Detection of adulteration of cold‐pressed lemon oil

Adulteration of cold‐pressed oil of the lemon Citrus limon with the lower quality steam‐stripped oil still occurs on a major scale. It has been known for many years that substances with ultraviolet absorption characteristics similar to those of the coumarins and psoralens present naturally in cold‐pressed lemon oil are added to the oil mixture to mask the adulteration. The present work has confirmed that substances such as ethyl p‐dimethylaminobenzoate and 7‐geranyloxycoumarin (auraptene) are still used to conceal the adulteration of cold‐pressed lemon oil. 7‐Methoxycoumarin (herniarin) and 5,7‐dipropyloxy‐4‐methylcoumarin were also identified in certain commercial lemon oil samples. These compounds are not natural components of lemon oil and have not been associated previously with its adulteration. A novel 5,8‐disubstituted psoralen was detected in authentic cold‐pressed lemon oil and identified as 5‐isopent‐2′‐enyloxy‐8‐(2′,3′‐epoxyisopentyloxy)psoralen(1). The concentrations of the natural coumarins and psoralens in lemon oil have been determined.