V Besson, Beda M Yapo and Kouassi L Koffi
The effect of the strength of nitric acid-extractant (pH 1.2, 1.6, and 2.0) on the yield, sugar composition and molecular weight, and gelling ability of pectin from soursop (Annona muricata) was investigated to find out the optimum conditions for producing marketable pectin. The results showed that the yield (3.5-12.9%) of pectin (AMP) extracted from Annona muricata pomace was pH-dependent. Likewise, its galacturonic acid content (GalA: 41.3-72.8%), total neutral sugar content (TNS: 11.4-24.3%), methylesterification degree (DM: 64-82), viscosity-average-molecular weight (Mv: 62-105), and gelling capacity (GC: 98-163) were significantly influenced by the extraction pH (p<0.05). Individual neutral sugar analysis revealed that arabinose was the most abundant, followed by galactose with a rather high presence of rhamnose. Partial structural analysis, by enzymatic degradations, suggested that AMP was mainly branched with an unusual galactoarabinan side chain type rather than with arabinogalactan-I. As the other extraction parameters, namely dried raw material to solvent ratio, temperature, and time, were fixed to 1:25 (w/v), 75°C, and 90 min, respectively; pH 1.2 was found to be the optimum pH condition for isolating, from soursop pomace, high methoxy pectin (DM >60%) with rather good yield (8.0%) and gelling power (>150).
