METHOD FOR DEODORIZING ALGAE

Abstract

A non-destructive and reversible process to deodorize Nannochloropsis algae is provided.

Claims

1. A process for deodorizing a Nannochloropsis algal biomass, comprising a) contacting the biomass with an adduct forming compound selected from metal sulfites, metal bisulfites, ammonium bisulfite, metal metabisulfites, SO.sub.2, or mixtures thereof, b) stirring or shaking, and c) collecting a solid from the suspension.

2. A process according to claim 1, wherein the Nannochloropsis is selected from the group consisting of N. gaditana, N. granulate, N. limnetica, N. oceanica, N. oculata and N. salina.

3. A process according to claim 2, wherein the Nannochloropsis is Nannochloropsis oculata.

4. The process according to any preceding claim, wherein the adduct forming compound in step (a) is either a metal sulfite selected from sodium, potassium sulfite and mixtures thereof, a metal bisulfite selected from sodium bisulfite, potassium bisulfite, and mixtures thereof, or a metal metabisulfite selected from sodium and potassium metabisulfite and mixtures thereof.

5. The process according to any preceding claim, wherein step (b) is performed for about 30 minutes to about 6 hours.

6. The process according to any preceding claim, wherein step (c) is performed by filtration or by decanting the supernatant and collecting the sediment.

7. The process according to any preceding claim, further comprising d) washing the solid with an aqueous solution and e) optionally drying.

8. The process according to claim 7, wherein the solid is washed with an aqueous solution selected from water, NaCl, H.sub.2O.sub.2, phosphate or citric acid solution.

9. The process of claim 7, wherein the solid is washed with water.

10. The process according to any preceding claim, wherein the Nannochloropsis algal biomass is in dry form.

11. The process according to any preceding claim, wherein the Nannochloropsis algal biomass is in sun dried, oven dried, air dried, spray dried or freeze dried form.

12. The process according to claims 1-9, wherein the Nannochloropsis algal biomass is in wet form.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 and FIG. 2 illustrate the removal trend of the aldehydes and ketones from the Nannocloropsis oculata algal biomass according to the present invention. See also Table 1, where the respective values are depicted.

DEFINITIONS

[0015] As used herein, “microalgae” are microscopic algae, typically found in freshwater and marine systems, living in both water and sediment. “Microalgal” may be defined in an analogous manner.

[0016] As used herein, the term “biomass” refers to carbon containing materials which result from growth of algae, but may also include material from other growing organisms. The term “microalgal biomass” and “algal biomass” are used interchangeably.

[0017] As used herein, an “adduct” is a chemical species AB, each molecular entity of which is formed by direct combination of two separate molecular entities A and B in such a way that there is change in connectivity, but no loss, of atoms within the moieties A and B.

DETAILED DESCRIPTION

[0018] According to a first embodiment of the present invention, a process to deodorize a microalgal biomass of Nannochloropsis algae is provided, comprising

[0019] a) contacting the biomass with an adduct forming compound selected from metal sulfites, metal bisulfites, ammonium bisulfite, metal metabisulfites, SO.sub.2 or mixtures thereof;

[0020] b) stirring or shaking;

[0021] c) collecting a solid from the suspension.

[0022] According to a second embodiment, the Nannochlropsis algae is selected from the group consisting of N. gaditana, N. granulate, N. limnetica, N. oceanica, N. oculata and N. salina. According to a preferred embodiment the Nannochlropsis algae is Nannochloropsis oculata.

[0023] The algal biomass is considered to be in dry form, when it contains less % water by weight than the harvested algal biomass. The microalgal biomass of Nannochloropsis provided in step (a) may be sun dried, oven dried, air dried, freeze dried, spray dried, or processed according to other standard food drying techniques known in the art and may contain 0 to 7% water by weight, preferably 0.5-6%, more preferably 1-5%; most preferably water content of dry biomass used in the present invention is 4% water by weight. Alternatively the algal biomass used in the present invention may be wet, with a water content of 7-99.95% by weight, preferably 7-98%, more preferably 7-85%, even more preferably 7-70% water by weight, most preferably 7-50%. In another embodiment, the wet algal biomass used in the present invention has a water content of 15-99.95% by weight, preferably 15-98%, more preferably 15-85%, even more preferably 15-70% water by weight, most preferably 15-50%.

