LAUSR

ABSTRACT Pectins from Araca (Psidium cattleianum Sabine) fruit pulp were extracted, purified and isolated, obtaining the Araca Purified Pectin (APP) under its sodium form. Yield was found 3.5% w/w of the initial dried material. From titration, monosaccharide analysis after total hydrolysis and 1H and HSQC NMR analyses, it was established that the pectins are formed of long galacturonic acid blocks (HG) partially methylated (degree of methyl-esterification – DM = 55.9 mol%) and acetylated (2 mol%) and RG-I blocks with side chains containing mainly arabinose and galactose. No gelation was observed in presence of calcium for the unmodified APP. Then, pectins were treated in alkaline conditions to de-esterify progressively the initial sample down to DM = 0 after 60 minutes of treatment. Each sample obtained was characterized by SEC and NMR demonstrating the stability of the main chains, where Rha, GalA and Mw remained unchanged independently of the length of alkaline treatment. One of this sample (APP-15) was selected to test the gelling ability and rheological behavior. The gel was formed by dialysis against 1 mol L-1 CaCl2 and its rheological study allows to conclude that a homogeneous physical gel is formed stabilized by cooperative GalA--Ca+2 junctions.