Use of Saccharum spontaneum (wild sugarcane) as biomaterial for cell immobilization and modulated ethanol production by thermotolerant Saccharomyces cerevisiae VS3

Saccharum spontaneum is a wasteland weed consists of 45.10 ± 0.35% cellulose and 22.75 ± 0.28% of hemicellulose on dry solid (DS) basis. Aqueous ammonia delignified S. spontaneum yielded total reducing sugars, 53.91 ± 0.44 g/L (539.10 ± 0.55 mg/g of substrate) with a hydrolytic efficiency of 77.85 ± 0.45%. The enzymes required for hydrolysis were prepared from culture supernatants of Aspergillus oryzae MTCC 1846. A maximum of 0.85 ± 0.07 IU/mL of filter paperase (FPase), 1.25 ± 0.04 IU/mL of carboxy methyl cellulase (CMCase) and 55.56 ± 0.52 IU/mL of xylanase activity was obtained after 7 days of incubation at 28 ± 0.5 °C using delignified S. spontaneum as carbon source under submerged fermentation conditions. Enzymatic hydrolysate of S. spontaneum was then tested for ethanol production under batch and repeated batch production system using “in-situ” entrapped Saccharomyces cerevisiae VS3 cells in S. spontaneum stalks (1 cm × 1 cm) size. Immobilization was confirmed by the scanning electron microscopy (SEM). Batch fermentation of VS3 free cells and immobilized cells showed ethanol production, 19.45 ± 0.55 g/L (yield, 0.410 ± 0.010 g/g) and 21.66 ± 0.62 g/L (yield, 0.434 ± 0.021 g/g), respectively. Immobilized VS3 cells showed maximum ethanol production (22.85 ± 0.44 g/L, yield, 0.45 ± 0.04 g/g) up to 8th cycle during repeated batch fermentation followed by a gradual reduction in subsequent cycles of fermentation.