Microwave pretreatment for enzymatic saccharification of sweet sorghum bagasse

Pretreatment of sweet sorghum bagasse (SSB) through microwave radiation was evaluated at four lime doses (0, 0.1, 0.15, and 0.2 g/g SSB), two water content of 10 or 20 ml/g SSB, and three exposure times as 2, 4, and 6 min. Optimal pretreatment condition was identified as 0.1 g lime and 10 ml water per g SSB in 4 min. Under this condition, sugar yield of 32.2 g/100 g SSB (equivalent to 52.6% of maximal potential sugars) was achieved. With the same water content and exposure time, but without lime, sugar yield of 39.8 g/100 g SSB (equivalent to 65.1% of maximal total sugars) was observed. The higher sugar recovery without lime was mainly due to high sugar release during pretreatment. But with lime, sugar degradation took place, which resulted in less sugar yield though lime did make cellulose more accessible to enzymes as evidenced by higher percentage of increase of total reducing sugars during enzymatic hydrolysis. Results from this study were strongly supported by FTIR and SEM images. Overall, in a very short time and simple setup, microwave radiation shows great promise to be a leading pretreatment technique for SSB.