Poster
Presentation 30:
Effects of temperature and pH on the
production of exopolysaccharide by Bifidobacterium longum
Y.M. Lo, L.H. Chu, and Y.F. Chu
Department of Animal and Food Sciences
Agriculture and Natural Resources
University of Delaware
531 S. College Ave
Newark, DE 19717
ymlo@udel.edu
(302) 831-1045
Bifidobacterium longum BB-79,
in addition to its advocated probiotic benefits in regulating humans gut
microflora, was found capable of fermenting lactose into an acidic exopolysaccharide
(EPS) that might contribute to the texture of dairy products. However,
the nutritional requirements for EPS production have yet to be determined,
mainly due to difficulties in maintaining anaerobic conditions. We
have constructed an anaerobic bioreactor with controllable environment
so that the effect of medium composition on EPS production could be evaluated.
The objective of this study was to
optimize EPS production by evaluating effects of temperature and pH on
cell growth and EPS production, respectively.
A series of fermentation were conducted
anaerobically with temperature and pH ranging from 31 to 41°C and 5.5
to 7.6, respectively. The initial lactose concentrations were controlled
at 3% in M17 broth. Concentrations of cells, EPS, and lactose were
closely monitored.
Under controlled temperature (37°C)
and pH (6.9), a 2% lactose concentration was found to reach the highest
specific cell growth rate (0.33 h-1), whereas cell yields remained
almost identical among all concentrations studied (0.14 g cells/g lactose).
On the contrary, a 5% lactose concentration resulted in a higher final
EPS concentration (0.53 g/L) than that at 2% (0.45 g/L). The highest
EPS production rate (0.24 g/h) was reached under 5% lactose concentration,
with a correspondent lactose consumption rate as high as 0.48 g/h.
A two-stage fermentation with lactose addition from 2 to 5% at the end
of the exponential phase further increased the final cell and EPS concentrations
to 2.45 and 1.45 g/L, respectively.
These results suggest that the optimal
combination of temperature and pH for
cell growth and EPS production were
37°C at 6.9 and 34°C at 5.5, respectively. A three-dimensional
(lactose, temperature, and pH) two-stage fermentation was capable of elevating
the final EPS concentration to 1.85 g/L, higher than that of lactose concentration
shift.
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