METHOD OF PROCESSING SEAWEED

Abstract

The present invention relates to a method of processing macroalgae in which superheated water is used in an initial pre-treatment step prior to extraction of a polysaccharide. In particular, the invention relates to a process for obtaining polysaccharide (e.g. alginate) from macroalgae or a part thereof. Certain aspects of the invention relate to a process for obtaining polysaccharide from macroalgae which results in enhanced polysaccharide yield and/or a shortened treatment time when compared to conventional extraction methods.

Claims

1. A process for obtaining polysaccharide from macroalgae, or part thereof, comprising the steps of: a pre-treatment step of exposing the macroalgae, or part thereof, to superheated water at a temperature of about 101° C. to 150° C. for a period of from 30 seconds to 60 minutes, wherein the superheated water is maintained in a liquid state by the application of pressure; and subsequently, an extraction step of extracting polysaccharide from the macroalgae, or part thereof; wherein the polysaccharide is an alginate selected from alginic acid, an alginate salt, and an alginate derivative.

2. The process according to claim 1, wherein the macroalgae is brown algae.

3. The process according to claim 1 or claim 2, wherein the macroalgae, or part thereof, is exposed to the superheated water at a temperature of about 105° C. to 130° C., for example 110° C. to 125° C., for example 112° C. to 118° C., preferably at 115° C., for example 110° C. to 130° C., preferably at 125° C.

4. The process according to any one of the preceding claims, wherein the superheated water is maintained in a liquid state by the application of pressure applied at approximately 105 to 500 kPa, for example 120 to 300 kPa, for example 140 to 240 kPa, for example 150 to 190 kPa, for example 165 to 170 kPa, for example 140 to 270 kPa, for example 130 to 235 kPa.

5. The process according to any one of the preceding claims, wherein the macroalgae is exposed to the superheated water for a period of about 2 to 40 minutes, for example 5 minutes to 25 minutes, for example 7 to 15 minutes, for example about 7 to 13 minutes.

6. The process according to any one of the preceding claims, wherein the step of extracting polysaccharide from the macroalgae, or part thereof, comprises contacting the macroalgae, or part thereof, with an alkali solution to yield an alginate composition.

7. The process according to claim 6, wherein the alkali solution is selected from: sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and sodium carbonate.

8. The process according to claim 7, wherein the alkali solution has a concentration of 0.1% to 3%.

9. The process according to any one of claims 6 to 8, wherein the ratio of alkali solution, for example sodium carbonate, to macroalgae stipe is from 3:1 to 20:1, for example 10:1 to 20:1, for example 5:1 to 15:1, by weight.

10. The process according to any one of claims 6 to 9, wherein the macroalgae, or part thereof, is soaked in the alkali solution for a period of about 2 minutes to 24 hours, for example 30 minutes to 24 hours, for example 2 to 18 hours, for example about 4 to 14 hours, for example 6 to 10 hours.

11. The process according to any one of claims 6 to 10, wherein the step of extracting polysaccharide from macroalgae, or part thereof, further comprises contacting the alginate composition with an acid, for example hydrochloric acid, wherein the acid is at a concentration sufficient to reduce the pH of the solution to 2 or less, to form an alginic acid precipitate.

12. The process according to any one of claims 6 to 10, wherein the step of extracting polysaccharide from macroalgae, or part thereof, further comprises contacting the alginate composition with an excess of calcium salt, for example calcium chloride at a concentration of about 500 mg/dL.

13. The process according to any one of claims 6 to 10, wherein the step of extracting polysaccharide from macroalgae, or part thereof, further comprises contacting the alginate composition with an anti-solvent, for example ethanol at a concentration of about 30 to 70%, for example 40 to 60%, for example approximately 50%, for example acetone at a concentration of about 30 to 70%, for example 40 to 60%, for example approximately 50%.

14. The process according to any one of the preceding claims wherein the macroalgae is a part thereof and the part is selected from leaf, bark and stipe.

15. The process according to any one of claims 1 to 13, wherein the macroalgae is a part thereof and the part is unpeeled stipe.

16. The process according to claim 14 or claim 15, wherein the part is stipe and wherein the stipe is preferably divided into portions having a dimension of less than 2 cm by cutting or blending.

17. The process according to any one of the preceding claims wherein the macroalgae is selected from the group consisting of: of Laminaria spp, Ascophyllum spp, Durvillaea spp, Ecklonia spp, Lessonia spp, Macrocytis spp and Sargassum spp.

