Growth of Candida utilis on Amberlite with Glucose and Ethanol as Sole Carbon Sources

Abstract

The results of Candida utilis growth on an anionic resin (Amberlite) at high glucose concentration and using ethanol as the sole carbon sources are presented. The yeast consumed 240 mg glucose (g initial dry matter)⁻¹ (IDM) reaching a final population of 5.6x10⁹ cells (g1DM)⁻¹ (initial inoculum size: 1x10⁷ cells (g IDM)⁻¹. It was also shown that respirometry was a reliable on-line method for monitoring growth. The respiratory quotient (RQ) showed the changes in the metabolism of the yeast during glucose consumption, from a fermentative to an oxidative route.When C. utilis was grown on gaseous ethanol enriched air, a final population of 3.25x10⁹ cells (g IDM)⁻¹ was attained. The importance of mineral salts concentration in the nutritive medium was clearly demonstrated. A two fold increase in the population was obtained when the mineral medium was not limiting. Small amounts of acetaldehyde and ethyl acetate were detected at the outlet of the reactor (1.88 µl l⁻¹ and 0.87 µl l⁻¹, respectively). Ethanol accumulated in the reactor up to 120 mg (g 1DM)⁻¹ (probably an inhibitory level for this yeast). RQ remained constant at around 0.6 during the fermentation.