When oranges are frozen on the tree, growers have a short time (about 24 hours) to get the fruit off the tree and processed into juice. After that time, the fruit deteriorates on the tree, and quality is ruined.
Basically what has happened is that the small vesicles or sacks that hold the juice of the fruit have been broken by the freezing, i.e., as the fruit freezes, it expands, and these membranes are broken; hence, the juice runs out of the fruit and is exposed to all sorts of organisms that break it down.
The juice that is frozen in the stores is from processed juice that is concentrated. Additionally, juice from navel oranges does not store well. It must be consumed very quickly after juicing, or it will oxidize and become bitter.
