limonin

Limonin is a bitter-tasting natural compound classified as a limonoid, a tetranortriterpenoid commonly found in Citrus species such as oranges, lemons, limes, and grapefruits. In fresh fruit it occurs mainly as limonin glucoside, a non-bitter glycoside, whereas the aglycone limonin is produced upon hydrolysis and is responsible for much of the bitterness observed in processed citrus products.

Occurrence and biosynthesis: Limonin is widely distributed in seeds, membranes, and sometimes the rind of citrus fruits. It belongs to the limonoid family, produced by the plant through triterpenoid biosynthesis via the mevalonate pathway. The bitter compound can form when limonin glucoside is cleaved, such as during extraction, storage, or acid treatment, releasing limonin.

Sensory effects and processing: Limonin is highly bitter and is a major factor in the bitterness of stored citrus juice. Because it is relatively insoluble in water, bitterness can persist even after extraction. Processes to reduce bitterness include seed removal, careful clarification, or debittering steps; bitterness tends to increase with time and exposure to acids.

Health and safety: Limonin itself is not considered acutely toxic at typical dietary levels. Some limonoids have been studied for potential bioactivities, including anti-cancer properties in laboratory studies, but evidence in humans is inconclusive and limonin’s primary significance in foods is sensory.