SUGAR COMPOSITION OF PECTIN AND HEMICELLULOSE EXTRACTS OF PEACH FRUITDURING SOFTENING OVER 2 HARVEST SEASONS

Changes in cell wall polysaccharides associated with peach fruit softe ning were characterized over two harvest seasons, Enzymically inactive cell walls were prepared from mesocarp tissues of peach fruit harvest ed at three stages of softening,. Pectina-associated and hemicellulose -associated polysaccharides were extracted from the cell walls sequent ially, and glycosyl residue compositions were determined by GLC. Pecti n extracts from both years were richest in galacturonosyl, arabinosyl, and rhamnosyl residues, Hemicellulose extracted with 1 M potassium hy droxide contained a high mole percentage of xylosyl, glucosyl, and fuc osyl residues. Hemicellulose extracted with 4 M potassium hydroxide co ntained a substantial amount of pectin-associated sugar residues in ad dition to hemicellulose-associated sugar residues, During softening in both years, sugar compositions for cell walls, aqueous phenol-soluble polysaccharides, and imidazole extracts reflected a decrease in galac turanosyl residues and a concomitant increase in arabinosyl residues o n a mole percent basis. The degree of change for galacturonosyl residu es in these fractions depended on season, with greater variation exhib ited from fruit at earlier stages of softening. With the notable excep tion of the seasonal variation exhibited for galacturonosyl residues i n cell walls, the relative stability of other glycosyl compositional c hanges over seasons indicates conserved changes for pectins and hemice lluloses occur during peach fruit softening.