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.
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.
Premise of the StudyTo enhance the understanding of the recent invasion process of the clonal waterweed Elodea nuttallii (Hydrocharitaceae), analyses of population structure and genotypic diversity need to be undertaken, for which genetic markers are needed.Methods and ResultsHigh‐throughput sequencing of DNA enriched for microsatellites was used to develop 24 loci that were characterized in E. nuttallii, 21 of which were polymorphic, with the number of alleles ranging from two to 10. In two populations, expected heterozygosity ranged among loci between zero and 0.796. In the congener E. canadensis, all markers yielded PCR products, 19 of which were polymorphic, with two to nine alleles and expected heterozygosity ranging from zero to 0.690 in two populations.ConclusionsThe markers described should be useful for future studies of population structure and clonal diversity of E. nuttallii as well as E. canadensis in their native and invasive range.
An error was inadvertently introduced during the processing of the original article [1]: Figure 6 and Figure 7 legends were unfortunately interchanged.Figure 6 shows: Foam generation u g and decay u d rates of samples 1-8 containing different fractions of a culture broth with U. maydis, as described in Table 1. The samples were measured as described in Sects. 2, 3. The error bars indicate the standard deviation of a triplicate.
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