CA2055390C - Microwave assisted process for extraction and apparatus therefor - Google Patents

Abstract

There is disclosed a method and apparatus for extraction of essential and other such oils from biological matter by exposure to microwave energy. The method involves exposure of microwaves to the oil containing cellular matter of the glandular system to extract the oil into a suitable non-aqueous organic medium after disruption of the oil containing cellular matter. The apparatus includes microwave applicators, solvent and starting material, storage means and multiple stages of treatment resulting in a high quality extracted product.

Description

MICROWAVE ASSISTED PROCESS FOR
EXTRACTION AND APPARATUS THEREFOR
This invention relates to an apparatus and improved method of extracting soluble natural products from biological matter using microwave energy and apparatus therefor.
Prior Art Various microwave advances have been documented where e.g. grains containing fats and oils have been dried by microwave heating, followed by steps to remove husks and to extract oils, e.g. U.S. 4,464,402, Gannon. Grains and seeds have been microwave treated to heat the extracted medium, e.g. Ganzler and Salgo, 1987, Z. Lebensm Unters Forsch 184: 274- 276. In these experiments, radiation was primarily employed to heat the extractant medium.
Microwave drying of food products followed by subsequent solvent extraction is disclosed in U.S. 4,554,132, Collins, but with no extraction process.
British 1,209,675 discloses inactivating enzymes of alm fruits with microwave radiation, followed by solvent extraction of palm oil.
Heitkamp et al., Canadian 987,993, describes a microwave induced migration of flavour and aroma constituents towards the surface in certain tissues such as tobacco or tea in the presence of moisture and optionally a solvent. Heitkamp does not teach any enhanced extraction of the flavour or aroma constituents into the extracted medium.
Additionally, Craveiro et al. in the Flavour and Fragrance Journal 4, 1989: 43-44, discuss the production of volatile material from plant material exposed to microwave energy in an air stream.

Ganzler, Salgo, and Valko in Journal of Chromatography, 371, 1986: 299-306, disclose microwave sample preparation for organophosphate pesticides, antinutritives and crude fat samples. Dried sample materials are milled to the point of particulation and suspended in an organic medium. The Ganzler et al. method describes an extraction in which the glandular and vascular matter of the dried sample material is destroyed mechanically prior to microwave treatment; this causes a loss of volatile oils and allows for undesirable materials to be obtained and the method requires a long centrifugation time. Further, the method indicates that the suspensions are cooled and subsequently re-exposed to microwaves. Thus, heating of the extraction environment occurs with no recovery of the extractant or any volatile oils.
Steam distillation and solvent extraction methods are known but employ high temperatures and dangerous organic solvents which produce a contaminated product.
Accordingly, there is a need for an extraction method and apparatus for producing maximum yields and recovery of volatile oils and other useful substances contained in cellular biological material by microwave inducement without any of the above limitations.
With the present invention, an extraction protocol for natural products is provided which is more selective and efficient.
SUMMARY OF THE PRESENT INVENTION
This invention employs microwave energy to generate a sudden temperature increase in the glandular and sometimes vascular systems of biological material which is contacted with a quantity of non-aqueous organic solvent.
According to one aspect of the present invention there is a process for extracting soluble products from biological material comprising: (a) subdividing a biological feed material into subdivided material; (b) contacting the subdivided material with a non-aqueous extractant which is transparent or partially transparent to microwave radiation;
(c) exposing the subdivided material, while in contact with sufficient extractant to enable extraction to occur, to a microwave energy source to effect differential heating between said biological material and said non-aqueous extractant to thereby express said soluble products from said biological material and cooling the expressed soluble products from said biological material with said non-aqueous extractant to a temperature below the temperature at which the expressed soluble products are extracted from the biological material; and, (d) separating the residual material from the extractant phase. Desirably in this process the biological material is plant tissue.
Preferably, the moisture content of the biological material is within about 25 to about 90% by weight. A preferred aspect in this process is where the biological material is subdivided sufficiently that all of the desired soluble products are accessible to the extractant. A still further preferred aspect is where the extractant is partially transparent to microwave and part of the extractant is impregnated into the material to become a dispersed component having a microwave absorption, before step (c). A yet further preferred aspect in this process is where the biological material contains desired labile or volatile components and the extractant is selected to be sufficiently transparent to the applied microwave radiation that the labile or volatile components will be extracted. A
still further preferred aspect of this process is where the biological material contains undesired labile or volatile soluble components and the extractant is selected from those partially transparent to the microwave so that sufficient heating due to microwave absorption will occur to remove or decompose the undesired components.
A still further preferred aspect of the above process is where the residual material after step (d) is contacted with a second extractant having different solvent or penetration characteristics than the first, and exposed to microwave radiation a second time to generate a second extraction product. A preferred aspect is where the ratio (L/kg) of the extractant to the subdivided material ranges from about 1:1 to about 20:1.
A still further preferred aspect of the above process is where the microwave radiation exposure has a duration of from about 10 to about 125 seconds at a power of about 200 to about 10,000 watts and a frequency of 800-30,000 MHz, and the dose is selected to enhance the extraction. A preferred aspect is where the product is recovered from the extractant phase and the depleted extractant phase is recycled to step (b). A
still further preferred aspect is where the biological feed material is in dry condition and is hydrated or rehydrated with moisture prior to step (c).
In accordance with another preferred aspect of the present invention there is a method for the microwave extraction of at least one natural product from a biological material, the microwave method characterized in that the steps comprise:
placing the biological material in an enclosure and surrounding the biological material with a non-aqueous extractant; subjecting biological material present in the enclosure to intermittent microwave irradiation to effect the evaporation of water contained in the biological material and to split cellular structures of the biological material to release the natural product therefrom; separating residual biological material from the extracted natural product, the method further including the steps of: utilizing reduced pressure during the microwave method; effecting heating during the microwave method;
and, obtaining natural product by conveying natural product in water vapour derived from the biological material. Preferably, the method intermittent microwave irradiation includes a plurality of intermittent microwave irradiation treatments. A preferred aspect of this method is the step for the separation of the residual biological material from the extract comprises the further steps of: condensing water vapour containing the extracted natural product; collecting the resulting mixture; and, separating the extracted natural product therefrom. A still further preferred aspect is where a part of the condensate obtained is returned to the enclosure, and there is included a step of hydro-distillation to obtain the natural product. A yet further preferred method where the microwave treatment is conducted at a temperature of at least 15°C. A still further preferred method where the microwaves used during the step of microwave irradiation have a frequency of below 30,000. Preferably the method where the step of microwave irradiation is conducted so as to apply power in a range from about 200 W to about 10,000 W. Further yet, the method includes the step of mechanically stirring the biological material.

