Patent Application
20090175985
The present invention relates to the use of silicon in food.
In the food industry, encapsulation may be used to stabilise an ingredient and to control the timing and rate of release of an ingredient. Encapsulation enables the protection of food components to ensure against nutritional loss and to mask or preserve flavours and aromas. Encapsulation also increases the stability of vitamin or mineral supplements which are normally sensitive to light, UV radiation, metals, humidity, temperature and oxygen.
In its simplest form, the encapsulant is typically a small sphere with a uniform wall around it. The material inside the sphere is often referred to as the core material, internal phase or fill, whereas the wall is sometimes called a shell, coating or membrane. However, many encapsulants bear little resemblance to these simple spheres and come in many forms.
Encapsulation techniques include the use of spray drying, spray cooling, fluidised bed technology, coacervabon and supercritical fluids. Other techniques include inclusion entrapment, which makes use of structures such as alginate beads and liposomes.
There is a continued need for alternative methods and/or products for protecting, controlling the release of, and/or masking the taste of ingredients in the food industry.
The present invention is based partly on the surprising finding that, despite being readily absorbed in many body fluids, silicon, and in particular silicon structures of high surface area, for example those greater than 1 m2/g such as mesoporous silicon, are stable in food.
In a first aspect of the present invention, food, or a food composition, comprising silicon is provided.
According to a further aspect of the present invention, there is provided a production process for said food or food composition, according to the first aspect of the present invention, comprising blending or combining said silicon and other components of the food or food composition.
According to another aspect of the present invention, the use of silicon in food for protecting and/or controlling the release of, and/or masking the taste of one or more ingredients is provided.
The silicon may be loaded with one or more ingredients. In particular, the silicon may be loaded such that the one or more ingredients are substantially fully encapsulated by or fully encapsulated by, partially encapsulated by or associated with the silicon which may be referred to as a silicon encapsulant. These ingredients may be selected from one or more of: oxygen sensitive edible oils; minerals; oxygen sensitive fats including dairy fats; oil soluble ingredients; vitamins; fragrances or aromas; flavours; enzymes; probiotic bacteria; prebiotics; nutraceuticals; amino acids; herbal extracts; herbs; plant extracts; edible acids; salt; antioxidants; therapeutic agents.
According to another aspect of the present invention, silicon, suitable for use in the first aspect of the invention, wherein the silicon is loaded with one or more of oxygen sensitive edible oils; minerals; oxygen sensitive fats including dairy fats; oil soluble ingredients; vitamins; fragrances or aromas; flavours; enzymes; probiotic bacteria; prebiotics; nutraceuticals; amino acids; herbal extracts; herbs; plant extracts; edible acids; salt; antioxidants; therapeutic agents is provided.
The one or more ingredients may be released after interaction with gastro-intestinal tract fluids such as saliva, gastric fluid or intestinal fluid.
The use of silicon according to the present invention seeks to provide one or more of the following: effective protection of ingredients to prevent loss of functionality through exposure to heat, light or moisture; an improvement in ingredient stability and/or nutritional quality; high wt % ingredient loading; a so-called burst release of aroma (particularly for use in hot beverages such as coffee); improved bioavailability for loaded ingredients; controlled release of ingredients in the intestine; a barrier to UV/blue light for photosensitive ingredients; easier handling during food processing; masking of particular tastes.
Typical etch rates (measured at about room temperature which is taken to be about 18° C.+/−4° C.) for the silicon structures in food, particularly those silicon structures comprising porous silicon, may be less than or equal to about 120 nm per day, for example less than or equal to about 80 nm per day, for example less than or equal to about 50 nm per day, for example less than or equal to about 20 nm per day or 10 nm per day. At temperatures, corresponding approximately to refrigerator temperatures (for example about 5° C.+/−1° C.), the etch rate may be less than about 10 nm per month.
The silicon being loaded with one or more ingredients includes wherein the silicon is used, in effect to coat or partially coat one or more ingredients. In particular, the silicon may be used to coat or partially coat breakfast cereals and the like or a product or products suitable for making beverages, such as coffee granules, coffee powder, tea, cocoa powder, chocolate powder. For example, when the ingredient is a microparticle (about 5-1000 μm in diameter), such as a powder or a small granule, or is a macroparticle (about 1 mm-20 mm), such as a granule or a typical cereal, said ingredient may be coated with silicon nanoparticles and/or microparticles.
As used herein, and unless otherwise stated, the term “silicon” refers to solid elemental silicon. Elemental silicon is usually described as being dark grey in colour. For the avoidance of doubt, and unless otherwise stated, it does not include silicon-containing chemical compounds such as silica, silicates or silicones, although it may be used in combination with these materials. The silicon may be about 95 to 99.99999% pure, for example about 96 to 99.9% pure. So-called metallurgical grade silicon is particularly preferred which typically has a purity of about 98 to 99.5%. The global production of metallurgical silicon is currently equal to about 1 million tons and the cost is about $2/kg.
The physical forms of silicon which are suitable for use in the present invention may be chosen from or comprise amorphous silicon, single crystal silicon and polycrystalline silicon (including nanocrystalline silicon, the grain size of which is typically taken to be 1 to 100 nm) and including combinations thereof. Any of the above-mentioned types of silicon, which are suitable for use in the present invention, may be porosified to form porous silicon, which may be referred to as “pSi”. The silicon may be surface porosified, for example, using a stain etch method or more substantially porosified, for example, using an anodisation technique. Preferred forms of porous silicon for use in the present invention are mesoporous, microporous or macroporous silicon. Microporous silicon contains pores possessing a diameter less than 2 nm; mesoporous silicon contains pores having a diameter in the range of 2 to 50 nm; and macroporous silicon contains pores having a diameter greater than 50 nm.
Preferred forms of silicon also include: submicron diameter polycrystalline particles; submicron diameter amorphous silicon particles; hollow silicon microparticles; agglomerated silicon nanoparticles; amorphous silicon coatings; micronised silicon alloys; micronised metallurgical grade silicon; cold pressed silicon particles. The silicon may be present in one or more of these forms.
The surface area and the size of the pores in the silicon may to some extent depend on the presence and the nature, of the loaded ingredient and, if appropriate, at what point in the body it is required for the ingredient to be released. For example, the BET surface area of the silicon is preferably in excess of 0.1 m2/g for microorganism entrapment, and preferably greater than 100 m2/g for biodegradability in intestinal fluid. The BET surface area is determined by a BET nitrogen adsorption method as described in Brunauer et al., J. Am. Chem. Soc., 60, p 309, 1938. The BET measurement is performed using an Accelerated Surface Area and Porosimetry Analyser (ASAP 2400) available from Micromeritics Instrument Corporation, Norcross, Ga. 30093. The sample is outgassed under vacuum at 350° C. for a minimum of 2 hours before measurement.