18. The process according to claim 17, wherein the macroalgae is Laminaria hyperborea.

19. The process according to any one of the preceding claims comprising the steps of: optionally removing bark from macroalgae, preferably portions of macroalgae stipe, for example by peeling; exposing the macroalgae, or part thereof, to the superheated water maintained at a temperature of about 105 to 130° C. within a pressurised vessel; soaking the macroalgae, or part thereof, in an alkali solution at a concentration of about 0.1 to 8% with periodic shaking for about 4 to 20 hours, to form an alginate salt solution, for example sodium alginate; removing macroalgae residues from the alginate salt solution, preferably by centrifugation; forming an alginic acid precipitate or an alginate salt precipitate; isolating the resultant precipitate, for example by filtration or centrifugation.

20. An alginate selected from alginic acid, an alginate salt, and an alginate derivative obtainable, obtained or directly obtained by a process as claimed in any one of claims 1 to 19.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0162] FIG. 1 illustrates a bar chart showing the amount (depicted as percentage) of alginate extracted from peeled and rinsed stipe of L. hyperborea. The data shown in FIG. 1 was generated as described in example 1.

[0163] FIG. 2 illustrates the percentage of alginate recovery from the stipe of L. hyperborea following pre-treatment with steam at 115° C. for 13, 26 and 52 minutes. The data shown in FIG. 2 was generated as described in example 2.

[0164] FIG. 3 illustrates the percentage of alginate recovery from dried and fresh samples of L. hyperborea following pre-treatment with superheated water at 115° C. for 0, 7, 13 and 26 minutes. The data shown in FIG. 3 was generated as described in example 3.

[0165] FIG. 4 illustrates the viscosity of alginate recovered from dried and fresh samples of L. hyperborea following pre-treatment with superheated water at 115° C. for 0, 7, 13 and 26 minutes. The data shown in FIG. 4 was generated as described in example 3.

EXAMPLES

[0166] All examples made use of Laminaria hyperborea. Examples 1 and 2 used peeled stipe which had been rinsed in water to provide a standard starting material. The preparation of the samples used in Example 3 is described below. Extraction yields relate to dry matter obtained from the rinsed stipe sections. The water content of the stipe was determined by loss on drying at 105° C. to determine the dry matter content of the stipe.

[0167] All examples made use of water for the superheated water treatment which was prepared as follows: potable (mains) water was first passed through a reverse osmosis system which removed the majority of the dissolved ions. The resultant water was then passed through a mixed bed of deioniser resin which removed the remainder of the dissolved ions and reduced the conductivity to a low level. In this way, the conductivity of the potable (mains) water was reduced from around 500 μS to between approximately 3 and 5 μS.

Example 1

[0168] a. Pre-Treatment

[0169] The stipe of L. hyperborea was peeled, rinsed and sectioned into approximately 0.5 cm portions by cutting. The stipe sections were subjected to a pre-treatment process, specifically the stipe was exposed to either; superheated-water (115° C. for 13 minutes or 125° C. for 30 minutes), boiling water (100° C. for 30 minutes) or acid (for 8 to 24 hours) or the stipe received no treatment at all.

[0170] The superheated water was generated by heating the water above its normal boiling point (over 100° C.) and maintained as a liquid by the application of pressure. The stipe sections were immersed in water contained within a suitable vessel. The water may be heated after the addition of the macroalgae sections or alternatively the macroalgae may be placed into the pressurised vessel followed by the addition of the superheated water.

[0171] Alternatively, the stipe sections were treated with sulfuric acid (0.04M) overnight or the stipe was exposed to boiling water (100° C.).

b. Extraction

[0172] Stipe sections (2-3 g) were extracted overnight by periodic shaking in 4% sodium carbonate solution (15:1 sodium carbonate solution to stipe) to form a solution containing water soluble sodium alginate. The liquid was separated from the undissolved solids within the solution by centrifugation. Hydrochloric acid was added to aliquots of the liquid to precipitate out water insoluble alginic acid from the solution. The mixture was then subject to centrifugation and the pellet was washed with water to remove soluble impurities and residual acid and re-centrifuged. The pellet was then dried for harvesting and the weight of the precipitate was expressed as a percent of the dry matter in the original stipe.

Example 2—Comparative

[0173] The stipe of L. hyperborea was peeled, rinsed and sectioned into approximately 0.5 cm portions by cutting. The stipe sections were subject to a pre-treatment process, specifically the stipe was exposed to saturated steam at 115° C. for 13, 26 and 52 minutes.

[0174] Stipe sections (2-3 g) were extracted as described in example 1 b (Extraction). Each time point experiment was analysed in triplicate. The results (% alginate) are shown in FIG. 2.

