OBTAINING HIGHLY CONCENTRATED HMO SOLUTIONS BY REVERSE OSMOSIS

Abstract

The present invention relates to a method for concentrating aqueous solutions of human milk oligosaccharides, in which an aqueous solution comprising at least one human milk oligosaccharide is subjected to a reverse osmosis process by means of a reverse osmosis membrane and is thereby concentrated to a final osmotic pressure of at least 70 bar measured with a freezing point osmometer. Moreover, the present invention refers to an according use of a reverse osmosis membrane, a corresponding reverse osmosis system containing such a membrane and a spray-dried HMO product obtainable by the method.

Claims

1.-15. (canceled)

16. A method for concentrating aqueous solutions of human milk oligosaccharides comprising subjecting an aqueous solution comprising at least one human milk oligosaccharide to a reverse osmosis process by means of a reverse osmosis membrane and concentrating the at least one human milk oligosaccharide to a final osmotic pressure of at least 70 bar measured with a freezing point osmometer.

17. The method according to claim 16 wherein the at least one human milk oligosaccharide comprises, preferably is 2-fucosyllactose.

18. The method according to claim 16 wherein the method does not comprise a step in which water is evaporated.

19. The method according to claim 16 wherein the reverse osmosis membrane has a retention for NaCl between 93 and 99.6%.

20. The method according to claim 16 wherein the reverse osmosis membrane is a dairy reverse osmosis membrane.

21. The method according to claim 16 wherein the method comprises the following subsequent steps: i) an aqueous solution comprising at least one HMO, especially 2-FL, is subjected to a reverse osmosis process by means of a RO membrane, especially a dairy RO membrane, and is thereby concentrated to a final osmotic pressure of at least 70 bar measured with a freezing point osmometer, ii) the at least one HMO, especially 2-FL, is crystallized from the concentrated solution, and iii) the crystals of the at least one HMO, especially of 2-FL are separated from the mother liquor by physical means, for example by filtration, and optionally washed and/or dried.

22. The method according to claim 21 wherein between steps i) and ii) the solution is further concentrated by evaporation of water in an evaporating device.

23. The method according to claim 21 wherein prior to step ii) acetic acid is added to the concentrated solution.

24. The method according to claim 16 wherein the method comprises the following subsequent steps: i) an aqueous solution comprising at least one HMO, especially 2-FL, is subjected to a reverse osmosis process by means of a RO membrane, especially a dairy RO membrane, and is thereby concentrated to a final osmotic pressure of at least 70 bar measured with a freezing point osmometer, ii) acetic acid is added to the concentrated solution obtained in step i), iii) the at least one HMO, especially 2-FL, is crystallized from the concentrated and acetic acid containing solution obtained in step ii), iv) the crystals of the at least one HMO, especially of 2-FL, containing acetic acid are separated from the mother liquor by physical means, for example by filtration, and optionally washed and/or dried, v) the crystals obtain in step iv) are re-dissolved to form an aqueous solution comprising the at least one HMO, especially 2-FL, and acetic acid, vi) the solution obtained in step v) is subjected to a diafiltration process by means of a NF or open RO membrane or by means of ion-exchange chromatography (IEX), wherein the acetic acid is at least partially removed from the solution, and vii) the solution obtained in step vi) is subjected to spray drying in a spray drying unit to obtain a spray-dried product containing at least one HMO, especially 2-FL.

25. The method according to claim 24 wherein between steps i) and ii) the solution is further concentrated by evaporation of water in an evaporating device.

26. The method according to claim 24 wherein in step vii), prior to spray drying, the acetic acid content of the aqueous HMO, especially 2-FL solution is reduced by applying NF or open RO membranes in a diafiltration process.

27. A method comprising utilizing a reverse osmosis membrane in a reverse osmosis process for concentrating aqueous solutions of human milk oligosaccharides to final osmotic pressures of at least 70 bar measured with a freezing point osmometer.

28. A reverse osmosis system containing a RO membrane, especially a dairy RO membrane, and an aqueous solution comprising at least one HMO, especially 2-FL, and having an osmotic pressure of at least 70 bar measured with a freezing point osmometer.

29. A spray-dried product containing at least one HMO, especially 2-FL, being obtainable by the method according to claim 16.

30. The product according to claim 29 wherein it has an acetic acid content of not more than 0.3 wt. %.

Description

DESCRIPTION OF FIGURES

[0074] FIG. 1: Schematic diagram of a batch reverse osmosis system suitable for concentrating aqueous solutions of HMOs according to the present invention:

[0075] (1) feed vessel, (2) feed, (3), pump, (4) membrane, (5) permeate, (6) pressure adjustment, (7) retentate, P.sub.F=pressure of feed, P.sub.P=pressure of permeate, P.sub.R=pressure of retentate;

[0076] FIG. 2: Schematic diagram of a batch reverse osmosis system suitable for concentrating aqueous solutions of HMOs according to the present invention having an extra crossflow pump:

[0077] (1) feed vessel, (2) feed, (3), pump, (4) membrane, (5) permeate, (6) pressure adjustment, (7) retentate, (9) extra crossflow pump, P.sub.F=pressure of feed, P.sub.P=pressure of permeate, P.sub.R=pressure of retentate.

[0078] FIG. 3: Schematic diagram of a batch diafiltration system suitable for removing acetic acid from aqueous solutions of HMOs according to the present invention:

[0079] (1) feed vessel, (2) feed, (3), pump, (4) membrane, (5) permeate, (6) pressure adjustment, (7) retentate, (8) replacement buffer, P.sub.F=pressure of feed, P.sub.P=pressure of permeate, P.sub.R=pressure of retentate.

EXAMPLES

Inventive Example

[0080] An aqueous feed solution containing 19.0 wt. % of 2-FL was concentrated by a batch reverse osmosis process at a temperature of 10 C. in a HP 7450 stirred test cell (Sterlitech, US) using the reverse osmosis membrane DairyRO-HF (Nitto-Denko Hydranautics, Japan) at a transmembrane pressure (TMP) of 61 bar. The mixture was concentrated until the maximum possible concentration at the applied pressure was reached.

[0081] At that point, a solution with an osmotic pressure of 104.6 bar measured with the freezing point osmometer Osmomat 3000basic (Gonotec, Germany) according to the manufacturer's manual could be reached in the retentate.

[0082] The final concentration of 2-FL in the retentate (C R) and permeate (CP) was analyzed by means of a halogen moisture analyzer HX204 (Mettler-Toledo, Germany). The concentration of 2-FL equals 100 wt. % minus the concentration of water (in wt. %) in the mixture. The results are shown in the following table, wherein the retention (R) was calculated according to the formula R=1C.sub.P/C.sub.R.

TABLE-US-00001 C.sub.R C.sub.P R 45.5 wt. % 0.09 wt. % 99.8%

Comparative Example

[0083] A batch reserve osmosis process was conducted as above for the Inventive Example with the deviation, however, that the nanofiltration membrane SUEZ DL (SUEZ, France) was used. Because of the limitations of the membrane, a TMP of only 40 bar could be applied.

[0084] An osmotic pressure of 64.7 bar (measured with Osmomat 3000basic) was reached in the retentate. For this, a TMP of 40 bar was required.

[0085] The final concentrations of 2-FL were analyzed as above giving:

TABLE-US-00002 C.sub.R C.sub.P R 38.5 wt. % 0.31 wt. % 99.2%

[0086] As can clearly be seen from the comparison between the Inventive Example on the one hand and the Comparative Example on the other hand, the final concentration of 2-FL in the retentate can remarkedly be enhanced by using a reverse osmosis membrane because of the latter's enhanced pressure tolerance.