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Bioethanol fermentation of clarified sweet sorghum (Sorghum bicolor (L.) Moench) syrups sealed and stored under vegetable oil

Klasson, K. Thomas K. Thomas, Stephanie A. Boone
Industrial crops and products 2021 v.163 no. pp. 113330
Sorghum bicolor, bacterial contamination, bioethanol, ethanol fermentation, feedstocks, fuel production, soybean oil, sugars, sweet sorghum, syrups, vegetable oil, yeasts
Sweet sorghum represents a readily available renewable carbohydrate feedstock for biofuel production. Generally, the sweet sorghum growing season and window for processing is short and it is often desirable to store a sugar-rich material for future processing. Therefore, we investigated the possibility of storing three different sweet sorghum sugar syrups under a layer of soybean oil; then we investigated subsequent yeast bioethanol fermentation.A layer of oil on the surface of the syrup reduced sugar loss in 30 and 40°Bx syrups, but the loss was still 21–36 %. Storage of 50°Bx syrup resulted in an 11–18 % loss of sugars with or without a surface layer of oil. Elevated levels of lactic and acetic acids, caused by bacterial contamination, almost completely inhibited yeast fermentation; however, when ethanol-producing microorganisms were part of the contamination, stored syrups produced a bioethanol at a yield of 83–91 %, compared to theoretical.