Process for producing and recovering erythritol from culture...

Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound

Reexamination Certificate

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C435S171000, C435S911000

Reexamination Certificate

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06440712

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for producing and recovering erythritol crystals, more specifically to a fermentative method of producing erythritol without at the same time producing higher viscous polysaccharides, which is advantageous for recovering erythritol crystals by direct crystallisation from the unrefined microorganism-free fermentation broth.
BACKGROUND OF THE INVENTION
Erythritol-producing yeasts which produce erythritol through fermentation include those belonging to the genera Moniliella, Trichonosporoides, or Trichonosporon, typically used species are
Moniliella tomentosa
var.
pollinis
, and
Trichonosporoides megachiliensis.
A conventional process for isolating and recovering erythritol from a culture medium obtained by culturing one of the erythritol-producing yeasts in an aqueous medium comprises subjecting said culture medium to a pre-treatment such as biomass removal by filtration, decolorisation with the use of active carbon, desalting and decolorizing the culture medium with ion exchange resins and then concentrating and cooling the same thereby crystallising the aimed erythritol.
Impurities, which affect isolation, crystallisation and/or recovery of erythritol, comprise the following constituents:
Polyols such as glycerol and ribitol
Oligosaccharides, including disaccharides and higher ones contained in the starting starch hydrolysate as well as reaction products formed therefrom.
Viscous microbial polysaccharides produced by the yeast.
Due to the formation of the polysaccharides the viscosity of the medium increases. This results in a decreased oxygen transfer rate and by anaerobic fermentation part of the carbohydrate source is converted into ethanol, thereby reducing the production of erythritol. Furthermore highly viscous fermentation broths give problems in filtering-off the cells and polyol recovery is very difficult.
EP 0 327 016 describes a process for recovering highly pure erythritol from an erythritol-containing culture medium, by passing the microorganism-free fermentation broth through chromatographic separation columns packed with alkali metal or ammonium type strongly acidic cation exchange resins. Removal of various salts, colouring material, various oligosaccharides and polysaccharides is obtained. The process comprises culturing an erythritol producing microorganism in an aqueous medium under aerobic conditions; removing the cells from the resulting culture medium; passing the obtained supernatant through separation columns packed with alkali metal or ammonium type strongly acidic cation exchange resins; eluting the same with water; collecting fractions containing erythritol as the main component therefrom; and then recovering erythritol from these fractions. This process requires very high consumption of water and the separated components are very diluted, resulting in high evaporation costs. Furthermore the investment cost of such separation equipment is high.
EP 0 908 523 relates to a process for producing high-purity erythritol crystals. The process comprises a crystallisation step and a crystal separating step wherein an erythritol concentration of the erythritol-containing aqueous solution is adjusted to 30-60% by weight at the beginning of the crystallisation step. Prior to the crystallisation step the process comprises a microbe-separating step, and a chromatographic separation.
Derwent Abstract of Japanese patent JP 10287603 describes the acidic treatment of the microorganism-free erythritol containing fermentation broth for hydrolysing the formed polysaccharides and impurities. The hydrolysis converts certain impurities into other less viscous by-products but in principle the overall purity is not increased. These by-products are subsequently removed by conventional separation methods such as activated carbon and ion exchange treatment.
Derwent Abstract of Japanese patent JP 01215293 describes the recovery of erythritol from a polysaccharide containing fermentation broth with ultrafiltration membranes. Polysaccharides, which make the microorganism-free fermentation broth turbid, are completely removed by the ultrafiltration with membranes with a cut-off of 1,000 to 100,000 daltons and erythritol is recovered from the purified medium.
U.S. Pat. No. 4,906,569 relates to a process for isolating and recovering highly pure erythritol at a high crystallisation yield from a culture medium of an erythritol-producing micro-organism, which comprises separating and removing various impurities and by-products such as various salts, colouring materials and polysaccharides. The impurities and by-products are removed through chromatographic separation with the use of a strongly acidic cation exchange resin.
All above cited references require in one way or another a purification step for removing formed polysaccharides, such as treatment with ion exchange resins, column chromatography, acid hydrolysis or ultrafiltration.
EP 0136805 describes a fermentation process in presence of high spore-forming colonies of the yeast-like fungus
Moniliella tomentosa
var.
pollinis
, resulting in 2.3-3.5% polysaccharides based on erythritol content. In presence of low spore-forming colonies up to 16-25% polysaccharides based on erythritol content are formed. Although with high spore-forming colonies the amount of polysaccharides is already reduced to 2.3-3.5% based on erythritol content, it is described that the culture broth is refined prior to concentration to 60% and to 80% dry substance. Erythritol is crystallised therefrom. Furthermore, long fermentation times up to 13 days are required to reach an erythritol yield of 34%.
Accordingly a need exist for a process for producing erythritol by fermentation and recovering erythritol crystals without purifying the micro-organism free fermentation culture medium. The recovery process should be free from 1) extensive refining, 2) generating big waste-streams, 3) high-energy demands, but should give a good recovery of highly pure erythritol crystals.
The current invention provides such a process.
SUMMARY OF THE INVENTION
The present invention discloses a process for producing erythritol by fermentation using micro-organisms and recovering erythritol crystals characterised in that said process is comprising the following steps:
a) taking as micro-organisms a polysaccharide negative erythritol producing strain which is producing less than 1% polysaccharides, preferably less than 0.1% polysaccharides based on erythritol content,
b) preparing a fermentation culture medium,
c) adding the micro-organisms to the fermentation culture medium,
d) allowing the micro-organisms to grow until at least 50 g/L erythritol is obtained in the fermentation medium,
e) removing the micro-organisms from the fermentation culture medium,
f) concentrating the unrefined micro-organism-free fermentation culture medium to dry substance higher than 80% w/w,
g) crystallising of erythritol, and
h) collecting erythritol crystals.
The present invention relates to a process wherein the unrefined micro-organism fermentation culture medium is concentrated to a dry substance of at least 85% w/w, more preferably higher than 90% w/w.
The present invention further discloses a process wherein the erythritol crystals are collected with a recovery of at least 85%.
The present invention relates to a process wherein the erythritol crystals have a purity of at least 98% w/w, preferably 99% w/w.
The present invention relates to a process wherein the micro-organism is allowed to growth in less than 10 days.
The present invention relates to a process wherein the fermentation culture medium is prepared in a bubbled column reactor or airlift.
The current invention further discloses a process wherein in step a)
Moniliella tomentosa
var
pollinis
TCV324 is used.
Furthermore, the present invention relates to a polysaccharide negative erythritol producing Moniliella strain producing less than 1% polysaccharides, preferably less than 0.1% polysaccharides based on erythritol content. The present invention further relates to a polysa

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