Modification of sunflower pectins with ammonium hydroxide
Lee, Stephen Chi-Kin
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Low-methoxyl pectin was extracted from sunflower heads and head-stalk mixtures (1:1, w/w) and modified either during or after isolation, by NH4OH demethylation. The number of processing steps was reduced substantially by modification during pectin isolation. The poor gelation characteristics of native sunflower pectins (pregelation, brittleness and lack of elasticity) were improved by NH4OH demethylation, especially with head pectins. The NH4OH treatments were effective in reducing the methoxyl, acetyl, and ash contents, and molecular weight, and in increasing the acid amide and galacturonic acid contents. It was presumed that the improved gelation characteristics were related to these changes in chemical composition, and to greater randomization of methoxyl and carboxyl groups along the polygalaturonic acid chains. For demethylation of rehydrated pectins, a high demethylation rate and high amidation efficiency were associated with a high degree of hydration of pectin particles, high NH4OH concentrations, and low temperature. For demethylation of pectin extracts and pectin precipitates, a high demethylation rate and high amidation efficiency were again associated with high concentrations of NH4OH and low temperature. The extent of demethylation and amidation were dependent upon reaction time, NH4OH concentration, and temperature. Reductions in molecular weight proceeded at a slower rate at higher concentrations of NH4OH and a low reaction temperature. A pH of 4.3 was optimal for gel formation in the case of pectins (head and head-stalk mixtures) from the 1976 sunflower crop, which contrasted with a value of 3.0 for pectins isolated from 1977 sunflower heads. Note:Page 7 is missing.