FUNCTIONAL YEAST PROTEIN CONCENTRATE

Abstract

The present invention relates to a method for preparing a yeast protein concentrate, said method comprising the lysis of yeast cells in a suspension that was adjusted to a particular pH prior to lysis, subsequently subjecting the soluble fraction obtained from lysis to filtration to reduce the content of molecules smaller than 30 kDa, and optionally drying the solution obtained from filtration. The present invention further relates to a yeast protein concentrate obtainable by the method of the invention. The yeast protein concentrate comprises a high amount of proteins which are still folded and are therefore capable of aggregation to form a solid protein matrix upon heating. In addition, the yeast protein concentrate of the invention will be of unobtrusive taste and is therefore particularly suited for use in the preparation of food items, such as meat substitute products.

Claims

1. Method for preparing a yeast protein concentrate comprising non-denatured yeast protein molecules, said method comprising (a) providing a suspension comprising yeast cells; (b) adjusting the pH of the suspension to a value between 6.5 and 8.5; (c) lysing the yeast cells by mechanical means; (d) subjecting the soluble fraction of the lysate to filtration to reduce the content of molecules smaller than 30 kDa; and (e) optionally, drying the solution obtained from filtration in step (d) to obtain a protein concentrate powder.

2. Method of claim 1, wherein method steps (a)-(d) are performed at a temperature below 40° C.

3. Method of claim 1, wherein the suspension in step (a) has a dry matter content of between about 5-20%.

4. Method of claim 1, wherein the suspension in step (a) is washed with a basic washing buffer prior to cell lysis.

5. Method of claim 1, wherein the content of molecules smaller than 10 kDa is reduced in step (d).

6. Method of claim 1, wherein lysing the yeast cells in step (c) is performed in a bead mill.

7. Method of claim 1, wherein the pH of the lysate is re-adjusted to a value between 6.5 and 8.5 after step (c).

8. Method of claim 1, wherein the protein solution obtained after filtration is sterilized.

9. Method of claim 1, wherein the protein solution obtained after filtration is freeze-dried or spray-dried to provide a powder.

10. Yeast protein concentrate, such as a Yeast protein concentrate powder, obtainable by a method of claim 1.

11. Yeast protein concentrate, such as a Yeast protein concentrate powder, comprising a mixture of proteins, wherein the folded proteins included in the protein concentrate unfold at a temperature range between 45° C. and 83° C.

12. Yeast protein concentrate according to claim 11, wherein the total amount of free amino acids, dipeptides and tripeptides is less than 20%, more preferably less than 18%.

13. Yeast protein concentrate according to claim 11, wherein at least 40% of the proteins contained in the concentrate powder have an apparent size of more than 5 kDa.

14. Yeast protein concentrate comprising at least 55% (w/w) total crude protein per dry matter, and wherein at least 40% of the proteins in the concentrate have an apparent size larger than 60 kDa.

15. Yeast protein concentrate according to claim 14, wherein said concentrate comprises at least 60% (w/w), at least 65% (w/w), or at least 70% (w/w) total crude protein per dry matter.

16. Yeast protein concentrate according to claim 14, wherein said concentrate comprises 30% (w/w) or less, preferably 25% (w/w) or less, and more preferably 20% (w/w) or less beta-glucans per dry matter.

17. Yeast protein concentrate according to claim 14, wherein said concentrate comprises at least 40% (w/w), at least 45% (w/w), or at least 50% (w/w) soluble crude protein per dry matter.

18. Yeast protein concentrate according to claim 14, wherein at least 20% (w/w) of the soluble crude protein in the concentrate can be precipitated by heating the concentrate to 90° C. for 10 minutes.

19. Yeast protein concentrate according to claim 11, wherein said concentrate is a liquid having a dry matter content of at least 1%, at least 1.5%, at least 2%, at least 2.5%, at least 3%, at least 3.5%, at least 4%, at least 4.5%, or at least 5%.

20. Yeast protein concentrate according to claim 11, wherein said concentrate is a powder having a dry matter content of at least 90%, at least 92%, at least 94%, or at least 96%.

