Ethanol production from mahula flowers using free and immo-bilized cells S. cerevisiae (CTCRI strain) started in the log phase of
the growth and maximum ethanol production was achieved during
the stationary phase (96 h) (Fig. 2). In the present study, there was
a marginal fall of 21% and 11.5% in total sugar concentration over
initial content with simultaneous production of 31 and 23.6 g eth-anol/kg flowers up to 24 h of fermentation for the free and immo-bilized yeast cells, respectively. The decrease in sugar reserve
might be also due to its utilization in part, for initial growth andethanol/kg flowers), respectively. The decrease might be due to
marginal leakage of cells from luffa matrix during each batch of
fermentation. Similar results were obtained on ethanol production
from cane molasses using alginate-luffa as the carrier matrix for
the immobilization of yeast cells [12] . In their study, the ethanol
production was same during the 1st and 2nd cycle of operation
(91.7 g/l cane molasses), with a marginal decrease (0.5%) in the
3rd cycle (90.6 g/l cane molasses).The growth and fermentation kinetics of free and immobilized
cells were also studied (Table 1). The ethanol concentration ( P) ob-tained with luffa immobilized cells (37.2 g/l) was 9.2% more than
that of free cells (33.8 g/l). The volumetric substrate uptake (Qs)
was also found to be more in case of immobilized cells (0.850 g/
l/h) than that of free cells (0.831 g/l/h). Likewise, the ethanol yield
(0.455 g/g) and volumetric productivity (0.387 g/l/h) by immobi-lized cells were more than that of free cells (0.424 g/g and
0.352 g/l/h).Ethanol production from mahula flowers with immobilized
cells in luffa sponge in our present investigation was found supe-rior over other immobilized matrices reported in our previous
studies. Swain et al. [2] reported that the average yield of ethanol
using immobilized (in Ca-alginate matrix) yeast cells were 206 and
152 g ethanol/kg flowers, from fresh and 12-month-stored mahula
flowers, respectively which was 6.3 and 2.63% more than free cells
[193 (fresh) and 148 (12-months stored) g ethanol/kg flowers].
Behera et al. [4] reported that ethanol production by yeast cells
immobilized in agar agar (151.2 g ethanol/kg flowers) and Ca-algi-nate (154.5 g ethanol/kg flowers) was found to be 1.39% and 3.5%
higher than the free cells (149.1 g ethanol/kg flowers) after 96 h
of fermentation. Furthermore, some limitations such as gel degra-dation, low physical strength and severe mass transfer limitation
were often observed in the use of Ca-alginate or agar agar-based
carriers [4,18,19].