Comparison of two-stage acid-alkali and alkali-acid pretreatments on enzymatic saccharification ability of the sweet sorghum fiber and their physicochemical characterizations

•A two-stage pretreatment process was studied for lignocelluloses pretreatment.•The two-stage process improved the saccharification efficiency of sweet sorghum fiber.•0.23 g·g−1 of glucose yield was achieved under the optimized condition of alkali-acid sequence.

Two-stage acid/alkali pretreatment was used to enhance the saccharification efficiency of sweet sorghum fiber. The physicochemical characterizations of the pretreated fibers were evaluated by SEM, FTIR and XRD. The acid and alkali sequence in the two-stage pretreatment process was compared, and their dosage was optimized. The results indicated that the two-stage pretreatment showed better saccharification performance when compared with conventional single stage pretreatment. And compared with the acid-alkali sequence, the alkali-acid sequence achieved higher glucose yield (0.23 g·g−1) under the optimized conditions, which was 1.64 and 1.21 times higher than that of the single stage and the acid-alkali pretreatments, respectively. Overall, the two-stage pretreatment process is a promising approach to achieve high fermentable glucose conversion rate of cellulosic material.