Another aspect of this invention provides a method of obtaining volatile oils from biological material containing such oils comprising: providing a source of biological material having a substantially intact glandular system, the material having a moisture content sufficient to permit the extraction of the volatile oils by microwave energy. In the method, the material is surrounded with a non-aqueous extractant for the volatile oils. Then, the material is exposed to a microwave energy source to effect differential heating between the material and the extractant to a temperature below that at which the expressed oils are extracted from the material. The process may include separating residual material from the extracted oil in the solvent and recovering the oil.
An advantageous method involves immersing the biological material having cellular matter containing the oils in a non-aqueous organic extractant, the source of material having a substantially intact glandular system and a moisture content sufficient to rupture the glandular system under microwave treatment. Thereafter, the source material is exposed to a microwave energy source to elevate the temperature of the biological material to a degree sufficient to rupture the glandular system and express the volatile oil from the biological material into the organic extractant.
Oils extracted during the process are cooled with the extractant. Further, an additional source of the biological material is added to the resulting extractant, containing extracted oils from the first step, and exposed so the combined material and the resulting extractant is treated with microwave energy sufficient to elevate the temperature of the material to rupture the glandular system of the material in the resulting extractant to express and disperse oil. This process may be repeated.
Subsequently, oils are separated from the further extractant thus obtained.
A preferred feature obtains concentrated extracts upon reducing the amount of solvent normally required.
In contrast to other procedures, this invention causes the microwave energy to be absorbed by the material being treated preferentially compared to the solvent, so that oils expressed are cooled by the surrounding solvent, avoiding exposure of the oils and sensitive materials to heat degradation by the microwave treatment of the biological material.
Therefore, Applicant's process is a "cool process" in which the solvent does not absorb energy so substantially all of the energy is imparted to the material being treated. The differential in temperature between the material and the extract ensures that the oil migrates towards the extractant.
Suitable extractants include organic solvents, e.g. hexane or other such suitable non-aqueous aliphatic organics. Generally, such materials are termed "microwave transparent", i.e. there is no significant energy absorption upon exposure due to the lack of a molecular dipole moment. Co-solvents may also be employed. The extractants should have a static dielectric constant of between about 0 to 28, or should be transparent to the microwave frequency of the microwave source.
If the biological material lacks moisture, rehydration or resolvation may be achieved, prior to microwave treatment, by incorporating a solvent which is not transparent to microwaves, i.e., those having a net dipole moment. These solvents include, for example, methanol, ethanol and mixtures of solvents, etc.
If a partially transparent organic solvent is used, the temperature of the same remains below that of the biological material and more specifically, the extracted oil, during a microwave treatment. This ensures that the oil containing matter will be cooled. It will also ensure the migration of the oil into the extractant.
Further, the invention employs an extraction media system either as a single extractant or a solution of two or more suitable and compatible extractants, in series, to obtain fractionated oil extractions.

