ISSN:
1432-0614
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract Production of lactic acid using Lactobacillus delbrueckii NRRL B445 recently renamed L. rhamnosus was studied in continuously recycled packed reactors at pH 6.3 and 42° C. Four inert adsorbent supports were used for immobilization: Raschig rings of sintered glass (Schott, FRG), beads of sintered glass (Schott), beads of porous glass (Poraver; Dennert, FRG) and irregular ceramic particles (Otto Feuerfest, FRG). The best support was found to be the beads of sintered glass, yielding the highest volumetric lactic acid productivity. Zeta potentials of L. rhamnosus showed the cells to be negatively charged at all pHs studied, the charge becoming less negative with increasing ionic strength. The surface charge did not control adhesion. A comparison between the immobilization carried out in batch and continuous tests with the different supports demonstrated that extrapolation from batch adsorption curves to continuous operation can introduce large errors. The effect of dilution rate was also stidied: a saturation concentration of adsorbed cells was achieved at all dilution rates, i.e., the immobilized cell component was almost invariant. Different diameters of Poraver beads were tested; clear evidence for mass transfer limitation was shown. Finally, the effects of pH and substrate concentration under immobilization were evaluated. The results indicate that pHs above or below the optimum for suspended cell systems can be used in the immobilized reactor while maintaining lactic acid productivity. To simplify downstream processing by keeping the glucose concentration close to zero in the effluent, the glucose concentration in the feed has to be chosen in conjunction with the dilution rate.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00170077
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