METHOD FOR PREPARING A FLOUR OF LIPID-RICH CRUSHED MICROALGAE

Abstract

The invention relates to a method for preparing a lipid-rich microalgal flour, which comprises the following steps: (a) providing a microalgal biomass comprising more than 50% of lipids by dry weight of biomass; (b) lyzing the microalgae, (c) concentrating the microalgal lyzate to a solids content of more than 25% by weight, preferably to a solids content of between 35% and 50% by weight, (d) applying a heat treatment to the lyzate thus concentrated, (e) homogenizing at high pressure the lyzate obtained in step (d), so as to obtain a stable emulsion, (f) drying said emulsion to obtain the microalgal flour.

Claims

1. A method for preparing a lipid-rich microalgal flour, comprising (a) providing a microalgal biomass containing more than 50% of lipids by dry weight of biomass; (b) lyzing the microalgal to for a microalgal lyzate, (c) concentrating the lyzate to a solids content of more than 25% by weight, preferably to a solids content of between 35% and 50% by weight, (d) heating the concentrated lyzate, (e) homogenizing at high pressure the lyzate obtained in step (d), so as to obtain a stable emulsion, (f) drying said emulsion to obtain the microalgal flour.

2. The method as claimed in claim 1, wherein the microalga is of the genus Chlorella.

3. The method according to claim 1, wherein the concentration of the microalgal lyzate is performed by evaporation.

4. The method as claimed in claim 3, wherein the concentration of the lyzate is performed at high temperature in an evaporator under the following conditions: flash inlet temperature: between 60 and 75° C., temperature in the flash: between 35 and 60° C., recirculation flow rate: between 25 and 45 m.sup.3/h.

5. The method according to claim 1, wherein the high-pressure homogenization is performed in a two-stage device, with a pressure: of between 150 and 170 bar in a first stage, and of between 35 and 45 bar in a second stage.

6. The method according to claim 1, wherein said emulsion is dried by atomization.

7. The method as claimed in claim 1, wherein the microalga comprises Chlorella protothecoides.

8. A method for preparing a lipid-rich microalgal flour, comprising which comprises the following steps comprising (a) lyzing a Chlorella microalgal biomass containing more than 50% of lipids by dry weight of biomass to form a lyzate, (b) evaporating water in said lysate to a solids content 35% and 50% by weight, to form a concentrate, (c) heating the concentrate deoxygenate and/or deodorize the concentrate, (d) forming a stable oil-in-water lysate emulsion, and (e) drying said emulsion to obtain the microalgal flour.

Description

SUBJECT OF THE INVENTION

[0046] There is thus still an unsatisfied need for a method for preparing a lipid-rich microalgal flour which does not necessitate working at a low solids content.

[0047] After extensive research, the Applicant company has found that this need can be met by providing a method for preparing a lipid-rich microalgal flour, which comprises the following steps:

[0048] (a) providing a microalgal biomass comprising more than 50% of lipids by dry weight of biomass;

[0049] (b) lyzing the microalgae,

[0050] (c) concentrating the microalgal lyzate to a solids content of more than 25% by weight, preferably to a solids content of between 35% and 50% by weight,

[0051] (d) applying a heat treatment to the microalgal lyzate thus concentrated,

[0052] (e) homogenizing at high pressure the concentrated lyzate thus obtained so as to obtain a stable emulsion,

[0053] (f) drying said emulsion to obtain the microalgal flour.

[0054] For the purposes of the present invention, the term “lipid-rich” means containing more than 50% of lipids.

[0055] For the purposes of the present invention, the term “stable emulsion” refers to the absence of phase separation of the oil and water phases.

[0056] In accordance with the invention, in step (a), the microalgae under consideration are preferably microalgae of the Chlorella genus, more particularly Chlorella protothecoides, even more particularly Chlorella deprived of chlorophyll pigments, by any method known per se to those skilled in the art (either because the culturing is performed in the dark under certain operating conditions well known to those skilled in the art, or because the strain has been mutated so as to no longer produce these pigments).

[0057] The microalgal biomass is a biomass preferentially prepared by fermentation, under heterotrophic conditions and in the absence of light, of a microalga of the Chlorella genus, preferably Chlorella protothecoides.

[0058] The fermentation conditions are well known to those skilled in the art. The appropriate culture conditions to be used are in particular described in the article by Ikuro Shihira-Ishikawa and Eiji Hase, “Nutritional Control of Cell Pigmentation in Chlorella protothecoides with special reference to the degeneration of chloroplast induced by glucose”, Plant and Cell Physiology, 5, 1964.

[0059] Other articles, such as the one by Han Xu, Xiaoling Miao, Qingyu Wu, “High quality biodiesel production from a microalga Chlorella protothecoides by heterotrophic growth in fermenters”, Journal of Biotechnology, 126, (2006), 499-507, indicate that heterotrophic culture conditions, i.e. in the absence of light, make it possible to obtain an increased biomass with a high content of lipids in the microalgal cells.

