Spray freezing

Abstract

The present invention relates to an improved method for preservation of e.g. microorganisms, especially lactic acid bacteria, said method includes spray freezing.

Claims

1. A process for removing liquid from a solution or suspension containing microorganisms, comprising: (a) preparing droplets of a solution or suspension containing microorganisms by spraying the solution or suspension; (b) spray-drying the droplets by contacting the droplets with a drying gas; (c) freezing the droplets obtained in step (b) with a cryogenic gas to obtain a frozen product; and (d) freeze-drying the frozen product under reduced pressure to a water activity (a.sub.w) below 0.20, to produce a freeze-dried product.

2. The process of claim 1, wherein the microorganisms comprise lactic acid bacteria (LAB).

3. The process of claim 2, wherein: spray-drying step (b) comprises spraying an aqueous suspension containing the LAB into a drying gas in a spray chamber; and freezing step (c) comprises contacting the product resulting from step (b) with a cryogenic gas in a chamber to obtain a frozen powder as the frozen product.

4. The process of claim 2, wherein: spray-drying step (b) comprises spraying a liquid suspension containing the LAB into a chamber containing a drying gas; and freezing step (c) comprises freezing the droplets resulting from step (b) by contacting the droplets with a cryogenic gas in a chamber to obtain a frozen suspension as the frozen product.

5. The process of claim 1, wherein the spraying of step (a) is carried out by passing the solution or suspension through a spray nozzle or a rotating atomizing device, wherein the spray nozzle or rotating atomizing device results in droplets having a size of from 10 to 500 micrometers, measured as Dv90 values in micrometers.

6. The process of claim 1, wherein the frozen product is collected by a cyclone having a maximum differential pressure drop across the cyclone of about 100 mm water column, or an electrostatic filter.

7. The process of claim 1, wherein the spray-drying step (b) and freezing step (c) are independently conducted at a pressure in the range of from 60 to 200 kPa.

8. The process of claim 1, wherein spray-drying step (b) is conducted with a retention time of less than 2 minutes in a spray dryer, and wherein the resulting product is directly introduced into a freezing chamber.

9. The process of claim 1, wherein spray-drying step (b) is carried out with a drying gas inlet temperature of at most 300 C.

10. The process of claim 1, wherein spray-drying step (b) is conducted at a temperature in the range from 20 C. to 250 C.

11. The process of claim 1, wherein, after spray-drying step (b), the droplets have a size of between 20 and 400 microns measured as Dv90 values.

12. The process of claim 1, wherein, after spray-drying step (b), the liquid content of the droplets is reduced by at least 5% by weight as compared to the liquid content of the starting suspension or solution.

13. The process of claim 12, wherein, after spray-drying step (b), the liquid content of the droplets is between 20% and 85% by weight of the total weight of the droplets.

14. The process of claim 1, wherein the drying gas and the cryogenic gas each independently contain less than 5% oxygen.

15. The process of claim 1, wherein the drying gas and the cryogenic gas are independently selected from the group consisting of an inert gas, a noble gas, carbon dioxide, an alkane gas, and mixtures of two or more thereof.

16. The process of claim 1, wherein the cryogenic gas has an inlet temperature in the range of from 50 to 250 C., and/or the cryogenic gas has a temperature of between 20 C. and 150 C. during the freezing step.

17. The process of claim 1, wherein the solution or suspension further comprises an additive selected from inositol, lactose, sucrose, trehalose, inulin, maltodextrin, skimmed milk powder, yeast extract, casein peptone, inosine, inosinemonophospate, glutamine and salts thereof, casein and salts thereof, ascorbic acid and salts thereof, and polysorbate.

18. The process of claim 17, wherein the ratio of microorganisms to additive is from 1:0.1 to 1:10 (w/w of the dry weights).

19. The process of claim 1, wherein the microorganisms are selected from a yeast, a Streptococcus species, a Lactobacillus species, a Lactococcus species, a Leuconostoc species, a Bifidobacterium species, an Oenococcus species, and a Bacillus species.

20. The process of claim 1, wherein the process is carried out in an apparatus comprising a two-chamber tower, the tower comprising: a first (upper) chamber comprising (i) an atomizer adapted to atomize the suspension or solution, and (ii) an inlet for the drying gas; and a second (lower) chamber comprising (iii) an inlet for the cryogenic gas, and (iv) an outlet coupled to a cyclone; wherein the drying gas having a temperature in the range from 20 C. to 250 C. and the suspension or solution are sprayed into the first (upper) chamber, and the cryogenic gas having a temperature in the range of from 50 to 250 C. is sprayed into the second (lower) chamber.