The average pore diameter of the silicon is preferably less than 100 μm for probiotic entrapment, since bacteria are typically 100 nm to 10 μm in size. Preferably, the average pore diameter is less than 500 nm for enzyme entrapment since protein sizes are in the range of about 5-20 nm. Preferably, the average pore diameter is less than 200 nm for improving the shelf life of oxygen sensitive nutrients. Preferably, the average pore diameter is less than 10 nm for storage of fragrances and volatile nutrients. The average pore diameter is measured using a known technique. Mesopore diameters are measured by very high resolution electron microscopy. This technique and other suitable techniques which include gas-adsorption-desorption analysis, small angle x-ray scattering, NMR spectroscopy or thermoporometry, are described by R. Herino in “Properties of Porous Silicon”, chapter 2.2, 1997. Macropore diameters are measured by electron microscopy. Alternative techniques include mercury porosimetry.
The use of silicon according to the present invention may impart a visually appealing appearance to the foods and, as such, according to a further aspect of the present invention, the use of silicon in food or a food composition for modifying the appearance of food is provided. This may include a glittering or glinting appearance. For example, PCT/GB01/03633, the entire contents of which are incorporated herein by reference, describes the use of mirrors comprising layers, which in turn comprise one or more of crystalline silicon, porous silicon, amorphous silicon and polycrystalline silicon in dermatological compositions. By using mirrors, which reflect different wavelengths of light, specific colouration of foods may be effected. This may be achieved by varying the porosities of adjacent layers comprising porous silicon between low and high porosity layers. Typically, the low porosity layers may have a porosity of up to about 65 vol %, for example about 25 vol % to 65 vol % and the high porosity layers have a porosity of at least about 60 vol %, for example about 60 vol % to 95 vol %. Each layer may comprise greater than 10 layers or greater than 100 layers, or greater than 200 layers or greater than or equal to 400 layers. Each layer from which the mirrors are formed has a different refractive index to its neighbouring layer or layers such that the combined layers form a Bragg stack mirror. Specific colours may also be imparted to silicon particles by surface porosification using stain etching or partial oxidation.
The methods for making the various forms of silicon which are suitable for use in the present invention are well known in the art.
In PCT/GB96101863, the contents of which are incorporated herein by reference in their entirety, it is described how bulk crystalline silicon can be rendered porous by partial electrochemical dissolution in hydrofluoric acid based solutions. This etching process generates a silicon structure that retains the crystallinity and the crystallographic orientation of the original bulk material. Hence, the porous silicon formed is a form of crystalline silicon. Broadly, the method involves anodising, for example, a heavily boron doped CZ silicon wafer in an electrochemical cell which contains an electrolyte comprising a 20% solution of hydrofluoric acid in an alcohol such as ethanol, methanol or isopropylalcohol (IPA). Following the passing of an anodisation current with a density of about 50 mA cm−2, a porous silicon layer is produced which may be separated from the wafer by increasing the current density for a short period of time. The effect of this is to dissolve the silicon at the interface between the porous and bulk crystalline regions. Porous silicon may also be made using the so-called stain-etching technique which is another conventional method for making porous silicon. This method involves the immersion of a silicon sample in a hydrofluoric acid solution containing a strong oxidising agent. No electrical contact is made with the silicon, and no potential is applied. The hydrofluoric acid etches the surface of the silicon to create pores.
Following its formation, the porous silicon may be dried. For example, it may be supercritically dried as described by Canham in Nature, vol. 368, (1994), pp 133-135. Alternatively, the porous silicon may be freeze dried or air dried using liquids of lower surface tension than water, such as ethanol or pentane, as described by Bellet and Canham in Adv. Mater, 10, pp 487-490, 1998.
Silicon hydride surfaces may, for example, be generated by stain etch or anodisation methods using hydrofluoric acid based solutions. When the silicon, prepared, for example, by electrochemical etching in HF based solutions, comprises porous silicon, the surface of the porous silicon may or may not be suitably modified in order, for example, to improve the stability of the porous silicon in the food or food composition. In particular, the surface of the porous silicon may be modified to render the silicon more stable in alkaline conditions. The surface of the porous silicon may include the external and/or internal surfaces formed by the pores of the porous silicon.
In certain circumstances, the stain etching technique may result in partial oxidation of the porous silicon surface. The surfaces of the porous silicon may therefore be modified to provide: silicon hydride surfaces; silicon oxide surfaces wherein the porous silicon may typically be described as being partially oxidised; or derivatised surfaces which may possess Si—O—C bonds and/or Si—C bonds.
Silicon hydride surfaces may be produced by exposing the porous silicon to HF.
Silicon oxide surfaces may be produced by subjecting the silicon to chemical oxidation, photochemical oxidation or thermal oxidation, as described for example in Chapter 5.3 of Properbes of Porous Silicon (edited by L. T. Canham, IEE 1997). PCT/GB02/03731, the entire contents of which are incorporated herein by reference, describes how porous silicon may be partially oxidised in such a manner that the sample of porous silicon retains some porous silicon in an unoxidised state. For example, PCT/GB02/03731 describes how, following anodisation in 20% ethanoic HF, the anodised sample was partially oxidised by thermal treatment in air at 50° C. to yield a partially oxidised porous silicon sample.
Following partial oxidation, an amount of elemental silicon will remain. The silicon particles may possess an oxide content corresponding to between about one monolayer of oxygen and a total oxide thickness of less than or equal to about 4.5 nm covering the entire silicon skeleton. The porous silicon may have an oxygen to silicon atomic ratio between about 0.04 and 2.0, and preferably between 0.60 and 1.5. Oxidation may occur in the pores and/or on the external surface of the silicon. Derivatised porous silicon is porous silicon possessing a covalently bound monolayer on at least part of its surface. The monolayer typically comprises one or more organic groups that are bonded by hydrosilylation to at least part of the surface of the porous silicon. Derivatised porous silicon is described in PCT/GB00/01450, the contents of which are incorporated herein by reference in their entirety. PCT/GB00/01450 describes derivatisation of the surface of silicon using methods such as hydrosilyation in the presence of a Lewis acid. In that case, the derivatisation is effected in order to block oxidation of the silicon atoms at the surface and so stabilise the silicon. Methods of preparing derivatised porous silicon are known to the skilled person and are described, for example, by J. H. Song and M. J. Sailor in Inorg. Chem. 1999, vol 21, No. 1-3, pp 69-84 (Chemical Modification of Crystalline Porous Silicon Surfaces). Derivitisation of the silicon may be desirable when it is required to increase the hydrophobicity of the silicon, thereby decreasing its wettability. Preferred derivatised surfaces are modified with one or more alkyne groups. Alkyne derivatised silicon may be derived from treatment with acetylene gas, for example, as described in “Studies of thermally carbonized porous silicon surfaces” by J. Salonen et al in Phys Stat. Solidi (a), 182, pp 123-126, (2000) and “Stabilisation of porous silicon surface by low temperature photoassisted reaction with acetylene”, by S. T. Lakshmikumar et al in Curr. Appl. Phys. 3, pp 185-189 (2003).
