Sweet Sorghum And Sweet Pearl Millet Carbohydrate Extraction and Preservation for Bioethanol Production and Bagasse Valorization: A Review

Highlights Sweet sorghum and sweet pearl millet are interesting feedstocks for ethanol production. Biomass and juice storage are key steps for carbohydrate preservation. Produced bagasse can be valorized in many ways, including as silage or for cellulosic ethanol production. Abstract. Sweet sorghum and sweet pearl millet have been considered as potential energy crops. They have many advantages in terms of ethanol production compared to corn and sugarcane, such as lower requirements for water and fertilizers, higher tolerance to drought, and lower competition with the food sector. Sweet sorghum and sweet pearl millet stems are rich in water-soluble carbohydrates (WSC) (sucrose, fructose, and glucose), and their biomass has to be crushed for juice extraction. However, the extraction efficiency of WSC varied widely depending on the press type used and the parameters considered during the pressing process (stripping stems from leaves or not, compressive force magnitude, smooth or grooved press rollers, number of times of biomass pressing, etc.). WSCs are easily degradable, causing technical challenges related to crop handling before pressing and juice storage thereafter. Some studies focused on stem preserving methods, whereas others dealt with extending the shelf life of the juice. To make the use of sweet sorghum and sweet pearl millet as energy crops more profitable, the bagasse (residue) generated from biomass pressing can be valorized in different ways, mainly as silage or for second generation ethanol production. The objective of this review was to assess the efficiency of different presses used for juice extraction and discuss various methods tested for WSC conservation from deterioration as well as possible bagasse valorization. Keywords: Bagasse, Carbohydrates, Ethanol, Press, Sweet pearl millet, Sweet sorghum.