Why Is an Orange Acidic?

Oranges are acidic because they contain several naturally occurring acids. Citric acid is the predominant organic acid found in oranges, followed by malic acid, with trace amounts of lactic, tartaric, benzoic, ascorbic and succinic acids.

Features

• Citric acid is the signature chemical compound of citrus fruits such as oranges, lemons and limes. Citric acid and malic acid contribute to the tartness of oranges which, in mature fruit, is balanced by the high levels of natural sugars (fructose and glucose). Oranges taste sweeter than lemons and limes, which have higher acid but lower sugar content.

Function

• Citric and malic acids are not only natural flavoring agents in oranges, they are also used as additives in food processing for their tart taste and preservative properties.

Identification

• The chemical name of citric acid is 2-hydroxypropane-1,2,3-tricarboxylic acid. The approximate amount of citric acid in oranges ranges from 8 to 25 mg per mL of juice and is the chief contributor to the acidity of the fruit. The approximate amount of malic acid---hydroxybutanedioic acid---ranges from 1.4 to 1.7 mg per mL of juice. The acidity in an orange yields an approximate average pH level of 4.35.

Benefits

• Oranges are an excellent source of ascorbic acid---more commonly known as vitamin C---with about 70 mg per average-sized fruit. Although significant from a nutritional standpoint, the amount of ascorbic acid in an orange does not significantly contribute to the tart taste.

Misconceptions

• Citric acid is often confused with ascorbic acid. They are, however, different chemical compounds. The molecular formula of citric acid is C6H8O7 while the formula for ascorbic acid is C6H8O6.