CHEMICAL AND GELATION CHARACTERISTICS OF AMMONIA‐DEMETHYLATED SUNFLOWER PECTINS

Publisher Website
Google Scholar
Abstract
Sunflower head and stalk pectins were demethylated by ammonia‐ethanol treatments over a range of concentrations, duration and temperature conditions. The de‐esterification treatments decreased the methoxyl and acetyl contents of the pectins and their molecular weights. The associated increases in proportions of acid amide and free carboxyl groups on the polygalacturonic acid molecules were greater in the modified pectins extracted from a head:stalk mixture (1:1 ratio) than in the modified head pectin samples. For all modified pectins there was a general increase in firmness and strength of the prepared gels as the percent esterification decreased from 32 to 14% in these samples. The modified head pectins were superior to those from the head‐stalk mixture in pectin solubility, absence of pregelation, and gel smoothness, elasticity, uniformity and stability. The improved gel characteristics of the demethylated pectins were attributed to the increase in acid amide groups and greater randomization of free carboxyl groups in the pectin molecules. The optimum pH of 4.3 for gel formation in the unmodified and most demethylated samples was higher than that of a commercial low‐ester pectin, suggesting a particular application in high pH dessert gels.