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.