Flavonoids, especially flavanones, flavones and polymethoxyflavones (PMFs) are distinctive bioactive compounds of Citrus fruits. Citrus peel and juice by-products potentially represent rich sources of these Citrus flavonoids that exhibit a myriad of biological activities both in in vitro and in vivo systems. Recently, much attention has been made toward biotransformation processes as a promising tool for the structural modification of natural products to be used in the drug and food industries along with its role in solving pollution problems related to Citrus by-products disposal. In this article, we present a state of the art review on both in vivo and in vitro biotransformation processes of Citrus juice and waste carried out by microorganisms, plant cell cultures, animal and human liver microsomes targeting its flavonoids composition. Such review highlights the main metabolic pathways for enzymatic and microbial reactions involved in these processes and suggest for reactions that need to be more capitalized for a wider application in industrial bioprocesses of Citrus by-products. Biotransformation and biocatalysis applications included employment of citrus by-products enriched in flavonoids as a low-cost, economical and natural sources of sugar substitutes, antifungal, anticancer drugs, hydrolyzable enzymes, probiotics and flavonoid aglycones. Further, biological effects of the biotransformed metabolites are discussed in relation to its parent compound highlighting potentials and or any limitations for each reaction type. Applications covered in Citrus biotransformation include for nutraceutical/food and cosmetics industries.
Keywords: Citrus; biotransformation; by-products; eukaryote; flavonoids; prokaryote.