METHOD FOR PREPARING AN AQUEOUS SOLUTION OF BETA-GLUCAN

Abstract

The presently claimed invention is directed to a method for the preparation of an aqueous solution comprising at least one beta-glucan comprising at least the steps of a) fermentation of at least one fungal strain in an a fermentation broth, b) addition of at least one acid to the fermentation broth to adjust the pH to a value in the range of ≧2.0 to ≦4.0 and c) filtration of the fermentation broth to obtain an aqueous solution comprising the at least one beta-glucan and at least one beta-glucan that is obtained by this method.

Claims

1-13. (canceled)

14. A method for the preparation of an aqueous solution comprising at least one beta-glucan comprising: fermenting at least one fungal strain which secretes the at least one beta-glucan into an aqueous culture medium to obtain a fermentation broth comprising the at least one beta-glucan, the water and biomass, b) adding at least one acid to the fermentation broth obtained in step a) to adjust the pH to a value in the range of ≧2.0 to ≦4.0 while maintaining the temperature of the fermentation broth in the range of ≧15 to ≦55° C. and c) filtering the fermentation broth obtained in step b) to obtain an aqueous solution comprising the at least one beta-glucan.

15. The method according to claim 14, wherein the concentration of the at least one beta-glucan in the fermentation broth obtained in step a) is in the range of ≧2 to ≦50 g beta-glucan per liter of fermentation broth.

16. The method according to claim 14, wherein the at least one beta-glucan is selected from the group consisting of schizophyllan and scleroglucan.

17. The method according to claim 14, wherein the fungal strains are Schizophyllum spec or Sclerotium spec.

18. The method according to claim 14, wherein the fermentation is carried out at a temperature in the range of ≧15 to ≦40° C. with aeration and flow.

19. The method according to claim 14, wherein the at least one acid is selected from the group consisting of at least one inorganic acid and at least one organic acid.

20. The method according to claim 19, wherein the at least one inorganic acid is selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, sulphuric acid, boric acid, hydrofluoric acid, hydrobromic acid and perchloric acid.

21. The method according to claim 19, wherein the at least one organic acid is selected from the group consisting of lactic acid, acetic acid, formic acid, citric acid, oxalic acid, uric acid and malic acid.

22. The method according to claim 14, wherein the pH in step b) is in the range of ≧3.0 to ≦4.0.

23. The method according to claim 14, wherein the at least one acid is added to the fermentation broth while maintaining the temperature of the fermentation broth in the range of ≧15 to ≦40° C.

24. The method according to claim 14, wherein the filtering is a crossflow microfiltration.

25. The method according to claim 14, wherein the filtering is carried out at a temperature in the range of ≧15 to ≦40° C.

26. An aqueous solution of at least one beta-glucan obtained by the method according to claim 14.

Description

EXAMPLES

[0080] 1. Determination of the Filtration Ratio (FR Value)

[0081] Principle of Measurement:

[0082] In the determination of the filtration ratio (FR value), the amount of filtrate which runs through a defined filter is determined as a function of time. The FR value is determined according to the following formula (I)

FR=(t.sub.190g−t.sub.170g)/(t.sub.70g−t.sub.50g)  (I),

where the variables and the equation have the following meaning:
t.sub.190g=time in which 190 g of filtrate are obtained,
t.sub.170g=time in which 170 g of filtrate are obtained,
t.sub.70g=time in which 70 g of filtrate are obtained,
t.sub.50g=time in which 50 g of filtrate are obtained.

[0083] Thus, in each case the time span which is required for in each case 20 g of filtrate to flow through the filter is determined, i.e. at an early time and at a late time in the filtration process, and the quotient is calculated from the two time spans. The larger the FR value, the higher the decrease in filtration velocity with increasing duration of the filtration process. This indicates increasing blockage of the filter, for example by gels or particles.

