Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Patent
1997-11-07
1999-08-03
Lilling, Herbert J.
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
435822, 435853, 435885, C12P 756
Patent
active
059324554
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel method for preparing pure lactic acid or a salt thereof by fermentation.
During the production cycle a solution comprising substantially pure feedstock is recycled through a bioreactor containing refreshed microorganism cells, such as bacterial cells or fungal mycelium.
During the refreshing cycle the microorganism cells are refreshed by recycling a feedstock solution enriched with nutrients, thus replenishing the capacity of the microorganisms to produce lactic acid.
FIELD OF THE INVENTION
Lactic acid is produced both by fermentation and by synthetic methods for a wide variety of applications. The purity of the product grades varies from technical lactic acid to slightly more purified food grade, and further to pharmaceutical grade. Often when lactic acid is employed as feedstock in an organic synthesis, a product of exceptionally pure thermally stable grade is necessary. Inexpensive lactic acid prepared by fermentation has generally been used for technical and food applications. Pharmaceutical and exceptionally pure (thermally stable) grades of lactic acid, on the other hand, have normally been produced by synthetic processes by which a comparatively pure product is directly obtained. Proper purification of lactic acid prepared by fermentation is known to be a cumbersome process requiring many steps, thus making up a large part of the production costs.
A new, ever increasing application for exceptionally pure (thermally stable) lactic acid is the preparation of lactide polymers. Lactide is a cyclic ester formed by two lactic acid molecules that can be controlledly polymerized. Polylactide is biologically degradable, on account of which property it is employed as a material for producing controlledly biodegradable support and attachment members used in bone surgery. Furthermore, on account of this property polylactide is considered as a potential raw material for compostable plastics. In addition to thermal stability, high optical purity is required of lactic acid employed to produce polylactides. Synthetically produced lactic acid is an equimolar mixture of the two optical isomers, and high-grade plastic cannot be prepared therefrom. On the other hand, nearly pure optical isomers can be produced by fermentation, by selecting a suitable producer organism. There are several possible homofermentative lactic acid bacteria for example of the genera Lactobacillus, Streptococcus and Pediococcus, such as Lactobacillus delbruckii for the preparation of L-lactic acid and Lactobacillus bulgaricus for the preparation of D-lactic acid.
The preparation of lactic acid by fermentation normally takes place by fermenting one batch at a time. It is also known to prepare lactic acid continuously with bacteria bound to a solid carrier and also by normal mixed fermentation. In all these methods, the production of lactic acid is strongly dependent on the growth of the bacterial population. Lactic acid bacteria are known to require a rich medium for growth, as their capacity to synthesize the growth factors they need is very small. Hence B group vitamins and a wide variety of different amino acids must be added to the medium. This addition is often made from yeast extract, which is typically needed in an amount of at least one tenth of the amount of sugar feedstock. The cost for such an amount of yeast extract is of the same order as that of sugar. That part of the nutrients which is not bound to the growing biomass remains in the product, thus lowering its purity. A special problem is presented by the nitrogenous nutrient components in view of preparing a thermally stable grade.
In light of the foregoing, it can be concluded that an ideal fermentation process for the industrial preparation of pure lactic acid would be a process that produced an essentially purer product than the hitherto known processes, necessitated substantially less nutrients than the hitherto known methods, and produced essentially less biomass. The invention to be described below meets these requirements.
DESC
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Koivikko Hannu
Viljava Tapio
Cultor Oy
Lilling Herbert J.
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