CHANGES IN THE PHYSICOCHEMICAL PROPERTIES OF PEACH FRUIT PECTIN DURING ON-TREE RIPENING AND STORAGE

Radius of gyration (size), intrinsic viscosity, molecular weight, perc entage of galacturonate, and percentage of neutral sugars were measure d for chelate-soluble (CSP) and alkaline-soluble (ASP) pectins extract ed from the cell walls of melting flesh (MF) and nonmelting flesh (NMF ) peach [Prunus persica (L.) Batsch]. Weight percentage of cell walls, pectin content, and firmness were measured also. Peaches were extract ed at 20, 21, and 22 weeks after flowering (WAF) and after various len gths of shelf storage at 25 +/- 2C for the peaches picked at 21 WAF. W eight percentage of cell walls and firmness decreased markedly between the 21st and 22nd WAF; and between the 3rd and 6th day of storage for MF peaches as compared to NMF peaches. During these same periods, the re were marked drops in the pectin content and the uronide content for MF as compared to NMF peaches. Size and intrinsic viscosity dropped m arkedly for CSP of MF peaches in comparison with NMF peaches during th ese same periods, whereas the molecular weight of CSP and ASP increase d in MF peaches over that measured for NMF peaches. These results sugg ested that alpha-D-galacturonase (E.C. 3.2.1.15) was involved in softe ning only in the latter stages of ripening MF peaches. Further, cell w all polymers containing long thin pectin aggregates were destroyed, wh ereas cell wall polymers containing short thick pectin aggregates rema ined.