Sugar beet juice fermentation by Zymomonas mobilis attached to stainless steel wire spheres

Abstract

The fermentation of sugar beet juice as well as juice syrup medium by Zymomonas mobilis inoculum attached to stainless steel wire spheres was investigated. A semi-synthetic sucrose medium enriched with mineral salts and yeast extract was used as the control. It was established that raw sugar beet juice ensured good Zymomonas mobilis culture growth and slightly decreased ethanol synthesis applying both flame-burned and TiCl4-treated wire spheres as carriers (Qx = 0.05-0.06 g/l × h; Qeth = 1.02-1.22 g/l × h). High ethanol yield was also observed in juice medium (Y = 0.45-0.46 g/g), however, levan synthesis with this medium decreased. The application of juice syrup brought about less growth effect and ethanol synthesis as compared to juice medium. The use of semi-synthetic sucrose medium resulted in high levan production (Qlev=0.6-0.7 g/l × h), however, reduced ethanol production by 40%. In conclusion, sugar beet juice or syrup is recommendable for the preparation of Zymomonas mobilis inoculum. The levan production stage has to be realized using an optimized semi-synthetic sucrose medium. The installed wire spheres filled with inocula provided the possibility for a repeated batch fermentation process, which could be recommended for both juice and semi-synthetic sucrose medium fermentation.