21. Method for preparing a protein gel, said method comprising (a) providing a yeast protein concentrate powder according to claim 11; (b) mixing the yeast protein concentrate powder with an aqueous carrier fluid; and (c) heating the mixture to a temperature of at least 55° C. to provide the protein gel.

22. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0081] FIG. 1 shows a schematic overview of a preferred embodiment for preparing a yeast protein concentrate powder according to the invention.

[0082] FIG. 2 shows the apparent molecular weight distribution of the proteins in a sample of the dried protein concentrate powder prepared in accordance with Example 1 described herein below.

[0083] FIG. 3 shows the apparent molecular weight distribution of the ultra-filtrated permeate from Example 2 described herein below as determined by size exclusion chromatography (SEC).

[0084] FIG. 4 shows the melting curve of the folded proteins of the protein concentrate. The dried protein concentrate was dissolved in water at 20% (w/w), and the melting curve was analysed using a Tycho NT.6 (NanoTemper Technologies GmbH, Munich).

EXAMPLES

[0085] The following examples are provided in order to illustrate the invention. It should however be understood that the scope of the invention is not limited by the examples. A skilled person will understood that several modifications can be made without deviating from the scope of the invention.

Example 1: Preparation Method Using Carbon Filtration

[0086] Saccharomyces cerevisiae A2W5 yeast cells were harvested from a yeast cell culture and suspended in water. The dry matter content was adjusted to 14%. The suspension had a volume of 1 L. The pH of the suspension was adjusted to pH 7.5 using NaOH.

[0087] Cell rupture was performed in a Dyno®-Mill Multi Lab Wab from Willy A. Bachofen AG (Muttenz, Switzerland) using yttria-stabilized zirconium oxide beads with a size of 0.25-0.35 mm. The flow rate was set to 7 kg/h and the rotor speed to 8 m/s. The bead filling volume was set to 65%.

[0088] The efficiency of cell rupture was confirmed by measuring the protein extraction yield using the method of Kjeldahl, J. Fresenius, Zeitschrift f. anal. Chemie (1883) 22:366.

[0089] The pH of the lysate obtained from the bead mill was adjusted to 7.6 using NaOH. Subsequently, the lysate was subjected to centrifugation for 120 minutes at 25000×g in a Heraeus Multifuge X3R. The supernatant was separated from the sediment and subjected to activated carbon filtration using an active carbon filtration cartridge (height: 5 cm, diameter: 6 cm) filled with steam activated Norit® SX Plus.

[0090] The solution obtained from activated carbon filtration was sterilized at a temperature of 130° C. for 3 seconds and subsequently spray-dried using the Mini Spray Dryer B-290 from Büchi Labortechnik GmbH (Essen, Germany) with a constant input temperature between 133-136° C. and output temperature at 93±2° C.

[0091] The powder so obtained was analyzed chemically and for the free amino acid content:

TABLE-US-00001 Parameter Amount (%) Dry matter content 96.3 Protein content 73 RNA concentration ≤11 Free nucleotide concentration ≤1 Trehalose content ≤2.5 Salt content 0.89

[0092] Free Amino Acid Analysis:

TABLE-US-00002 Amino acid Concentration %(w/w) Ala 3.9 Arg 0.13 Asp 0.21 AspNH2 ≤0.1 Cys 0.13 Glu 6.37 Gly 0.17 His ≤0.1 Ile 0.12 Leu 0.15 Lys ≤0.1 Met ≤0.1 Orn 0.16 Phe ≤0.1 Pro 0.77 Ser 0.13 Thr ≤0.1 Trp ≤0.1 Tyr ≤0.1 Val 0.31 total ≤15

Example 2: Preparation Method Using Ultrafiltration

[0093] The experiment described in Example 1 was repeated with the exception that an ultrafiltration was used instead of activated carbon filtration. Ultrafiltration was done with a polyethersulfone (PES) UF GR 81PP membrane having a MWCO of 10 kDa. Seven support plates were equipped with a stop disk such that 14 filters were used in total. The filter setup was washed according to the manufacturer's instructions. In the beginning the retentate flow rate was 2.3 L/min and the permeate flow rate was 0.064 L/min. After 20 min, the retentate flowed with 2.2 L/min, while the permeate flowed out with 0.054 L/min. The permeate was analyzed using Size Exclusion Chromatography (SEC). The results are shown in FIG. 3. It can be seen that only particles that were smaller than the cutoff of the membrane were able to pass. This indicates that the yeast proteins remained in the retentate and there was no significant protein loss. The solution obtained from ultrafiltration was sterilized and spray dried as described above in Example 1.

