Citrus fruits with 100 million tons per season are the largest sector of world fruit production, and about 34% of Citrus fruits are used to make juices. Peels are the largest share of byproduct (residue) of Citrus juice and other Citrus processing industries, of which major portion is wasted worldwide. In United States and Brazil alone 2 million dry tons of Citrus waste products (peels) are generated annually. Dry Citrus peels are rich in pectin, cellulose and hemicellulose and can be used as a fermentation substrate. Citrus waste products are processed into extracts for flavonoids, essential oils and d-limonene. Citrus fruits and leaves are traditionally used as anticancer in India and other countries. Researchers listed ancient and medieval uses of Mediterranean-grown C. medica and C. aurantium as anticancer agents. Anticancer potentials of C. aurantifolia, C. paradisi, C. deliciosa, C. aurantium, C. limon, C. jambhiri and C. pyriformis fruit essential oils on various cancer cell lines were also investigated. Most of these studies reported flavonoids, limonoids, vitamin C and β-carotene as the antioxidants and cancer risk reducing factors in Citrus plants. C. reticulata peels (extracts, essential oils) showed significant activity against DLA cell line in MTT assay. Chemical profiles of Citrus peel oils and peel extracts were analyzed by gas chromatographic techniques (GC-FID, GC-MS) and HPTLC-densitometry, respectively. We found C. reticulata peel water extract inducing cell cycle arrest of DLA in G0/G1 phase followed by nuclear condensation, membrane blebbing, formation of apoptotic bodies and DNA damage leading to apoptosis. In in vivo experiments, C. reticulata peel extract pre-treated mice were significantly protected from DLA compared to post-treated mice without any conspicuous toxic symptoms. Citrus peels have volatiles (essential oils, limonoids) and non-volatiles (mainly polymethoxy flavones) as bioactive/anticancer constituents. The results showed the use of Citrus peels, which is wasted in huge amounts, as cancer preventive food additives and as anticancer agents.
