Internal breakdown (IB) is the limiting factor in the storage and postharvest handling of stone fruits. The symptoms of IB appear when fruits are kept for prolonged periods at temperatures below 10C and include leatheriness, mealiness, browning and bleeding of the flesh, and failure to ripen normally. We investigated the changes in phenolic compounds associated with IB of stone fruits. Twenty-eight phenolic compounds were separated by HPLC. Ten of these components were significantly affected by chilling temperatures. The concentration of six phenols changed in response to ripening after chilling temperatures, parallel to the appearance of IB symptoms. Most phenols showed a concentration gradient from the inside to the outside of the fruit, Comparison between peach cultivars showed characteristic differences in phenol metabolism during ripening. In both cultivars the most predominant phenol, chlorogenic acid, showed little change in concentration during storage. The structure of key phenolic compounds will be determined in order to elucidate the biochemical relationship between the phenols and the related enzymes. In this respect, a method was developed to detect phenylalanine ammonia-lyase (PAL) activity in peach fruit.
Hendrik van Gorsel and Adel A. Kader
Dangyang Ke, Hendrik van Gorsel and Adel A. Kader
`Bartlett' pears (Pyrus communis L.) tolerated up to 10 days of exposure to atmospheres containing 1.0%, 0.5%, or 0.25% O2 at 0, 5, or 10C without any detrimental effects on their quality attributes. The fruits also tolerated 4 to 6 days of exposure to air enriched with 20%, 50%, or 80% CO2 at the three temperatures. The beneficial effects of exposures to the O2-reduced or CO2-enriched atmospheres included reduction of respiration and ethylene production rates and retardation of skin yellowing and flesh softening. While 1.0% or 0.5% O2 and 20% CO2 did not increase ethanol and acetaldehyde contents, 0.25% O2 slightly increased and 50% or 80% CO2 dramatically increased the contents of these two volatiles in juice of the fruits. The effects of low O2 or high CO2 on the above attributes generally became more pronounced at the higher temperatures. The low O2 or high CO2 treatments did not significantly affect either soluble solids content or titratable acidity. Low O2 did not influence, but high CO2 slightly increased pH of the fruits.