Pectin esterase, polygalacturonase and gel formation in peach pectin fractions

Peaches (Prunus persica cv. Hermoza) were stored at 0C in regular air (RA) or in controlled atmosphere (CA 10% CO2, 3% O-2) for 4 weeks and then ripen ed for 4 days at 20 degreesC. Woolliness developed in the regular air store d fruit while the controlled atmosphere stored Fruit ripened normally. In t he woolly fruit symptoms of the disorder were greater in the inner mesocarp than in the enter. Polygalacturonase (PG) and pectin esterase (PE) activit ies differed in the outer and inner mesocarp of the affected fruit. PCI act ivity was low and PE activity was high in the inner mesocarp of the woolly fruit during ripening relative to the outer mesocarp, while in the healthy fruit, activities were similar. in both areas. Cell wall fractions of water -soluble, CDTA-soluble and carbonate-soluble pectins were prepared from fi freshly harvested peaches and incubated with PE and PG from ripe peaches at different ratios. Only the CDTA-soluble fraction formed a gel with peach e nzymes, and the rate of gelation increased with increasing amounts of PE re lative to PC. Both water-soluble and CDTA-soluble pectin fractions formed g els with commercial PE (extracted from orange peel). The PE extracted from peaches was stable when stored at 0 degreesC for 9 days, while PG activity was stable only for 1 day. We suggest that PE, acting on pectins in the cel l wall in vivo may cause Eel formation and that the CDTA-soluble polymers h ave the capacity to bind apoplastic water and create the dry appearance obs erved in woolly fruit. (C) 2000 Elsevier Science Ltd. All rights reserved.