All citrus fruits contain ascorbic acid, also called vitamin C, and are considered acidic fruit. The higher the ascorbic acid content, the better the taste and quality of the fruit. Oranges, lemons, limes, grapefruit and other citrus fruits are among the most detoxifying foods and also contain other important nutrients such as vitamin A. Citrus fruits also contain citric acid and pantothenic acid, which is a B vitamin that helps to oxidise fats, carbohydrates and some amino acids.
Ascorbic acid, or vitamin C, has a chemical make-up of C6H8O6. The amount of ascorbic acid in citrus fruit depends on several factors. When fruit such as oranges are picked late in their season, the concentration of ascorbic acid is lower than in fruit picked earlier. Cultural practices, such as how much water and fertiliser the tree received during its growing season, also affect ascorbic acid content. For example, when trees are given fertilisers that are high in nitrogen, the fruit will have a lower acid content. Temperature also affects ascorbic acid content. When citrus fruit is grown in places that have cooler nights, vitamin C content is higher than in fruits grown in tropical locations. The fruit is not the only place where ascorbic acid is found in citrus fruits--up to 75 per cent is located in the peel.
Citric acid has a chemical make-up of C6H8O7, one more oxygen atom than ascorbic acid. It is found in all citrus fruits and some other foods. Lemons and limes have the highest citric acid content of the citrus fruits. Citric acid is a white powder at room temperature and then it crystallises when added to hot water. It is added to processed food products such as fruit- flavoured candies, soft drinks and sourdough breads because it helps to enhance their tart flavours.
Lemons and Limes
Lemons and limes are the winners in the citrus acidity count. Vitamin C (ascorbic acid) can comprise up to 32 per cent of the fruits' weight. Lemon juice contains 187 per cent vitamin C. Citric acid makes up 5 per cent to 6 per cent of the fruits' content. Lemons contain approximately 3 per cent pantothenic acid. Fresh lime juice contains 121 per cent vitamin C and 1 per cent pantothenic acid.
Oranges have the smallest concentration of vitamin C of all the citrus fruits. One medium orange typically contains between 50 and 70 mg of vitamin C. Oranges also have .08 to 1 per cent citric acid. Different varieties of oranges have differing amounts of vitamin C. The cultivar "Pineapple" has the most, followed by the Hamlin variety. Valencia oranges, the most common oranges grown for their juice, have the lowest amount of vitamin C. Orange peel has 53 per cent of the fruit's vitamin C, while the juice contains 26 per cent ascorbic acid. The pulp and "rag" have 21 per cent.
Grapefruit, Tangerines and Other Citrus
Grapefruit is higher in vitamin C than oranges, second only to its citrus relatives lemons and limes. One cup of measured segments contains 120 per cent vitamin C, 1.5 per cent to 2.5 per cent citric acid and 7 per cent pantothenic acid. Mandarin oranges, tangelos and most other types of tangerine-type fruit must have 8 per cent acidity in order to be considered for the commercial market. Their vitamin C content is 87 per cent, which is typically lower than oranges because tangerines have lower acid levels overall.