Effect of storage regimes on pectolytic enzymes, pectic substances, internal conductivity and gel breakdown in cold stored ‘Songold’ plums

Improvement of Storability and Shelf-life of ‘Blackamber’ Plums Treated with 1-methylcyclopropene

Rapid softening is one of the most important factors that limits the market life of plums. To avoid this problem, ‘Blackamber’ plums were treated with 0, 150, 300 and 600ppb of 1-methylcyclopropene (1- MCP) and their quality evaluated after 15, 30 and 50 days of storage at 0°C, immediately and after 6 days at 25°C. 1-MCP treatment effectively decreased ethylene production during storage and shelf-life in fruits kept 15 and 30 days at 0°C. In contrast, fruits kept for 50 days at 0°C showed a significant increase in ethylene production during shelf-life. Changes in ethylene production by 1-MCP were associated with a decrease of firmness loss and maintenance of titratable acidity but not with the development of red flesh colour. Soluble solids content of the fruit was not affected by the 1-MCP treatment. In this assay no significant symptoms of chilling injury (CI) or rot were observed. Overall, the results presented in this assay ascertained ethylene on quality changes in ‘Blackamber’ plums. They also showed that 1- MCP could be considered commercially to improve the storage life and resistance to mechanical bruising in ‘Blackamber’ plums without prejudicial effects on quality.

Compositional changes in cell wall polysaccharides from Japanese plum ( Prunus salicina Lindl.) during growth and on-tree ripening

Climacteric Japanese plums were harvested at six developmental stages with no intermediate storage period, and cell wall compositional changes were analyzed. Arabinose proved to be the principal neutral monosaccharide constituent in cell walls during growth and the most dynamic neutral sugar in pectic fractions. Arabinose loss from tightly bound pectins was found to be a relatively early feature in the sequence of cell wall biochemical modifications, thus suggesting a softening-related role during Japanese plum on-tree ripening. Depolymerization of matrix glycans started at the end of the cell expansion phase and increased throughout ripening. Pectin solubilization was first detected during early ripening. Firmness loss did not correlate with polyuronide depolymerization early in ripening, but the last softening phase was associated with a strong depolymerization of cell wall polyuronides as well as a decrease in the arabinose/galactose ratio in loosely bound pectins. This is the first work that characterizes the temporal sequence of cell wall polysaccharide changes in Japanese plum.

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% O2) for 4 weeks and then ripened for 4 days at 20 degrees C. Woolliness developed in the regular air stored fruit while the controlled atmosphere stored fruit ripened normally. In the woolly fruit symptoms of the disorder were greater in the inner mesocarp than in the outer. Polygalacturonase (PG) and pectin esterase (PE) activities differed in the outer and inner mesocarp of the affected fruit. PG activity 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 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 enzymes, and the rate of gelation increased with increasing amounts of PE relative to PG. Both water-soluble and CDTA-soluble pectin fractions formed gels with commercial PE (extracted from orange peel). The PE extracted from peaches was stable when stored at 0 degrees C for 9 days, while PG activity was stable only for 1 day. We suggest that PE, acting on pectins in the cell wall in vivo may cause gel formation and that the CDTA-soluble polymers have the capacity to bind apoplastic water and create the dry appearance observed in woolly fruit.