Phase equilibrium and bioproduction of the aroma compound 2-phenylethanol in a biphasic aqueous system

Abstract

2-Phenylethanol (PEA) is a very important natural aroma compound with a roselike odor. The solid–liquid phase equilibrium (SLE) with higher alkanols (decan-1-ol, hexadecan-1-ol, octadecan-1-ol and eicosan-1-ol), alkanes (eicosane) and oleic acid has been determined at ambient pressure in order to explore their potential application for continuous product extraction during fermentation. A dynamic method was used over a broad range of mole fractions and temperatures from (246 to 338) K. Complete liquid miscibility and simple liquidus curves were observed for all binary (alkan-1-ol + PEA) systems. Liquid–liquid equilibrium (LLE) with the upper critical solution temperature was observed in case of (eicosane, or oleic acid + PEA) mixtures. Decan-1-ol was chosen as the best solvent for PEA. The influence of pressure on SLE was determined up to 700 MPa and at three different temperatures (303.15, 313.15 and 323.15) K. The experimental data were correlated with the non-random two-liquid equation, and both SLE and LLE data were described with average low root-mean-square deviation σ T = 1.25 K for SLE and in mole fraction σ x = 0.004 for LLE. The experimental data were in a very good agreement with the predictions of the group contribution model Mod. UNIFAC(Do) using published parameters. The main aim of this study was to determine the best solvent for a biphasic in situ product removal at temperature T = 303.15 K. Two solvents, decan-1-ol and oleic acid, were further tested for their influence on yeast cell growth, and both were found to be biocompatible. The well-known oleic acid was found to give better results than decan-1-ol in terms of extraction capability, biocompatibility and overall performance in the bioprocess.