Browsing by Author "Oraby, Amira"

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Open Access
Factors affecting the synthesis of cellobiose lipids by Sporisorium scitamineum
(2020) Oraby, Amira; Werner, Nicole; Sungur, Zehra; Zibek, Susanne
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 &-hydroxyl group (CL-B). The produced cellobiose lipids precipitate as needle like crystals at an acidic pH value of 2.5.
Open Access
Fermentation and recovery of cellobiose lipids using foam fractionation
(2023) Oraby, Amira; Hug, Daniel; Weickardt, Isabell; Maerz, Lea; Nebel, Sabrina; Kurmann, Jasper; Rupp, Steffen; Tovar, Günter E. M.; Zibek, Susanne
Cellobiose lipids (CL) are glycolipids secreted by many Ustilaginaceae species in aerobic fermentations characterised by excessive foaming. While increasing CL concentrations remains an aim for its industrial production, excessive foaming during fermentation presents a challenge even at laboratory scale. Foam fractionation (FF) provides a solution to the foaming problem and facilitates the proceeding purification of CL. Here, we present a first CL fermentation process applying FF. With our set-up, we manage to exploit the excessive foaming for continuous product separation. The set-up includes a foam collecting vessel (FCV) with inserts for CL accumulation and foamate recirculation to minimise biomass and nutrient loss. Integrating a foam column (FC) into the fermenter headspace enabled foam enrichment, resulting in the recovery of > 90% of the produced CL from the separated fractions consisting of foam depositions in the fermenter headspace and the FCV. We also increased the fermenter filling volume and thus achieved a higher fermentation capacity. The separated CL fraction was purified via ethanol extraction to obtain CL with purities > 90%. We further examined the effects of different culture media constituents, including biomass and CL, on foam generation and decay and assessed the effect of FC geometries on product enrichment and recovery. In this work, a FF set-up is presented that enables a stable CL fermentation without additional foam mitigation methods. At the same time, the application of FF separated a fraction that was highly enriched in CL during fermentation, resulting in highly pure CL after a simple ethanol extraction.
Open Access
Foam fractionation methods in aerobic fermentation processes
(2022) Oraby, Amira; Weickardt, Isabell; Zibek, Susanne
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.
Open Access
Integrated process design and optimisation for the production of cellobiose lipids from Ustilago sp.
(2024) Oraby, Amira; Rupp, Steffen (Prof. Dr.)
Open Access
Life cycle assessment as a driver for process optimisation of cellobiose lipids fermentation and purification
(2024) Oraby, Amira; Briem, Ann-Kathrin; Bippus, Lars; Rupp, Steffen; Zibek, Susanne
Purpose: Cellobiose lipids (CL) are biosurfactants produced by various Ustilaginaceae species in aerobic fermentations. They show high potential for application as alternatives to conventional oleochemical- or petrochemical surfactants. To ensure their environmentally friendly performance, we aimed to assess CL production from a life cycle perspective at an early developmental stage to identify process steps that have the highest impact on the environment. With this information, optimisation approaches can be derived.
Materials and methods: Following a cradle-to-gate approach, we modelled the CL fermentation and purification process based on experimental data from the lab scale and process simulation data at a 10 m 3 scale. For LCA, the impact categories (IC) abiotic depletion potential (ADP), eutrophication potential, photochemical ozone creation potential, global warming potential, acidification potential, and the primary energy demand were calculated for all process steps. Based on the obtained results, process bottlenecks were identified, and alternative process scenarios varying the related process parameters were simulated. These were used to assess the environmental impact reduction potential (EIRP) of an optimised process and draw recommendations for experimental process optimisation.
Results and discussion: The obtained results showed that the fermentation caused ~ 73% of ADP and more than 85% of all other ICs. The major contributor was the electricity consumption for continuous fermenter aeration. Thus, reducing the fermentation duration from the initial 14 to 5 days would result in a decrease in all investigated ICs of up to ~ 27-52%. An increase in CL concentration results in a decrease in all ICs of a similar magnitude due to the higher yield per batch at comparable energy and material consumption. Although the share of purification process steps to all ICs is overall relatively small, implementing foam fractionation for in situ product recovery showed an additional EIRP of 18-27% in all purification IC shares.
Conclusions: The conducted LCA showed that overall, more EIRP can be achieved by optimising fermentation process parameters compared to purification process steps. This is mainly due to the long fermentation duration and large energy consumption for fermenter aeration. This highlights the importance of using LCA as a driver for process optimisation to identify process steps with high EIRP. While some of the results are specific to CL, other obtained results can be transferred to other fermentations.
Open Access
Past, present and future of glycolipids from Ustilaginaceae : a review on cellobiose lipids and mannosylerythritol lipids
(2024) Münßinger, Sini; Beck, Alexander; Oraby, Amira; Zibek, Susanne
The glycolipids cellobiose lipids (CL) and mannosylerythritol lipids (MEL) are biosurfactants mainly synthesized by microorganisms of the Ustilaginaceae family. They have a large structural diversity, varying in their sugar moieties and the attached fatty acids, resulting in a prospectively broad range of applications. This literature review provides a detailed overview of known microbial producers of CL and MEL, and their respective metabolic pathways that result in different molecular structures. Further, current advances in the aerobic fermentative synthesis of the glycolipids and their purification methods are illustrated. All influencing factors identified to date with regard to the fermentation are highlighted in detail: For CL synthesis usually hydrophilic carbon sources are used as substrate, whereas hydrophobic carbon sources are usually metabolized to MEL. Nitrogen limitation was described as a major trigger for glycolipid synthesis and an acidic pH range was favored for increased CL production. An overview of applied fermentation parameters in recent publications (e.g., substrate‐concentrations, feeding approaches) demonstrates the future potential of CL and MEL production optimization. Foaming during fermentation is either combated or exploited by foam fractionation as the first purification step. The current purification processes focus on solvent extractions and chromatography in the laboratory scale and a need for development was identified for future scale‐up. Finally, environmental hotspots during CL and MEL production are presented and future optimization potentials are highlighted.
Open Access
Techno-economic analysis as a driver for optimisation of cellobiose lipid fermentation and purification
(2022) Oraby, Amira; Rupp, Steffen; Zibek, Susanne
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.