Comparative study of cell wall polysaccharides from pulp and peel of dragon fruits (Hylocereus spp.)

Cell wall polysaccharides from the pulp and the peel of white-flesh and red-flesh dragon fruits (Hylocereus spp.) were isolated using various solvents in order to obtain different pectin fractions. The galacturonic acid (GalA) content, the degree of methoxylation (DM), the neutral sugar composition and the molar mass distribution of these pectin fractions were determined, as well as their affinity towards some specific anti-pectin antibodies. The results showed that cell wall polysaccharides of dragon fruit samples contained significant amounts of pectic substances with a low average DM value. No remarkable differences between the pectic substances of the different dragon fruit varieties were observed while there were large differences between the pectic fractions of the peel and the pulp samples. The pectic substances in the peel are fairly linear and highly water-soluble whereas in the pulp, on the contrary, pectin is more branched and contains comparable amounts of loosely-bound, ionically-bound and strongly-bound pectic fractions. Using anti-pectin antibodies with different specificities (towards different pectin structures), it was revealed that a wide range of epitopes, including long blocks of unesterified GalA residues as well as blocks with consecutive esterified GalA residues, are present in the pectin fractions of peel/pulp dragon fruits.