Utilization of non-particulated material for treatment yields superior results compared to finely ground or particulated dried material. Use of substantially whole or large pieces of material avoids destruction of glandular and vascular systems resulting in higher and more valuable extraction of desired products.
Glandular tissue refers to those organs responsible for various sections, i.e.
nectary secretions. Vascular tissue refers to channels for fluid conveyance.
Generally, the volatile oils for extraction from biological material include the essential oils located in the glandular system. Such oils cant' the odour or flavour of the material and are used in perfumes and flavourings. As is known, the volatile, i.e. essential, oils are distinguished from the fixed oils, e.g. cottonseed, linseed or coconut oils, etc., in that the former oils are not glycerides of fatty acids.
As used herein, the term "volatile oils" includes not only those substances derived from plant and animal materials such as essential oils, but also substances such as lipids, fatty oils, fatty acids, etc., which, while not having the same degree of volatility as essential oils, are expressed or "volatilized" from the glandular or like system of such plant and animal materials by the process described herein.
The present invention is applicable to many types of tissue, e.g. plant material for flavouring and fragrance purposes, and other tissues e.g. animal tissue.
Examples of plant material include Canadian pepper mint, seaweeds such as Irish moss, microalgaes, various types of vegetables, e.g. onions, garlic, and the like.
In the case of animal tissue, liver, kidney, egg yolk, etc., or animal products, e.g. sea anemones, sea cucumber and crustaceous products (e.g. lobster or other shell fish), warm and cold water fish (e.g. trout, etc.), can be employed to extract pigments, oils, etc.
Other biological materials that may be used include bacterial cultures, cell cultures, tissue cultures, yeasts, fermentation broths, and any resulting biomass materials from such cultures or the like. One preferred application relates to the extraction of the desirable oils from fish components such as the liver which are a source of desirable acids for pharmaceutical and human purposes, e.g. volatile oils comprising omega-3 and omega-6 oils, fatty acids, and the like and the resulting biomasses therefrom.
The present invention also provides an apparatus for the extraction of essences and other substances from biological material, comprising at least one microwave applicator and means for feeding a mixture of biological material and an extractant through the applicator. Means are provided for separating liquid from the treated mixture and removing the extractant from the filter liquid, and desirably means for removing the extract from the resulting separated liquid.
In a still further embodiment of the present invention, there is provided an apparatus for extraction of a natural product from biological material in a microwave treatment system, comprising: an enclosure adapted to retain biological material for microwave treatment and heating of the contents therein; microwave generating means for generating intermittent microwave irradiation within the enclosure to effect release of the natural product; vacuum means to reduce pressure in the system; and, means for recovering natural product extracted from the biological material. Desirably, in this apparatus, the means for recovering the natural product includes condensing means.
Preferably, in the apparatus, there is included means for an intermittent operation of the microwave generating means. Still further, a desirable embodiment is where the apparatus also includes stirring means for stirring the biological material.
Additionally, such apparatus also preferably includes means enabling the rerouting of the condensed material obtained at the means for the recovery of the natural product from within the enclosure.
The microwave applicator may operate within known parameters, e.g. a power rating of about 200 to 10,000 Watts and a frequency range of within about 800 to 30,000 MHz or higher. Any wavelength within the microwave spectrum which is absorbed to some extent by a component of the material can be used as only minor changes in the irradiation time are necessary to compensate for changes in absorption.
Several applicators may be provided in parallel.

The apparatus provides a solvent reservoir of suitable material compatible with the organic solvents, and solvent inlet and sample inlet means. The mixture is fed into or through the applicator by a suitable means, e.g. a pump, and is subsequently passed into the filtering means, e.g. filter paper stages, Teflon (TM) screening, etc., for removal of residual plant material. In addition, the apparatus may include means for removing any water content derived from samples being treated; such means may include, e.g.
suitable desiccants for this purpose which may be incorporated as a separate stage or into e.g. the filtering means.
The material is preferably pumped to a separator, e.g. a rotary vaporizer, etc., for separation of the solvent from the oil material. The solvent may, additionally, be passed through a condenser for condensing the solvent.
The use of suitable connecting lines, e.g. glass tubing, Teflon (TM), quartz or other microwave transparent equipment for microwave treatment interconnect the apparatus. In addition, the lines include suitable valves, e.g. glass or Teflon (TM) stopcocks, etc.
In another aspect of the present invention, there is provided an apparatus for the extraction of essences and other substances from biological material, comprising:
at least one microwave applicator;
a mixing tank for mixing the biological material with extractant;
pump means for feeding a first mixture of biological material and an extractant from the mixing tank through the microwave applicator for treatment thereby;
means for separating extractant containing extract liquid extracted from the treated mixture;
means for recycling the separated extractant for subsequent mixing with biological material to be treated to form a second mixture; and, means for feeding the second mixture to a microwave applicator.