21. The process of claim 1, wherein the process is carried out in an apparatus comprising a chamber having (i) an atomizer for atomizing the solution or suspension, (ii) an inlet for the drying gas, (iii) an inlet for the cryogenic gas, and (iv) an outlet.

22. The process of claim 1, further comprising packaging the freeze-dried product.

23. The process of claim 21, wherein the inlet for the drying gas is integrated in the atomizer.

24. The process of claim 21, wherein the outlet is connected to a cyclone.

25. A product obtained by the process of claim 1.

26. The product of claim 25, packaged in an airtight container.

Description

FIGURES

(1) FIG. 1 depicts a preferred spray drying equipment that can be used according to the invention.

(2) TABLE-US-00001 (a) drying gas supply (b) drying gas heater (c) Inlet temperature control loop (d) Combined spray drying/freezing chamber (e) Liquid feed supply (f) Liquid feed pump (g) Atomization device (h) Cyclone separator (i) Warm water scrubber unit (j) Exhaust fan (k) Chamber pressure control loop (l) Outlet temperature control loop (m) powder discharge (y) cryogenic gas inlet

(3) FIG. 2 depicts the stability data for the strain ST-44 after 3 months storage at 20 C. and at +5 C., cf. example 4.

(4) FIG. 3 depicts the stability data for the strain ST-4895 after 3 months storage at 20 C. and at +5 C., cf. example 2.

(5) FIG. 4 depicts a spray drying/freezing apparatus according to the invention

(6) TABLE-US-00002 1. Drying gas supply 2. Supply fan 3. Heater 4. Cryogenic gas supply 5. Nozzle (with optionally gas supply shown) 6. Liquid feed 7. Liquid feed tank 8. Protein or Microorganism suspension, optional with cryoprotectant 9. Water inlet 10. Liquid feed pump 11. Drying chamber 12. Freezing chamber 13. Frozen powder discharge 14. Cyclone 15. Exhaust fan 16. Exhaust gas T. Temperature regulator P. Pressure regulator F. Drying gas regulator

(7) FIGS. 5 and 6 depicts preferred embodiments of the apparatus

EXPERIMENTAL

Example 1

(8) A sample of 1281 g of Streptococcus thermophilus (strain ST-Fe 2) concentrate was kept at <5 C. This contained 1.7E+11 CFU/g with approx. 12.8% (w/w) dry solids. Parallel to this 579 g of solution was prepared by adding the following ingredients to 470 g of cold tap water (approx. 10 C.) under agitation: 33 g sodium ascorbate, 32 g sodium caseinate, 22 g inositol and 22 g monosodium glutamate (MSG).

(9) The sample and the additive solution were mixed. This resulted in 1.86 kg of liquid formulation with approx. 14.6% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 1.2E+11 CFU/g and was kept cold (<5 C.) throughout the test.

(10) A GEA Niro Mobile Minor laboratory spray dryer was modified to accommodate spray drying using two 380 mm top extension sections followed by liquid nitrogen injection in the lower fixed section of the standard spray chamber to accommodate in-situ freezing of the partially dehydrated product droplets arriving from the upper section of the chamber. The upper spray drying section was supplied with heated pure nitrogen drying gas and the lower freezing section was supplied with liquid nitrogen capable of generating a frozen particulate colder than 100 C.

(11) The upper spray dryer section inlet temperature was kept at 190 C., using a nitrogen drying gas kept at a mass flow-rate of approx. 100 kg/h. A 2-fluid nozzle (Schlick 0-2) was used for the atomization of the above mentioned liquid formulation, using an atomization gas flow of approx. 5 kg/h (Nitrogen) equivalent to an atomization pressure of 0.8 Bar(g)

(12) The liquid formulation was sprayed into the upper spray dryer section. The feed-rate was kept at 2 kg/h and the spray drying/freezing chamber outlet temperature was kept in the range 140 to 110 C.

(13) A free-flowing frozen powder with an average particle size of 105 micron was collected below the downstream cyclone. After 55 min. about 1100 g of partially dehydrated frozen formulation has been collected, which corresponds to a yield of about 70%. The moisture content was now 18.5% (w/w) measured as total volatiles on a Sartorious IR at 115 C. This corresponds to a reduction of the total water amount in our product of approx. 24% (w/w).

