Uptake of lactose and continuous lactic acid fermentation by entrapped non-growing Lactobacillus helveticus in whey permeate |
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Authors: | J Øyaas I Storrø D W Levine |
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Institution: | (1) Department of Biotechnology, Norwegian Institute of Technology, 7034 Trondheim, Norway, NO;(2) SINTEF, Applied Chemistry, 7034 Trondheim, Norway. Fax: 47 73596995, NO |
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Abstract: | Continuous production of lactic acid from lactose has been carried out in a stirred-tank reactor with non-growing Lactobacillus helveticus entrapped in calcium alginate beads. A considerably longer operation half-life was obtained in a continuously operated reactor
than in a batch-operated reactor. It is possible to simulate the action of entrapped non-growing cells on the basis of information
from diffusion and kinetic experiments with suspended free cells. The simulation fit the experimental data over a broad range
of substrate concentrations if the specific lactic acid production rate, q
P, was used as a variable parameter in the model. The dynamic mathematical model used is divided into three parts: the reactor
model, which describes the mass balance in a continuously operated stirred-tank reactor with immobilized biomass, the mass-transfer
model including both external diffusion and internal mass transfer, and the kinetic model for uptake of substrate on the basis
of a Michaelis-Menten-type mechanism. From kinetic data obtained for free biomass experiments it was found, with the use of
non-linear parameter estimation techniques, that the conversion rate of lactose by L. helveticus followed a Michaelis-Menten-type mechanism with K
S at half-saturation=0.22±0.01 g/l. The maximum specific lactose uptake rate for growing cells, q
S,max, varied between 4.32±0.02 g lactose g cells-1 h-1 and 4.89 ±0.02 g lactose g cells-1 h-1. The initial specific lactose uptake rate for non-growing cells, q
S,0, was found to be approximately 40% of the maximum specific lactose uptake rate for growing cells.
Received: 4 October 1995/Received last revision: 23 April 1996/Accepted: 29 April 1996 |
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