ADSORPTION STUDIES FOR THE SEPARATION OF L-TRYPTOPHAN FROM L-SERINE AND INDOLE IN A BIOCONVERSION MEDIUM

L-tryptophan was produced from L-serine and indole by immobilized Esch erichia coli cells in organic-aqueous systems. Selective adsorption wa s the method chosen to enable both product separation and L-serine reu tilization. Amongst various adsorbents tested activated carbons and ne utral polymeric resins (XAD-4 and XAD-7) showed good performance. The neutral resins could selectively concentrate the L-tryptophan from dil ute aqueous solutions and adsorbed only 5% of the unconverted L-serine . High separation factors (L-tryptophan/L-serine and indole/L-tryptoph an) were obtained with these adsorbents. Despite a lower capacity, the XAD-7 resin had the advantage of desorbing L-tryptophan with basic or acidic solutions, while organic solvents were required to desorb, at the same concentration levels, this compound from XAD-4. In a packed b ed column filled with XAD-4 resin or activated carbon, total L-tryptop han adsorption and recovery were achieved at linear velocities up to 5 .0 cm/min and 3.2 cm/min respectively. Successive sorbent reutilizatio n, following continuous sorption and elution steps, was carried out in packed bed columns with the neutral resins and activated carbon. The L-form of tryptophan, after crystallization, was identified by HPTLC.