CULTIVAR AND MATURITY EFFECTS ON MUSKMELON (CUCUMIS-MELO) COLOR, TEXTURE AND CELL-WALL POLYSACCHARIDE COMPOSITION

Cell wall polysaccharides (CWP) of two types of melons were isolated a nd purified. Fractionations were performed using cyclohexane trans-1,2 -diamine tetraacetate (CDTA), Na2CO3, guanidinium thiocyanate (GTC) an d KOH. Alditol acetate derivatives of neutral sugars from each CWP fra ction were prepared and analysed by gas chromatography. Trifluoro-acet ic acid insoluble fractions were analysed colorimetrically and uronic acid was determined. The CDTA and Na2CO3 fractions were found to be co mposed of typical pectic materials containing primarily galacturonic a cid with the neutral sugars arabinose, galactose, rhamnose and a small er amount of xylose. As maturity increased, CDTA fraction yields incre ased, though total neutral sugar CWP compositions decreased. GTC and K OH fractions were typical of hemicellulose, and contained principally xylose, glucose, galactose, mannose and fucose, with very small amount s of uronic acid, arabinose and rhamnose. The residues contained princ ipally glucose and galactose, with smaller amounts of mannose, xylose, arabinose and fucose. With the exception of xylose and glucose, all n eutral sugars decreased significantly during ripening in both the Cant aloupe and Honey Dew melons. Total uronic acid did not change as matur ity increased, except for Cantaloupe, where total uronic acid decrease d from the ripe to overripe stages. Relationships between firmness, dr ip loss and other composition measurements, as well as the total CWP s ugar 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 incre ased.