Alkali Pretreatment and Enzyme Hydrolysis to Enhance the Digestibility of Rice Straw Cellulose for Microbial Oil Production

The alkali and alkali ethanolysis were used for pretreatment and delignification of rice straw. The combined hydrothermal- alkali method presented the high efficiency for removing the lignin. The pretreatment condition was optimized and achieved the highest of delignification (92.5%) under 30% (w/v) NaOH at a ratio of rice straw to alkali solution of 1 : 10 (w/v) at 121°C for 20 min. The highest yield of the remaining cellulose was 81.5% (w/w). The enzymatic hydrolysis of the rice straw cellulose was optimized for enhancement the digestibility via Response Surface Methodology (RSM). The cellulase activity, buffer solution, and hydrolysis time were evaluated. The optimum condition was cellulase activity at 935.18 U, 10 mL of buffer solution 10% (w/v) with hydrolysis time for 120 h, represented the maximum sugar yield with 136.6 g/L (0.54 g/g rice straw). The rice straw hydrolysate was further used as carbon source for microbial oil production by oleaginous yeasts.