Optimization of alkali pre-treatment of sweet sorghum [Sorghum bicolor (L.) Moench] residue to improve enzymatic hydrolysis for fermentable sugars
Pallavi Punia, Lakhvinder Singh
Abstract
Sweet sorghum was used as a bioenergy crop to improve the enzymatic hydrolysis for releasing fermentable sugars as compared to other crops. Effective pre-treatment with NaOH at 121℃ for up to 50minutes was reported in this study before enzymatic hydrolysis. The response surface methodology approach was used to optimize the parameters for alkali pre-treatment. The optimized parameters of pre-treated SSR were 1-3% NaOH concentration, 0.5-1.5 mm particle size, 10-50 min time studied using box-behnken design. The findings suggest that 2% NaOH with a 1mm reduction in particle size in 50minutes leads to enzymatic saccharification for fermentable sugars with a maximum loading of 62.7% of cellulose. Enzymatic hydrolysis was performed with the aid of enzymes cellulase and xylanase. The optimum conditions obtained for fermentable sugars were 50℃, 72 hours of hydrolysis duration with 20FPU/g substrate of enzyme loading for 20g/L sorghum residue from one factor at a time approach. Maximum concentration of 78.3±0.23g/L of glucose, 5.4±0.47g/L of xylose with 1.53±0.11g/L of cellobiose was obtained from hydrolysate after 72hrs enzymatic treatment. The characterization, before and after pre-treatment were done by FTIR and FESEM shows effective pre-treatment is important for delignification and increase in cellulose digestibility for improving the enzymatic hydrolysis.