Lipid-rich microalgal flour and method for preparing same

Abstract

A microalgal flour having a particle size of between 30 and 150 μm and compressibility, measured by way of POWDER TESTER HOSOKAWA, of between 45 and 55%, has a flow value, determined according to a test A, of between 55 and 60% by weight for residue at 2,000 μm, dispersibility and wettability, expressed according to a test B, by the height of the product decanted in a beaker, of a value of between 0 and 2 mm; and a degree of humidification of a value of more than 70%, and preferably of more than 80%, of the total powder.

Claims

1. A process for preparing a microalgal flour, the size of the flour particles being between 30 and 150 μm in diameter said flour having a compressibility, as measured on HOSOKAWA powder tester, of between 45% and 55%, the microalgal flour having: a flow value, determined according to a test A, of between 55% and 60% by weight for the oversize at 2000 μm; a dispersibility and wettability, expressed, according to a test B, by the height of the product decanted in a beaker, having a value of between 0 and 2 mm; and a degree of wetting having a value of more than 70% of the total powder; wherein the process comprises: 1) preparing an emulsion of lipid-rich microalgal flour in water with a solids content of between 15% and 50% by dry weight, wherein this emulsion is prepared by mechanically lysing microalgal cells and wherein the lipid-rich microalgal flour comprises at least 10% by dry weight of lipids, 2) introducing this emulsion into a high-pressure homogenizer, 3) spraying this emulsion in a flat-bottom spray dryer equipped with an air broom for sweeping the spray drying chamber with low-pressure air in its lower portion, while making adjustments to ensure that: a) the temperature of the main drying air is between 160° and 240°C., b) the temperature of the air in the air broom portion is at most 70°C., c) the ratio of the flow rate of the air from the air broom to the flow rate of the main drying air has a value greater than ⅓ d) the temperature of the cooling air is between 25° and 35°C., such that the flour leaving the spray dryer has a temperature of between 60°C. and 90°C., 4) collecting the microalgal flour thus obtained.

2. The method as claimed in claim 1, wherein the temperature of the air in the air broom portion is at most 65°C.

3. The method as claimed in claim 1, wherein the ratio of the flow rate of the air from the air broom to the flow rate of the main drying air has a value between ⅓ and ½.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention thus relates to the microalgal biomass suitable for human consumption which is rich in nutrients, in particular in lipids.

(2) The invention more particularly relates to a microalgal flour which can be incorporated into food products in which the oil content of the microalgal flour can enable total or partial replacement of the oils and/or fats present in conventional food products.

(3) For the purposes of the invention, the term “microalgal flour” means the dried product of breaking the cell walls of the microalgal biomass, in particular by mechanical means.

(4) For the purposes of the invention, the microalgae under consideration are species which produce appropriate triglyceride oils and/or total lipids.

(5) The microalgal biomass comprises at least 10% by dry weight of oils or lipids, preferably at least 25% to 35% or more by dry weight of oils or lipids.

(6) More preferably still, the biomass contains at least 40%, at least 50%, at least 75% by dry weight of oils or lipids.

(7) The preferred microalgae of the invention may grow in heterotrophic conditions (on sugars as source of carbon and in the absence of light).

(8) The applicant company recommends choosing lipid-rich microalgae of the Chlorella genus.

(9) The microalgae used may be chosen, non-exhaustively, from Chlorella protothecoides, Chlorella kessleri, Chlorella minutissima, Chlorella sp., Chlorella sorokiniama, Chlorella luteoviridis, Chlorella vulgaris, Chlorella reisigffi, Chlorella effipsoidea, Chlorella saccarophila, Parachlorefia kessleri, Parachlorefia beijerinkii, Prototheca stagnora and Prototheca moriformis. Preferably, the microalgae used according to the invention belong to the Chlorella protothecoides species.

(10) The microalgae are cultured in liquid medium in order to produce the biomass as such.

(11) According to the invention, the microalgae are cultured in a medium containing a carbon source and a nitrogen source in the absence of light (heterotrophic conditions).

(12) 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).

(13) The production of biomass is carried out in fermenters (or bioreactors).

