Qin Zhang, Chi-ming Lo, and Lu-Kwang Ju

Department of Chemical and Biomolecular Engineering

The University of Akron

Akron, Ohio 44325-3906

 Affinity foam fractionation involving selective binding between enzymes and substrates/analogs can be a powerful and economical bioseparation tool.  In this study we showed that the biosurfactant rhamnolipids (RLs) can be used as the affinity foaming agent to selectively separate β-glucosidase from cellulase of Trichoderma reesei.  Produced by Pseudomonas species, RLs consist of one or two molecules of rhamnose and one or two molecules of β-hydroxyalkanoic acids, with pKa ranging from 4.8 to 5.6.  According to our HPLC-MS analysis, the RLs used in the study had two predominant components: one di-rhamnose (molecular weight = 650) and the other mono-rhamnose (MW = 530), in a molar ratio of 52:48.  Both RLs had a chain of two inter-esterified β-hydroxydecanoic acids.  When added to fermentation broths of T. reesei or the solutions of commercial cellulose, the RLs significantly improved the foaming and selectively brought β-glucosidase into the foamate, reaching up to 20-fold enrichment ratios (without enriching the endo-glucanase and exo-glucanase).  The selectivity is attributed to the di-rhamnose of RLs, which resembles the disaccharide substrate (cellobiose) to β-glucosidase.  The effects of operating conditions (pH, air flowrate, RLs concentration, and the ratio of RL concentration to cellulase FPU) on the affinity foam fractionation were systematically investigated and an empirical model established