the species and variety. The degree of ripeness of fruit
has a significant influence on the content of sugars, minerals
and acids. The sugar content in fully ripe apples is high
due to complete hydrolysis of starch. Then, during storage,
sugars content begins to decrease, as they are consumed in
respiration process.
During ripening on the tree, the organic acid content in
apples increases, reaches a maximum for a few days before
harvest and then slightly decreases. However, acid content
during storage has been gradually declining. It is thought
that part of them, in addition to sugars, may be consumed
in the process of respiration. Storage leads to softening of
fruits, which is mediated by loss of cell-to-cell adhesion.
Tissue from soft fruits has rounded cells, bigger cell separation
and larger intercellular spaces. Analyses of
pectin fractions have shown that apple softening is usually
associated with the increased content of water-soluble
pectin and reduced galactose and arabinose residues. A
number of cell-wall-modifying enzymes that have been
found in ripening apples may cause softening. The enzyme
originally considered responsible for pectin solubilization,
and therefore, softening was polygalacturonase (PG), with
activities of both exo-PG and endo-PG detected in ripening
apples. Direct measurements of turgor showed that