Improvement of the compositional quality of monocot pectin extracts contaminated with glucuronic acid-containing components using a step-wise purification procedure

The analysis of the uronic acids within crude pectin extracts from banana peel and pineapple flesh, by a modified meta-hydroxydiphenyl assay in the presence and absence of sodium tetraborate, revealed a non-negligible amount of glucuronic acid (4.1–7.2 g/100 g) together with a much higher quantity of galacturonic acid (37.5–42.8 g/100 g). This suggested that fragments of glucuronic acid-containing heteroxylans, notably glucuronoarabinoxylans (GAXs), accompanied pectins extraction. A step-wise purification process was therefore developed to efficaciously remove, from pectin extracts, GAX contaminants including non-pectin-incorporated neutral sugar (NS) components. It primarily consisted in treating dialysed pectin extracts or not with 78–85% acidified methanol, which led to the precipitation of pectin-rich fractions while the bulk of GAX and free NS materials were solubilised in the aqueous acid–methanol mixture. Subsequently, advantage was taken of the multivalent ion-binding selectivity and ‘exclusivity’ of the pectin polymer anionic (carboxyl) groups to produce GAX and NS oligosaccharide contaminants-free final isolates, and hence greatly enriched in pectin components.