Yeast recycles performance in a cellulosic sugar cane hydrolysate media

Cellulosic hydrolysate obtained by enzymatic saccharification of sugarcane bagasse pulp was submitted to an alcoholic fermentation by Saccharomyces cerevisiae Pe-2, strain provided by Pedra Agroindustrial Mill, Serrana-SP; Brazil. Firstly, the bagasse was pre-treated by H₃PO₄ 1.5% (w/v) at 120ºC for 20 min followed by delignification employing NaOH 1.5% (w/v), 120ºC for 30 min, in a 350-L stainless steel-coated cast iron reactor, equipped with a stirrer, and heated through a jacket with thermal oil. After these processes, the material was hydrolyzate by commercial cellulase (15 FPU/g substrate) supplemented by β-glucosidase (10 UI/g substrate) in bottles containing 1L of medium under agitation in an orbital shaker at 150 rpm, 50ºC and 72h. Finally, the hydrolysate was concentrated until approximately 120 g.L^-1 of glucose in a water bath at 100 °C. The yeast pre-inoculum was obtained from YPD medium in a 250 mL Erlenmeyer flask, containing 100 mL of medium under agitation at 200 rpm, 33°C, and 24h. The inoculum used was prepared with glucose (30 g.L^-1), yeast extract (5.0 g.L^-1), KH₂PO₄ (1.0 g.L^-1), urea (5.0 g.L^-1), KCl (1.0 g.L^-1), CaCl₂.2H₂O (1.0 g.L^-1), oligo-elements (1 ml.L^-1) and thiamine (1 mg.L^-1) under same conditions for pre-inoculum. Batch fermentations were performed, under cell recycle, in a bioreactor with 700 mL of working volume at 250 rpm and 33°C. Results showed a good performance of the yeast with the highest global productivity of 6.45 g.L^-1.h^-1 at fifth batch, yield of 87.4 %, and ethanol concentration of 47.1 g/L obtained from a cellulosic hydrolysate without sterilization.