Conversion of sugar beet residues into lipids by Lipomyces starkeyi for biodiesel production

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: This study demonstrates for the first time that SBP and molasses can be blended to create a feedstock for the sustainable production of lipids by L. starkeyi. The data obtained pave the way to further improve lipid production by designing a fed-batch process in bioreactor.

Short‐chain alcohols inactivate an immobilized industrial lipase through two different mechanisms

“…Therefore, data highlight the importance of finding a trade‐off between the alcohol concentration required by a given reaction and the enzyme performance and strengthen the stepwise addition of alcohols during the process as a possible solution to counteract the irreversible inactivation of N‐435 induced by high alcohol concentrations. [ 36,45–47 ] On the other hand, the inactivation of N‐435 by tBuOH is more pronounced than those induced by MeOH and EtOH and not consistent with the beneficial effect (i.e., increase of product yields) reported when tBuOH is used as a solvent in biodiesel transesterification reactions. [ 16,21–23,36 ] We cannot exclude that the glycerol produced during transesterification stabilizes CALB and prevents its aggregation, as reported for other proteins [ 48,49 ] and would hypothesize that the outcomes of tBuOH in transesterification reactions could be due to a combination of negative (i.e., inactivation of the enzyme) and positive (i.e., better dissolution of MeOH and glycerol) effects.…”

“…The phenomenon of enzyme leaching is commonly observed when lipases are immobilized by interfacial activation on hydrophobic support as in the case of N‐435 and has to be considered with caution when planning the conditions for the use of this enzyme in industrial application. [ 14,45–47 ]…”

Scheffersomyces stipitis ability to valorize different residual biomasses for vitamin B9 production

“…Thus, the use of SBP requires finding a compromise between a sufficiently high concentration of sugars and S. stipitis 's tolerance to inhibitors. Martani and colleagues have already characterized sugars and acids released during the pre‐treatment process of SBP (Martani et al, 2020 ).…”

“…Sugar beet molasses was diluted 1:4 (vv −1 ) with distilled water prior to autoclave sterilization. A pre‐treatment step and enzymatic hydrolysis were required on SBP to release the sugars contained in the (hemi)cellulose fraction; a 10% stock was prepared as described by Martani and colleagues (Martani et al, 2020 ). A 10% stock of UGM was prepared as follows: 100 g of total solids (TS) of ground biomass was suspended in distilled water to a final volume of 1 L; after sterilization in an autoclave, the suspension was centrifuged in order to separate the solids from the liquid phase; the pH was adjusted to 5.5 with NaOH 15 M and stored at 4°C.…”

“…We selected a simple autoclave pre‐treatment since it allowed the release of almost all the available sugars. Pre‐treatment conditions for SBP were adapted from Martani and colleagues, while no pre‐treatment was necessary for SBM (Martani et al, 2020 ).…”