RESUMO
Bioethanol is a potentially safe and renewable alternate source of energy. However, ethanol production from value added food and feedstock has not shown growth as estimated. Of late, the second generation processes of production of ethanol, such as from lignocellulosic biomass out of agricultural/domestic waste, has been gaining considerable momentum. Here, we attempted optimizing the conditions of physiochemical pretreatment as well as fermentation process using wheat straw by Pichia stipitis NCIM 3498 (now known as Schefferomyces stipitis). We have also studied the influence of process variables, such as incubation temperature, inoculum concentration and different nutrients, on ethanol production. Pulverized wheat straw consists of 32±0.31% cellulose, 48±0.37% hemicellulose and 17±0.15% lignin on dry solid (DS) basis. Wheat straw delignified with 1% HNO3, yielded 11.54% xylose and 1.54% glucose under steam explosion [15 psi (121°C) for 60 min], with a hydrolytic efficiency of 59.56%. Simultaneous Saccharification and Fermentation (SSF) of pretreated wheat straw by crude cellulose (produced by Trichoderma reesei NCIM 1052) and S. stipitis were investigated in the present study. Important process variables for ethanol production from pretreated wheat straw were optimized using response surface methodology (RSM) based on central composite design (CCD) experiments. A three level CCD experiments with central and axial points was used to develop a statistical model for optimization of process variables viz. incubation temperature (30, 32 and 34°C) X1, inoculum level (2, 4 and 6%) X2 and nutrients (1/2/3) X3. Data obtained from RSM on ethanol production were subjected to the analysis of variance (ANOVA), analyzed using a second order polynomial equation, and contour plots were used to study the interactions among three relevant variables of the fermentation process. The fermentation experiments were carried out at flask level. The processing parameters setup for reaching a maximum response for ethanol production was obtained when applying the optimum values for temperature (34°C), inoculum level (6%) and fermentation medium (ammonium sulphate, KH2PO4, peptone and yeast extract) for S. stipitis. Maximum ethanol concentration 7.15 g/L was obtained after 72 h from S. stipitis at the optimized process conditions in anaerobic batch fermentation.
RESUMO
Bioethanol, is a potential alternate source of energy, renewable and safe. Ethanol production from value added food and feedstock has also not shown growth as estimated. Of late, the second generation processes of production of ethanol, such as from lignocellulosic biomass out of agricultural/domestic waste has been gaining considerable momentum. Here, we explored a new approach for optimizing the conditions of physiochemical pretreatment as well as fermentation process using peels of Ananas cosmosus as substrate and immobilized yeast Pachysolen tannophilus MTCC 1077 and Pichia stipitis NCIM 3498. We have also studied the influence of process variables such as incubation temperature, inoculum concentration and different nutrients on ethanol production. Pulverized peels of A. cosmosus recorded 25 ± 0.31% cellulose, 28 ± 0.18% hemicellulose and 8 ± 0.07% of lignin on dry solid (DS) basis. Peels of A. cosmosus delignified with 1% H2SO4 yielded 18.89% glucose, 38.81% xylose and 29.31% fructose under thermochemical pretreatment using autoclave (121°C, 20 min.), with a hydrolytic efficiency of 75.52 ± 0.45%. FTIR spectroscopy results not only indicated the penetration of H2SO4 in the amorphous region of the biomass and degradation of hemicelluloses but also showed the structural differences before and after pretreatment. The enzymes required for hydrolysis were prepared from culture supernatants of Trichoderma reesei NCIM 1052 using wheat bran as carbon source under submerged fermentation conditions on rotatory shaker incubator (at 28°C for 10 days ). Enzyme activity (U/ml) of crude cellulase produced by T. reesei NCIM 1052 was 311.1 µmole/ml/min. Delignified A. cosmosus peel yielded 51.71 ± 0.44 g/l glucose when enzymatically hydrolysed by crude cellulase at the substrate enzyme ratio of 1:5. Simultaneous saccharification and fermentation (SSF) of peels of A. cosmosus by crude cellulase and separately entrapped Pichia stipitis NCIM 3498 (now known as Scheffersomyces stipitis) and Pachysolen tannophilus MTCC 1077 cells in calcium alginate beads were also investigated in the present study. The fermentation experiments were carried out at flask level. The processing parameters setup for reaching a maximum response for ethanol production was obtained when applying the optimum values for temperature (32°C), inoculum level (6%) and fermentation medium (ammonium sulphate, KH2PO4, peptone and yeast extract) for P. tannophilus MTCC 1077 and temperature (30°C), inoculum level (2%) and fermentation medium (ammonium sulphate, KH2PO4, peptone and yeast extract) for S. stipitis NCIM 3498. Maximum ethanol concentration 10.5 g/l and 10.9 g/l was obtained from P. tannophilus MTCC 1077 and S. stipitis NCIM 3498, respectively at the optimized process conditions in anaerobic batch fermentation.