Another method involves a sugar molecule. As the fruit grows, if limonoids are bonded with a sugar molecule, limonoid glucosides develop, and the fruit and juice are not bitter. Citrus species and environmental stresses such as cold snaps or drought play roles in determining the amounts of each compound that are produced. For example, fruit subjected to freezing temperatures will produce bitter limonoids. Genetic engineering is now under study as a method of delivering a maximum of limonoid glucosides without the bitter taste.
Researchers now know the genetic code for the gene that causes the formation of limonoid glucoside.
They hope to use this information to reduce or eliminate production of bittering compounds or to increase the amount of limonoid glucosides in citrus fruit. The limonoids may be bitter, but they are good at fighting diseases. More than 300 limonoids have been identified. Other limonoid properties include antifungal, bactericidal, and antiviral effects. Studies at several universities and commercial laboratories have shown limonoids to inhibit tumor formation in animals.