Journal of Energy Bioscience 2025, Vol.16, No.5, 263-272 http://bioscipublisher.com/index.php/jeb 264 in emission reduction and resource recycling. Finally, this paper puts forward the research and policy directions for the future sustainable industrial development. 2 Agronomic and Biochemical Traits of Sweet Potato 2.1 Agronomic traits Sweet potatoes (Ipomoea batatas) grow well in tropical, subtropical and even some temperate regions. It is adaptable to various types of soil, including sandy soil, loam and clay, and only requires good drainage. Compared with major grains, it requires less water and fertilizer, and has strong drought resistance, growing well even on poor soil (Tedesco et al., 2023). Many varieties are resistant to pests and diseases, especially those improved through breeding (Vieira et al., 2015). Most varieties mature in 120–180 days, faster than sugarcane or maize. High-yield types can reach over 30 tons per hectare under good conditions. The vines and leaves grow vigorously, offering materials for feed or biogas (De Paula Batista et al., 2019). 2.2 Biochemical composition Sweet potato roots are rich in starch (15%~30%) and sugars, easy to hydrolyze for bioethanol (Wu et al., 2021a; 2021b). The high water content (60%~80%) supports anaerobic digestion, improving biogas yield (De Paula Batista et al., 2019). With high carbohydrate and moisture levels, sweet potato is an efficient biofuel feedstock (De Paula Batista et al., 2019; Wu et al., 2021a). The vines contain proteins and fibers, suitable for feed or biogas use (Vieira et al., 2015; Sheikha and Ray, 2017). Peels and residues are rich in organic matter and trace elements, useful for compost or soil improvement. Proper use of all parts supports “whole-plant utilization” (Sheikha and Ray, 2017; De Paula Batista et al., 2019). 2.3 Comparison with other crops Compared with cassava, sugarcane or corn, sweet potatoes are more adaptable to specific soil and climatic conditions (Vieira et al., 2015; Tedesco et al., 2023). Sweet potatoes grow rapidly, have high yields, and do not compete with staple food crops (Sheikha and Ray, 2017). Its starch content is comparable to that of cassava, and it is easy to be converted into ethanol with low energy consumption (Hariharan et al., 2020). Unlike sugarcane, sweet potatoes do not require complex juicing processes, and compared with corn, their by-products have higher feed and fiber values. Sweet potato residues perform better in biogas fermentation than corn stalks or bagasse (De Paula Batista et al., 2019). It shows strong advantages in energy conversion, adaptability, and resource use (Tedesco et al., 2023). 3 Sweet Potato Bioethanol Production 3.1 Starch conversion technology Sweet potatoes have a high starch content, so the first step is to convert the starch into fermentable sugar. This process involves liquefaction and saccharification using α -amylase and glucoamylase. Recent studies have shown that hydrolysis can proceed well at 28 ℃~42 ℃, and the use of simultaneous saccharification fermentation (SSF) can shorten the reaction time and increase the yield. For high-viscosity residues, cellulase and pectinase help release glucose and reduce viscosity (Wang et al., 2016). The optimized process can achieve nearly 80% ethanol production within approximately 22 hours (Carvalho et al., 2023). The combined use of enzymes can also increase the release of sugar in the residue (Gou et al., 2023). 3.2 Fermentation process Common microbes include Saccharomyces cerevisiae and S. diastaticus (Abdullah et al., 2015; Rizzolo et al., 2021). Factors such as temperature, yeast concentration, and pH affect ethanol yield. The best results are at 35 ℃ ~37 ℃ and 40%~45% (v/v) yeast (Abdullah et al., 2015). SSF technology is widely used because it reduces sugar loss and viscosity, improving efficiency (Zhang et al., 2011; Hariharan et al., 2020). Ethanol yield can reach over 91% at both lab and industrial scales (Zhang et al., 2011). Adding xylanase can further improve fermentation of thick materials (Wang et al., 2016).
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