The recycling feature of the invention permits exposure of the biological material to recover any remaining extract not previously recovered. In this manner, an absolute maximum of extract is obtained. The apparatus may include outlets to remove the more heat sensitive compounds so that the same are prevented from re-exposure.
The extraction process is made even more effective by the presence of a plurality of microwave applicators sequentially arranged, i.e. in parallel, series or various combinations thereof.
Accordingly, a further preferred aspect of the present invention provides an apparatus for the extraction of essences and other substances from biological material comprising:
a plurality of microwave applicators arranged in sequence;
means for feeding a mixture of biological material and extractant through the plurality of microwave applicators for treatment thereby in small cross-section containers or conduits; or recycling means for recycling the extractant and treated biological material.
Various analytic instruments may be connected at a number of positions in the apparatus to effect analysis of the extractant, liquid extracted, a mixture of the two, etc.
Such analysis may be performed in concert with the process using, e.g.
chromatographic, spectrophotometric, magnetic resonance and similar equipment.
Reference will now be made to the drawing, illustrating a preferred embodiment and, in which:
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a diagrammatic representation of the apparatus of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS
With respect to the method, it generally proceeds as follows: the microwave rays travel freely through the microwave-transparent extraction medium and are allowed to reach the inner glandular and vascular systems of the biological material [a microwave transparent medium can be defined as a medium that does not possess a significant static dielectric constant, i.e. net dipole moments, e.g. hexane (1.9), carbon tetrachloride (2.2), and liquid C02 (1.6 at 0°C and 50 atm.) as opposed to large dielectric constant substances, e.g. water (80.4)]. A portion of these rays is absorbed by the material; the absorption efficiency is largely related to the moisture content (or added absorbing component) of the material at the time the extraction process is carried out. The result is a sudden rise in temperature inside the material which is more pronounced in the glandular and the vascular system. The temperature keeps rising until the internal pressure exceeds the capacity of expansion of the cell walls thus creating a cellular explosion. Substances located in the cells are free to flow out of the cells migrating to the surrounding medium that is cool and traps and dissolves the oils.
The solid material can be filtered with the resulting solution being processed in the same manner as any other natural product extract.
The extractant amount used to contact or submerse the feed material can vary widely, normally sufficient to extract substantially all of the desired components to totally physically cover the biological material. The ratio of extractant to feed material (L/kg) can be e.g. about 1:1 to about 20:1.
Electron micrograph examination of freshly extracted plant material reveals that the degree of disruption in the gland system of, e.g. Canadian pepper mint, is as large for a 20-second microwave-induced extraction as it is for conventional 2-hour steam distillation and for 6-hour Soxhlet extraction processes. Electron micrographs also provide an explanation for the superior quality of the extracts obtained as the relatively short period of extraction, e.g. 2 to 3 minutes, can be varied so that the penetration power based on the extraction medium can be controlled. In the case of an essential oil from pepper mint, using e.g. hexane as solvent, the short extraction period combined with the use of non-particulated fresh material prevents pigments and other undesirable components that are located within the plant to be accessed by the extractant.
Ground material is used in conventional steam distillation and other extraction processes where the final mesh size is very critical, and implies an extra step, compared to this invention.
Direct visual examination corroborates this phenomenon as extracts obtained by this invention are far less pigmented than steam distillation counterparts.
This invention permits the possibility of using a system of extraction media, whether as a single extractant or a solution of two or more extractants, also in series, in order to obtain fractionated extracts in a matter of minutes and making use of the same equipment. Current technology requires separate distillation processes that are costly and time consuming. Different and extensive instrumentation is also required, resulting in a much large capital investment. This invention enables a producer to perform a series of extraction and fractionation processes at the same site, using the same equipment, in less time than is required by current technology.
The duration of irradiation to extract the oils varies with the variety of the plant or other biological material; typical times being from about 10 to 100 seconds.
Irradiation times also vary with the moisture content of the feed material; the moisture content of the material should be from about 25% to about 90%. This extraction method can be used for batch processes as well as for continuous processes.
The product may be recovered from the extractant (after separation from the residual solid plant material as by screening, filtering or centrifuging) or suitable known recovery techniques. The depleted extractant phase may be recycled without further purification.
Reference will now be made to the examples of the invention provided below wherein microwave radiation-induced extraction was used. Disruption of the glandular and vascular systems of a variety of materials, as in the particular manner described herein, demonstrate the improvements. These include, for example, yield, quality of the extract, reduced time and production costs, reduced raw material costs (because of reduced raw material preparation costs), reduced number of operations, and reduced process-related hazards (to humans and to facilities), or a combination thereof, over the conventional extraction processes.

Monarda fistulosa, a novel species of Monarda is a new product for perfumery and flavouring starting materials. It produces much higher concentration of geraniol in its essential oil than other genera within the Monarda. For comparative purposes, the essential oil of Monarda fistulosa was obtained by this method. In this example, 30 g of the fresh plant material were tom into fairly large pieces (same lot as for steam distillation) and placed in a 400 ml beaker and immersed in 175 ml of hexane and the temperature of the mixture was recorded; the mixture was submitted to a 15-second microwave irradiation period (of 500W and at 2450MHz) and the temperature of the medium was again recorded; this last step was repeated twice without taking further temperature measurements (i.e. a total of 45 seconds of microwave irradiation was applied and a total of 4 temperature measurements were taken). The data indicates that the internal temperature of the plant material became elevated during the exposure to thereby establish the required temperature gradient necessary for high extraction efficiency of the oils, etc. into the cooler hexane medium (temperatures of only 15, 29, 44 and 57°C were reached by passive heat conduction from the plant material for microwave exposure period of 0, 15, 30 and 45 seconds, respectively). The yield was found to be 1.49%.
The cellular temperature of the plant material is high, i.e. of the order of 100°C
owing to moisture content, and the intracellular moisture diffuses into the hexane to cause a slight temperature change which is low in comparison to the oil material.

