Bioethanol production from carob pods by solid-state fermentation with Zymomonas mobilis

The production of bioethanol from carob pod particles by solid-state fermentation (SSF) using Zymomonas mobilis was investigated. Wheat bran particles were mixed with carob pods as filler and support for bacterial growth. The Plackett–Burman (P–B) experimental design was used for initial screening of various factors affecting the process including temperature, initial moisture content, carob particle size, wheat bran particle size, pH, initial cell concentration, peptone and yeast extract concentration and fermentation time. Then the five most effective factors (temperature, carob particle size, peptone concentration, initial cell concentration and fermentation time) were optimised for maximum ethanol-concentration production by response surface methodology (RSM). The maximum of 0.30 g ethanol g−1 initial sugar was produced at 31 °C with initial moisture content of 80% (w/w), carob particle size 1 mm, peptone concentration 0.7% (w/w), initial cell concentration 6.74 × 108 cells g−1 carob and fermentation time 43 h.