Process optimization for the production of enzymatically modified rhamnolipids

IVANA MAGARIO; ANKE NEUMANN; OLIVER VIELHAUER; FRANK LEITERMANN; CHRISTOPH SYLDATK

Hamburgo

Congreso; Biocat 2006 - 3rd International Congress on Biocatalysis; 2006

Hamburg University of Technology

Rhamnolipids are biosurfactants being used e.g. as surface cleaning agents. They are produced by Pseudomonas sp. and, though there are different kinds of them, the most relevant have a bond of one or two units of L-(+)-rhamnopyranoside with a (R,R)-3-(3-hydroxydecanoyloxy)decanoic acid. Enzymatic modification of the mixture resulting from the production by Pseudomonas sp. is proposed in order to obtain a unique species with higher tensoactive properties as well as a starting material for further modification. The cleavage of a rhamnolipid molecule into one unit of L-(+)- rhamnose and rhamnolipid 1 is attempted by means of the L-rhamnosidase activity of the commercial naringinase. As a result, the same ratio of the interesting by-product L-(+)-rhamnose is also gained, which is starting material for the synthesis of flavor agents. Based on reaction engineering methods, this contribution focuses on the systematic investigation of this bioconversion as a model system for optimization of the enzymatic process for further industrial application. Therefore, characterization of the biotransformation of rhamnolipid 3 into rhamnolipid 1 by soluble enzyme was first accomplished. Hereby the utilization of organic solvents for increasing substrate solubility and thus increasing the reaction rate was also considered. As the stability of the enzyme is a desirable factor, investigation of its thermal inactivation in dependency on the temperature and pH was also assayed by means of response surface methodology. At optimal reaction conditions, mathematical modeling of the reaction kinetics was applied taking into account product inhibition and mass transfer phenomena due to the existence of an emulsion system at these conditions. The recovery and reuse of isolated enzymes plays an important role for the economy of an enzymatic process. Moreover, based on the reaction kinetics, the use of an enzyme column reactor (plug-flow model) seems to be an appropriate process design, whereas the inhibitor product rhamnose could be in-situ separated. Therefore immobilization assays of the enzyme onto different supports have been carried out. A rational selection of the immobilization method and its optimization toward coupling activity and stability should be hereby performed. In addition to the use of conventional porous supports, non-porous functionalised micro-magnetic beads for avoiding diffusion limitation in the three-phase reaction process has been likewise tested.