Isolation and structural characterisation of papaya peel pectin

- Potential of papaya peel as source for the extraction of pectin
- Physicochemical and immunological analysis of pectin in Local and Solo papaya peel
- Mainly lowly methyl-esterified, linear Ca2+-cross-linked pectin with high molar mass
- Limited amount of highly methyl-esterified, branched water-soluble pectin

As pectins are structurally highly variable between plant species, waste streams of other sources than the commercially used citrus peel and apple pomace may contain industrially useful forms of pectin. The potential of papaya peel as a source for the extraction of pectin in countries of the South was investigated in this study. In particular, pectin extracted from the peel of a wild (Local) and an ameliorated (Solo) papaya variety was structurally characterised. Pectin was examined via physicochemical (sugar composition, solubility, linearity, branching, degree of methoxylation, molar mass) and immunological (binding of anti-pectin antibodies) analysis of fractionated cell walls and isolated polymers. Cell-wall material isolated from papaya peel appeared to be rich in pectin, indicating a potential (industrial) source of this polysaccharide. The peel of both papaya varieties predominantly consisted of low methyl-esterified, linear Ca2+-cross-linked homogalacturonan with high molar mass, while only a limited amount of high methyl-esterified, branched water-soluble pectin could be retrieved from Solo and Local papaya peel. Differences between pectins obtained from the peel of the wild and ameliorated papaya varieties were rather limited. However, rhamnogalacturonan-I (a branched domain of pectin) retrieved from the peel of Solo had generally longer and/or more arabinan, galactan and/or arabinogalactan side chains than rhamnogalacturan-I from the peel of the Local papaya variety. In addition, pectin from Local papaya peel presented a lower degree of methyl-esterification than pectin from the Solo variety. The structural characteristics of papaya peel pectin revealed by this study can form a basis for understanding its functional properties as ingredient in food systems.