Journal of Energy Bioscience 2025, Vol.16, No.3, 117-127 http://bioscipublisher.com/index.php/jeb 120 NaOH has the best effect. It can effectively remove lignin and achieve an enzymatic hydrolysis rate of 87.7% (Bhati and Sharma, 2025). If silage is first used and then pretreated with NaOH, it can not only reduce the loss during the fermentation process, but also increase the sugar yield. Some experiments even reached 94.45% (Zhao et al., 2024). These treatment methods also have problems, such as using more energy and chemicals, and producing some inhibitors, which are not conducive to large-scale production (Rao and Binod, 2014; Dong et al., 2019; Santos et al., 2021). The lignin and cellulose of sorghum are too tightly attached, which makes it easy for the enzyme to stick to it and "work in vain", which will reduce the conversion efficiency. Therefore, it is necessary to further improve the efficiency of delignification and optimize the amount and type of enzymes used to truly solve this problem (Dong et al., 2019; Bhati and Sharma, 2025). 4 Pretreatment and Processing Technologies 4.1 Mechanical, thermal, and chemical methods: steam explosion, dilute acid, alkaline, ionic liquids Pretreatment is a critical step to make sorghum biomass easier to convert into sugars and ethanol. It can break up the hard wood fiber structure, help release more sugars, and achieve better fermentation results. Mechanical and thermal methods are more common, such as steam explosion and liquid hot water treatment (LHW). These methods use high temperature and pressure to destroy cell walls, making it easier for subsequent enzymes to enter and decompose (Bedzo et al., 2022; Kreetachat et al., 2025). Chemical methods are also commonly used, such as using dilute acids (such as sulfuric acid and hydrochloric acid) or alkalis (such as sodium hydroxide and ammonia), as well as alkaline hydrogen peroxide. These methods can remove most of the lignin and some of the hemicellulose, making cellulose more accessible (Chen et al., 2012; Koradiya et al., 2016; Santos et al., 2021; Batog and Wawro, 2022; Saïed et al., 2024). Recently, there are also some new methods, such as using ionic liquids or organic solvents (such as glycerol and ethanolamine) to treat sorghum. These solvents perform well in delignification and releasing sugars (Joy et al., 2021; Joy and Krishnan, 2022). 4.2 Recent advances in sorghum-specific pretreatment In recent years, there have been many new advances in pretreatment methods designed specifically for sorghum. The organic solvent method using a mixture of glycerol and ammonia can also clean up lignin very well and release more sugars at low temperatures. More importantly, the glycerol used can come from the byproduct of biodiesel, which can also save money (Joy et al., 2021; Joy and Krishnan, 2022). Another method is "microwave + ammonia" treatment. It can make the structure of sorghum looser and remove more lignin, which ultimately improves the efficiency of saccharification and fermentation (Chen et al., 2012). Another technology is called ammonia fiber expansion (AFEX), which can produce more sugar and ethanol at high solid content after optimization (Li et al., 2010). Some people have also tried to combine alkaline hydrogen peroxide with some enzymes (such as laccase). This combination not only has a good delignification effect, but is also more environmentally friendly (Santos et al., 2021; Batog and Wawro, 2022). 4.3 Impacts on sugar yield and fermentability Different pretreatment methods have a great influence on sugar output and fermentation effect. Dilute acid and alkaline hydrogen peroxide pretreatment can well retain polysaccharides and remove lignin. After treatment, the yields of glucose and xylose can be increased, up to 91.09% and 88% (Santos et al., 2021; Saïed et al., 2024; Kreetachat et al., 2025). Using modified organic solvent method or ammonia water pretreatment can also make cellulose better decomposed by enzymes, and the digestibility can reach 72% to 89%. The total sugar yield can be as high as 421.35 mg/g, and the maximum ethanol can reach 42.3 g/L (Li et al., 2010; Joy et al., 2021; Joy and Krishnan, 2022). Methods such as "microwave + ammonia water" or liquid hot water method can also produce a lot of sugar and ethanol without high enzyme dosage (Chen et al., 2012; Kreetachat et al., 2025). Moreover, these treatment methods do not produce many inhibitors, making them more suitable for fermentation (Koradiya et al., 2016; Santos et al., 2021). Different sorghum varieties respond differently to various pretreatment methods. Therefore, it is necessary to adjust the treatment conditions according to the characteristics of the specific variety in order to obtain the most sugar and ethanol (Joy et al., 2021).
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