Collagen is the most abundant protein in the human body. The collagen superfamily includes more than 20 different collagen types, which serve a structural function in the body. Collagen is found in the skin, connective tissues, blood vessel walls and in your eye. Collagen is rich in the amino acids proline and lysine. Vitamin C aids the formation of collagen. Though fruits do not contain collagen, fruits that supply protein or provide vitamin C furnish your body with the building blocks of this important structural protein.
In addition to its function in the formation of collagen, vitamin C helps protect cells from free radical damage. Bell peppers, a vegetable fruit, are an excellent source of vitamin C. One medium red pepper provides 380 percent of the daily value of vitamin C. Vitamin C is highly sensitive to temperature. Cooking peppers can result in a loss of over half of the vitamin C content. To maximize the vitamin C content of bell peppers, eat them raw.
Strawberries have more vitamin C, per serving, than most fruits, including citrus fruits. One cup of strawberries packs more than 150 percent of the daily value for vitamin C. Vitamin C functions in the cross-linking of collagen, which increases its tensile strength. This strengthens important tissues, including your bones and skin. Collagen also helps your skin retain its elasticity, keeping you looking younger for longer.
Not only are lemons high in vitamin C, they have the most protein of all fruits. The higher a fruit's protein content, the greater the amount of the amino acids, proline and lysine, which are used in collagen's formation. One cup of lemon juice contains 128 percent of the daily value of vitamin C. Lemons contain 16 percent protein, twice the amount found in oranges and three times the protein in grapefruits.