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

Harvested nectarine fruit [Prunus persica (L.) Batsch 'Flavortop'] were held 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 were conducted after removal from storage for 1, 3, or 5 weeks and a shelf life of 5 additional days at 20 OC. After 5 weeks storage, 87% of control fruit developed woolliness (mealiness in texture accompanied by dry tasting fruit as a result of reduced juice content), while only 7% of delayed-cooling fruit showed signs of woolliness, Firmness of fruit in the delayed- cooling 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 (65%). Along with woolliness, viscosity of the resuspended alcohol insoluble residue (cell. wad material) of expressed juice increased, implying accumulation of large molecular-weight polymers. The high performance liquid chromatography 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 arabinose content in these polymers reflected greater side chain removal from 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.