- Citric acid is an acid that gives lemons, oranges and other citrus fruits their sour taste. Lemon juice has 6-7% of the acid. Carl Wilhelm Scheele, a Swedish chemist, first isolated citric acid from lemon juice in 1784. Very soluble in water, pure citric acid forms colourless, odourless crystals. Having a melting point of 153° C, citric acid can combine with metals to form salts called citrates.
- pH is a number used to indicate the concentration of hydrogen ions in a solution. The number generally ranges from 0 to 14. A pH below 7 indicates that a solution is acidic, and a pH above 7 indicates that a solution is basic (alkaline), A neutral solution, such as pure water, is neither acidic nor basic and has a pH of 7 at 25° C. pH stands for potential of hydrogen. pH is measured using an electronic pH meter or with acid-base indicators. The colour of an indicator depends on the concentration of hydrogen ions. pH paper contains several indicators that change colour at different pH’s. When dipped into a solution, the paper’s colour indicates the approximate pH of the solution.
- Citrus fruits have both citric acid and ascorbic acid. Ascorbic acid is also known as Vitamin C.
Acid content is measured by pH. The pH is measured on a scale from 0 to 14, with "0" being the most acidic, "7" being neutral and "14" being the most alkaline. The most acidic of the citrus fruits are: Tangerine: pH 3.90; grapefruit, pH 3.38; lime: pH 2.40; and lemon: pH 2.30. The least acidic of the citrus fruits are mandarin, pH 11.50; orange, pH 4.35; and kumquat: pH 3.95. The acid levels of fruits decrease as the fruit ages.
- Alkaline means that a compound or solution contains an alkali. Alkaline substances usually have a pH level that is greater than 7 on the pH scale. Alkaline substances usually accept hydrogen ions when dissolved in water.
- The pH levels of citrus fruits can cause damage to tooth enamel. Typically, the lower the pH, the more damage is done to the teeth. Oranges have a higher pH level, at 4.35, and are less damaging to teeth than lemons at 2.75, limes at 2.88, and grapefruits at 3.65. A diet that is high in citrus can gradually erode the enamel on a person's teeth due to the higher pH levels of citrus fruits.