Example 3: Preparation of a Protein Gel

[0094] The powders obtained in Examples 1 and 2 were tested for their gelling properties upon reconstitution in water. For this purpose, the protein powder was dissolved in tap water to give a 20% (w/w) solution.

[0095] Next, the melting temperature range of the proteins in the protein concentrate was measured between room temperature and 95° C. using a Tycho NT.6 (NanoTemper Technologies GmbH, Munich). FIG. 4 shows that the proteins inside the invented product mainly melt between 45° C. and 83° C. The protein gel was assessed by a sensory panel of at least 7 people for gel firmness and flavour profile. There was a general agreement within the panel regarding the main perception of the samples. The taste was described as salty, sweet and roasted. There was no strong yeast flavour noted by the panel. At the same time, the gel was found to be firm and resembled cooked egg white in terms of its consistency.

Example 4: Determination of the Total Crude Protein Content

[0096] A sample of the liquid yeast protein concentrate obtained after activated carbon filtration in Example 1 was analyzed for the content of total crude protein per dry matter. The liquid concentrate had a dry matter concentration of 5.3% (w/w). A 500 mg sample of the aliquot was analyzed by the Kjeldahl method using a FOSS Kjeltec-Analyser 8400 with a Kjeltec-Sampler 8420, a Tecator-Digestor Auto with a Tecator-Scrubber for the digestion step. To calculate the total crude protein content the conversion factor 6.25 was used. As a result, a total crude protein content of 70.5% (w/w) per dry matter was measured for the liquid yeast protein concentrate.

Example 5: Determination of the Soluble Crude Protein Content

[0097] A sample of the liquid yeast protein concentrate obtained after activated carbon filtration in Example 1 was diluted to a dry matter concentration of 1% (w/w) using deionized water. This solution was stirred at 20° C. for 30 minutes. A 2 ml-Eppendorf tube was filled with 1.5 ml of the diluted protein solution. The tube was centrifuged at 25,000×g for 20 min at 4° C. After centrifugation, 1 ml of the supernatant was removed from the tube and subjected to Kjeldahl protein measurement as described in Example 4. As a result, a soluble crude protein content of 61.3% (w/w) per dry matter was measured.

Example 6: Determination of Heat-Reactive Protein Portion

[0098] Another aliquot of the sample used in Example 5 having a dry matter concentration of 1% (w/w) was used as described above by stirring at 20° C. for 30 minutes. A 2 ml-Eppendorf tube was filled with 1.5 ml of the diluted protein solution. The tube was then heat-treated by putting it into a 90° C. water bath for 10 minutes. Afterwards, the tube was placed on ice for 10 minutes. Subsequently, the tube was centrifuged at 25,000×g for 20 min at 4° C. After centrifugation, 1 ml of the supernatant was removed from the tube and subjected to Kjeldahl protein measurement as described in Example 4. As a result, a soluble crude protein content after heat treatment of 32.8% (w/w) per dry matter was determined. The portion of the soluble crude protein that can be precipitated by heat is determined by the following formula:

100%−(Amount of soluble crude protein after heat incubation/Amount of soluble crude protein)×100%)

[0099] Using the soluble crude protein content measured in Example 5 and the soluble crude protein after heat incubation measured in Example 6 in the above formula, the following is obtained:

100%−(32.8%/61.3%×100%)=100%−53.5%=46.5%

[0100] Accordingly, the above calculation shows that 46.5% of the soluble crude protein can be precipitated by heating as described above.