Cultivar and Maturity Effects on Muskmelon ( Cucumis melo Colour, Texture and Cell Wall Polysaccharide Composition

Abstract

Cell wall polysaccharides (CWP) of two types of melons were isolated and purified. Fractionations were performed using cyclohexanetrans-1,2-diamine tetraacetate (CDTA), Na2CO3, guanidinium thiocyanate (GTC) and KOH. Alditol acetate derivatives of neutral sugars from each CWP fraction were prepared and analysed by gas chromatography. Trifluoro-acetic acid insoluble fractions were analysed colorimetrically and uronic acid was determined. The CDTA and Na2CO3 fractions were found to be composed of typical pectic materialscontaining primarily galacturonic acid with the neutral sugars arabinose, galactose, rhamnose and a smaller amount of xylose. As maturity increased, CDTA fraction yields increased, though total neutral sugar CWP compositions decreased. GTC and KOH fractions were typical of hemicellulose, and contained principally xylose, glucose, galactose, mannose and fucose, with very small amounts of uronic acid, arabinose and rhamnose. The residues contained principally glucose and galactose, with smaller amounts of mannose, xylose, arabinose and fucose. With the exception of xylose and glucose, all neutral sugars decreased significantly during ripening in both the Cantaloupe and Honey Dew melons. Total uronic acid did not change as maturity increased, except for Cantaloupe, where total uronic acid decreased from the ripe to overripe stages. Relationships between firmness, drip loss and other composition measurements, as well as the total CWP sugar composition, were also determined. Only the CDTA fraction yields were negatively correlated with the changes in firmness of both melons and positively correlated with changes in drip loss as maturity increased.