[0024] Drying the microalgal biomass is advantageous to facilitate further processing. Drying refers to the removal of free surface moisture/water from predominantly intact biomass or the removal of surface water from a slurry of homogenized (e.g. by micronization) biomass. In some cases, drying the biomass may facilitate a more efficient microalgal oil extraction process. The deodorization method of the present invention may be performed either before or after the drying procedure on dry or wet biomass respectively.

[0025] The algal biomass is contacted with an aqueous solution of the adduct forming compound/s according to known methods to the skilled person and a suspension is formed according to step (a). A bonus to the method is that the use of organic solvent is not required.

[0026] According to step (b), the metal sulfites or SO2 react with aldehydes and/or ketones and bisulfite adducts are formed, which are subsequently removed from the algal biomass. Metal sulfites are preferably selected from sodium sulfite, potassium sulfite and lithium sulfite;

[0027] metal bisulfites are preferably selected from sodium bisulfite, potassium bisulfite and lithium bisulfite; and metal metabisulfites are preferably selected from sodium metabisulfite, potassium metabisulfite and lithium metabisulfite. Mixtures thereof may also be used. Most preferably sodium metabisulfite is used.

[0028] Bisulfite adducts formation is strongly dependent on the reactivity of the carbonyl group of the aldehydes and ketones. The inventors found that aldehydes and sterically unhindered cyclic and methyl ketones were efficiently removed from the algal biomass.

[0029] A pH adjustment step may be required in some cases, depending on the adduct forming compound used. It has been observed that in very acidic pH values, the color of the algae in the suspension changes, and this is not desired in most cases. The pH of the suspension may range between 2-12, preferably 3.5-8, more preferably 4-7, even more preferably 4-6 and most preferably 4-5.

[0030] Collecting a solid, according to step c of the present invention, is carried out by methods known to the skilled synthetic chemist for separating solids from liquids, such as filtration, or decanting the supernatant and collecting the sediment.

[0031] According to another embodiment, the process further comprises:

[0032] d) washing the solid with water and

[0033] e) optionally drying.

[0034] Washing, according to step (d), is carried out with an aqueous solution selected from water, aqueous solutions of NaCl, H.sub.2O.sub.2, phosphate, acetate or citric acid. Water is the preferred means.

[0035] Drying, according to step (e), may be performed by any method known to the skilled person. The inventors of the present specification, found that freeze drying is the optimal method in this case, since the organoleptic properties of the deodorized algal biomass remain intact. It was observed that by oven drying, the dry solid had a crumbly texture and a dark green-brown color, which makes it unattractive to the consumer.

[0036] Head space solid phase microextraction (HS-SPME) with gas chromatography-mass spectrometry (GC-MS) was used to analyse the deodorized algae samples reconstituted in D.M. water and measure the odorous volatile compounds content. GC-MS analysis was performed on a Shimadzu GC-2010 coupled with GCMS-Q2010.sup.Plus Mass Spectrometer. Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS) SPME fibers 1 cm were used for extraction.

[0037] Table 1 shows the effect of the sodium metabisulfite concentration on the removal of the aldehydes and ketones. For the purpose of these measurements, the samples were treated with aqueous solutions of MBSF or water (control) for 10 minutes, followed by washing with DM water, and freeze drying.