Subsequent to the mixture of the oils and extractant medium cooling, the mixture was then filtered over a small quantity of sodium sulphate (to remove traces of water) and washed with 50 ml of fresh hexane. The extract was reduced, the yield was determined and the extract analyzed by gas chromatography coupled to a mass selective detector (the mass spectral data being compared to a library of standards).
The data are summarized in Table I.
The same experiment was repeated until the last filtration step. At that point, the extract was used as an extraction medium to perform two other sets of experiments, i.e.
a total of 90g of plant material was extracted (in three lots of 30g, each being exposed to three irradiation sequences of 15 seconds) in a single aliquot of hexane.
The total extraction was then filtered (over a small quantity of sodium sulphate), rinsed with another 50 ml of fresh hexane and reduced. The yield was determined and the contents analyzed under the same conditions as per above. The yield (1.54%) and the sample contents proved to be identical to those noted above within the experimental error. Table I which summarizes the analytical results illustrating the microwave-assisted extract was of greater commercial market value by virtue of its enhanced content of geraniol.

TABLE I
Component Relative Concentration Microwave process Steam Distillation Octen-3-of 0.23 0.28 Myrcene ---- 0.59 P-Cymene ---- 0.12 a-Terpinene 0.21 0.96 Linalool 0.37 0.62 Nerol 0.57 0.33 Geraniol 98.48 94.83 Germascreen D 0.14 1.47 Total 100.0 99.20 A cumulative and sequential use of microwave-assisted extractions, combined with use of an appropriate solvent provides an extract in greater yield than conventional steam distillation products (0.94%) alone. Furthermore, the time required to reduce and/or evaporate the extract to dryness is reduced to one-third. The latter enhances the process efficiency and reduces costs associated with manpower and energy consumption; in fact, reduction and/or evaporation of the solvent is the rate-determining step of this microwave-assisted extraction process. In the above, three complete extracts are produced within ten minutes, whereas the same extract would have required a minimum of eight hours by steam distillation.

Intact garlic cloves having a 30% moisture content were immersed in 250 ml of dichloromethane. The immersed samples were then irradiated with microwave radiation at 625 Watts and a frequency 2,450 MHz for a single 30-second exposure period. The samples, being completely intact, illustrated exemplary constituent extraction with no contamination of the extracted constituents with less desirable constituents. Yields were to 22.2% for diallyl sulfide, 28.4% for 3-vinyl-1,2-dithi-5-ene and 49.4% for 2-vinyl-1,3-dithi-4-ene. The analysis of the products produced by the process herein is identified as N-wave2.
For comparative purposes, garlic samples were subjected to the following known techniques, namely hydrodiffusion (HD,); hydrodistillation (HD2);
supercritical fluid carbon dioxide extraction (COZ); N-wave, utilizing a macerated garlic in a solvent extraction (dichloromethane) with microwave irradiation (4 times) for 125 seconds.
TABLE II
GARLIC CONSTITUENTS
Constituent HD, HDZ COZ N-wave, N-wave2 Allyl methyl sulfide ---- ---- --- 1.23 ----Dimethyl sulfide ---- ---- 1.41 ---- ----Diallyl sulfide 1.33 3.89 ---- ---- ----Allyl methyl sulfide 3.05 5.32 5.58 8.12 ----Methyl prop-1-enyl disulfide---- ---- --- 5.41 ----Methyl prop-2-enyl disulfide---- 1.26 -- ---- ---Dimethyl trisulfide ---- - - 1.12 Diallyl disulfide 31.2 30.7 16.7 17.7 22.2 Dipropenyl disulfide 1.38 1.83 ---- --- ---Dipro-2-enyl disulfide 4.76 6.88 1.41 ---- ---Allyl methyl trisulfide 11.2 12.4 ---- 7.38 ---3-vinyl-1, 2-dithi-5-ene ---- ---- 23.3 4.47 28.4 2-vinyl-1, 3-dithi-4-ene 1.84 ---- 46.5 34.3 49.4 Diallyl trisulfide 33.8 22.4 ---- ---- ----Dipropenyl trisulfide ---- ---- ---- 2.29 ----Diallyl tetrasulfide 1.04 ---- ---- ---- ----Dipropenyl tetrasulfide 4.24 1.32 ---- ---- ----HD, denotes hydrodiffusion; HD2 denotes hydrodistillation; C02 denotes supercritical fluid extraction with C02; N-wave, denotes macerated garlic in dichloromethane with 4 irradiations of 125 seconds; N-wave2 denotes intact garlic cloves in dichloromethane and irradiated for a single 30-second microwave irradiation period.
The data clearly illustrates that even under brief exposure time (30 seconds) coupled with a cool medium for the extraction of the constituents, the present invention greatly exceeds the conventional techniques of hydrodiffusion, hydrodistillation, supercritical fluid extraction and, more importantly, microwave extraction where the sample was macerated and over-exposed to microwave energy.