(14) 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 microalgal growth and the lipids.

(15) In the technical field to which the invention relates, it is sought to prepare an algal flour.

(16) This microalgal flour within the context of the invention is prepared from the concentrated microalgal biomass which has been mechanically lyzed and homogenized, the homogenate then being dried.

(17) The microalgal flour according to the invention, having a particle size between 30 and 150 μm and having a compressibility, measured on a HOSOKAWA powder tester, of between 45 and 55%, is characterized in that it has: a flow value, determined according to a test A, of between 55% and 60% by weight for the oversize at 2000 μm, a dispersibility and a wettability, expressed, according to a test B, by: the height of the product decanted in a beaker, having a value of between 0 and 2 mm; a degree of wetting having a value of more than 70%, preferably more than 80% of the total powder.

(18) In the technical field to which the invention relates, the microalgal flour has particle size and compression parameters which are commonly found in Chlorella microalgal flours dried by the conventional route (single-effect spray drying): The microalgal flour according to the invention has a particle size of between 30 and 150 μm.

(19) This measurement is carried out on a Coulter® LS laser particle size analyzer, equipped with its small volume dispersion module or SVM (125 ml), according to the constructor's specifications (in the “Small Volume Module Operating instructions”). The microalgal flour according to the invention has a compressibility, measured on a HOSOKAWA powder tester, of between 45% and 55%.

(20) The compression or compressibility value C is obtained by calculating the ratio of the aerated bulk density value (=A) to the packed density value (=B), which are themselves determined using an apparatus sold by the company HOSOKAWA under the trade name Powder Tester, type PTE, by applying the method recommended in the operating instructions for measuring aerated bulk density and packed density, according to the following equation:

(21) $C=\frac{100\left(B-A\right)}{B}$

(22) By way of comparison, the compression value for a microalgal flour dried by single-effect spray drying is of the order of 47%.

(23) However, surprisingly and unexpectedly, the microalgal flour in accordance with the invention is characterized by its noteworthy flow, wettability and dispersibility properties. The microalgal flour according to the invention has flow properties, measured according to a test A, which are better than those measured for a microalgal flour dried by the conventional route.

(24) The test A consists in measuring the degree of cohesion of the microalgal flour.

(25) This cohesion test is inspired by the cohesion test described in the operating instructions of the Powder Characteristics Tester, type PTE, sold by the company HOSOKAWA.

(26) The test A first of all consists in sieving the microalgal flour according to the invention on a sieve with a mesh opening of 800 μm.

(27) The fraction of the flour having a size of less than 800 μm is then recovered and placed in a closed container, and undergoes mixing by epicycloidal motion using a Turbula laboratory mixer, type T2C.

(28) By virtue of this mixing, according to its own characteristics, the microalgal flour in accordance with the invention will express its propensity to agglomerate or to repel.

(29) The flour mixed in this way is then deposited on a 2000 μm sieve for another sieving operation.

(30) Once the sieving has ended, the oversize on this sieve is quantified and the result gives an illustration of the “cohesive” or “tacky” nature of the microalgal flour.

(31) Thus, a free-flowing powder, which is therefore not very cohesive, will virtually not be stopped by this sieve with wide openings.

(32) The protocol is as follows: sieving the required amount of product on an 800 μm sieve in order to recover 50 g of product having a size less than 800 μm, placing these 50 g of flour having a size of less than 800 μm in a glass jar with a volume of 1 liter (Ref. BVBL Verrerie Villeurbannaise-Villeurbanne France) and closing the lid, placing this jar in the mixer (Turbula, model T2C), adjusted to the speed of 42 rpm (Willy A. Bachofen Sarl-Sausheim-France) and mixing for 5 minutes, preparing the sieve (of the brand Saulas—Diameter 200 mm; Paisy Cosdon—France) which will be placed on a siever (Fritsch, model Pulverisette type 00.502); details of the assembly starting from the bottom to the top: siever, sieve bottom, 800 μm sieve, 2000 μm sieve, siever lid, depositing the powder resulting from the mixing on the top of the column (2000 μm sieve), closing with the siever lid and sieving for 5 minutes on the (Fritsch) siever, with an amplitude 5 in the permanent position, weighing the oversize on this sieve.

