Analysis of cell wall components in juice of 'Flavortop' nectarines duringnormal ripening and woolliness development

Harvested nectarine fruit [Prunus persica (L.) Batsch 'Flavortop'] were hel d for 5 days at 20 degrees C, or stored at 0 degrees C either immediately ( control), or after 2 days at 20 degrees C (delayed-cooling). Observations w ere conducted after removal from storage for 1, 3, or 5 weeks and a shelf l ife of 5 additional days at 20 OC. After 5 weeks storage, 87% of control fr uit developed woolliness (mealiness in texture accompanied by dry tasting f ruit as a result of reduced juice content), while only 7% of delayed-coolin g fruit showed signs of woolliness, Firmness of fruit in the delayed- cooli ng treatment was less at the beginning of ripening than control fruit, but after shelf life in both treatments, fruit reached the same final softness. Expressible juice was lower in woolly fruit (46%) than in healthy fruit (6 5%). Along with woolliness, viscosity of the resuspended alcohol insoluble residue (cell. wad material) of expressed juice increased, implying accumul ation of large molecular-weight polymers. The high performance liquid chrom atography profile confirmed there were more large pectin polymers (2000 to 76 Ku) in the cell wall components of juice from woolly fruit and a lower a rabinose content in these polymers reflected greater side chain removal fro m pectins in the juice of woolly fruit, Accumulation of larger sized pectin polymers along with high viscosity correlated with lower polygalacturonase activity in woolly fruit. Degradation of soluble pectin released into the juice of woolly fruit may have been impeded by repressed polygalacturonase activity.