A combination of evaporation and chemical preservation for long‐term storage of fresh sweet sorghum juice and subsequent bioethanol production

Evaporation and chemical preservation were combined for long‐term storage of sweet sorghum juice (SSJ). The preserved SSJ was further used as substrate for ethanol fermentation. Different chemicals including hydrogen peroxide, sodium hypochlorite, sodium benzoate, and methyl paraben were used as co‐preservatives and were added into concentrated SSJ that contains ~40% (w/v) of sugars. The effects of chemical preservatives on sugar storage and ethanol fermentation were compared. The results showed that methyl paraben has better sugar preservation ability and an acceptable yeast toxicity when compared with other chemicals. The addition of methyl paraben in concentrated SSJ was further evaluated and optimized. By adding 0.4 g/L of methyl paraben, 95.1% of fermentable sugars in SSJ were preserved after a 90‐day preservation at room temperature. Ethanol concentration of 121.1 ± 4.6 g/L with a yield of 0.45 ± 0.02 g/g was obtained using the preserved SSJ in batch fermentation. PRACTICAL APPLICATIONS: Ethanol production by sugar‐containing juices is of interest because it is more effective, cheaper, and easier than the lignocellulosic routes. However, the commercialization of the bioethanol plants that uses the sweet sorghum juice as a substrate has long suffered from the deterioration of sugars. As a consequence, the ethanol fermentation process is limited by the short intermittent substrate supplementation in order to satisfy the harvest of the fresh stalks. This work comes up with a novel “evaporation+chemical” preservation method. The synergistic effect of high concentration of sugars and methyl paraben preservative showed inspiring sugar preservation results. Most of the sugars in the sweet sorghum juice were preserved for at least 90 days at room temperature and can be used for ethanol fermentation effectively. The continuity of fermentation can be significantly improved, which showed promising results in year‐round operations.