Fresh rainbow trout (Salmon galrdneri) was provided and the pectoral fins, together with the dorsal fin and the head, were removed to form a source material for a first extraction (38.5g). From the same fish, the complete internal parts were separated to provide a source material for a second extraction (34.9g).
Each of these source materials were then subjected to a sequential series of microwave extractions (3 X 15 seconds) using the same extractant, according to the present invention. The apparatus employed was that described in Example 1; the extractant employed for each source material was hexane (a single 60 ml aliquot)which immersed the materials completely. It is important to note that the source materials were in a non-particulated state. In addition, the temperature of the extractant remained at a point where the extractant functioned to cool the expressed oil from these source materials.
The oils expressed from the starting materials were then separated from the hexane by procedures described previously and recovered products were analyzed for their fatty acid contents.
Agricultural Handbook 8-15 (U.S. Department of Agriculture, 1987), discloses the pressing of rainbow trout to separate essential oils from edible parts yields, by conventional techniques, to obtain a total of about 3.4% of lipids. Generally, pressing techniques require a significant amount of time. In addition, the percentage yield using the process of the present invention, for the essential oils, and using only trout fins and a small content of flesh as source material, is approximately equivalent (3.9%) to the same yields by conventional techniques when using whole edible fish parts. On the other hand, using the fish internal parts with the present invention, approximately five-fold (16.1 vs. 3.4%) increase in the amount of essential oils was obtained compared to conventional techniques.
Figure 1 shows an apparatus of the present invention having a reservoir 10 with an inlet 11 for the biological material and an inlet 12 for the solvent previously discussed, which may be stored in solvent reservoir 13. Feeding solvent into the tank 10 is controlled by valve 14. The mixture of solvent and biological material is stirred by a stirrer 15. A pump 16 feeds mixed solvent and plant material through a microwave applicator 17, with a typical power rating of about 200 to about 10,000 Watts and a typical operating frequency of between 800 to about 30,000 MHz. Further, pump feeds the treated material and solvent to a filtering apparatus 19. Also, a microwave source could be positioned within the supply tubing to enclose it within the feed material tube. This will permit the use of metal tubing (e.g. steel tubing) while only using e.g. a reinforced housing. The microwaves act directly on the material to disrupt the same, subsequently releasing the oils or other substances into the extractant for cooling thereby. It will be understood that the elements of the apparatus are linked by suitable conduit which may be TefIonT"", glass tubing, and other such suitable materials which will be readily apparent to those skilled in the art. Typically, the conduit employed to link the components of the system will be from about 1 to about 10 cm. in diameter and more desirably, between about 2 to about 5 cm. in diameter.
In one form, the apparatus includes a plurality of microwave applicators 17, each of which is independently controllable. The applicators 17 may be positioned such that they are serially arranged between pumps 16 and 18 or in parallel with respect to each other or further, in a combination of these. In this manner, a plurality of feeds from tank 10 may be simultaneously treated or a single feed may be repeatedly treated, both in small incremental volumes.
With more specific reference to the serial arrangement of the applicators 17, numerous advantages accrue. In the case where the materials to be extracted are contained in distinct compartments, such as pockets, cells, or sub-cellular entities which may be surrounded by further distinct entities that in effect constitute "walls" such as a different medium, membranes or other parting entities of different density, thicknesses or expansion abilities, serial treatment will successfully result in the extraction of the desired material. Various examples of the foregoing include fat pockets in water and proteins (meat) or the contents of vacuoles in the chloroplasts of plant material.
With the individually controllable serial arrangement of the applicators 17, a sequence of discrete irradiations with short exposure times can be applied so as to effect the rupture of selected compartments to thereby extract selected materials. This is in contrast to the use of a single applicator 17, for a single irradiation treatment, which necessitates a longer residence time, greater exposure to microwave energy, to effect similar recovery and a concomitant loss in the required selectivity. As an example of the advantageous arrangement disclosed hereinabove, it can be seen that pumping a mixture of microwave transparent extractant and plant material having two or more types of vacuoles, through a small diameter conduit (e.g. two-five centimetres in diameter) to pass through three microwave applicators 17 in sequence with a short exposure time (e.g. three-six seconds) at each applicator 17, will yield a final extract more concentrated in the desired component "A" compared to the same mixture exposed to a single applicator for the same duration of time. The single irradiation of the same duration will result in a lower recovery having a different extract composition and further, if the duration is extended to provide the same recovery as that produced from multiple irradiations, the extract composition is significantly different and often less desirable when compared thereto. This selectivity cannot be obtained from other processes nor apparatus configuration in the same time period. It will be appreciated by those skilled in the art that any form of suitable sample extraction means may be inserted into the apparatus after each microwave applicator 17 in order to enhance selectivity or for advantageous removal of the more delicate components so that the same are not degenerated from over-exposure to microwave energy.
In terms of the parallel arrangement of the applicators 17, further advantages are realized. For example, the ability to effect an extraction at a homogeneous temperature by passing the material to be treated through each applicator 17 within a small diameter conduit (a plurality of these being in parallel) at a flow rate chosen to permit proper residence time to thereby effect the desired yields of extraction is a direct advantage of this disposition of the applicator 17. This parallel arrangement of small conduits also avoids having to contend with effectiveness-reducing factors such as localized overheating and underheating of the material which can give rise to artifacts or to lower yields, respectively, when a single larger volume is treated.
Other advantages inherent to this latter arrangement include reduced manufacture and operation costs and reduced complexity in overall plant design, etc.
Further, the arrangement provides for a directly scalable operation (e.g. by 10%
increments in the case of a system employing 10 applicators) and for an apparatus on which maintenance can be performed during the operation of the process.
Having regard to the foregoing, and based on the advantages inherent to the serial and parallel arrangement of microwave applicators, the combination of serial and parallel arranged applicators has added effectiveness, i.e. in a parallel arrangement of modules, each module may comprise a series of applicators for combined advantages.
Returning to the basic apparatus, a plurality of filters used with or without desiccants may be provided in the filter, acting in parallel. This enables filtered residual biological solids to be removed periodically from individual filters, without shutting down the apparatus.
From filter 19, the filtered solvent and oils are pumped by pump 20 to a separator 21 or recycled to the microwave applicator 17 via valves 51 and 52 and tube 50 for further treatment. Separator 21 is heated, as by external heater 22, controlled by a temperature controller 23, to evaporate the solvent. The remaining substance or substances in the separator 21 is drawn off periodically at outlet 24 controlled by valve 25.
Evaporated solvent is passed through a condenser 26, and condensed solvent is fed back into a main reservoir 27 where it is then fed to the solvent reservoir 13, controlled by valve 28. In a modification, the condensed solvent could be fed directly to the solvent reservoir 13.
Some condensed solvent can be diverted through the filter 19 to increase the extraction in the filter. This is provided by pipe 30, controlled by valves 31 and 32.
Various relief valves are provided, as at 33 and 34, for opening the apparatus to atmospheric pressure.
The apparatus is useful for obtaining volatile oils and other substances by the use of microwaves to disrupt the glandular cells containing such oils. The apparatus can be combined with other conventional apparatus, e.g. a distribution valve 40 is provided between microwave applicator 17 and filter 19. From the valve, depending upon its setting, the mixed biological material and solvent can be fed to the filter 19, as described above, or fed via connection 41 to a conventional steam distillation plant.