TABLE-US-00001 TABLE 1 0% 0.5% 1.0% 5.0% 10.0% 20.0% MBSF MBSF MBSF MBSF MBSF MBSF Analyte (ref. ex. 7) (ref. ex. 6) (ref. ex. 5) (ref. ex. 4) (ref. ex. 3) (ref. ex. 2) Name Area Similarity.sup.1 Area Area Area Area Area Aldehydes Isopentanal 1752183 89% 281610 272720 60207 ND ND 2- 273731 84% ND ND ND ND ND Methylbutanal Pentanal 1574983 90% ND ND ND ND ND trans-2- 265148 93% 84891 54392 ND ND ND Methyl-2- butenal trans-2- 746731 89% 202921 168191 143385 ND ND Penten-1-al Hexanal 10681018 97% 2433369 1152529 636175 315941 290714 2-Hexenal 1132379 91% 120636 6810 8707 ND ND cis-4-Hepten- 1492530 92% 55678 ND ND ND ND 1-al Heptanal 3635617 97% 946459 350191 234851 ND ND Benzaldehyde 1878233 96% 486352 415371 176306 73539 81960 (E)-2-Octen- 323309 94% 33573 35554 60452 28597 42087 1-al Nonanal 833685 95% 468292 359572 258248 71750 49862 Ketones Isopropyl 1383025 93% 103264 ND ND ND ND ketone 6-Methyl-5- 13430122 93% 13320616 10350409 5585488 6665486 5272939 heptene-2- one 3,5-Octadiene-2- 1463160 91% 1008530 970487 696176 659840 575853 one 6-Methyl- 385529 89% 289636 269243 187707 194345 162380 3,5-heptadien-2- one 2-Heptanone 481184 84% 412050 299070 287153 252852 161082 trans-beta- 3248251 94% 2490068 2584660 2479652 2389275 2363725 Ionone .sup.1Similarity of the mass-to-charge ratio (m/z) to ions of known m/z. One of the commonly used approaches for annotation of mass spectra is the similarity search in a database of theoretical spectra generated from a database of substances.

[0038] The content of the odorous compounds in the deodorized algae biomass is either reduced to non-detectable levels, either significantly reduced, and this ability is seen to improve by increase of the sodium metabisulfite concentration. The latter may range from 0.5% to 30%, preferably may be 0.5%, 1%, 5%, 10%, 15%, 15%, 20%, 25% or 30% by weight, and most preferably 20% by weight.

[0039] Another major advantage of the deodorization method described herein, is that no significant EPA loss was observed. Minimal loss of other fatty acids present in the algal biomass was also found.

[0040] The process is further non-destructive and reversible, maintaining the functionality of the products. The formed adducts may be further treated to form the compounds that were initially removed from the algal biomass and which may have valuable properties. The simple, yet very efficient method to deodorize Nannochloropsis algae biomass, which selectively removes the odorous compounds, leaving the nutritional components fairly intact is illustrated by way of examples.

EXAMPLES

[0041] The Nannochloropsis used in the examples of the present invention, were spray dried after harvesting, and contained up to 7% water by weight.

Example 1

[0042] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 20% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then dried under vacuum in an oven for 2 hours at 45 ° C. to afford 17.6 g of dry powder.

Example 2

[0043] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 20% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.2 g of dry powder.

Example 3

[0044] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 10% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.4 g of dry powder.

Example 4

[0045] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 5% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.0 g of dry powder.

Example 5

[0046] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 1% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 16.9 g of dry powder.

Example 6

[0047] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium metabisulfite solution 0.5% w/v. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.4 g of dry powder.

Example 7

[0048] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL D.M. water. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.3 g of dry powder.

Example 8

[0049] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium bisulfite solution 20% w/v at pH 4—5 adjusted with sodium phosphate dibasic. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.0 g of dry powder.

Example 9

[0050] A 250 mL round bottom flask equipped with a magnet stirring bar is charged with 20 g N. oculata powder followed by 100 mL sodium bisulfite solution 5% w/v at pH 4—5 adjusted with sodium phosphate dibasic. The suspension is stirred under inert atmosphere for 2.5 hours at ambient temperature and then, the solid is collected by filtration under reduced pressure. The filter cake is spray-washed with 2×100 mL D.M. water, suck dried for 30 minutes and then freeze-dried for 18 hours to afford 17.2 g of dry powder.