MOLECULAR CHARACTERISTICS OF PECTIC CONSTITUENTS IN RELATION TO FIRMNESS, EXTRACTABLE JUICE, AND WOOLLINESS IN NECTARINES

'Flavortop' nectarines [Prunus persica (L.) Batsch] were either stored for 4 weeks at -0.5C or not subjected to cold storage before being ripened at 15C. The differences in extractable juice, woolliness, composition, and gelling characteristics of extracted pectins between the two treatments were determined during ripening. As ripening progressed, the extractable juice in both treatments decreased to low values after which it increased with further ripening. Woolliness only occurred in fruit that was cold stored. Nectarines became woolly from the 2nd day and peaked on the 6th day of ripening in fruit cold stored for 4 weeks. As fruit firmness decreased, the soluble pectin concentration increased to the same extent in both treatments at the expense of insoluble pectin. In cold-stored fruit, the viscosity of pectin increased gradually until the 6th day of ripening, while in noncold-stored fruit maximum viscosity was higher and occurred between the 4th and 6th day of ripening. From the 6th day, the viscosity decreased in both treatments to levels lower than the initial viscosity. The extractable juice was lowest when the viscosity of soluble pectins and percentage of woolly fruit were highest. Molecular mass distribution of soluble pectins decreased considerably during ripening at 15C.