tissue and in cut-out sirups was investigated. In cut-out sirups, dextrins present in the alcohol precipitate interfere with determination of pectins by the colorimetric carbazole method, and the pectins interfere with the chromatographic separation and determination of separated maltodextrins by copper reducing methods. The addition of dextrins to pectins results in a 10% increase in carbazole values when added at equal concentration, and interference increases linearly with further increase in dextrin content. The Somogyi micromethod was even more sensitive to interference by pectins. A combination of precipitation with calcium and colorimetric carbazole determination of galacturonic acid in the precipitate was developed and found applicable.During investigation of the effect of replacement of sucrose by corn sirup solids on the changes occurring in canned peaches during processing and storage, the authors observed that the alcohol precipitate obtained from cut-out sirups in the presence of added corn sirup solids differed in appearance and composition from that obtained from sucrose sirups (6). The precipitate was opaque, chalky in appearance, and sticky rather than the gelatinous translucent precipitate characteristic of pectins. The alcohol precipitates obtained from cutout sirups containing added corn sirup solids were heavier and more voluminous. In the colorimetric carbazole determination, they develop a brownish red color on heating with concentrated sulfuric acid. Alcohol precipitates from sucrose sirups, however, were colorless before addition of carbazole.Dische (7-9), in developing his carbazole procedure