Proportions of calcium, magnesium, phosphorus and potassium extractable by water or ethanol from apple fruit tissue, in relation to length of storage, orchard factors and storage disorders

Calcium, magnesium, phosphorus and potassium were measured in residues of samples of Cox's Orange Pippin apples stored in air at 2.8‐4.4°C, removed at intervals and extracted with either distilled water or 75% ethanol. Little potassium was left in the residue after extraction with water, but 15% remained after extraction with ethanol. More phosphorus (85%) was extracted by ethanol than by water. Calcium and magnesium became less soluble during storage. Higher proportions of calcium and magnesium were removed by water than by ethanol initially but, whereas these differences between solvents remained fairly constant for calcium, those for magnesium decreased. When decreases in proportions of soluble calcium and magnesium were small little bitter pit and no breakdown developed in the fruit. Little change in the proportions of mineral constituents, other than phosphorus occurred whilst the fruit was on the tree during the 6 weeks before harvest. Proportions of phosphorus remaining in the residues after extraction with either solvent diminished, especially during the 3 weeks before harvest when apples had been sprayed with calcium nitrate. Otherwise orchard treatments had little effect on the proportions of mineral constituents that could be extracted. Although symptoms developed when the proportion of calcium insoluble in water rose above 40% of the total, some increases in susceptibility to bitter pit caused by orchard treatment or storage conditions were not associated with differences in insoluble calcium.