Biosurfactants – Production and optimization

Surfactants are produced worldwide in the order of 18 million tons and used as detergents, emulsifiers, dispersants and foaming agents in a wide variety of sectors, from the textile industry to mining. Surfactants are synthesized both on the basis of fossil raw materials and from renewable raw materials, such as palm oil, using chemical processes. However, the structural diversity of such chemically produced surfactants is limited and the sustainability of the tropical vegetable oils used is currently the subject of controversial debate.

Cells of the fungus Ustilago maydis.
Cells of the fungus Ustilago maydis in the haploid, vegetative individual stage (left). Mannosylerythritollipids settle as oily pearls at high product concentrations (middle with structural formula), cellobiose lipids as acicular crystals (right, with structural formula).

Biosurfactants – Bacterially produced surfactants

Under natural conditions, microorganisms 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 Candida 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 particularly formed by smut fungi of the genera Pseudozyma and Ustilago in larger quantities. Their antimicrobial properties also make them interesting for use in clinical and pharmaceutical applications.

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.

Range of services

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

Goals and strategies

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

Results and prospects

Multifermenter system to optimise cultivation conditions.
Multifermentation system for optimizing cultivation conditions.

Through process optimization of the manufacturing 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. These were transferred from the shaking flask to the reactor scale (1 L, 10 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 were specifically altered, thus increasing the emulsion-stabilizing effect and solubility. The fermentation process is currently being further improved in order to achieve a production with the highest possible space-time yield.

Foam separation during fermentation, Ustilago maydis and cellobiose lipid crystals, purified CL.
Foam separation during fermentation, Ustilago maydis and cellobiose lipid crystals, purified CL.

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. If this 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 are 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 are identified and validated experimentally.. The findings obtained serve to continuously improve the economy and ecology of the overall process.

 

Prospects

In parallel, we are researching genomes and transcriptomes of promising production strains using next-generation sequencing methods to elucidate the biosurfactant metabolism and its regulatory mechanisms and to change the product spectrum and productivity of the strains using metabolic engineering.