Limonene is a natural ingredient in many fruits (mainly citrus), vegetables and spices. It is rich in essential oils of citrus fruits (especially peels), spices and herbs. The limonene content in orange peel essential oil is as high as 90%~95%(w/w). Food seasonings, wine and some vegetable oils (barley oil, rice bran oil, olive oil and palm oil) are rich sources of these compounds.