Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-08-11
2001-11-20
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S531000, C204S534000, C204S537000, C204S538000
Reexamination Certificate
active
06319382
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates a process for the fermentative production of lactic acid and for the isolation of lactic acid from a lactic acid-containing solution.
BACKGROUND OF THE INVENTION
European patent No. 230.021 describes a process in which glucose is fermented continuously to lactate, after which lactic acid is extracted from the solution by means of electrodialysis, where pH in the fermentor is controlled by removing the lactic acid at the same rate as the rate at which it is formed, the contents of the fermentor being recirculated over the electrodialysis unit. Yeast extract and inorganic salts are used as nutrients. A disadvantage of this system is that bacteria in the fermentor liquid are known to adsorb to the electrodialysis membranes, causing the electrical resistance in the electrodialysis unit to increase, which results in a substantially increased power consumption for the electrodialysis process.
Boyaval et al. (
Biotechnology Letters
Vol. 9, No. 3, 207-212, 1987) describe a bioreactor for lactic acid fermentation using a three-stage fermentation process that includes the production of biomass and lactic acid in the first stage, separation and concentration of the cells by ultrafiltration in the second stage, and lactate concentration and purification by electrodialysis in the third stage. It is reported, however, that this system exhibits the disadvantage of clogging of the ultrafiltration membranes, resulting in drastic restriction of permeate flow.
U.S. Pat. No. 4,110,175 also describes a general method for electrolytic purification of organic acids, including lactic acid. An improved version of this method is described in U.S. Pat. No. 5,002,881, in which lactic acid is formed as ammonium lactate through fermentation of a glucose-containing medium, which makes it possible to use ultrafiltration to separate the ammonium lactate from the fermentation liquid, as the retentate from the ultrafilter is returned to the fermentor. In this way there is no adsorption of bacteria to the membranes in the subsequent electrodialysis processes, and power consumption is therefore lower. The microorganism used in the patent is
Bacillus coagulans,
which has the property of not needing any special nutrient medium containing yeast extract or corn steep liquor, which are otherwise known to be necessary to maintain lactic acid fermentation when lactic acid bacteria are used. Prior to electrodialysis, the fermentor liquid is concentrated by means of reverse osmosis (RO), and the concentrated liquid is subsequently treated in an electrodialysis unit in which lactic acid is formed from ammonium lactate by means of bipolar membranes in a single operation. In this operation ammonium hydroxide is formed at the same time and can be returned to the fermenter as a medium for neutralisation of lactic acid. in this process, however, amino acids are used as a nutrient for the fermenting bacteria, which results in the disadvantage of relatively high costs. A further disadvantage is that RO used for concentration will result in non-converted organic matter (residual glucose and amino acids) being included in the electrodialysis treatment with bipolar membranes, where they contribute to reducing the process efficiency. Also, the resulting product might not be heat-stable due to the presence of residual sugars in the lactic acid.
The formation of amino acids from whey proteins and the use of whey protein as a nutrient in the fermentation of lactose in whey is described in U.S. Pat. No. 4,698,303. However, U.S. Pat. No. 4,698,303 has the disadvantage of requiring an independent hydrolysis for the production of amino acids from whey protein, the hydrolysis being carried out as a separate acidic enzymatic process, after which the hydrolysed product is fed to the membrane fermenter as a nutrient.
U.S. Pat. No. 5,503,750 discloses a method for the production and recovery of lactic acid using a combination of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).
WO 96/41021 discloses a method for recovering and purifying organic acids, e.g. lactic acid, using electrodialysis, where nanofiltration and contact with a chelating agent are employed to reduce fouling of ion-selective membranes used in electrodialysis.
EP 0393818-A discloses a method for purifying lactic acid using an electrodialysis step, a bipolar electrodialysis step, treatment with a strong cationic ion exchange resin and treatment with a weak anionic ion exchange resin.
BRIEF DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a process by which lactic acid can be produced and isolated in a simple and inexpensive manner, so as to eliminate the disadvantages of the prior art processes discussed above.
One aspect of the present invention thus relates to a method for fermentation of lactic acid from a sugar-containing fermentation liquid in a fermentor by means of lactic acid-forming bacteria, in which whey protein is present or is added as a nutrient substrate for the lactic acid-forming bacteria, the method comprising adding at least one protein-hydrolysing enzyme to the fermentor during the fermentation, so that hydrolysis of protein to amino acids takes place simultaneously with the fermentation of sugar into organic acid, and isolating lactic acid resulting from the fermentation.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, a sterilised growth medium comprising a sugar-containing solution and whey protein, e.g. whey permeate from production of whey protein concentrate, with an admixture of protein-hydrolysing enzymes, in the following called proteases, is subjected to continuous fermentation in a fermentor by means of a bacteria culture which produces lactic acid.
The “sugar” in the sugar-containing solution used according to the present invention can be any suitable sugar for lactic acid fermentation, for example a monosaccharide such as glucose, fructose or galactose, a disaccharide such as sucrose, maltose, cellobiose or lactose, or a polysaccharide. A mixture of different sugars can of course also be used. The sugar may suitably be derived e.g. from a whey permeate, but it may also be derived from any other source.
In a preferred embodiment, the pH in the fermentation liquid is kept substantially constant within the range of about pH 5-7 by addition of ammonia, typically in the form of ammonia gas, which forms a water-soluble salt with lactic acid. Although it is possible to maintain the desired pH value by means of other bases, e.g. NaOH, Ca(OH)
2
or CaCO
3
, this is less preferred for several reasons, among them being the fact that calcium ions are undesired in the fermentation liquid, and the fact that ammonia is less expensive than bases such as NaOH. Furthermore, the use of ammonia as the base has the advantage that it provides a source of nitrogen for the lactic acid bacteria, which has been found to result in improved growth of the bacteria compared to e.g. NaOH.
In another preferred embodiment, the fermentation liquid is subjected to an ultrafiltration process which retains the retentate containing bacteria culture and non-hydrolysed whey protein, and allows dissolved matter to pass, including lactic acid formed in the fermentation process. The lactic acid may e.g. be in the form of ammonium lactate when ammonia is added as a base as described above.
The permeate from the ultrafiltration process is then preferably treated in an ion exchange unit, preferably utilising a chelating resin which primarily binds divalent ions, so as to replace calcium and magnesium ions as well as possible iron ions present in the permeate with sodium ions, thus preventing precipitation of salts, for example calcium salts such as calcium phosphate that might otherwise lead to a slow irreversible scaling of the membranes in a subsequent electrodialysis treatment of the permeate. Moreover, the removal of iron ions results in the final lactic acid product being non-coloured.
The resulting eluate from the ion exchange operation is then preferably concentr
Birch & Stewart Kolasch & Birch, LLP
Lactascan ApS
Phasge Arun S,.
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