Pectic acid acetyl groups

Rha, Ara and Gal are the neutral sugar components from all the fractions. Xyl is not present in Fla and is significantly present in the hemicellulose fractions, indicating that this monosaccharide is component of hemicellulosic polymers. Chemical composition of the water fractions were determined (Table V). High protein contents and the presence of O-acetyl-groups were observed in four aqueous fractions. Neutral sugar and uronic acid composition points to inclusion of these polymers in the class of pectic polysaccharides. 

There is the further, although remote, possibility that the only substantial variation in the composition of pectinic acids obtained from fruits and beets, and from some other sources, might be the result of differences in the occurrence in these of natural enzymes acting upon pectic substances. Pectinic acids isolated from beets have been shown to contain acetyl groups,8 the mode of attachment of which to the poly-... 

Direct titrimetric method is a classic method for DE determination (National Research Council, 1972). In this method, pectin is first washed by acidic alcohol to convert the free carboxyl groups to the protonated form and is then washed with alcohol and dried. The washed sample is then dissolved in water and titrated with standard base and acid. The uronic content and DE are calculated from the neutralization and saponification equivalents of the pectic carboxyl groups. The existence of acetyl groups in some pectin samples leads to an overestimate of DE in the titration method. In this case, the copper binding method is an alternative approach (Keijbets and Pilnik, 1974). In the copper binding method, the amounts of copper ions that bind to the pectin molecules before and after saponification are measured by the complexometry, the ratio of which gives the DE. 

---