The effect of orange peel oil on ethanol production by the ethanologenic bacterium Zymomonas mobilis was investigated. Orange peel oil was added in various amounts to determine its effects on ethanol production. Fermentation of model sugar solutions was conducted at 30 and 37 degrees C. The minimum orange peel oil concentration that inhibited ethanol production by Z. mobilis was determined after 24, 48, 72 and 96 h for both temperatures. Minimum inhibitory orange peel oil concentrations for ethanol production at 30 degrees C were 0.05% after 24 h, 0.10% after 48 h, 0.15% after 72 h, and 0.20% after 96 h. Minimum inhibitory orange peel oil concentrations for ethanol production at 37 degrees C were 0.05% after 24h, 0.10% after 48h, and 0.20% after 72h. orange peel oil did not inhibit ethanol production after 96 h at a temperature of 37 degrees C. (C) 2008 Elsevier Ltd. All rights reserved.