[0084] The FR value is determined by the following method:

[0085] 1.1. Equipment [0086] a) Sartorius pressure filtration apparatus 16249; filter diameter 47 mm; with 200 ml digestion cylinder (Øi=41 mm) [0087] b) Isopore membrane 1.2 μm; Ø47 mm; No. RTTP04700 available from Merck Millipore [0088] c) Balance

[0089] 1.2. Preparation of the Glucan Solution

[0090] First, 50 g of a mixture of the glucan solution obtained from the experiments and water is prepared, i.e. in a ratio such that the concentration of the glucan is 1.75 g/l. The mixture is stirred for 10 min and checked visually for homogeneity. If the mixture is still inhomogeneous, further stirring is effected until the mixture is homogeneous. The mixture is then made up to a total amount of 250 g with 200 g of ultrapure water. Thereafter, stirring is effected for at least 1 h for homogenization, after which the pH is adjusted to 6.0 with 0.1 M NaOH and stirring is then effected again for 15 min. The pH of 6.0 is checked again. The final concentration of the glucan in the mixture is 0.35 g/l.

[0091] 1.3. Carrying Out the Filtration Test

[0092] The filtration test is effected at room temperature (T=25° C.) at a pressure of 1.0 bar (compressed air or N.sub.2). [0093] place coarse support grid on the sieve tray [0094] place fine support grid on the sieve tray [0095] place membrane filter on top [0096] insert seal (O-ring) [0097] screw sieve tray and outlet tap to the cylinder [0098] close outlet tap [0099] introduce 220 g (about 220 ml) of solution [0100] screw upper cover to cylinder [0101] clamp on inlet air tube [0102] check pressure and adjust to 1.0 bar [0103] place beaker on the balance under the filtration apparatus. Press tare. [0104] open outlet tap [0105] the test is stopped when no more filtrate emerges.

[0106] By means of the balance, the amount of filtrate is determined as a function of time. The mass indicated in each case can be read visually but of course also automatically and evaluated.

[0107] 2. Preparation of the Fermentation Broth, Acidification and Determination of the FR Value and the Viscosity

[0108] Schizophyllum commune was used for the experiments and schizophyllan was produced in a batch fermentation at a temperature of about 24° C. as described in “Udo Rau, Biopolymers, edited by A. Steinbüchel, WILEY-VCH publishers, Volume 6, pages 63 to 79”.

[0109] At the end of the fermentation process an aqueous solution of HNO.sub.3 (53 wt % HNO.sub.3) was added to the reactor containing the fermentation broth via a pipeline. The pH value was measured by using an installed pH value probe and the temperature was measured by means of a sensor. The aqueous solution of HNO.sub.3 was added at a rate that allows to maintain the temperature of the fermentation broth in the range of 28 to 32° C. Usually the addition of the aqueous solution of HNO.sub.3 took place during a period of 2 to 10 min.

[0110] The FR value is determined as described above.

[0111] The viscosity of the aqueous solution containing schizophyllan is determined at a concentration of 0.35 g/l at a temperature of 25° C. and a shear rate of 7 s.sup.−1 with a ThermoScientific HAAKE™ RheoStress™ (plate/cone PP60H/C60/1° Ti) in a solution containing salts (NaCl 132, MgCl.sub.2 10.5, CaCl.sub.2 42.6, Na.sub.2SO.sub.4 0.27 and NaBO.sub.2 0.182, in each case g/L).

TABLE-US-00001 amount fer- concentration amount aqueous so- pH be- Viscosity exam- mentation schizophyllan lution of HNO.sub.3 (53 fore fil- FR at at 7 s.sup.−1 ple broth [m.sup.3] [g/L] wt. % HNO.sub.3) [kg] tration pH 6 [mPa .Math. s] 1 100 5.3 100 3.87 1.17 30.5 2 95 6.3 95 3.68 1.21 29.4 3 93 5.2 102 3.24 1.24 36.2 4 93 4.9 110 3.39 1.16 36.5  5* 89 5.5 0 4.21 3.65 33.0  6* 88 5.6 0 4.21 2.57 36.4 *= comparative examples

[0112] When the pH value of the fermentation broth was lowered ≦2.0, the cells dissolved by means of lysis. The presence of cell walls and cell contents has a negative impact on the FR value. The solutions containing schizophyllan that was prepared according to the inventively claimed process have a very good quality as evidenced by their low FR value and are suitable for the use in enhanced oil recovery applications as evidenced by their high viscosity.