[0060] The solid and liquid growth media are generally available in the literature, and the recommendations for preparing the particular media which are suitable for a large variety of microorganism strains can be found, for example, online at www.utex.org/, a website maintained by the University of Texas at Austin for its algal culture collection (UTEX).

[0061] In the light of their general knowledge and the abovementioned prior art, those skilled in the art responsible for culturing the microalgal cells will be entirely capable of adjusting the culture conditions in order to obtain a suitable biomass, preferably rich in lipids.

[0062] The production of biomass is performed in fermenters (or bioreactors). The specific examples of bioreactors, the culture conditions, and the heterotrophic growth and methods of propagation can be combined in any appropriate manner in order to improve the efficiency of the microbial growth and of the lipids.

[0063] In one particular embodiment, the fermentation is performed in fed-batch mode with a glucose flow rate adjusted so as to maintain a residual glucose concentration of from 3 to 10 g/l.

[0064] During the glucose feed phase, the nitrogen content in the culture medium is preferably limited so as to allow the accumulation of lipids in an amount of 30%, 40%, 50% or 60%. The fermentation temperature is maintained at a suitable temperature, preferably between 25 and 35° C., in particular 28° C. The dissolved oxygen is preferably maintained at a minimum of 30% by controlling the aeration, the counter-pressure and the stirring of the fermenter.

[0065] Preferably, the biomass obtained, which is thus useful in the present invention, has a solids content of at least 20%, preferably between 20% and 40%, with a lipid content of more than 50% by dry weight.

[0066] For example, the biomass used in the method that is the subject of the present invention has a solids content of at least 20%, preferably between 20% and 40% and with a lipid content of more than 50% by dry weight, a fiber content of from 10% to 50% by dry weight, a protein content of from 2% to 15% by dry weight and a sugar content of less than 10% by weight.

[0067] In accordance with the invention, in step (b), the biomass cells used for the production of microalgal flour are lyzed in order to release their oil or lipids.

[0068] The cell walls and the intracellular components are milled or reduced, for example using a bead mill, to non-agglomerated cell particles or debris.

[0069] In the mill, the cells are agitated in suspension with small beads. Rupture of the cells is caused by the shear forces, the milling between the beads, and the collisions with beads. In fact, these beads rupture the cells so as to release the cell content therefrom. The description of an appropriate bead mill is, for example, given in the patent U.S. Pat. No. 5,330,913.

[0070] Preferably, antioxidants are added to the biomass before performing the lysis.

[0071] A microalgal lyzate in the form of a particle suspension in the form of an “oil-in-water” emulsion is thus obtained.

[0072] In accordance with the invention, in step (c), the lyzate is concentrated so as to obtain a lyzate with a solids content of more than 25% by weight, preferably between 35% and 50% by weight.

[0073] This concentration is preferably performed by evaporating off the water at high temperature, and not by centrifugation.

[0074] The evaporator used is preferably: [0075] a falling-film evaporator for a biomass with a solids content of not more than 33%, [0076] a forced-flow evaporator for a biomass with a solids content of between 20 and 45%,

[0077] under the following conditions: [0078] flash inlet temperature: between 60 and 75° C., preferably 68° C. [0079] temperature in the flash: between 35 and 60° C., preferably 40° C. [0080] recirculation flow rate: between 25 and 45 m.sup.3/h, preferably 40 m.sup.3/h.

[0081] In accordance with the invention, in step (d), the concentrated lyzate is heat-treated. This heat treatment especially allows deoxygenation/deodorization of the lyzate with a high solids content.

[0082] Preferably, step (d) is performed at high temperature for a short time (HTST, or ultra-high temperature, UHT), for example at 140° C. for 6 seconds.

[0083] In accordance with the invention, step (e) consists in homogenizing the lyzate obtained on conclusion of step (d), so as to generate a stable oil-in-water emulsion, despite the high solids content of said lyzate.

[0084] This homogenization is preferably performed in a two-stage device, for example a Gaulin homogenizer sold by the company APV, with a pressure: [0085] of between 150 and 170 bar, preferably 160 bar in the first stage, and [0086] of between 35 and 45 bar, preferably 40 bar in the second stage.

[0087] In accordance with the invention, the final step (step f) consists in drying the emulsion to obtain the microalgal flour.

[0088] The drying is preferably performed by atomization. On conclusion of this step during which the water is removed, a dry powder containing the cell debris and the lipids is obtained.

[0089] After drying, the water content or the moisture content of the powder is generally less than 10%, preferentially less than 5%.

[0090] Optionally, a pH adjustment of the lyzate before the heat treatment step may be performed.

[0091] By virtue especially of the heat treatment followed by high-pressure homogenization of the lyzate, the method that is the subject of the present invention advantageously makes it possible to obtain a lipid-rich milled microalgal flour from a biomass of microalgae, especially of chlorellae, containing more than 50% of lipids and having a solids content of at least 20%.