Methods for making silicon powders such as silicon microparticles and silicon nanoparticles are well known in the art. Silicon microparticles are generally taken to mean particles of about 5 to 1000 μm in diameter and silicon nanoparticles are generally taken to mean particles possessing a diameter of about 100 nm and less. Silicon nanoparticles therefore typically possess a diameter in the range of about 1 nm to about 100 nm, for example about 10 nm to about 100 nm. Fully biodegradable mesoporous silicon typically has an interconnected silicon skeleton with widths in the 2-5 nm range. These methods for making silicon powders are often referred to as “bottom-up” methods, which include, for example, chemical synthesis or gas phase synthesis. Alternatively, so-called “top-down” methods refer to such known methods as electrochemical etching or comminution (e.g. milling as described In Kerkar et al. J. Am. Ceram. Soc., vol. 73, pages 2879-2885, 1990.). PCT/GB02/03493 and PCT/GB01103633, the contents of which are incorporated herein by reference in their entirety, describe methods for making particles of silicon, said methods being suitable for making silicon for use in the present invention. Such methods include subjecting silicon to centrifuge methods, or grinding methods. Porous silicon powders may be ground between wafers or blocks of crystalline silicon. Since porous silicon has lower hardness than bulk crystalline silicon, and crystalline silicon wafers have ultrapure, ultrasmooth surfaces, a silicon wafer/porous silicon powder/silicon wafer sandwich is a convenient means of achieving for instance, a 1-10 μm particle size from much larger porous silicon particles derived, for example, via anodisation.
The surface of silicon particles prepared by “top down” or “bottom up” methods may also be a hydride surface, a partially oxidised surface, a fully oxidised surface or a derivatised surface. Milling in an oxidising medium such as water or air will result in silicon oxide surfaces. Milling in an organic medium may result in, at least partial derivatisation of the surface. Gas phase synthesis, such as from the decomposition of silane, will result in hydride surfaces. The surface may or may not be suitably modified in order, for example, to improve the stability of the particulate silicon in the food or food composition.
Particle size distribution measurements, including the mean particle size (d50/μm) of the silicon particles are measured using a Malvem Particle Size Analyzer, Model Mastersizer, from Malvem Instruments. A helium-neon gas laser beam is projected through a transparent cell which contains the silicon particles suspended in an aqueous solution. Light rays which strike the particles are scattered through angles which are inversely proportional to the partide size. The photodetector array measures the quantity of light at several predetermined angles. Electrical signals proportional to the measured light flux values are then processed by a microcomputer system, against a scatter pattern predicted from theoretical particles as defined by the refractive indices of the sample and aqueous dispersant to determine the particle size distribution of the silicon.
Other examples of methods suitable for making silicon nanoparticles include evaporation and condensation in a subatmospheric inert-gas environment. Various aerosol processing techniques have been reported to improve the production yield of nanoparticles. These include synthesis by the following techniques: combustion flame; plasma; laser abalation; chemical vapour condensation; spray pyrolysis; electrospray and plasma spray. Because the throughput for these techniques currently tends to be low, preferred nanoparticle synthesis techniques include: high energy ball milling; gas phase synthesis; plasma synthesis; chemical synthesis; sonochemical synthesis.
The preferred methods of producing silicon nanopartides are described in more detail.
High energy ball milling, which is a common top-down approach for nanoparticle synthesis, has been used for the generation of magnetic, catalytic, and structural nanoparticles, see Huang, “Deformation-induced amorphization in ball-milled silicon”, Phil. Mag. Lett., 1999, 79, pp 305-314. The technique, which is a commercial technology, has traditionally been considered problematic because of contamination problems from ball-milling processes. However, the availability of tungsten carbide components and the use of inert atmosphere and/or high vacuum processes has reduced impurities to acceptable levels.
Particle sizes in the range of about 0.1 to 1 μm are most commonly produced by ball-milling techniques, though it is known to produce particle sizes of about 0.01 μM.
Ball milling can be carried out in either “dry” conditions or in the presence of a liquid, i.e. “wet” conditions. For wet conditions, typical solvents include water or alcohol based solvents. The present inventors have found that, for use in connection with the present invention, isopropanol or water are particularly useful. This usefulness is partly based on the subsequent ability of the silicon to agglomerate, which may be of particular use in encapsulating certain ingredients, such as bacteria.
Silane decomposition provides a very high throughput commercial process for producing polycrystalline silicon granules. Although the electronic grade feedstock (currently about $30/kg) is expensive, so called “fines” (microparticles and nanoparticles) are a suitable waste product for use in the present invention. Fine silicon powders are commercially available. For example, NanoSi™ Polysilicon is commercially available from Advanced Silicon Materials LLC and is a fine silicon powder prepared by decomposition of silane in a hydrogen atmosphere. The particle size is 5 to 500 nm and the BET surface area is about 25 m2/g. This type of silicon is particularly useful in the present invention because it has a strong tendency to agglomerate, reportedly due to hydrogen bonding and Van der Waals forces. This agglomeration results in a high surface area form of silicon which is useful for the loading of ingredients therein in a similar manner as porous silicon is when produced by known, for example, electrochemical techniques.
Plasma synthesis is described by Tanaka in “Production of ultrafine silicon powder by the arc plasma method”, J. Mat. Sci., 1987, 22, pp 2192-2198. High temperature synthesis of a range of metal nanoparticles with good throughput may be achieved using this method. Silicon nanoparticles (typically 10-100 nm diameter) have been generated in argon-hydrogen or argon-nitrogen gaseous environments using this method.
Solution growth of ultra-small (<10 nm) silicon nanoparticles is described in US 20050000409, the contents of which are incorporated herein in their entirety. This technique involves the reduction of silicon tetrahalides such as silicon tetrachloride by reducing agents such as sodium napthalenide in an organic solvent. The reactions lead to a high yield at room temperature.
In sonochemistry, an acoustic cavitation process can generate a transient localized hot zone with extremely high temperature gradient and pressure. Such sudden changes in temperature and pressure assist the destruction of the sonochemical precursor (e.g., organometallic solution) and the formation of nanoparticles. The technique is suitable for producing large volumes of material for industrial applications. Sonochemical methods for preparing silicon nanoparticles are described by Dhas in “Preparation of luminescent silicon nanoparticles: a novel sonochemical approach”, Chem. Mater., 10, 1998, pp 3278-3281.
Lam et al have fabricated silicon nanoparticles by ball milling graphite powder and silica powder, this process being described in J. Crystal Growth 220(4) p 466-470 (2000), which is herein incorporated by reference in its entirety. Arujo-Andrade et al have fabricated silicon nanoparticles by mechanical milling of silica powder and aluminium powder, this process being described in Scripta Materialia 49(8) p 773-778 (2003).
Silicon microparticles or nanoparticles may be transformed into a porous agglomerated form by thermal processing, compression techniques or by the application of centrifugal forces. The agglomerated forms comprise a unitary body with macropores and/or mesopores and/or micropores.
PCT/GB2005001910 the contents of which are incorporated herein in their entirety describes how particulate silicon, which may or may not be porous, may be consolidated to form a multiplicity of bonded silicon particles typically under the influence of pressure. The pressure may, for example be applied uniaxially or isostatically. Typical uniaxial pressures may be in the range of 10 MPa to 5000 MPa and the isostatic pressure may be in the range of 10 MPa to 5000 MPa.
The consolidation may be carried out such that the unitary body or silicon structure formed possesses a surface area greater than 100 cm2/g and preferably greater than 1 m2/g.
