A few of the commonly eaten acidic fruits are oranges, grapefruit and tomatoes. These fruits also generally contain the highest content of acids when compared to other fruit.
Fruit that is considered a high-acid fruit is defined by having a pH level of 4.6 or lower. This can be caused by a number of different reasons, such as having an acid added to them like vinegar or lemon juice. Some other fruits are just naturally high in acid. Additionally, fermented fruits tend to have a higher acid content as a result of acid production from bacteria during fermentation.
High-acid fruits have a better ability to prevent growth of botulinum bacteria spores than lower-acid fruits. That being said, it is always a much safer bet to process properly any type of fruit in boiling water during canning. The temperature and boiling times varies from fruit to fruit.
Some fruits that contain high acid can cause heartburn in certain people that have a low tolerance for it. An easy way to help prevent the heartburn is to consume foods that help produce saliva in the mouth, such as sour foods. The saliva helps neutralize the high-acid fruit and assists in preventing heartburn.