(33) The microalgal flour therefore has between 55% and 60% by weight for the oversize at 2000 μm.

(34) By way of comparison, the flow value for a conventional microalgal flour is of the order of 71%. The microalgal flour according to the invention has quite noteworthy dispersibility and wettability properties.

(35) This dispersibility and this wettability are expressed according to a test B, by: the height of the product decanted in a beaker, having a value of between 0 and 2 mm; a degree of wetting having a value of more than 70%, preferably more than 80% of the total powder.

(36) This surprising and unexpected character is based on the fact that the compressibility and flow measurements demonstrate that the microalgal flour in accordance with the invention remains quite cohesive, just like the conventional microalgal flours, since after mixing, which does not use much mechanical energy (sieving time of barely 5 mins), 55% to 60% of the particles smaller than 800 μm still cannot pass through a 2000 μm sieve, the openings of which are nonetheless 2 to 4 times larger.

(37) It is readily deduced therefrom that such a flour, exhibiting such a behavior, should be poorly dispersible and hence difficult to use in a preparation where uniform distribution of the ingredients is recommended.

(38) Likewise, the wettability thereof should be low.

(39) Wettability is a technological property very often used to characterize a powder resuspended in water, for example in dairy industries.

(40) It reflects the ability of a powder to become immersed after having been deposited at the surface of water (Haugaard Sorensen et al., “Méthodes d'analyse des produits laitiers déshydratés” [“Methods for analyzing dehydrated milk products”], Niro A/S (publisher), Copenhagen, Denmark, 1978), and thus reflects the capacity of the powder to absorb water at its surface (Cayot and Lorient, “Structures et technofonctions des protéines du lait” [“Structures and technofunctions of milk proteins”]. Paris: Airlait Recherches: Tec and Doc, Lavoisier, 1998).

(41) The measurement of this index conventionally consists in measuring the time required for a certain amount of powder to penetrate into the water through its free surface at rest.

(42) According to Haugaard Sorensen et al. (1978): a powder is said to be “wettable” if its “Index of Wettability”; is less than 20 seconds; the swelling ability of the powder should also be associated with the wettability. This is because, when a powder absorbs water, it gradually swells. The structure of the powder then disappears when the various constituents are solubilized or dispersed.

(43) This swelling ability is expressed as a % of wetted product.

(44) Among the factors which influence wettability are the presence of large primary particles, the reintroduction of fines, the density of the powder, the porosity and the capillarity of the powder particles and also the presence of air, the presence of fats at the surface of the powder particles and the reconstitution conditions.

(45) The test B, developed by the Applicant company, consists here in considering more particularly: the behavior of the microalgal flour powder when brought into contact with water, by measuring, after a certain contact time, the height of the powder which decants when the powder is placed at the surface of the water; its capacity for water uptake (expressed in %).

(46) The protocol for this test is as follows: 500 ml of demineralized water at 20° C. are placed in a low-form beaker of 600 ml (Fischerbrand FB 33114 beaker), 25 g of the microalgal flour powder are uniformly placed at the surface of the water, without mixing, the behavior of the powder over time is observed, the height of the decanted product at the bottom of the beaker is measured.

(47) A very cohesive powder of low wettability will remain at the surface of the liquid, while a powder of better wettability will decant more easily.

(48) The microalgal flour according to the invention has a dispersibility and a wettability, expressed, according to the test B, by: the height of the product decanted in a beaker, having a value of between 0 and 2 mm; a degree of wetting having a value of more than 70%, preferably more than 80% of the total powder.

(49) However, by way of comparison, the microalgal flour conventionally dried by single-effect spray drying stays at the surface of the water, and does not hydrate sufficiently to be able to decant to the bottom of the beaker.

(50) The microalgal flour in accordance with the invention is able to be obtained by a particular way of conducting a process for spray drying, using a flat-bottom spray dryer (or FBSD) coupled to an air broom for sweeping the spray drying chamber with low-pressure air (or AB).