The consolidation of the silicon particulate product may result in a porous unitary body, the pores being formed from the spaces between the bonded silicon particles. However, and as mentioned above, the free silicon particles may themselves be porous prior to consolidation, for example by the use of stain etching or anodisation techniques.
The consolidated product or so-called unitary body may itself be further porosified by anodisation or stain etching and/or may be fragmented. Fragmentation techniques include mechanical crushing or the use of ultrasonics.
The formation of the unitary body may be carried out within a selected temperature range. Cold pressing means that the consolidation is carried out up to a temperature of about 50° C. and from as low as 50° C.
The surface area of a silicon unitary body formed by a cold pressing technique may be high, relative to that of a silicon unitary body formed by a hot pressing technique. This is because hot pressing can result in rearrangement of the surface silicon atoms, causing cavities and defects to be removed.
The consolidation process may comprise combining the particulate silicon prior, and/or during and/or after consolidation with the ingredient or ingredients to be loaded in such a manner that the ingredient is located in the pores between the bonded silicon particles.
The food may be in the form of a beverage or non-beverage. Suitable foods for use in the present invention may comprise one or more of the following: meat; poultry; fish; vegetables; fruit; chocolate and confectionary; cereals and baked products including bread, cakes, biscuits, nutrition bars; pastry; pasta; dairy products such as milk, cream, butter, margarine, eggs, ice cream, cheese. The food may be in the form of any of the following: convenience meals; frozen food; chilled food; dried food; freeze dried food; rehydrated food; pickles; soups; dips; sauces.
Suitable beverages include alcoholic and non-alcoholic beverages. Particular examples of suitable drinks include water, for example bottled water; tea; coffee; cocoa; drinking chocolate; fruit juices and smoothies; wine; beer; ales; lager; spirits. The beverages may for example be in the form of granules, including those which have been freeze dried, which are suitable for making instant coffee and tea and the like. As such, the present invention extends to products suitable for making beverages, such as instant beverage powders and granules. These include coffee granules, coffee powder, coffee tablets, tea, cocoa powder, chocolate powder. Other suitable products include coffee oil and concentrates, for example, fruit juice concentrates.
The pH of the food is preferably such that the silicon does not dissolve in the food over a significant period of time and will thus afford an acceptable shelf-life. The pH of the food is typically less than or equal to about 7.5 and preferably less than or equal to about 7 or preferably less than or equal to about 6 and even more preferably less than about 4.6. The lower limit of pH may typically be about 2. For macroporous silicon and micronised metallurgical grade silicon, the typical pH range is 2 to 9 and for mesoporous and silicon nanoparticles, the typical pH range is 2 to 6.
In order to realise the etch rates referred to herein in the “Summary of Invention”, the pH of the food is preferably less than or equal to about 7.5 and preferably less than or equal to about 7.
Preferably, the silicon is present in the food with one or more loaded ingredients. Typically, the one or more ingredients are present in the range, in relation to the loaded silicon, of 0.01 to 60 wt %, for example 1 to 40 wt % and for example 2 to 10 wt %. The ingredients may be selected from at least one of the following: oxygen sensitive edible oils; minerals; oxygen sensitive fats including dairy fats; oil soluble Ingredients; vitamins; fragrances or aromas; flavours; enzymes; probiotic bacteria; prebiotics; nutraceuticals; amino acids; herbal extracts; herbs; plant extracts; edible acids; salt; antioxidants.
Oxygen sensitive edible oils include polyunsaturated fatty acids which themselves include canola oil, borage oil, evening primrose oil, safflower oil, sunflower oil, pumpkinseed oil, rosemary oil, rice bran oil, flaxseed oil, wheatgerm oil, grapeseed oil, linseed oil. Some of these oils contribute linoleic acid, alpha-linoleic acid, oleic acid, palmitic acid, stearic acid. Also included are marine oils, for example, those derived from fish such as tuna, herring, mackerel, sardine, cod liver and shark.
Preferably, in order to delay oil degradation, the silicon comprises nanometre sized pores (including porous silicon and agglomerated silicon nanoparticles).
Suitable minerals include: macrominerals comprising Ca, P, Mg, Na, K; microminerals comprising Fe, Zn, Cu, Se, Cr, I, Mn, Mo, F. Suitable trace elements include Ni, V, B, Co.
The blending and compression of particular metal powders with silicon powder may be used to create edible microbatteries. Following ingestion, the gastrointestinal fluid acts as an electrolyte. If the metal is less noble than silicon then the resulting galvanic coupling increases the dissolution of that metal resulting in increased bioavailability.
Suitable vitamins include Ascorbic Acid, Beta-carotene, Biotin, Choline, Folic Acid, Niacin, Pantothenic Acid (Vitamin B5), Phylloquinone (Vitamin K), Pyridoxine (Vitamin B6), Riboflavin (Vitamin B2), Thiamin (Vitamin B1), Vitamin A, Vitamin B12, Vitamin D, Vitamin E and mixtures thereof. The vitamin and silicon may be combined by allowing the vitamin to impregnate the silicon, optionally in the presence of gentle heat, typically in the range of 40° C. and 200° C.
Suitable fragrances, aromas and flavours are non-toxic and suitable for foodstuffs and will be readily apparent to the skilled person, see Bauer et al, “Common Fragrances & Flavours”, Wiley, 1997, pp 278. Preferred fragrances, aromas and flavours are “Generally Recognised As Safe” (GRAS) by the FDA. Alcohols, aldehydes, ketones, esters and lactones are classes of compounds most frequently used in natural and artificial fragrances.
More specifically, suitable flavours (or flavouring agents) include: one or more of spice oleoresins derived from allspice, basil, capsicum, cinnamon, cloves, cumin, dill, garlic, marjoram, nutmeg, paprika, black pepper, rosemary and tumeric; essential oils such as anise oil, caraway oil, clove oil, eucalyptus oil, fennel oil, garlic oil, ginger oil, peppermint oil, onion oil, pepper oil, rosemary oil, spearmint oil; citrus oils including orange oil, lemon oil, bitter orange oil and tangerine oil; alliaceous flavours which include garlic, leek, chive, and onion; botanical extracts such as arnica flower extract, chamomile flower extract, hops extract, and marigold extract; botanical flavour extracts such as blackberry, chicory root, cocoa, coffee, kola, liquorice root, rose hips, sarsaparilla root, sassafras bark, tamarind and vanilla extracts; protein hydrolysates such as hydrolyzed vegetable protein (HVP's), meat protein hydrolyzates, milk protein hydrolyzates; natural and artificial compounded flavours which include those disclosed in S. Heath, Source Book of Flavours, Avi Publishing Co., Westport, Conn., 1981, pp. 149-277. Particular flavour compounds are, for example: benzaldehyde, diacetyl (2,3-butanedione), vanillin, ethyl vanillin and citral (3,7-dimethyl-2,6-octadienal). The flavouring agent may be in the form of an oil, aqueous solution, non-aqueous solution or an emulsion. Flavour essences, i.e. the water soluble fraction derived from fruit or citrus can be utilized, and typically at lower levels than the ingredients mentioned above.
