Citrus Peels: An Excellent Raw Material for the Bioconversion into Value-added Products

Citrus by-products are the processing wastes generated after citrus juice extraction and constitute about 50% of fresh fruit weight. This solid residue is comprised of the peel (flavedo and albedo), pulp (juice sac residue), rag (membranes and cores) and seeds. The disposal of fresh peels is becoming a major problem for many factories. Usually, citrus juice industries dry the residue and it is either sold as raw material for pectin extraction or pelletized for animal feeding, though none of these processes is very profitable. This residual material is a poor animal feed supplement because of its extremely low protein content and high amount of sugar. The application of agroindustrial byproducts in bioprocesses offers a wide range of alternative substrates, thus helping to solve pollution problems related to their disposal. Attempts have been made to use citrus by-products to generate several value-added products, such as enzymes, single cell protein, natural antioxidants, ethanol, organic acids, polysaccharides and prebiotics. This article reviews developments regarding processes and products that have employed citrus peels as a substrate for biotechnological applications. _____________________________________________________________________________________________________________