Conversion of sugar beet residues into lipids by Lipomyces starkeyi for biodiesel production
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Microbial Cell Factories Open Access
RESEARCH
Conversion of sugar beet residues into lipids by Lipomyces starkeyi for biodiesel production Francesca Martani†, Letizia Maestroni†, Mattia Torchio, Diletta Ami, Antonino Natalello, Marina Lotti, Danilo Porro and Paola Branduardi*
Abstract Background: Lipids from oleaginous yeasts emerged as a sustainable alternative to vegetable oils and animal fat to produce biodiesel, the biodegradable and environmentally friendly counterpart of petro-diesel fuel. To develop economically viable microbial processes, the use of residual feedstocks as growth and production substrates is required. Results: In this work we investigated sugar beet pulp (SBP) and molasses, the main residues of sugar beet processing, as sustainable substrates for the growth and lipid accumulation by the oleaginous yeast Lipomyces starkeyi. We observed that in hydrolysed SBP the yeast cultures reached a limited biomass, cellular lipid content, lipid production and yield (2.5 g/L, 19.2%, 0.5 g/L and 0.08 g/g, respectively). To increase the initial sugar availability, cells were grown in SBP blended with molasses. Under batch cultivation, the cellular lipid content was more than doubled (47.2%) in the presence of 6% molasses. Under pulsed-feeding cultivation, final biomass, cellular lipid content, lipid production and lipid yield were further improved, reaching respectively 20.5 g/L, 49.2%, 9.7 g/L and 0.178 g/g. Finally, we observed that SBP can be used instead of ammonium sulphate to fulfil yeasts nitrogen requirement in molasses-based media for microbial oil production. Conclusions: Keywords: Lipomyces starkeyi, Sugar beet pulp, Molasses, Tags, Fames, Biodiesel, Biorefinery Background The depletion of fossil reserves, the environmental concerns about greenhouse gas (GHG) emissions and the increasing demand for energy are boosting the conversion from a fossil-based economy into a bio-based economy. In this context, biodiesel is receiving an everincreasing attention as an alternative fuel source because of its renewability, biodegradability, non-toxicity and lower emission of pollutants compared to petro-diesel [1]. In addition, biodiesel is safer for transportation, distribution and handling than petroleum diesel, and blends up to 20% of biodiesel can be used in current engines
*Correspondence: [email protected] † Francesca Martani and Letizia Maestroni have contributed equally to this work Department of Biotechnology and Biosciences, University of Milano Bicocca, 20126 Milan, Italy
without modifications [1]. This “green” fuel is obtained from oils through a transesterification reaction where triacylglycerols (TAGs) react with a short-chain alcohol (typically methanol) in the presence of a catalyst to form fatty acid alkyl esters (FAAEs). The main feedstocks used for the production of biodiesel are vegetable oils, animal fats and waste cooking oils. Vegetable oils are considered the most promising due to their characteristics, composition and abundance: however, due to the food versus fuel deb
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