Biotechnological conversions of bio-diesel derived waste glycerol into added-value compounds by higher fungi: production of biomass, single cell oil and oxalic acid

Waste bio-diesel derived glycerol was used as the sole carbon source by higher fungi; two Lentinula edodes strains were flask cultured in carbon-limited conditions and displayed satisfactory growth in media presenting weak agitation, pH 4.0 and temperature 25 degrees C. Maximum biomass of 5.2g/l was produced. Mycelia were synthesized, containing around 0.1 g of fat per g of biomass, with linoleic acid ((Delta 9,12)C8:2) being the principal cellular fatty acid produced. Two Aspergillus niger strains were grown in nitrogen-limited flask cultures with constant nitrogen and two different initial glycerol concentrations into the medium. In 250-ml flask cultures, large-sized pellets were developed, in contrast with the trials performed in 2-l flasks. Nitrogen limitation led to oxalic acid secretion and intra-cellular lipid accumulation; in any case, sequential production of lipid and oxalic acid was observed. Initially, nitrogen limitation led to lipid accumulation. Thereafter, accumulated lipid was re-consumed and oxalic acid, in significant quantities, was secreted into the medium. In large-sized pellets, higher quantities of intra-cellular total lipid and lower quantities of oxalic acid were produced and vice versa. Maximum quantities of oxalic acid up to 20.5-21.5 g/l and lipid up to 3.1-3.5 g/l (corresponding to 0.41-0.57 g of fat per g of biomass) were produced. Lipid was mainly composed of oleic ((Delta 9)C18:1) and linoleic ( (Delta 9,12)C18:2) acids. (C) 2010 Elsevier B.V. All rights reserved.