PHYSIOLOGICAL FACTORS ASSOCIATED WITH OVERRIPENESS, INTERNAL BREAKDOWN AND GEL BREAKDOWN IN PLUMS STORED AT LOW-TEMPERATURE

Plums (Prunus salicina cv. Songold) were stored at -0.5-degrees-C for up to 50 d. On the day of harvest and thereafter at ten-day intervals, sub-samples were stored at 15-degrees-C and allowed to ripen for eight days, with evaluations every two days. Low temperature storage prior to ripening at 15-degrees-C was a prerequisite for plums to ripen. Overripeness was inhibited by low-temperature storage but developed when fruit was ripened at, or before, 30 d of storage. Longer storage resulted in the development of gel and internal breakdown at both -0.5-degrees-C and during ripening. The transition from overripeness to gel and internal breakdown was associated with significant increases in electrolyte leakage and internal conductivity at a time that viscosities of water soluble pectins were high. The resulting decrease in extractable juice suggested that cell fluids which leaked through cell membranes had bound with pectic substances. This was associated with development of gel and internal breakdown.