With such an application, the solvent is water and the mixed biological material and water can be treated in the microwave applicator, the water being heated.
Alternatively, the water can be heated by the microwave applicator 17 until it reaches the vapour phase, under pressure, and is allowed to condense via connection 41, through the biological material that would be placed into the steam distillation reservoir (hydrodistillation and hydrodiffusion).
Valve 40 can alternately be set to permit flow through connection 42 to a solids/liquid extraction plant. The mixed plant material and solvent may or may not be treated in the microwave applicator for the duration of the initial fill-up reflux sequence.
The reflux of this operation could be returned directly to pump 16 for subsequent operations.
For improved operation, it may be desirable to operate the system under vacuum conditions. More particularly, solvent removal by evaporation is greatly facilitated by reducing the pressure while maintaining a relatively low temperature.
Connections at 43 and 44 provide for connection to a vacuum source.
A preferred apparatus form is utilized in conjunction with a supercritical fluid extraction process wherein the microwave applicator utilizes a system of tubing, such as glass, quartz or the like connected to or enclosed within an outer tubing of metal (e.g. steel) and in which the microwave apparatus uses an axially positioned microwave generator within the tube and through which the material to be irradiated flows. In this way, a continuous process with its advantages can be utilized. Other arrangements may be employed where the microwave generating means surrounds a microwave transparent conduit where the generating means is shielded by suitable material, e.g.
metal. In such a case, the transparent conduit material can be Teflon (TM) or glass.
The apparatus provides for increased extraction of certain essences and other substances which must be removed, or are preferably removed, without the application of heat, as by heating with a solvent.

As a further advantage to the apparatus disclosed herein, sample purity detection means such as chromatography means and, more specifically, gas chromatography means may be associated in the apparatus at various positions therein to monitor the product at various stages of processing, e.g. at the output of the apparatus subsequent microwave treatment, after the filtration steps or after the purification stage. The choice of location for such analytic apparatus will depend on the information required by the user. The purity detection means will additionally be positioned such that the process as disclosed herein can continue in an uninterrupted manner while samples are collected at the various points in the apparatus.

Claims (32)

1. A process for extracting soluble products from biological material comprising:
(a) subdividing a biological feed material into subdivided material;
(b) contacting the subdivided material with a non-aqueous extractant which is transparent or partially transparent to microwave radiation;
(c) exposing the subdivided material, while in contact with sufficient extractant to enable extraction to occur, to a microwave energy source to effect differential heating between said biological material and said non-aqueous extractant to thereby express said soluble products from said biological material and cooling the expressed soluble products from said biological material with said non-aqueous extractant to a temperature below the temperature at which the expressed soluble products are extracted from the biological material; and, (d) separating the residual material from the extractant phase.

2. The process of claim 1, wherein the biological material is plant tissue.

3. The process of claim 1 or 2, wherein the moisture content of the biological material is within about 25 to about 90% by weight.

4. The process of any one of claims 1 to 3, wherein the biological material is subdivided sufficiently that all of the desired soluble products are accessible to the extractant.

5. The process of any one of claims 1 to 4, wherein the extractant is partially transparent to microwave and part of the extractant is impregnated into the material to become a dispersed component having a microwave absorption, before step (c).

