Ethanol production from carob extract by using Saccharomyces cerevisiae in biofilm reactor

Carob, widely grown in Mediterranean countries, contains several types of sugars such as 34-42% sucrose, 7-10% glucose, and 10-12% fructose. Due to the high sugar concentration, it is used for production of many value added products via fermentation such as ethanol, lactic acid, citric acid, pullulan, and mannanase. In this study, ethanol production conditions from carob extract through repeated-batch fermentation by using Saccharomycess cerevisiae in biofilm reactor were optimized by response surface methodology. Initial sugar concentration (4-10ºBx), agitation speed (100-200 rpm), and pH (5.0-6.0) were used as variable parameters. Results showed that initial sugar concentration had a significant effect on yield and maximum production rate. Optimum conditions were found to be 7.71ºBx, 120 rpm, and 5.18, respectively. After validation experiments ethanol concentration, yield, maximum production rate, and sugar utilization yield were determined as 24.51 g/L, 48.59%, 2.14 g/L/h, and 87.33%, respectively and fermentation time was reduced to 12 h using a biofilm reactor due to high biomass concentration as biofilms. Moreover, the effect of nitrogen sources used in media and non-enriched medium were also investigated. According to results while ethanol production, yield, and maximum production rate were considerably reduced compared to optimized conditions in biofilm reactor, sugar utilization yield was slightly similar. Consequently, whether ethanol production from carob extract in biofilm reactor was victoriously performed, fermentation time was significantly decreased compared to data in the literature.