Bioconversion of pomegranate residues into biofuels and bioactive lipids

Pomegranate residues (PRs) (i.e. the solid residues remaining after juice extraction), generated currently in abundance in Greece, contain a variety of carbon sources and therefore can be regarded as a potential feedstock for chemical and biotechnological processes rather than as waste materials. In the current project, the polysaccharides contained in PRs were extracted and hydrolyzed in a one-step process without the use of chemical reagents and the resulting broth was used as substrate in biotechnological applications, including ethanol and single cell oil (SCO) production. The yeasts Meyerozyma guilliermondii, Scheffersomyces coipomoensis, Sugiyamaella paludigena and especially Saccharomyces cerevisiae, were able to efficiently convert PR derived reducing sugars into bioethanol. Ethanol production under anaerobic conditions ranged from 3.6 to 12.5 g/L. In addition, the oleaginous yeasts Lipomyces lipofer and Yarrowia lipolytica as well as M. guilliermondii, S. coipomoensis and S. paludigena were tested for their ability to accumulate lipids suitable as feedstock for biodiesel production. Lipids were accumulated at concentrations up to 18% and were rich in palmitic acid (C16:0) and oleic acid (C18:1). Finally, the oleaginous fungus Cunnichamella echinulata was cultivated on PR based solid substrates for {gamma}-linolenic acid (GLA) production. The fermented bio-products (i.e. fermented substrate plus fungal mycelia) contained up to 4.8 mg GLA/g of dry weight. Phenolic removal (up to 30%) was achieved by several of the above mentioned microorganisms, including C. echinulata, L. lipofer, M. guilliermondii, S. paludigena and Y. lipolytica. We conclude that PRs can be used as a raw material for microbial growth, ethanol and SCO production, which is of economic and environmental importance.