Water-Soluble Carbohydrate Extraction from Sweet Pearl Millet and Sweet Sorghum Biomass as Affected by Bagasse Impregnation

Abstract

<abstract> <b><sc>Abstract.</sc></b> The extraction of the sugary juice from sweet sorghum and sweet pearl millet biomass is a major step for first-generation bioethanol production. However, an important amount of water-soluble carbohydrates (WSC) remains in the bagasse following a single pressing of the biomass in-field. Therefore, bagasse impregnation is required to collect residual carbohydrates. This study investigated the effects of bagasse impregnation liquid (water or juice from the first pressing of the biomass) and three impregnation durations (0, 30, or 60 min) for a second pressing on the WSC concentrations of the biomass, the bagasse, and the juice of sweet sorghum and sweet pearl millet. Our results showed that the impregnation duration had no effect on WSC concentration in the biomass, bagasse, and juice. However, water was more efficient than the first-pressing juice in extracting the residual WSC remaining in the biomass after the first pressing. The use of water for bagasse impregnation allowed extraction of a total of about 36% and 47.5% of WSC from sweet sorghum and sweet pearl millet biomass, respectively, compared to 28% and 41% when the first-pressing juice was used. Sweet sorghum and sweet pearl millet juice extracted from the biomass impregnated with water contained 21% and 28.5% more WSC, respectively, than the juice extracted from the biomass impregnated with the first-pressing juice. When pressing is carried out in-field, impregnation of the bagasse with water for a second pressing is highly recommended for more residual WSC extraction. However, the required quantity of water needs to be optimized.