3.6. Kinetics of cell growth and kefiran production in optimized
growth medium
The kinetics of cell growth and kefiran production were evaluated
for the cells cultivated in the finally optimized medium in
comparison with the un-optimized medium. The optimized
production medium contained (g L1): sucrose, 20; yeast
extract, 6; phosphate, 0.25; sodium acetate, 5. Fig. 6 shows
the kefiran production, cell growth and changes of pH value,
where the obtained data showed a sigmoid representation during
the fermentation. The maximal concentration of kefiran
obtained reached 1.28 g L1, which corresponds to an increase
of 58.02% in comparison with the production obtained in the
un-optimized medium (0.81 g L1). Furthermore, the optimized
production medium gave higher cell biomass, where
the maximal cell biomass reached 1.57 g L1 (1.0 g L1 in the
un-optimized medium, Fig. 5). These obtained results are in
good agreement with the results obtained by Dailin et al.
(2014), who investigated medium optimization of kefiran production
using L. kefiranofaciens in shake-flask level. Their
optimized medium increased the maximal cell biomass by
about 90% to reach 1.92 g L1, concomitant with 5-fold
increase in kefiran production (1.29 and 0.26 g L1 for optimized
and non-optimized medium, respectively).
3.7. Kinetics of cell growth and kefiran production during batch
cultivation in 16-L stirred tank bioreactor under uncontrolled pH
condition
In order to evaluate the scalability of the cultivation process,
the cell growth and kefiran production were studied in a
16-L pilot scale stirred tank bioreactor using the optimized
medium under un-controlled pH conditions. The results
obtained in Fig. 7 show that cells grew exponentially with a
growth rate of 0.051 g L1 h1, reaching a maximal cell mass
of 2.76 g L1 after 72 h. As reported by Elmarzugi et al.
(2010) for lactic acid bacteria, the maximal cell growth was
obtained when Lactococcus lactis cells were cultivated under
uncontrolled pH conditions. Kefiran was produced along
during the exponential growth phase which shows that kefiran
production is associated with the cell growth. The rate of kefiran
production was 0.053 g L1 h1, which is almost likely the
same as the growth rate, where the maximal kefiran produced
reached about 1.9 g L1 at 40 h. pH increased along the cultivation
process, reaching 8.45 by the end of the cultivation