Ethanol production from mahula ( Madhuca latifolia L.) flowers using free and immobilized (in Luffa cylindrical L. sponge discs) cells of Zymomonas mobilis MTCC 92

A novel immobilization method involving Zymomonas mobilis immobilized in a luffa ( Luffa cylindrica L.) matrix for ethanol production from mahula ( Madhuca latifolia L.) flowers was investigated. The dried spongy fruits of luffa, a cucurbitaceous crop available in abundance in tropical and sub-tropical countries, have been found to be a promising material for immobilizing microbial cells. In our study, the cells not only survived, but they were also active physiologically for four growth cycles, yielding ethanol at 251.1 ± 0.012, 247.9 ± 0.08, 243.4 ± 0.042 and 240.71 ± 0.033 g/kg flowers in the first, second, third, and fourth cycles, respectively, after 96 h fermentation. Ethanol production by the immobilized cells was 9.2% higher than that by free cells. The ethanol yield ( Yp/s ), volumetric substrate uptake ( Qs ), and final sugar to ethanol conversion rate (%) obtained with luffa-immobilized cells of Z. mobilis were 0.439 ± 0.004 g/g, 0.994 ± 0.009 g/l/h, and 87.8%, respectively, which were 7.06, 2.62, and 6.92% higher than that of free cells.