(14) The obtained partially dehydrated frozen powder contained now 1.5E+11 CFU/g. The frozen powder was freeze dried, performed at a chamber pressure of 0.3 mbar with temperature increasing from 42 C. to 32 C. with 1.5 C./min. The freeze drying was ended when the weight of the product has been constant/stable for at least 2 hours. The dried product had an acceptable stability after 3 months storage at 5 C. (pH 5.6 as measured using standard CINAC analysis).

Example 2

(15) Example 1 was repeated using the same equipment, conditions and additive solution, but with the strain ST-4895. Thus a sample of 1281 g Streptococcus thermophilus strain ST-4895 concentrate was mixed with 579 g of additive solution, resulting in 1.86 kg of liquid formulation with approx. 14.6% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 1.2E+11 CFU/g. After drying and freezing, a frozen powder was obtained.

(16) The spray-frozen powder was freeze dried (cf. example 1). The stability of the dried product was compared with a freeze-dried product obtained from a standard pellet-frozen concentrate of ST-4895. Performance of the freeze dried products was examined by using standard CINAC analysis. For three months stability data, see FIG. 3. The product produced by the process according to present invention is stable, even if compared with the pellet-frozen product.

Example 3

(17) Example 1 was repeated using the same equipment, conditions and additive solution, but with the Streptococcus thermophilus strain ST-143. Thus, a sample of 1281 g of Streptococcus thermophilus (strain ST-143) concentrate was mixed with 579 g of additive solution. This resulted in 1.86 kg of liquid formulation with approx. 14.6% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 1.2E+11 CFU/g. After drying and freezing, a frozen powder was obtained.

Example 4

(18) Example 1 was repeated using the same equipment, conditions and additive solution, but with the Streptococcus thermophilus strain ST-44. Thus, a sample of 1281 g of strain ST-44 concentrate was mixed with 579 g of additive solution.

(19) This resulted in 1.86 kg of liquid formulation with approx. 14.6% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 1.2E+11 CFU/g. After drying and freezing, a frozen powder was obtained.

(20) The spray-frozen powder was freeze dried as in example 1, and the stability of the dried product was compared with a product obtained by freeze drying a pellet-frozen concentrate of ST-44 (method as in example 2). For three months stability data, see FIG. 2. The product produced according to the present invention is stable, even if compared to the pellet-frozen product.

Example 5

(21) A sample of 2640 g of Bifidobacterium animalis ssp. lactis (strain BB-12) concentrate was kept at <5 C. This contained 2E+11 CFU/g with approx. 14.5% (w/w) dry solids. Parallel to this 1080 g of solution was prepared by adding the following ingredients to 876 g of cold tap water (approx. 10 C.) under agitation: 60 g sodium ascorbate, 79 g skimmed milk powder, 33 g inositol and 33 g MSG. The sample and the additive solution were mixed. This resulted in 3.72 kg of liquid formulation with approx. 15.7% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 1.4E+11 CFU/g and was kept cold (<5 C.) throughout the test. After drying and freezing preformed as in example 1, a frozen powder was obtained. The frozen powder was freeze dried, and the dried product had an acceptable cell count after 3 months storage at 5 C (2.9E+11 CFU/g).

Example 6

(22) A sample of 1145 g of Lactobacillus bulgaricus (strain LB CH-2) concentrate was kept at <5 C. This contained 1.1E+11 CFU/g with approx. 11.5% (w/w) dry solids. Parallel to this 375 g of solution was prepared by adding the following ingredients to 282 g of cold tap water (approx. 10 C.) under agitation: 27 g sodium ascorbate, 36 g skimmed milk powder, 15 g inositol and 15 g MSG. The sample and the additive solution were mixed. This resulted in 1.52 kg of liquid formulation with approx. 14.7% (w/w) dry solids to be spray dried. This liquid formulation contained now approx. 8.5E+10 CFU/g and was kept cold (<5 C.) throughout the test. After drying and freezing preformed as in example 1, a frozen powder was obtained. The frozen powder was freeze dried, and the dried product had an acceptable stability after 3 months storage at 5 C (pH 6 as measured using standard CINAC analysis).

REFERENCES

(23) EP1234019B1 (Danisco A/S) U.S. Pat. No. 6,010,725A (Nestle SA) Semyonov et al (Food Research International 43, 193-202 (2010) U.S. Pat. No. 7,007,406 (Wang) WO15063090A2, WO14029758A1, WO14029783A1 (Chr Hansen A/S) ISO 13320:2009 standard for Particle size analysisLaser diffraction methods

(24) All references cited in this patent document are hereby incorporated herein in their entirety by reference.