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

Abstract

Abstract Among eight apple cultivars (Malus domestica Borkh) held at 0 or 20°C for 4 or 8 weeks, mealiness was highest in ‘Starking Delicious’ (83%) and lowest in ‘Golden Delicious’ (0%) after 20°C 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°C, 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°C. In ‘Starking Delicious’ fruit, the ratio of pentose in WSP to total pentose increased during storage at 20°C. Among pentoses, arabinose (Ara) content in the fruit stored at 20°C decreased more than in the fruit stored at 0°C. 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°C. 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-Gal 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°C. The possible effect on mealiness of the release of T-Ara and increase of T-Gal in pectic substances is discussed.