(51) The flat-bottom spray dryer is conventionally used to dry fat-rich materials or hygroscopic products, or in a more practical sense, in places where there is a lack of space, etc. However, to the knowledge of the Applicant company, it has never been used coupled to an air broom for sweeping the spray drying chamber with low-pressure air for drying lyzed biomass of microalgae in general and Chlorella in particular.

(52) With regard to the device coupling FBSD and AB, it is especially recommended for drying fruits, vegetable pulp and fruit juices, or even meat extracts.

(53) In order to dry the lyzed microalgal biomass, following this principle of spray drying, it is possible to use for example an FBSD equipped with the AB sold by the companies CE Rogers, Marriott Walker, Henningsen Foods or Food Engineering Co. and Henszey Co.

(54) Surprisingly and unexpectedly, the Applicant company thus observed that drying the microalgal flour by using, for example, this FBSD/AB process, made it possible not only to prepare a product with standard compressibility, particle size profile and flowability in a high yield, but especially to confer upon it unexpected flow, wettability and water-dispersibility properties, without it being necessary to use granulation binders or anti-caking agents.

(55) Indeed, the processes described previously (such as single-effect spray drying which is conventionally used for drying biomasses or microalgal flours) do not make it possible to obtain all the desired characteristics.

(56) The process for preparing the microalgal flour in accordance with the invention thus comprises the following steps: 1) preparing an emulsion of lipid-rich microalgal flour in water with a solids content of between 15% and 50% by dry weight, 2) introducing this emulsion into a high-pressure homogenizer, 3) spraying it in an FBSD equipped with an AB device in its lower portion, such that: a) the temperature of the main drying air is between 160 and 240° C., b) the temperature of the air in the air broom portion is at most 70° C., preferably at most 65° C., more preferably between 50 and 60° C., c) the ratio of the flow rate of the air from the AB to the flow rate of the main drying air has a value greater than ⅓, preferably between ⅓ and ½, d) the temperature of the cooling air is between 25 and 35° C., such that the flour leaving the spray dryer has a temperature of between 60° C. and 90° C., 4) collecting the microalgal flour thus obtained.

(57) The first step of the process of the invention consists in preparing an emulsion of lipid-rich microalgal flour in water with a solids content of between 15% and 50% by dry weight. In particular, the solids content may be between 25% and 45%, preferably between 35% and 45%. In addition, the lipid content of the microalgal flour or of the microalgal biomass is preferably a minimum of at least 10%, 20%, 30%, 40%, 50% or 60% by dry weight, for example between 20% and 80% or between 30% and 70%. Optionally, the degree of milling of the microalgal biomass may be at least from 25% to 75% of lyzed cells, for example 50%, 85% or 95% of cell lysis, and is preferably 85% or 95%.

(58) As will be exemplified below, the biomass obtained at the end of fermentation typically has a lipid content of approximately 50%, from 10% to 50% fibers, 2% to 15% proteins, 30% sugars and 10% starch.

(59) The biomass is then: deactivated by flash heat treatment (HTST treatment), washed by diluting with an aqueous solution and concentrating by centrifugation, milled in a ball mill thus creating an “oil-in-water” emulsion.

(60) The second step of the process of the invention consists in introducing this emulsion into a high pressure homogenizer.

(61) The Applicant company recommends carrying out this homogenization of the emulsion in a two-stage device, for example a Gaulin homogenizer sold by the company APV, with a pressure of 160 bar at the first stage, and 40 bar at the second stage.

(62) The third step of the process of the invention consists in spraying this solution in an FBSD equipped with an AB device in its lower portion, such that: a) the temperature of the main drying air is between 160 and 240° C., b) the temperature of the air in the AB portion is at most 70° C., preferably at most 65° C., more preferably between 50 and 60° C., c) the ratio of the flow rate of the air from the AB to the flow rate of the main drying air has a value greater than ⅓, preferably between ⅓ and ½, d) the temperature of the cooling air is between 25 and 35° C., such that the flour leaving the spray dryer has a temperature of between 60° C. and 90′C.

