Background: As the circular economy advocates a near total waste reduction, the industry has shown an increased interest towards the exploitation of various residual biomasses. The origin and availability of biomass used as feedstock strongly affects the sustainability of biorefineries, where it is converted in energy and chemicals. Here, we explored the valorization of Camelina meal, the leftover residue from Camelina sativa oil extraction. In fact, in addition to Camelina meal use as animal feed, there is an increasing interest in further valorizing its macromolecular content or its nutritional value. Results: Camelina meal hydrolysates were used as nutrient and energy source for the fermentation of the carotenoid-producing yeast Rhodosporidium toruloides in shake flasks. Total acid hydrolysis revealed that carbohydrates accounted for a maximum of 31 ± 1.0% of Camelina meal. However, because acid hydrolysis is not optimal for subsequent microbial fermentation, an enzymatic hydrolysis protocol was assessed, yielding a maximum sugar recovery of 53.3%. Separate Hydrolysis and Fermentation, Simultaneous Saccharification and Fermentation, and SSF preceded by presaccharification of Camelina meal hydrolysate produced 5 ± 0.7, 16 ± 1.9, and 13 ± 2.6 mg/L of carotenoids, respectively. Importantly, the presence of water-insoluble solids, which normally inhibit microbial growth, correlated with a higher titer of carotenoids, suggesting that the latter could act as scavengers. Conclusions: This study paves the way for the exploitation of Camelina meal as feedstock in biorefinery processes. The process under development provides an example of how different final products can be obtained from this side stream, such as pure carotenoids and carotenoid-enriched Camelina meal can potentially increase the initial value of the source material. The obtained data will help assess the feasibility of using Camelina meal to generate high value-added products.

Background: The great interest in the production of highly pure lactic acid enantiomers comes from the application of polylactic acid (PLA) for the production of biodegradable plastics. Yeasts can be considered as alternative cell factories to lactic acid bacteria for lactic acid production, despite not being natural producers, since they can better tolerate acidic environments. We have previously described metabolically engineered Saccharomyces cerevisiae strains producing high amounts of L-lactic acid (>60 g/L) at low pH. The high product concentration represents the major limiting step of the process, mainly because of its toxic effects. Therefore, our goal was the identification of novel targets for strain improvement possibly involved in the yeast response to lactic acid stress.

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.

Background: The sustainability of biorefineries is strongly related to the origin, the availability and the market of the biomass used as feedstock. Moreover, one of the pillars of circular economy aims at reducing waste, ideally to zero. These considerations well justify the increasing industrial interest in exploiting many and diverse residual biomasses. This work focuses on the valorization of the leftover from Camelina sativa oil extraction, named Camelina meal. Despite Camelina meal is used as animal feed, there is an increasing interest in further valorizing its macromolecular content or its nutritional value. Results: Here we valorized Camelina meal hydrolysates by using them as nutrient and energy source for shake-flask fermentations where Rhodosporidium toruloides , a yeast natural producer of carotenoids, accumulated these pigments as desired product. Initially, by total acid hydrolysis we determined that in Camelina meal carbohydrates account for a maximum of 30.8 ± 1.0 %. However, since the acid hydrolysis is not optimal for subsequent microbial fermentation, an enzymatic hydrolysis protocol was assessed, obtaining a maximum sugar recovery of 53.3%. Having stated that, by Separate Hydrolysis and Fermentation, with or without water insoluble solids (SHF, SHF+WIS), or Simultaneous Saccharification and Fermentation (SSF) we obtained 5.51 ± 0.67, 12.64 ± 2.57, and 15.97 ± 0.67 mg/L of carotenoids, respectively, from Camelina meal hydrolysate. Significantly, the presence of WIS, possibly containing microbial inhibitors, correlates with a higher titer of carotenoids, which can be seen as scavengers. Conclusions: The proposed study paves the way for the development of bioprocesses based on the exploitation of Camelina meal, scarcely investigated in the field before, as feedstock. The processes depicted provide an example of how different final products of industrial interests can be obtained from this leftover, such as pure carotenoids and carotenoid-enriched Camelina meal for the feed industry, without diminishing but possibly increasing its initial value. These data provide valuable basis for the economic evaluations necessary to assess the feasibility of a bioprocess based on Camelina meal to obtain high-value added products.

BackgroundLipids 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.ResultsIn 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. ConclusionsThis 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.