Preferably, with regard to fragrant oils, sustained release is carried out using microporous silicon or mesoporous silicon possessing a pore diameter in the range of about 1-10 nm. The small pore size suppresses the release of the fragrant volatiles.
Preferred food aromas (or aromatising agents) include food aromas for liquid food products, particularly instant soups and beverages such as coffee. Other suitable food aromas include those used in desserts such as instant puddings, and frozen food products such as frozen pizza. The food aromas may also be those suitable for use in food which needs to be reconstituted with hot water or milk or heated by the consumer prior to consumption. Suitable food aromas include the following: cheese aroma; aromas for hot soluble coffee-based beverages such as coffee, hazelnut, amiaretto, chocolate, cream and vanilla; aromas for hot soluble tea-based beverages such as raspberry, cream and vanilla; aromas for hot cocoa-based beverages such as raspberry, amaretto, cream, chocolate and vanilla; aromas for hot soups such as mushroom, tomato, beef and chicken; aromas for beverages such as coffee, tea, cherry, grape, and strawberry; aromas for dessert products such as raspberry, chocolate, butterscotch, cherry, grape, strawberry, banana, and vanilla; aromas for other products such as cream, seafood, meat, garlic and onion. The aroma flavour may be part of an aromatizing composition which may optionally also include one or more other constituents such as a non-volatile edible fat or oil, a surfactant, a wetting agent, a foaming agent, an extremely volatile solvent, a propellant, dissolved edible solids, an antioxidant, or an aroma precursor. The total amount of such additional constituents will preferably not usually be more than about 40% by weight, based on the total weight of the silicon and aroma constituents. Suitable non-volatile edible fats or oils include coffee oil or triglyceride oils used as a source of flavour or as a flavour solvent. A surfactant may also be present which acts as a spreading agent or emulsifier to control the droplet size of the aromatizing composition and its degree of spreading on the surface of a food product. Suitable highly volatile solvents such as acetone and acetaldehyde may be used as a co-solvent for the volatile food aroma and modify the rate of evaporation of the aroma delivery system. A dissolved or entrapped propellant gas such as air, nitrogen, carbon dioxide, nitrous oxide, or a gas generator such as a chemical carbonation reagent, may be included to increase buoyancy or to accelerate aroma release and evaporation. Dissolved edible solids increase the viscosity of the composition. Antioxidant additives such as butylated hydroxyanisole, butylated hydroxyl toluene, tertiary butylhydroquinone, vitamins A, C and E and derivatives, and various plant extracts such as those containing carotenoids, tocopherols or flavonoids having antioxidant properties, may be included to increase the shelf-life of the aromatized carrier. Aroma precursors that would not react during storage but would react to generate aroma during food preparation may also be included in the aromatizing composition.
The production of dehydrated food compositions often involves processing conditions such as elevated temperature, which often causes loss of desirable food aroma. One known technique of overcoming such loss is to add additional aroma and flavour to dehydrated foodstuffs and beverages. Such aromas and flavours are usually complex, comprising many organoleptically active compounds, which combine to create the characterizing aroma of the product. Since aromas and flavours are often extremely powerful and unstable in their undiluted state, they are combined with a carrier to render them more stable and easier to handle. The carriers are preferably neutral or complementary in organoleptic impact and do not contribute to the characterizing aroma of the product. Desirable characteristics of carriers for liquid systems include blandness and miscibility with other liquid carriers and with liquid aromas. Traditional carriers include ethanol, propylene glycol, glycerol, vegetable oil, benzyl alcohol, triacetin, tripropionin, triethyl citrate, and tributyrin.
The aroma constituent of an aromatizing composition characterizes its aroma, i.e., the innate quality that gives the aroma its special attributes among and over other aromas. The aroma constituent may, and often does, include a plurality of aroma ingredients which together result in the characterizing aroma. When a preparation aroma is desired upon rehydration of such flavours and aromas in a dehydrated food or beverage, such compositions are limited in effectiveness because of poor aroma release. When a solid carrier is used, the release of aroma is poor because the diffusion of rehydrating liquid into the particle during rehydration inhibits the counter-diffusion of aroma out. In this way the vast majority of the characterizing aroma constituents end up in the rehydrating liquid. An aroma burst can be obtained by increasing the loading of characterizing aroma constituents into the carrier but this typically leads to an overwhelmingly strong or unbalanced flavour in the product when consumed.
Likewise, poor aroma release is obtained when traditional liquid carriers are used, whether or not they are encapsulated. Those which are water-soluble, suffer the same problems as with soluble solid carriers. The flux of water into the carrier inhibits the diffusion of the aromas out. Furthernore many carriers have a density greater than 1.0 g/cc so they sink in the product during hydration and aromas are released into the rehydrating liquid rather than being released at the surface to effect preparation aroma. Finally, those conventional carriers which do float and are insoluble in water are of an oily or fatty nature. Though these can be arranged to release aroma at the surface they leave an unsightly and often organoleptically and visually undesirable “slick” at the surface of the product.
Natural essential oils from botanical sources are typically intensely flavoured and naturally aromatic due to their inherent volatility. This makes them an ideal choice as aromatizing constituents for use in the manufacture of food products. Unfortunately, volatile essential oils do not exist in all food sources used to manufacture food products. In addition, essential oils that do occur naturally in some foods are often not sufficiently abundant or readily extracted to permit their economical use in processed foods, and some are not approved for food use. Furthermore, many processed foods, due to their intended use, are not able to be manufactured with natural food ingredients that may contain essential oils.
Instant beverage powders typically must quickly and completely dissolve in water without producing insoluble floating or suspended matter or sediment in order to be acceptable to the consumer, and foods or ingredients derived from foods that do contain naturally occurring volatile oils are often not completely water soluble. In response to these limitations, natural or synthetic flavouring agents are typically used to impart the desired character and identity to such food products. In many cases, especially when economically flavoured, the flavouring agent may contain a natural essential oil, such as encapsulated orange oil powders which are used to flavour imitation or orange-flavoured instant beverages. Orange oil is readily and economically pressed from discarded orange peels.
One well known example of food processing that results in loss of aroma is the manufacture of “instant” (or soluble) coffee powder. Unless additional steps are taken in its manufacture, there is very little aroma associated with hot coffee beverages prepared from instant coffee powder relative to the aroma of hot coffee beverages prepared by brewing roast and ground coffee. Many attempts have been made to enhance the aroma of instant coffee products, including the use of particular types of coffee beans, the use of particular coffee roasting conditions, and the addition of coffee aroma. A particular problem which has been noted in connection with instant coffee is the relative lack of coffee aroma that is generated at the time that a hot instant coffee beverage is prepared compared to the coffee aroma that is generated when brewing coffee. This problem of poor preparation aroma (i.e., poor aroma burst or “above-cup aroma” at the time of preparation of an instant coffee beverage) is noted in U.S. Pat. No. 5,399,368 (U.S. Pat. No. '368) and in U.S. Pat. No. 5,750,178 (U.S. Pat. No. '178). Each of these patents, the contents of which are incorporated herein in their entirety by reference, describes several prior art attempts to provide an initial burst of above-cup coffee aroma, such as by coating soluble coffee powder with an aqueous emulsion of an aromatic coffee substance, or by employing particulate aromatized coffee glass. It is reported in U.S. Pat. No. '368 and U.S. Pat. No. '178 that these and other previously known procedures had not been successful in achieving good preparation aroma. U.S. Pat. No. '368 proposes a method of coextruding capsule particles in which a liquid core material containing aromatized coffee oil is encapsulated within a shell of hardened coffee glass. The shell encapsulates a core of aromatized coffee oil saturated with an inert gas under pressure. U.S. Pat. No. '178 also describes known techniques for aromatizing instant coffee and notes that techniques which may provide good package aroma (i.e., aroma in a coffee container) do not provide good preparation aroma. U.S. Pat. No. '178 reports that the method of U.S. Pat. No. '368 provides excellent entrapment of the aroma but that complex machinery and careful control are required. U.S. Pat. No. '178 proposes a modified method of preparing the aromatized coffee capsule particles which method is said to have the advantage of simplicity.
