Pigments contribute greatly to the aesthetic appeal of foods. The chemical forms of some pigments are easily altered under conditions that may also affect the structural integrity of the tissue. Heating, pH changes, and oxidation reactions can affect pigment quality. The predominant meat pigment is myoglobin. Reactions of myoglobin determine the color of fresh and cured meats. Plant pigments may be categorized as carotenoids, chlorophylls, and flavonoids. Included in the flavonoid group are the phenolic compounds, which are the substrates in the enzymatic browning of fruits and vegetables. Preservation of desirable color, flavor, and textural qualities present at harvest of ripe fruits and vegetables depends greatly on control of the deteriorative changes caused by endogenous enzymes. Sometimes colorants are added to foods to enhance their marketability.