Biosurfactants – Production and optimization

Biosurfactants – Bacterially produced surfactants

Several microorganisms naturally form a multitude of surface-active substances, so-called biosurfactants, which cover a broad spectrum of chemical structures. These include glycolipids, lipopeptides, lipoproteins and heteropolysaccharides. The properties of these biosurfactants are comparable or even superior to many synthetic surfactants in terms of surface activity and degradability and are therefore of interest for many industrial applications.

Improved manufacturing and processing processes, more efficient production strains and the increased demand for "green" products have brought some biosurfactants to market maturity in recent years. One example of this is the sophorose lipid from Starmerella bombicola, which is now produced by various surfactant manufacturers as an additive for household cleaners and dishwashing detergents.

Glycolipids with great potential

Two classes of biosurfactants that have also proven to be promising detergents, emulsifiers and active ingredients in cosmetics, crop protection and industrial applications are cellobiose lipids (CL) and mannosylerythritollipids (MEL). They are formed by smut fungi of the genera Moesziomyces and Ustilago in larger quantities. Their antimicrobial properties also make them interesting for use in clinical and pharmaceutical applications.

Recently, another class of microbial biosurfactants, so called polyol lipids (PL), have been investigated in our research group. These biosurfactants can also be produced from sugars via fermentation with Rhodotorula species.

However, industrial production of these biosurfactants still requires improvements in the yield during fermentation and in the reproducibility of the product composition. The aim of these investigations is to increase the productivity of cultivation and the use of renewable raw materials as substrates.

• Fermentation and sample production of fermentatively produced biosurfactants
• Chemical-enzymatic modification
• Scale-up of fermentation up to 300 L at Fraunhofer IGB and up to max. 10 m³ at the Fraunhofer Center for Chemical-Biotechnological Processes CBP, Leuna

Fraunhofer IGB deals with the optimization of the biotechnological synthesis of glycolipids, in particular cellobiose lipids (CL) and mannosylerythritollipids (MEL) using different fungi and different substrates such as mono- and disaccharides, vegetable oils or residues. In this way, tailor-made structural mixtures are to be created and tested for their application-specific suitability.

The objectives are the characterization and optimization of biosurfactants for use in cleaning agents, in cosmetics or for special applications in industry, as well as efficient fermentative production of the biosurfactants. We are pursuing various approaches for the optimization of biosurfactants and the fermentation process such as:

• Optimization of bioprocess control strategies
• Enzymatic modification of the produced biosurfactants
• Genetic modification of the specific metabolic pathways of the microorganisms used
• Simplification and intensification of downstream processing (DSP)

Through optimization of the fermentation process for the two biosurfactants CL and MEL, we currently achieve product concentrations of > 20 g/L for CL and 50 g/L for MEL. The processes were transferred from the shaking flask to the reactor scale (1 L, 10 L, 42 L). Various cultivation methods, substrates and processing strategies were investigated.

The quantities currently produced are sufficient for comprehensive technical application investigations of the respective biosurfactants. By enzymatic and chemical modification, the hydrophilic and hydrophobic properties of the glycolipids produced can be altered specifically, thus changing the surface active properties and solubility. The fermentation process is continuously being improved to achieve production with the highest possible space-time yield.

In the area of downstream processing (DSP), various process steps such as solid-liquid separation, microfiltration, salting out, liquid-liquid and solid-liquid extraction were investigated and combined with each other in order to produce high-purity biosurfactant samples for application studies.

Strategies for avoiding foam

We are currently investigating various methods to avoid foam formation during fermentative MEL production. For CL, a fraction with a high cellobiose lipid concentration was collected by continuously separating the foam produced during fermentation by so-called foam fractionation. If the foam fraction is purified directly, only seven percent of the solvent quantity is required for the extraction of the cellobiose lipids, compared to conventional purification of the entire reactor content.

Software-assisted process optimization

The individual process steps were evaluated by means of a life cycle analysis and a techno-economic assessment during the course of development. With the aid of these assessments, process bottlenecks were identified and validated experimentally.. The findings obtained serve to continuously improve the economy and ecology of the overall process.

Prospects

We are currently researching different induction methods for increasing biosurfactant synthesis, alternative fermentation raw materials based on waste materials, model-based control strategies for a more robust fermentation process, and further intensified DSP processes with the aim of further improving the economics and ecology of the overall process.