Techno-Economic Analysis as a Driver for Optimisation of Cellobiose Lipid Fermentation and Purification.

Cellobiose lipids (CL) are glycolipids synthesized by Ustilaginaceae species with potential application as detergents or in cosmetics. This study identified process optimisation potential for CL fermentation based on process modelling and techno-economic analysis. Using a stoichiometric equation based on laboratory data, we calculated the maximum possible CL yield YP/S of 0.45 gCL·gglucose -1 at the biomass yield of 0.10 gBiomass·gglucose -1 with an Ustilago maydis strain. Due to substrate inhibition that may occur at high glucose concentrations, a fed-batch process to increase biomass and CL concentrations was considered in our model. Simulation of different process scenarios showed that the choice of aeration units with high oxygen transfer rates and adaptation of power input to oxygen uptake can significantly decrease electricity consumption. We further assessed scenarios with different fermentation media and CL purification methods, suggesting additional process optimisation potential. Here the omission of vitamins from the fermentation medium proved to be a possible mean to enhance process economy, without compromising CL productivity.

Foam fractionation methods in aerobic fermentation processes.

Inherently occurring foam formation during aerobic fermentation of surface-active compounds can be exploited by fractionating the foam. This also serves as the first downstream processing step for product concentration and is used for in situ product recovery. Compared to other foam prevention methods, it does not interfere with fermentation parameters or alter broth composition. Nevertheless, parameters affecting the foaming behavior are complex. Therefore, the specific foam fractionation designs need to be engineered for each fermentation individually. This still hinders a widespread industrial application. However, few available commercial approaches demonstrate the applicability of foam columns on an industrial scale. This systematic literature review highlights relevant design aspects and process demands that need to be considered for an application to fermentations and proposes a classification of foam fractionation designs and methods. It further analyses substance-specific characteristics associated with foam fractionation. Finally, solutions for current challenges are presented, and future perspectives are discussed.

Environmental Impacts of Biosurfactants from a Life Cycle Perspective: A Systematic Literature Review.

Biosurfactants are considered as an environmentally friendly and sustainable alternative to conventional fossil-derived and chemically produced surfactants. Their production pathways, physicochemical properties, and applications are widely researched and discussed in literature. In this context, investigating the different impacts from the entire life cycle of biosurfactants is important to understand and mitigate potential environmental hotspots. Life Cycle Assessment (LCA) is an internationally accepted and standardized methodology to analyze the environmental impacts of products from a holistic view. Therefore, this study provides a detailed overview of existing LCA studies of biosurfactants by means of a systematic literature research. The focus specifically lies on articles that investigated microbial biosurfactants. However, the systematic approach used ensured a broader overview related to bio-based surfactants as well. Furthermore, two related topics, ecotoxicity and biodegradability of biosurfactants, were identified and discussed based on the search findings. After screening over 2,500 documents using Scopus and Google Scholar, six relevant LCA articles of biosurfactants could be identified. The identified articles are divided into LCA studies of alkyl polyglycosides, chemically produced bio-based surfactants, and LCA studies of microbial biosurfactants, their content analyzed and discussed in context. In conclusion, the number of available LCA studies is very limited and their results are often not comparable. To the best of the authors' knowledge, this review is the first of its kind to provide a detailed overview of LCA studies of biosurfactants. Consequently, the need for implementing more LCA studies becomes clear.

Factors Affecting the Synthesis of Cellobiose Lipids by Sporisorium scitamineum.

Cellobiose lipids (CL) are extracellular glycolipids that are produced by many microorganisms from the family Ustilaginaceae. The sugarcane smut fungus Sporisorium scitamineum has been long known as a producer of the glycolipids mannosylerythritol lipids (MEL) and was recently described to additionally secrete CL as a byproduct. In fact, we identified 11 homologous genes in S. scitamineum by in silico analysis sharing a high similarity to the CL biosynthesis gene cluster of Ustilago maydis. We here report the first systematic cultivation of S. scitamineum targeting the synthesis of CL with high product titers and its transfer to the bioreactor. In an initial screening we examined different fermentation media compositions, consisting of a mineral salts solution with vitamins and/or trace elements, three carbon sources (glucose, fructose, sucrose), three pH values (2.5, 4.0, 6.7) and three levels of C/N values (42.2, 83.8, 167.2 molC⋅molN -1) with urea as nitrogen source. A pH of 2.5 proved to result in the highest product titers. An increase of urea concentration from 0.6 to 1.2 g⋅L-1 had a positive effect on biomass formation, however the glycolipid formation was favored at a C/N ratio of 83.8 molC⋅molN -1, using 0.6 g⋅L-1 urea. Amongst the examined carbon sources, sucrose resulted in an increase in the secretion of cellobiose lipids, compared to glucose. Comparing different media compositions, vitamins were identified as not necessary for CL synthesis. We obtained a concentration of cellobiose lipids of 8.3 ± 1.0 g⋅L-1 in shaking flasks. This increased to 17.6 g⋅L-1 in the 1 L bioreactor with additional feeding of carbon source, with a final purity of 85-93%. As a side product, erythritol and mannosylerythritol lipids (MEL) were also synthesized. Via HPTLC coupled MALDI-TOF MS we were able to analyze the secreted CL structures. S. scitamineum produces a mixture of acylated low molecular weight D-glucolipids, linked to a 2,15,16-trihydroxy-hexadecanoic acid via their ω-hydroxyl group (CL-B). The produced cellobiose lipids precipitate as needle like crystals at an acidic pH value of 2.5.