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Pilot plant clarification of sweet sorghum juice and evaporation of raw and clarified juices

Brett Andrzejewski, Gillian Eggleston, Randall Powell
Industrial crops and products 2013 v.49 pp. 648-658
aseptic conditions, evaporation, fermentation, hybrids, juices, glucose, turbidity, fructose, brix, cultivars, sucrose, yeasts, ethanol production, ethanol, probability, bioethanol, syrups, manufacturing, Saccharomyces cerevisiae, pH, foams, Sorghum bicolor, sweet sorghum
One of the fundamental processing areas identified by industry for the commercial, large-scale manufacture of liquid biofuels and bioproducts from sweet sorghum (Sorghum bicolor L. Moench) is the clarification of juice to make it suitable for concentration into syrup for long-term storage, year-round supply, efficient transport, and acceptable fermentation yields. Pilot plant studies were conducted to evaluate the clarification of juices (80°C; target limed pH of 6.3; 5ppm polyanionic flocculant) from a sweet sorghum hybrid and cultivar M81E on three sample dates across a 3-month (September–November) processing season in 2011. Turbidity removal across pilot plant clarification was 95–98% after only 30–50min retention time (Rt). The higher Rt at the pilot than laboratory scale caused a slight loss of total fermentable sugars (sucrose+glucose+fructose) to acid degradation, thus a slightly higher target limed pH of ∼6.5 is recommended to preserve sugars during clarification and downstream thermal evaporation. Under non-optimized fermentation conditions (Saccharomyces cerevisiae yeast 10% (w/w); 35°C; 14h; 18 Brix), higher and less variable bioethanol yields with less foam formation occurred under sterile than non-sterile conditions for both raw and clarified syrups. Ethanol yields ranged from 7.1 to 8.2% (56.0–64.7g/L) and 5.8 to 8.4% (45.8–66.3g/L) and sterile and non-sterile conditions, respectively. Moreover, under sterile conditions, there were no significant differences at the 5% probability level for ethanol yields between the raw and clarified syrups, indicating clarification did not impede fermentation. Overall, clarification of the juices reduced the loss of fermentable sugars during the evaporation stage, and allowed for better syrup storage.