OPTIMIZATION OF ACID HYDROLYSIS OF PINEAPPLE LEAF RESIDUE AND BIOCONVERSION TO ETHANOL BY SACCHAROMYCES CEREVISIAE

In this study, response surface methodology (RSM) with central composite design (CCD) was employed to optimize the dilute acid hydrolysis of pineapple leaf residue pretreated by milling and drying in an oven at 110 degrees C overnight. The three manipulated variables were sulfuric acid concentration (0.2-5 M), temperature (110-130 degrees C), and hydrolysis time (30-120 min). The maximal 23.33 g/L RSM-predicted glucose yield was obtained at 0.24 M sulfuric acid concentration, 111 degrees C temperature, and 94 min hydrolysis time. A verification experiment indicated a highly reproducible glucose yield of 20.89 g/L (10.5% deviation from model prediction). The glucose resulting under optimal conditions was finally fermented to ethanol by using baker's yeast (Saccharomyces cerevisiae). The fermentation conditions were as follows: 1.5 g yeast per 50 mL substrate incubated at 30 +/- 2 degrees C. The highest ethanol yield of 9.75 g/L (0.47 g/g glucose) at 72 h was over 90% of the theoretical ethanol yield produced from glucose fermentation, which was 10.74 g (0.51 g/g glucose). The ethanol yield achieved appears quite attractive and demonstrates that pineapple leaves have excellent potential as an alternative feedstock for ethanol production.