The amount of preparation aroma which can be achieved by incorporating aromatized coffee particles, such as those described in U.S. Pat. No. '368 and U.S. Pat. No. '178, in an instant coffee product, depends in part on the amount of such particles employed. Good preparation aroma can be achieved by employing a sufficient amount of the aromatized capsules. However, the more capsules that are employed, the more capsule material, particularly coffee oil, that is introduced. The added coffee oil accumulates as an oil film on the surface of the coffee beverage. Such oil films are readily apparent and are widely known to impair consumer acceptance of instant coffee.
The present invention provides good food preparation aroma without necessarily requiring the use of natural essential oils or the use of amounts of other ingredients, such as vegetable oils, that would adversely affect the properties of foods.
Silicon, in the form of high porosity micron sized particles is particularly useful in the delivery of a burst of aroma. The porosity of the silicon may be such that the silicon floats on the surface of the beverage thereby releasing the aroma in the desired “above-cup” location. HF etched porous silicon is also useful in this respect—not only can it be made highly porous and micron sized but it may also be hydrophobic. The high temperature (e.g. 70-100° C.) of the beverages provide so-called burst release of volatile aromas previously entrapped at room temperature within the mesopores or micropores. The silicon carrier structure need not be water soluble on the timescales needed for aroma release and hence does not need to be fully porous.
The use of silicon according to the present invention provides one or more of the following attributes: tunable density to ensure aroma released from floating not submerged particles; non-toxic nature with full or partial biodegradability into silicic acid; non-oily nature thereby avoiding undesirable “slick” on drink surface; hydrophobicity and nanoscale porosity.
Suitable enzymes are selected from the classes of carbohydrases, pectic enzymes, celluloses, proteases, oxidases, and lipases. Examples include amylase, bromelain, catalase, ficin, glucoamylase, glucose isomerase, glucose oxidase, invertase, lactase, lipase, papain, pepsin, pullulanase and rennet.
Probiotics are dietary supplements containing potentially beneficial microorganisms or bacteria. More specifically, probiotic refers to microorganisms that form at least a part of the transient or endogenous flora and thereby exhibit a beneficial prophylactic and/or therapeutic effect on the host organism. The prophylactic and/or therapeutic effect of a lactic acid-producing bacteria suitable for use in the present invention may result, in part, from a competitive inhibition of the growth of pathogens due to one or more of the following: (i) superior colonizabon abilities; (ii) parasitism of undesirable microorganisms; (iii) the production of lactic acid and/or other extracellular products possessing anti-microbial activity. A probiotic bacteria which is suitable for use in the present invention may advantageously possess one or more of the following characteristics: (i) the ability to produce lactic acid; (ii) beneficial function within the gastrointestinal tract; (iii) non-pathogenic. Lactic acid production markedly decreases the pH (i.e., increases acidity) within the local micro-floral environment and does not contribute to the growth of many undesirable, physiologically-deleterious bacteria and fungi. Thus, by the mechanism of lactic acid production, the probiotic inhibits growth of competing pathogenic bacteria. Typical lactic acid-producing bacteria which are useful as probiotics in the present invention include efficient lactic acid producers such as non-pathogenic members of the Bacillus genus which produce bacteriocins or other compounds which inhibit the growth of pathogenic organisms. Exemplary lactic acid-producing, non-pathogenic Bacillus species Include, but are not limited to: Bacillus coagulans; Bacillus coagulans Hammer, and Bacillus brevis subspecies coagulans.
Examples of lactic acid-producing Lactobacillus species include, but are not limited to: Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus DDS-1, Lactobacillus GG, Lactobacillus rhamnosus, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus gasserii, Lactobacillus jensenii, Lactobacillus delbruekii, Lactobacillus, bulgaricus, Lactobacillus salivarius and Lactobacillus sporogenes (also designated as Bacillus coagulans). Exemplary lactic acid-producing Sporolactobacillus species include all Sporolactobacillus species, for example, Sporolactobacillus P44.
Examples of lactic acid-producing Bifidiobacterium species include, but are not limited to: Bifidiobacterium adolescentis, Bifidiobacterium animalis, Bifidiobacterium bifidum, Bifidiobacterium bifidus, Bifidiobacterium breve, Bifidiobacterium infantis, Bifidiobacterium infantus, Bifidiobacterium longum, and any genetic variants thereof.
The Bacillus species, particularly those species having the ability to form spores (e.g., Bacillus coagulans), are preferred for use in the present invention. The ability to sporulate makes these bacterial species relatively resistant to heat and other conditions, provides for a long shelf-life in product formulations, and is ideal for survival and colonization of tissues under conditions of pH, salinity, and the like within the gastrointestinal tract. Moreover, additional useful properties of many Bacillus species include being non-pathogenic, aerobic, facultative and heterotrophic, thus rendering these bacterial species safe and able to readily colonize the gastrointestinal tract.
A prebiotic is a natural or synthetic substance that supports the growth of and/or nurtures probiotics. More specifically the prebiotic is a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon. They are typically carbohydrates of relatively short length. Examples are the inulin-type fructans such as lactulose and inulin.
