The effect of harvesting time on the biochemical and ultrastructural changes in Idared apple

Apples were harvested at three different times (1st, 2nd and 3rd) then stored at 1-3degreesC, 85-90% R.H. for 5 months. Firmness, ethylene productivity, the distribution of calcium and potassium and the ion leakage were measured. The ultrastructure of the cell wall was studied by SEM and TEM and be activity of beta-galactosidase and polygalacturonase and pectin content were determined. The ethylene evolution of fruits decreased by the harvest and storage time. At the beginning of storage, the ethylene productivity in the 1st harvest apple increased up to a maximum value then declined. The 2nd harvest fruits produced less ethylene than that observed in 1st harvest fruits. No ethylene production was found in the 3rd harvest fruits. Firmness was different according to harvest time, but that difference disappeared during storage. The permeability of membranes increased as a function of harvests and storage. The distribution of calcium was typical at the beginning, the highest concentration of calcium being near the core and skin, but by the end of the storage calcium moved from the skin towards the core. Potassium content was the highest near the core and decreased towards the skin, both in the fresh and stored apples. The activities of polygalacturonase and beta-galactosidase were not influenced by the harvest time, but changed as a function of storage time. The autolysis of pectin and soluble carbohydrates increased during storage, mostly in the 3rd harvest. At the beginning of storage, the cell wall and middle lamellae of the 1st harvest fruits' flesh were not damaged. Large degradation of the middle lamellae was observed in the 2nd and 3rd harvest fruits. Lower membrane permeability, pectin degradation and PG enzyme activity were found in the 1st harvest apples. The Idared apple should be harvested close to the climacteric maximum for better and longer storage.