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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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http://hdl.handle.net/123456789/2443
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| Title: | EVALUATION OF YEAST BIOMASS PRODUCTION USING MOLASSES AND SUPPLEMENTS |
| Authors: | TAMENE, MILKESSA JIRU |
| Advisors: | Dr. Dawit Abate |
| Keywords: | Supplements
Molasses
Leavening action
Biomass
Baker’s yeast (Saccharomyces cerevisiae) |
| Copyright: | Aug-2009 |
| Date Added: | 4-May-2012 |
| Publisher: | AAU |
| Abstract: | Three yeast strains of saccharomyces cerevisiae, namely commercial baker’s yeast (BA),
an isolate from teff dough (TE) and an isolate from tella(TL) were cultivated in the
laboratory by submerged method to determine biomass yield. The biomass of these yeast
strains was compared with respect to molasses concentrations(3% w/v,5% w/v,8% w/v
and 10% w/v), pH(3.5,4.0,4.5,5.0 and 5.5),growth temperatures ( 250C,300C and 370C),
duration of incubation( 24,48,72 and 96 hrs) and the effect of addition of supplements as
treatments; T1-(NH4)2SO4 (0.5 % w/v),T2-(NH4)2SO4 (0.5 % w/v) and KH2PO4 (0.3 %
w/v),T3-(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 % w/v) and peptone (2% w/v),T4-
(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 % w/v),yeast extract(1%w/v) ,MgSO4.7H2O (0.05
% w/v ) and CaCL2.2H2O (0. 004 % w/v ),T5-(NH4)2SO4 (0.5 % w/v), KH2PO4 (0.3 %
w/v), peptone (2%w/v),yeast extract(1%w/v),MgSO4.7H2O (0.05%w/v) and CaCL2.2H2O
(0.004% w/v), biotin(0.005%w/v) and calcium panthetonate (0.0001% w/v). The contents
of molasses were analyzed before the cultivation process and it was found that the
molasses used for this study contains 43.1 % sugar, 0.25% total nitrogen, 1.56 % crude
protein, 17.9 % moisture content, 82.1% dry weight and 11.7 % total ash. With respect to
molasses concentration, BA isolate showed maximum biomass yield at 5%, 8% and10%
concentrations, whereas TE isolates showed the same trend at 5% and 8% concentrations.
TL isolate was found to accumulate the maximum yield at 8% molasses concentrations.
In all cases, the isolates showed similarity in high biomass accumulation when they were
grown at 8% w/v molasses concentration. Concerning the effect of pH on the growth of
yeasts, isolate BA was found to be effective at all pH values except pH 5.5; whereas TE
isolate was effective at pH 4.0, pH 4.5 and 4.5. Furthermore, isolate BA and isolate TE
were also effective at pH 4.5. At pH 3.5 and 5.5, there was a steady decrease in biomass
yield by all the isolates. With respect to incubation temperatures, the different isolates
displayed biomass yield ranging from 1.27g/l to 3.25g/l. All isolates showed slow growth
at 250C, and 370C with subsequent slow increase as the incubation temperatures
increased. The highest biomass was observed at 300C by isolates BA (2.98-3.2g/l in 24-
72 hrs), TE (2.91-3.1g/l); whereas isolate TLshowed biomass increase of 2.81g/l
.Supplementing molasses media with (NH4)2SO4 (0.5% w/v) (Treatment1) increased the
biomass of TL (5.6-5.9g/l), TE (5.6-6.2g/l), and BA (6.1-6.4g/l within 24 and 72 hrs. In
all cases the maximum biomass was achieved within 48 hrs. When this compared with
biomass accumulation on molasses alone, the inclusion of the supplemental nitrogen
source showed 1.5-2 fold increase in yeast dry weight by all isolates. Comparing the
growth of the isolates on molasses and ammonium sulphate as control the isolates did not
show significant difference in biomass with further treatments (T2-T5). The
incorporation of all the necessary supplements resulted in maximum biomass production
by BA (8.0 g/l), followed by TE (7.5 g/l) and TL (6.5 g/l). In all the biomass propagation
processes, the commercial baker’s yeast strain, BA was superior in giving high biomass
yield. Further more the leavening action of the two yeast strains, i.e., an isolate from teff
dough (TE) and commercial baker’s yeast (BA) was compared at room temperature and
300C. BA was found to be higher than TE both at room temperature and 300C. |
| URI: | http://hdl.handle.net/123456789/2443 |
| Appears in: | Thesis - Biology
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