A nutraceutical ingredient provides medical or health benefits, including the prevention and treatment of disease. In general, a nutraceutical is specifically adapted to confer a particular health benefit on the consumer. Suitable nutraceuticals for use in the present invention may be selected from Aloe Vera (Aloe ferox, A. barbadensis), Artichoke, Asian Ginseng (Panax ginseng), Astragalus, Bee Pollen, Bilberry (Vaccinium myrtillus), Black Cohosh, Capsicum-Cayenne, Hot Pepper (Capsicum species), Cascara Sagrada (Rhamnus purshiana), Cat's Claw (Uncaria tomentosa), Chamomile (Matricaria recutita), Cranberry, Dandelion (Taraxacum officinale), Donq Quai (Angelica sinensis), Echinacea (Echinacea purpurea and related species), Evening Primrose Oil (Oenothera biennis), Feverfew (Tanacetum parthenium), Fructo-oligosaccharides, Garlic (Allium sativum), Ginger (Zingiber officinale), Ginkgo (Ginkgo biloba), Ginseng, Glucarate, Glucosamine, Goldenseal (Hydrastis canadensis), Gotu Kola (Centella Asiatica), Grape Seed Extract, Green Tea, Guarana (Paullinacupana), Hawthorne (Crataegus oxyacantha), Inositol, Inulin, Isoflavones, Kava Kava (Piper methysticum), L-carnitine, Lecithin, Licorice (Glycyrrhiza glabra and G. uralensis), Lycopene, Milk Thistle (Silybum marianum), Mod. Citrus Peel, Nettles, Oligofructose, Omega-3s, Passiflora, Passion Flower (Passiflora incamata), Pau d'Arco, (Tabebuia impetiginosa), Peppermint (Mentha piperita), Phospholipids, Polyphenol, Psyllium (Plantago ovata and P. Major), Pycnogenol, Queroetin D-llmonene, Reishi, Ribonucleic Acid, Royal Jelly, St. John's Wort (Hypericum perforatum), Saw Palmetto (Serenoa repens; Sabal serrulata), Schisandra, Soybean Isoflavones, Tumeric Valerian (Valeriana officinalis) and mixtures thereof.
Suitable amino acids for use in the present invention may be selected from Alanine, Arginine, Aspartic Acid, Asparagine, Carnitine, Cysteine, Cystine, Glutamic Acid, Glutamine, Glutathione, Glycine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Ornithine, Phenylalanine, Proline, Serine, Taurine, Threonine, Tryptophan, Tyrosine, Valine and mixtures thereof.
Suitable plant extracts include one or more plant sterols, these include beta-sitosterol, campesterol, stigmasterol. Suitable plant stanols include sitostanol, octacosanol, policosanol.
Suitable herbs include black walnut, burdock, chamomile, comfrey, Echinacea, eucalyptus, hawthorn, hyssop, ginkgo, hyssop, lemon balm, milk thistle, mullein, peppermint, psyllium, sage, saw palmetto, sheep sorrel, slippery elm, St John's Wort, thyme, turkey rhubarb, valerian, vitex.
Herbs suitable for use for medicinal purposes are described in The Natural Pharmacy by M. Polunin & C. Robbins (Dorling Kindersley 1999), 144 pp. In particular, pages 30-131 list suitable herbs. Suitable culinary herbs are described in Food Commodities, 2nd Edition pp 158-163 by B. Davis (Butterworth Heinemann 1994).
Suitable edible acids for use in the present invention may be selected from citric acid, ascorbic acid, malonic acid, acetic acid, tartaric acid, sorbic acid, fumaric acid, malic acid, phosphoric acid, succinic acid and nicotinic acid.
Suitable antioxidants for use in the present invention may be selected from sodium carbonate, calcium carbonate, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), lecithins, sodium lactate, calcium lactate, calcium malate and ammonium citrate.
Methods for incorporating the silicon into food are numerous. Suitable mixing equipment for use in the present invention is diverse and includes, for example, screw mixers, ribbon mixers and pan mixers. Other examples include high speed propeller or paddle mixers for liquid food or beverages; tumble mixers for dry powders; Z-blade mixers for doughs and pastes. Suitable grinding machines include hammer, disc, pin and ball millers. Extrusion is an important very high throughput (about 300-9000 kg/hr) technique for mixing and providing shape to foodstuffs and is suitable for use in the present invention. Cold and hot extruders may be used. These can be single or twin screw. Extruded foods include cereals, pasta, sausages, sugar or protein based products.
The ingredient may be combined with the silicon prior and/or during and/or after the mixing process.
The ingredient or ingredients may be loaded onto and/or into the silicon in various ways. For example, the one or more ingredients may be deposited onto the surface of the silicon particles, incorporated into the pores of porous silicon, incorporated into the pores formed by the agglomeration or consolidation of silicon particles (particularly nanoparticles) or bound or otherwise associated with the surface of the silicon. For example, the silicon may be used, in effect to coat or partially coat one or more ingredients. In particular, the silicon may be used to coat or partially coat breakfast cereals or a product or products suitable for making beverages, such as coffee granules, coffee powder, tea, cocoa powder, chocolate powder. Suitable methods for loading the ingredient with the silicon include the techniques of pan coating, fluidised bed, spray drying, spray chilling, enrobing, dusting/breading, co-extrusion. Of these physical methods, spray drying of a silicon suspension is preferred. These are all well known techniques, details of which may be found in standard texts, for example, for a number of these techniques see Food Processing Technology, Principles and Practice by P J Fellows, second edition, Woodhead Publishing Ltd.
The ingredient to be loaded with the silicon may be dissolved or suspended in a suitable solvent, and silicon particles may be incubated in the resulting solution for a suitable period of time. Both aqueous and non-aqueous slips have been produced from ground silicon powder and the processing and properties of silicon suspensions have been studied and reported by Sacks in Ceram. Eng. Sci. Proc., 6, 1985, pp 1109-1123 and Kerkar in J. Am. Chem. Soc. 73, 1990, pp 2879-85. The removal of solvent will result in the ingredient being deposited on the surface of the silicon particles. However, if the particles comprise porous silicon, or agglomerated or consolidated particles (for example, agglomerated or consolidated nanoparticles) of silicon the solution of the ingredient will penetrate into the pores of the silicon by capillary action, and, following solvent removal, the ingredient will be present in the pores. Preferred solvents are water, ethanol, and isopropyl alcohol, GRAS solvents and volatile liquids amenable to freeze drying.
Higher levels of loading, for example, at least about 15 wt % of the loaded ingredient based on the loaded weight of the silicon may be achieved by performing the impregnation at an elevated temperature. For example, loading may be carried out at a temperature which is at or above the melting point of the ingredient to be loaded. Quantification of gross loading may conveniently be achieved by a number of known analytical methods, including gravimetric, EDX (energy-dispersive analysis by x-rays), Fourier transform infra-red (FTIR), Raman spectroscopy, UV spectrophotometry, titrimetric analysis, HPLC or mass spectrometry. If required, quantification of the uniformity of loading may be achieved by techniques that are capable of spatial resolution such as cross-sectional EDX, Auger depth profiling, micro-Raman and micro-FTIR.
The loading levels can be determined by dividing the volume of the ingredient taken up during loading (equivalent to the mass of the ingredient taken up divided by its density) by the void volume of the porous silicon prior to loading multiplied by one hundred
The total quantity of silicon present in the food according to the present invention, may be about 0.01 to 50 wt %, preferably from about 0.01 to 20 wt % and even more preferably 0.1 to 5 wt %.
Embodiments of the invention will now be described, by way of example only and without limitation, with reference to the accompanying drawings, in which:
a and 1b illustrate the effects of mesopororus silicon on the shelf life of coffee granules.
a and 2b illustrate the effects of mesopororus silicon on the shelf life of coffee granules under humid conditions.
a and 3b illustrate the release kinetics of a mesoporous silicon sample loaded with peppermint oil and an unloaded mesoporous silicon sample, respectively.
Embodiments of the present invention will now be described, by way of example only, with reference to the following examples.
The fabrication of high surface area silicon powders with equipment that is scaleable to high throughput is demonstrated by Example 1.
