Involvement of terminal-arabinose and -galactose pectic compounds in mealiness of apple fruit during storage

Among eight apple cultivars (Malus domestica Borkh) held at 0 or 20 degreesC for 4 or 8 weeks, mealiness was highest in 'Starking Delicious' (83%) and lowest in 'Golden Delicious' (0%) after 20 degreesC for 8 weeks. In 'Starking Delicious' and 'Golden Delicious' fruit, total uronic acid contents [amount of water (WSP) + hexametaphosphate (HMP) + HCl soluble (HCP) pectic fractions] of the alcohol insoluble solids (AIS) of flesh hardly changed during storage at 20 degreesC, although the ratio of uronic acid in WSP to total uronic acid increased during storage. Total (WSP + HMP + HCP) pentose contents in AIS decreased in most cultivars during storage, and the decrease was greatest in the fruit stored at 20 degreesC. In 'Starking Delicious' fruit, the ratio of pentose in WSP to total pentose increased during storage at 20 degreesC. Among pentoses, arabinose (Ara) content in the fruit stored at 20 degreesC decreased more than in the fruit stored at ODC. The linkages of the arabinose residue in each fraction were mainly T (terminal)-Ara, 5-Ara and 3,5-Ara, determined by methylation analysis. The ratio of T-Ara and 3,5-Ara to total arabinose linkage decreased both in HMP and HCP. The decrease in T-Ara and 3,5-Ara was higher in 'Starking Delicious' fruit compared with that in 'Golden Delicious' fruit in storage at 20 degreesC. The: linkages of the galactose residues in each fraction identified were mainly T-Gal, 3,6-Gal, 2,4-Gal and 6-Gal. The ratio of T-Cal to total galactose linkage increased both in HMP and HCP. The increase in T-Gal was higher in 'Starking Delicious' fruit than in 'Golden Delicious' fruit in storage at 20 degreesC. The possible effect on mealiness of the release of T-Ara and increase of T-Gal in pectic substances is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.