(63) In this way, as will be exemplified below, for a flow rate of the main drying air fixed at 2200 kg/h, the flow rate of the air from the AB will be more than 750 kg/h, preferably between 800 and 900 kg/h.

(64) As will also be exemplified below, these operating conditions make it possible to limit the formation of deposits on the walls of the spray drying chamber and thereby to optimize the drying yield at more than 90%, preferably at more than 95%, more preferably still at 99%.

(65) Moreover, it is these parameters for controlling the AB, more than the act of spray drying in the FBSD, which make it possible to obtain products with such wettability and water-dispersibility properties.

(66) The last step of the process in accordance with the invention consists, finally, in collecting the microalgal flour thus obtained.

(67) This microalgal flour is of use in the food sector. Thus, the present invention relates to the use of the flour according to the present invention, or obtained by means of the process according to the present invention, in the food sectors. In particular, it relates to a method for preparing a food composition comprising the addition of such a microalgal flour to ingredients of the food composition or to the food composition. Such uses are, for example, described in patent applications WO 2010/045368, WO 2010/120923 or US 2010/0297296.

(68) The invention will be understood more clearly from the examples which follow, which are intended to be illustrative and nonlimiting.

EXAMPLES

Example 1

Obtaining the Chlorella protothecoides Microalgal Biomass by Fermentation

(69) The fermentation protocol is adapted from the one described entirely generally in patent application WO 2010/120923.

(70) The production fermenter is inoculated with a pre-culture of Chlorella protothecoides. The volume after inoculation reaches 9000 l.

(71) The carbon source used is a 55% w/w glucose syrup sterilized by application of a time/temperature scheme.

(72) The fermentation is a fed-batch fermentation during which the glucose flow rate is adjusted so as to maintain a residual glucose concentration of from 3 to 10 g/l.

(73) The production fermenter time is from 4 to 5 days.

(74) At the end of fermentation, the cell concentration reaches 185 g/l.

(75) During the glucose feed phase, the nitrogen content in the culture medium is limited so as to allow the accumulation of lipids in an amount of 50%.

(76) The fermentation temperature is maintained at 28° C.

(77) The fermentation pH before inoculation is adjusted to 6.8 and is then regulated on this same value during the fermentation.

(78) The dissolved oxygen is maintained at a minimum of 30% by controlling the aeration, the counter pressure and the stirring of the fermenter.

(79) The fermentation must is heat-treated over an HTST zone with a scheme of 1 min at 75° C. and cooled to 6° C.

(80) The biomass is then washed with decarbonated drinking water with a dilution ratio of 6 to 1 (water/must) and concentrated to 250 g/l (25% DCW “Dry Cell Weight”) by centrifugation using an Alfa Laval Feux 510.

(81) The cells are deactivated by heat treatment through an HTST zone at 75° C. for 1 minute.

(82) For the rest of the operations, the temperature is maintained under 8-10° C.

(83) The concentration of interstitial soluble material is reduced by washing the biomass by diluting (3:1 (V.sub.water/V.sub.biomass)) and concentrating by centrifugation (disk-nozzle centrifuge).

(84) After this step, the solids content of the biomass is approximately 25% at the separating outlet, then concentrated to 45% by evaporation.

(85) The washed biomass is milled using a ball mill of bead mill type, with a degree of milling of 95%.

(86) The coarse “oil-in-water” type emulsion produced in this way is homogenized under pressure in a two-stage Gaulin homogenizer (160 bar at the first stage/40 bar at the second stage) after adjusting the pH to 7 using potassium hydroxide.

(87) The biomass obtained at the end of fermentation typically has a lipid content of approximately 50%, from 10% to 50% fibers, 2% to 15% proteins, 30% sugars and 10% starch, the percentages being expressed as dry weight of total biomass.

Example 2

Drying the Homogenized “Oil-in-Water” Emulsion of Microalgal Flour

(88) The homogenized emulsion obtained in example 1 is dried: in a single-effect spray dryer (liquid dried by a single pass through the flow of heat then recovered at the bottom of the tower at the cyclone or the sleeve filter), sold by GEA Niro, so as to obtain a control microalgal flour in accordance with what is commercially available.

