The essential oils of the lemon are taken from the bright yellow peel. This outer peel is called the flavedo and it is covered with tiny glands. Each gland contains one drop of essential oil. To extract the organic oil, the glands of the peel must be physically broken open. The main volatile oils in lemon peels are limonene, alpha-terpinene, alpha-pine, and the main polyphenols in lemon peels are eriocitrin, hesperidin, narirutin, and diosmin.
Expression or Cold Pressing
Expression refers to the process of slowly breaking down lemon peel under mechanical pressure to release the oils from the glands of the peel. This process uses Ecuelle a piquer or an apparatus designed to extract oils from fruit rinds. It began in France as a bowl lined with needles to prick the fruit’s peel and a funnel to collect the released oils. It has been modernized to accommodate commercial practices, but uses the same principles of poking and agitating the rind.
Cold-pressed means that the oil was expressed at a low temperature. The low temperature preserves the volatile oil, which provides the rich scent of the plant. The oil that is produced will range in color from a deep emerald green to yellow, depending on the how mature the plant was and which variety of lemon was used. If the oil is clear, heat was most likely used in processing, although a cloudy appearance is probably the result of bacteria or wax that has precipitated since processing.
Distillation extraction means exposing a plant to water or steam to break down the plant material and release the essential oil. The oils are cooled and condensed for collection. Distillation is used for lemon peel extraction, although the resulting oil lacks the rich color and odor of fresh lemon peels. This more mild scent may be the motivation for steam distillation, but it has two other advantages.
Steam distilled lemon peel oil will not contain the waxy residue that a cold-pressed oil would contain. This makes them less likely to clog oil diffusers, stain fabric and, as they are less biologically active, extends the shelf life.
The other result of steam distillation is to create an oil that is psoralen free or does not contain the furocoumarins. Furocoumarins have been found to be photocarcinogenic. When these compounds are exposed to light, they can cause mutations in cells that lead to cancer. This correlation between the use of lemon peel extracts containing furocoumarins and skin cancer was first explored in lemon oil as a topical application, such as lotions, in animal studies.
The way this photocarcinogenesis happens is not straightforward, making it hard to know whether all use of lemon oil is a risk factor for developing skin cancer. More recent human studies have found an increase in the incidence of melanoma, basal cell carcinoma and squamous cell carcinoma in people who eat more citrus fruit, although these studies were focusing on furocoumarins from oranges and grapefruit, not specifically lemons. More studies are needed to understand this phenomenon, but it does create value for “psoralen free” lemon peel extracts.
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