6. The process of any one of claims 1 to 5, wherein the biological material contains desired labile or volatile components and the extractant is selected to be sufficiently transparent to the applied microwave radiation that the labile or volatile components will be extracted.

7. The process of any one of claims 1 to 6, wherein the biological material contains undesired labile or volatile soluble components and the extractant is selected from those partially transparent to the microwave so that sufficient heating due to microwave absorption will occur to remove or decompose the undesired components.

8. The process of any one of claims 1 to 7, wherein the residual material after step (d) is contacted with a second extractant having different solvent or penetration characteristics than the first, and exposed to microwave radiation a second time to generate a second extraction product.

9. The process of any one of claims 1 to 8, wherein the ratio (L/kg) of the extractant to said subdivided material ranges from about 1:1 to about 20:1.

10. The process of any one of claims 1 to 9, wherein the microwave radiation exposure has a duration of from about 10 to about 125 seconds at a power of about 200 to about 10,000 watts and a frequency of 800-30,000 MHz, and the dose is selected to enhance the extraction.

11. The process of any one of claims 1 to 10, wherein the product is recovered from the extractant phase and the depleted extractant phase is recycled to step (b).

12. The process of any one of claims 1 to 11, wherein the biological feed material is in dry condition and is hydrated or rehydrated with moisture prior to step (c).

13. Apparatus for the extraction of essences and other substances from biological material, comprising:

at least one microwave applicator;
means for feeding a mixture of biological material and an extractant through the microwave applicator for treatment thereby;
means for separating liquid from the treated mixture; and, means for removing the extractant from the resulting separated liquid.

14. The apparatus set forth in claim 13, including a mixing tank for mixing biological materials with extractant.

15. The apparatus set forth in claim 13 or 14, wherein the microwave applicator is an applicator for containing supercritical liquid extractant.

16. The apparatus set forth in any one of claims 13 to 15, including a conduit system extending between the means.

17. The apparatus set forth in claim 16, wherein the conduit system includes means for connecting a vacuum source thereto.

18. The apparatus set forth in any one of claims 13 to 16, the apparatus further including:
an extractant reservoir;
means for controllably feeding extractant to a mixing tank;
a mixing tank for mixing the biological material with said extractant;
the means for feeding a mixture of extractant and biological material comprising pump means for feeding the mixture from the mixing tank to said microwave mixing tank; and, means for isolating essences from the microwave treated mixture.

19. The extraction apparatus of any one of claims 13 to 18, comprising multiple microwave applicators arranged in one of (a) series, (b) parallel or (c) a combination of (a) and (b), each applicator operating on mixture flowing in a conduit of about 1 to about 10 cm. in diameter;
means to mix extractant and material to be extracted; and, means to feed this mixture to each conduit.

20. In a method for the microwave extraction of at least one natural product from a biological material, the microwave method characterized in that the steps comprise:
placing the biological material in an enclosure and surrounding the biological material with a non-aqueous extractant;
subjecting biological material present in the enclosure to intermittent microwave irradiation to effect the evaporation of water contained in the biological material and to split cellular structures of the biological material to release the natural product therefrom;
separating residual biological material from the extracted natural product, the method further including the steps of:
utilizing reduced pressure during the microwave method;
effecting heating during the microwave method; and, obtaining natural product by conveying natural product in water vapour derived from the biological material.

21. The method according to claim 20, wherein the step of intermittent microwave irradiation includes a plurality of intermittent microwave irradiation treatments.

22. The method according to any one of the claims 20 or 21, wherein the step for the separation of the residual biological material from the extract comprises the further steps of:
- condensing water vapour containing the extracted natural product;
- collecting the resulting mixture; and, - separating the extracted natural product therefrom.

23. The method according to claim 22, wherein a part of the condensate obtained is returned to the enclosure, and there is included a step of hydro-distillation to obtain the natural product.

24. The method according to any one of the claims 20 to 23, wherein microwave treatment is conducted at a temperature of at least 15°C.

25. The method according to any one of the claims 20 to 24, wherein the microwaves used during the step of microwave irradiation have a frequency of below 30,000.

26. The method according to any one of the claims 20 to 25, wherein the step of microwave irradiation is conducted so as to apply power in a range from about 200 W
to about 10,000 W.

27. The method according to any one of claims 20 to 26, which includes the step of stirring the biological material.

28. An apparatus for extraction of a natural product from biological material in a microwave treatment system, comprising:
- an enclosure adapted to retain biological material for microwave treatment and heating of the contents therein;
- microwave generating means for generating intermittent microwave irradiation within the enclosure to effect release of the natural product;
- vacuum means to reduce pressure in the system; and, - means for recovering natural product extracted from the biological material.

29. The apparatus according to claim 28, wherein the means for recovering the natural product includes condensing means.

30. The apparatus according to claim 28 or 29, wherein there is included means for an intermittent operation of the microwave generating means.

31. The apparatus according to any one of claims 28 to 30, wherein there is included stirring means for stirring the biological material.

32. The apparatus according to any one of the claims 28 to 31, wherein the apparatus includes means enabling the rerouting of the condensed material obtained at the means for the recovery of the natural product from within the enclosure.