Two-step acid and alkaline ethanolysis/alkaline peroxide fractionation of sugarcane bagasse and rice straw for production of polylactic acid precursor

Abstract

Sugarcane bagasse and rice straw were subjected to acid and alkaline ethanolysis and sequential enzymatic hydrolysis to produce glucose for lactic acid production. Influence of physico-chemical treatments using ultrasonic bath and ultrasonic probe was studied compared with mechanical stirring. The results showed that the highest glucose yield with least contamination of xylose was obtained from acid ethanolysis fractionation (5N H2SO4+50%, v/v ethanol) when stirred at 90°C for 4h. Alkaline ethanolysis accomplished high amount of both glucose and xylose released, however it was not favorable substrate for homofermentative lactic acid bacteria. In order to enhance enzymatic hydrolysis of acid ethanolysis fractionated samples, lignin was subsequently removed by the second step alkaline/peroxide delignification. The maximum lactic acid was obtained at 23.6±0.2g/L from Lactobacillus casei fermentation after 72h when hydrolysate from two-step acid hydrolysis and alkaline/peroxide fractionated sugarcane bagasse containing 24.6g/L initial glucose concentration was used as substrate. © 2014 Elsevier B.V.