[0175] The yield of alginate determined following steam pre-treatment at 115° C. increased as the treatment time increased from 13, 26 and 52 minutes, with the largest yield of alginate found with steam pre-treatment for 52 minutes. The yield of alginate extracted from the stipe of the macroalgae after 52 minutes of steam pre-treatment was comparable to the alginate recovery following pre-treatment with super-heated water for 13 minutes (see FIG. 1). Therefore, pre-treatment of macroalgae stipe with super-heated water produces a high yield of alginate under a short period of treatment time.

[0176] The quality of the alginate product was assessed by measuring the viscosity of a solution of the alginate in water. The viscosity of 0.5% by weight solution sodium alginate was measured by the falling ball viscometer method. Pre-treatment for 13 minutes resulted in the alginate having a viscosity of approximately 2.6 mPa.Math.s following superheated water pre-treatment and a viscosity of 1.5 mPa.Math.s following steam pre-treatment. The lower viscosity of the steam treated alginate indicated more degradation of the alginate product. Due to the low concentration of the sodium alginate solution used in the assessment, the ball did not reach terminal velocity and therefore the measured viscosity values are not absolute. Nevertheless, the higher value following pre-treatment with superheated water is indicative of the reduced extent of degradation of the recovered alginate product.

Conclusion

[0177] Pre-treatment with superheated water results in higher yields compared to either boiling water or acid overnight treatment. Pre-treatment with superheated water requires a short treatment time when compared to steam pre-treatment and results in a higher quality product.

Example 3

[0178] Dried, flaked L. hyperborea and freshly shredded L. hyperborea stipe with bark were subjected to a pre-treatment process using superheated water followed by extraction of alginate.

[0179] Preparation of dried, flaked L. hyperborea: the leaf and epiphytes were removed, but the bark was left on prior to shredding and drying. The dried L. hyperborea stipe was then re-hydrated prior to carrying out the superheated water pre-treatment.

[0180] Preparation of freshly shredded L. hyperborea stipe: the leaf and epiphytes were removed and the stipe with bark was soaked in demineralised water to remove salt so that the solution conductivity was less than 200 μS. The soaked stipe was then blended using a Tefal Blendforce II, type BL42 blender with a 600 W motor on the highest power setting.

[0181] For both dried and fresh materials, the particle size of the stipe was in the range of approximately 500 to 1000 μm.

[0182] Samples of the materials were transferred to a pressure cooker and subjected to a pre-treatment process using superheated water at a temperature of 115° C. and a pressure of 168.8 kPa for 0, 7, 13 and 26 minutes. Stipe (50 to 75 g) was extracted for 60 minutes by periodic shaking in 0.25% sodium carbonate solution (5:1 sodium carbonate solution to stipe) to form a solution containing water soluble sodium alginate. The liquid was separated from the undissolved solids within the solution by filtration through a 100 μm nylon filter. Hydrochloric acid was added to aliquots of the liquid to precipitate out water insoluble alginic acid from the solution. The mixture was then subjected to filtration through a 100 μm nylon filter and the gel was washed with water to remove soluble impurities and residual acid and re-filtered. The washed gel was then converted to the sodium form and precipitated with alcohol and dried. The weight of the recovered alginate was expressed as a percent of the dry matter in the salt depleted stipe.

[0183] Each time point experiment was analysed in triplicate. The results (% alginate) are shown in FIG. 3 and in Table 1 below.

TABLE-US-00001 TABLE 1 Sample Dried Sample Fresh Sample SHW pre-treatment time Alginate yield Alginate yield (min) (% of dry) (% of dry) 0 37.8 36.8 7 39.1 43.1 13 48.9 50.4 26 38.0 43.1

[0184] Superheated water pre-treatment of both dried and fresh stipe with bark produces a high yield of alginate. The alginate obtained from the unpeeled stipe (both dried and fresh samples) was found to be substantially free from colour confirming that the quality of the alginate is not adversely impacted by the presence of the pigment-containing bark in the initial sample.

[0185] The quality of the alginate product obtained from both the dried and fresh starting materials was also assessed by measuring the viscosity of a 1% solution of the alginate in water. Viscosity was measured by the falling ball viscometer method and the measured values are shown in FIG. 4 and Table 2 below.

TABLE-US-00002 TABLE 2 Sample Dried Sample Fresh Sample SHW pre-treatment time Viscosity Viscosity (min) (mPa .Math. s) (mPa .Math. s) 0 3504 3833 7 2032 959 13 638 580 26 287 260

[0186] For both dried and fresh materials, the viscosity of the extracted alginate decreased as the duration of the superheated water pre-treatment increased, and the viscosity results are similar regardless of the initial state of the sample. The lower than expected viscosity seen in the fresh sample at 7 min SHW time may be due to the age of the sample when tested and may be the result of microbial degradation.