(89) Or in a flat-bottom spray dryer equipped with an internal air broom for sweeping the spray drying chamber with low-pressure air, to obtain the microalgal flour in accordance with the invention.

(90) The control single-effect spray drying operating conditions are as follows: input temperature of 160° C., temperature of 60° C. in the drying section, cooling temperature of the air: 21° C. output temperature: 60° C.

(91) With regard to the spray drying process in accordance with the invention, it consists in spraying the high-pressure-homogenized suspension in a flat-bottom spray dryer equipped with an air broom in the following manner: Feed system: feed tank with helical mixer and heating jacket; mono pump; duplex filter Spray dryer: Centrifuge, 160 mm in diameter, Powder discharger: rotary device to avoid agglomeration at the bottom of the chamber, Output air: air loaded with particles leaves the chamber at the bottom; the dry powder is separated from the air in a sleeve filter.

(92) The parameters for executing spray drying in the flat-bottom spray dryer are as follows: Feed: emulsion with 20% solids at a temperature of 50-65° C. turbine at 16 400 rpm flow rate of the emulsion: 60 kg/h-160 kg/h Main air: Flow rate: 2200 kg/h Temperature: 165-220° C.

(93) Two configurations for executing the sweeping with air (air broom) are produced: 1. standard execution, 2. optimized execution to produce the microalgal flour in accordance with the invention.

(94) The standard execution for sweeping with air (air broom) (according to the constructor's specifications) is as follows (for 1 test): air flow rate: 700 kg/h at a temperature of 70° C. Output temperature at the bottom of the chamber: 95° C. Cooling air: 600 kg/h at a temperature of 30° C. Air temperature before the sleeve filter: 81° C.

(95) The production efficiency here is <90% and the formation of deposits on the walls of the spray drying chamber is observed.

(96) The execution of sweeping with air (air broom) optimized by the Applicant company to give the microalgal flour in accordance with the invention is as follows (test carried out in triplicate): air flow rate: 850 kg/h at a temperature of 65° C. Cooling air: 800 kg/h at a temperature of 30° C.

(97) The production efficiency here is 99% and the formation of deposits on the walls of the spray drying chamber is not observed.

Example 3

Characterizing the Microalgal Flour in Accordance with the Invention

(98) In the table below, the values for the following parameters are presented: particle size, compressibility, flowability by cohesion test (2000 μm) wettability, water-dispersibility

(99) for the “single-effect spray drying” control, for the non-optimized “air broom” control and for the three batches of microalgal flour in accordance with the invention.

(100) TABLE-US-00001 Particle Aerated bulk Packed Compress- size density density ibility (D 4,3 - μm) (g/ml) (g/ml) (%) Single-effect spray 40 0.27 0.51 47 drying control “Non-optimized” 133 0.35 0.45 22 air broom control Batch 1 55 0.3 0.59 49 Batch 2 90 0.26 0.54 52 Batch 3 110 0.27 0.53 49

(101) TABLE-US-00002 Dispersibility (% product wetted after Cohesion Wettability 2 minutes - constant 2000 μm (mm) value subsequently) Single-effect spray 71 0 0 drying control Remains at the surface of the water “Non-optimized” 65 0 0 air broom control Penetration into the water; no decanting Batch 1 59 2 70 Batch 2 59 0 80 Penetration into the water; no decanting Batch 3 57 0 80 Penetration into the water; no decanting

(102) Entirely logically, it is observed that the conventional microalgal flour (“single-effect spray drying” control), characterized by “cohesive” particles, does not become sufficiently hydrated to decant, whereas the microalgal flour in accordance with the invention does this readily, despite its cohesive character. Thus, the conventional microalgal flour is deposited on the surface of the water without penetrating into the water. Conversely, the microalgal flour in accordance with the invention hydrates well and does not decant at the bottom of the beaker.

(103) With regard to the standard “air broom” test, it is observed that the powder obtained does not have any wettability or water-dispersibility.