Storage temperature affects the pH level of some juices, particularly orange juice, which has a higher pH level when it is cold and a lower pH level at temperatures higher than normal room temperature. Citric acid is present in most fruits and fruit juices.
Orange juice has a pH level or around 3.5, but is already quite acidic, thanks to the citric acid found in the juice. Citric acid is a weak acid, which means it will not completely dissolve in water.
Although the pH level of orange juice does change based on temperature, these changes are fairly small. Assuming the baseline pH level of orange juice is 3.5, temperature variables may cause changes in the range of 3.46 or 3.54, basing calculations on the pKa of citric acid.
However, because citric acid is not the only component of orange juice, basing calculations purely on the acid will not necessarily give accurate pH changes, although they will tend to be in a similar range.
Most fruits contain citric acid in varying quantities, meaning that many fruit juices also contain it. In general, the same method and analysis can be applied to most fruit juices. Because changes in pH level are so small however, it is unlikely to be noticeable to anyone drinking the juice.