Process for the heterotrophic production of microbial products with high concentrations of omega-3 highly unsaturated fatty acids

Abstract

Disclosed is a process for growing the microflora Thraustochytrium, Schizochytrium, and mixtures thereof, which includes the growing of the microflora in fermentation medium containing non-chloride containing sodium salts, in particular sodium sulfate. In a preferred embodiment of the present invention, the process produces microflora having a cell aggregate size useful for the production of food products for use in aquaculture. Further disclosed is a food product which includes Thraustochytrium, Schizochytrium, and mixtures thereof, and a component selected from flaxseed, rapeseed, soybean and avocado meal. Such a food product includes a balance of long chain and short chain omega-3 highly unsaturated fatty acids.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of copending and commonly assigned U.S. patent application Ser. No. 07 / 911,760, filed Jul. 10, 1992 which is incorporated herein in its entirety by reference which is a divisional of U.S. patent application Ser. No. 07 / 580,778, filed Sep. 11, 1990 which is incorporated herein in its entirety which issued as U.S. Pat. No. 5,130,242 which is a continuation-in-part of copending and commonly assigned U.S. patent application Ser. No. 07 / 439,093, filed Nov. 17, 1989 which is incorporated herein in its entirety by reference which is a continuation-in-part of U.S. patent application Ser. No. 07 / 241,410, filed Sep. 7, 1988 which was previously expressly abandoned.FIELD OF THE INVENTION [0002] The field of this invention relates to heterotrophic organisms and a process for culturing them for the production of lipids with high concentrations of omega-3 highly unsaturated fatty acids (HUFA) suitable for hu...

AI Technical Summary

Benefits of technology

[0020] One aspect of the present invention is the growth of Thraustochytrium, Schizochytrium, and mixtures thereof with high omega-3 HUFA content, in fermentation medium containing non-chloride containing sodium salts and preferably sodium sulfate. More particularly, a significant portion of the sodium requirements of the fermentation are supplied as non-chloride containing sodium salts. For example, less than about 75% of the sodium in the fermentation medium is supplied as sodium chloride, more preferably less than about 50% and more preferably less than about 25%. A particular advantage of the present invention is that the medium provides the source of sodium needed by the microflora to grow in the absence of a significant amount of chloride which can corrode the vessel in which the microflora are being grown and other fermentation or downstream processing equipment. It has been surprisingly found that microflora of the present invention can be grown at chloride concentrations of less than about 3 gl / l, more preferably less than about 500 mg / l, more preferably less than about 250 mg / l and more preferably between about 60 mg / l and about 120 mg / l while still attaining high yields of biomass per sugar of about 50% or greater. As discussed below, an additional advantage of the present invention is the production of microflora that are high in omega-3 HUFA content but have a small enough cell aggregate size to be consumed by larval shrimp, brine shrimp, rotifers and mollusks.

[0021] Non-chloride containing sodium salts can include soda ash (a mixture of sodium carbonate and sodium oxide), sodium carbonate, sodium bicarbonate, sodium sulfate and mixtures thereof, and preferably include sodium sulfate. Soda ash, sodium carbonate and sodium bicarbonate tend to increase the pH of the fermentation medium, thus requiring control steps to maintain the proper pH of the medium. The concentration of sodium sulfate is effective to meet the salinity requirements of the microflora, preferably the sodium concentration is (expressed as g / l of Na) is greater than about 1.0 g / l, more preferably between about 1.0 g / l and about 50.0 g / l and more preferably between about 2.0 g / l and about 25 g / l.

[0022] It has been surprisingly found that fermentation of the strains in the presence of a non-chloride containing sodium salt and particularly, sodium sulfate limits the cell aggregate size of the strains to less than about 150 microns, preferably less than about 100 microns, and more preferably less than about 50 microns. As used herein, the term cell aggregate size refers to the approximate average diameter of clumps or aggregates of cells in a fermentation medium of a microfloral culture. Typically, greater than about 25 percent of the cell aggregates in a microfloral culture have cell aggregate size below the average size, more preferably greater than about 50 percent and more preferably greater than about 75 percent. Microfloral cells produced in accordance with the present invention meet cell aggregate size parameters described above while in fermentation medium as well as after freezing and / or drying of the biomass if resuspended in liquid or physically agitated, such as by a blender or vortexer. The present process is particularly important for microflora which replicate by successive bipartition (wherein a single cell replicates by dividing into two cells which each divide into two more, etc.) because as cells repeatedly and rapidly undergo this process, the cells tend to clump forming multi-cell aggregates which are often outside the cell aggregate size parameters identified above. Schizochytrium replicate by successive bipartition and by forming sporangia which release zoospores. Thraustochytrium, however, replicate only by forming sporangia and releasing zoospores. For Thraustochytrium which replicate by sporangia / zoospore formation, clumping can be a problem as well, particularly because even though the number of cells in an aggregate may not be as great as aggregates formed by successive bipartition, the individual cell sizes of Thraustochytrium tend to be larger, and thus, clumps of a small number of cells are larger. However, one deposited strain of Thraustochytrium, ATCC 26185, has been identified which does not exhibit significant aggregation.

[0023] In another aspect of the present invention, it has been found that by restricting the oxygen content of the fermentation medium during the growth of Thraustochytrium, Schizochytrium, and mixtures thereof, the lipid content of the strains can be increased. The optimum oxygen concentration for lipid production can be determined for any particular microflora by variation of the oxygen content of the medium. In particular, the oxygen content of the fermentation medium is maintained at an oxygen content of less than about 40% of saturation and preferably between about 5% of saturation and about 40% of saturation.

[0024] Growth of the strains by the invention process can be effected at any temperature conducive to satisfactory growth of the strains; for example, between about 5° C. and about 48° C., preferably between about 15° C. and about 40° C., and more preferably between about 25° C. and about 35° C. The culture medium typically becomes more alkaline during the fermentation if pH is not controlled by acid addition or buffers. The strains will grow over a pH range from 5.0-11.0 with a preferable range of about 6.0-8.5.

[0025] Various fermentation parameters for inoculating, growing and recovering microflora are discussed in detail in U.S. Pat. No. 5,130,242. The biomass harvested from a fermentation run can be dried (e.g., spray drying, tunnel drying, vacuum drying, or a similar-process) and used as a feed or food supplement for any animal whose meat or products are consumed by humans. Similarly, extracted omega-3 HUFAs can be used as a feed or food supplement. Alternatively, the harvested and washed biomass can be used directly (without drying) as a feed supplement. To extend its shelf life, the wet biomass can be acidified (approximate pH=3.5-4.5) and / or pasteurized or flash heated to inactivate enzymes and then canned, bottled or packaged under a vacuum or non-oxidizing atmosphere (e.g., N2 or CO2). The term “animal means any organism belonging to the kingdom Animalia and includes, without limitation, any animal from which poultry meat, seafood, beef, pork or lamb is derived. Seafood is derived from, without limitation, fish, shrimp and shellfish. The term “products” includes any product other than meat derived from such animals, including, without limitation, eggs or other products. When fed to such animals, omega-3 HUFAs in the harvested biomass or extracted omega-3 HUFAs are incorporated into the flesh, eggs or other products of such animals to increase the omega-3 HUFA content thereof.

Problems solved by technology

However, there are several significant problems with these fish oil supplements, including bioaccumulation of fat-soluble vitamins and high levels of saturated and omega-6 fatty acids, both of which can have deleterious health effects.

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