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Kinetic Study of the Conversion of Different Substrates to Lactic Acid Using Lactobacillus bulgaricus
Author(s) -
BurgosRubio Concepción N.,
Okos Martin R.,
Wankat Phillip C.
Publication year - 2000
Publication title -
biotechnology progress
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.572
H-Index - 129
eISSN - 1520-6033
pISSN - 8756-7938
DOI - 10.1021/bp000022p
Subject(s) - lactic acid , fermentation , lactose , substrate (aquarium) , chemistry , galactose , lactobacillus , hydrolysis , yield (engineering) , food science , lactic acid fermentation , microorganism , biochemistry , bacteria , chromatography , biology , materials science , ecology , genetics , metallurgy
Abstract Lactic acid fermentation includes several reactions in association with the microorganism growth. A kinetic study was performed of the conversion of multiple substrates to lactic acid using Lactobacillus bulgaricus . Batch experiments were performed to study the effect of different substrates (lactose, glucose, and galactose) on the overall bioreaction rate. During the first hours of fermentation, glucose and galactose accumulated in the medium and the rate of hydrolysis of lactose to glucose and galactose was faster than the convesion of these substrates. Once the microorganism built the necessary enzymes for the substrate conversion to lactic acid, the conversion rate was higher for glucose than for galactose. The inoculum preparation was performed in such a way that healthy young cells were obtained. By using this inoculum, shorter fermentation times with very little lag phase were observed. The consumption patterns of the different substrates converted to lactic acid were studied to determine which substrate controls the overall reaction for lactic acid production. A mathematical model (unstructured Monod type) was developed to describe microorganism growth and lactic acid production. A good fit with a simple equation was obtained. It was found experimentally that the approximate ratio of cell to substrate was 1 to 10, the growth yield coefficient ( Y XS ) was 0.10 g cell/g substrate, the product yield ( Y PS ) was 0.90 g lactic acid/g substrate, and the α parameter in the Luedeking‐Piret equation was 9. The Monod kinetic parameters were obtained. The saturation constant ( K S ) was 3.36 g/L, and the specific growth rate (μ m ) was 1.14 l/h.