Lurie, S., Department of Postharvest Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel
Zhou, H.-W., Department of Postharvest Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel
Lers, A., Department of Postharvest Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel
Sonego, L., Department of Postharvest Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel
Alexandrov, S., Department of Food Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel
Shomer, I., Department of Food Science, Volcani Center, Agricultural Research Organization, P.O.B. 6, Bet Dagan 50250, Israel

Peach fruit (Prunus persica cv. Hermosa) were allowed to ripen immediately after harvest or after 30 days of 0°C storage. The fruits lost 75-80% of their firmness after 5 days at 20°C. During ripening after harvest there was a loss of both uronic acid and methyl groups from the cell wall. Cell wall labelling with JIM 7, a monoclonal antibody which recognized pectins with a high degree of methylation, was lower in ripe fruits than in freshly harvested fruits. However, ripe fruit cell walls did not cross-react with JIM 5, which recognizes pectins with low methylation. During storage, de-methylation occurred and in fruit ripened after storage there was little further change in pectin methylation or pectin content in the cell walls. The labelling of stored or stored plus ripened cell walls with JIM 7 was similar, but the cell walls of fruit ripened after storage showed some low cross-reactivity with JIM 5. The in vitro activity and mRNA abundance of pectin esterase (EC 3.1.1.11) was not correl-ated with the amount of de-esterification as measured chem-ically or by immune-labelling in the cell walls. Eighty percent of the fruits which ripened after storage developed a woolly texture. It is suggested that woolliness is due to de-esterification of pectins, not accompanied by depolymeri-zation, which leads to the formation of a gel-like structure in the cell wall.