Metallurgical grade silicon of purity 99.1 wt % with major impurities Fe (0.48 wt %) Al (0.19 wt %) and Ca (0.07 wt %) and commercially available in micronised form, with a particle size distribution of d10=1.40 μm, d50=6.19 μm and d97=42.37 μm, was used. The dry powder was subjected to high energy wet milling in a Hosokawa Alpine 90 AHM cylindrical ball mill. The grinding media was zircon oxide (diameter 0.4-0.7 mm) with a silicon carbide lining. Circulation grinding was used. The drive motor was run at 2.2 kW and the mill volume at 0.25 litres. Runs A1 and A2 used isopropanol (IPA) as the liquid carrier. For Runs B1-B3, the grinding of the silicon was carried out in water. Table 1 summarises the milling conditions and particle size distribution characteristics of the particles produced.
The data in Table 1 demonstrates that, following a few hours milling time, average particle size can be reduced to the submicron diameter range, for both of the liquid media investigated.
Runs B1-B3, which were conducted in the presence of water, were carried out under higher energy milling conditions. Within five hours, 97% of particles had diameters below 1 micron, with 50% having diameters less than 430 nm. The estimated surface areas were in the range 5-100 m2/g. For comparison, mesoporous silicon of 60% porosity prepared by anodisation, has surface areas around 200 m2/g.
High resolution cross-sectional scanning electron microscopy (HRSEM) images and EDX spectra were generated in order to assist in the analysis of the milled material. The EDX spectra showed that milling in water introduces significant oxidation and a more hydrophilic surface. The surface may, optionally, be treated with HF in order to remove the oxidation at the surface.
Milling in IPA introduces significantly less oxidation according to the EDX spectra generated but may, for example, leave SiC bonding at the surface and thus a more hydrophobic surface. The IPA milled material could thus provide the additional benefit of adsorbing hydrocarbons from plastic packaging which is intended for use with food.
The stability of porous silicon was tested in a range of foods and drinks. Tests were carried out at 5° C. and 18° C. which were taken to be representative of refrigerated and room temperature conditions. Samples A and B were prepared. Sample A is a porous silicon sample possessing a porosity of 70 vol % (+/−10%), and a thickness of 0.631 μm (+/−0.02 μm) on non-porous bulk silicon. Sample A was prepared via the anodisation, under constant current density of 100 mA/cm2 for 10 seconds, of a non-porous bulk silicon sample. The electrolyte comprised equal volumes of 40 wt % HF and MeOH and the p+ silicon wafer had a resistivity of 5-20 mΩcm.
Sample B is a porous silicon sample possessing a porosity of 75 vol % (+/−5%), and a thickness of 3.531 μm (+/−0.02 μm). Sample B possesses a 200 nm thick outer region of 54 vol % (+/−10%) porosity. Sample B was prepared via the anodisation, under varying current density of 5 mA/cm2 for 30 seconds followed by 50 mA/cm2 for 120 seconds, of a non-porous bulk silicon sample. The electrolyte comprised 40 wt % HF and isopropanol in a 2:1 volume ratio and the p+ silicon wafer had a resistivity of 0.89-1.34 mΩcm.
Samples A and B were immersed in a range of foods and drinks. HRSEM was used to monitor the thickness of the porous silicon over time thus giving estimates of the rates of corrosion. The results are presented in Table 2.
Metallurgical grade silicon microparticles possessing a d50 of 10 μm are partially porosified via a stain-etching method in an HF based solution to provide a high density of pores in the range of 5 to 50 nm diameter. Fish oil, ranging in an amount of 10 wt % to 60 wt % of the silicon is incorporated via the action of capillary flow which may optionally be in the presence of additional hydrostatic pressure.
Metallurgical grade silicon powder possessing a d50 of 50 μm is dipped in HF to remove the oxide coating, rinsed and seeded with probiotic culture. The bacteria coated particles are then consolidated by cold pressing.
Metallurgical grade silicon particles are partially compressed into porous electrodes by cold pressing. The compressed particles are then subjected to anodisation in concentrated (40-50 wt %) HF to create microporous silicon, see Canham J. Appl. Phys., 72, 1992, p 1232. Fragrant oils are loaded by gaseous transport and capillary condensation.
Ferrosilicon feedstock containing 75 wt % silicon and 25 wt % iron is subjected to mechanical attrition using high energy ball milling to produce high surface area powder with particles in the range of 0.1-10 μm possessing a mean diameter of 1 μm and a d50 of 5 μm. Alternatively, pure iron powder may be blended with silicon powder and co-milled.
Metallurgical grade silicon is micronised by mechanical attrition to particles of 10 μm mean diameter and a d50 of 50 μm. These are stain etched to a level of porosity which is in the range 60-80% (equivalent to 0.5-0.9 g/cm3). The pore diameters are typically in the range 2-10 nm. Coffee oil is impregnated by capillary condensation at room temperature, which may carried out with the assistance of pressure. The preferred density of the aroma loaded particles is less than that of hot coffee or soup; i.e. suitably less than 1.2 g/cm3 and preferably in the range 0.8-1.0 g/cm3. The silicon particles are mixed with the coffee oil at a range of 0.1-10 wt % ratio.
The effect of porous silicon powder on the shelf life of coffee was investigated. A mesoporous silicon membrane of 70 vol % porosity was lifted off a wafer by applying a high current density pulse, and hand milled into microparticles of a broad size distribution. Nescafe coffee granules were also hand milled. A portion of the milled granules were then manually mixed with the milled porous silicon (50:50 wt % ratio). The mixture was stored in air over a period of five days. The air humidity varied widely over the range 20%-70% relative humidity. Temperature variations between night and day would also have varied significantly, but were not recorded.
The resistance to humid conditions was investigated for freeze-dried instant coffee (Kenco Decaffeinated, Best Before September 2007 L5256), with and without mesoporous silicon.
A blend of 10 wt % porous silicon and 90 wt % coffee, prepared by simple physical agitation of powder and granules, was compared with pure coffee under water saturated air (100% humidity) at 23° C.+/−2° C. for 2.5 hrs in the dark. The pure coffee sample took on the characteristic “sticky” resinous appearance of heavily oxidised material. The surface had the porous molten-like morphology shown in
A process to form uniform composites suitable for use as coffee tablets was investigated. Coffee granules were cold-pressed with porous silicon and a hygroscopic binder with applied forces between 3 and 12 kN (kilo Newtons). The dissolution of the tablets was studied in freshly boiled water. The tablet took about 10 seconds to dissolve, thereby releasing the porous silicon microparticles to the surface meniscus.
Mesoporous silicon micro particles possessing a broad particle size distribution were shown to float effectively on boiling water and hot coffee simply by adding hot water to mesoporous silicon particles and a mixture of coffee and silicon microparticles.
To quantify the release kinetics of a flavour (and aroma) from floating mesoporous silicon, gravimetric measurements were made on large membrane segments of mesoporous silicon in water. A 52.64 mg membrane segment was immersed in pure peppermint oil (Cariad, UK), then excess oil removed on filter paper. The loaded sample was then floated on 200 ml of delonised water in a 250 ml coffee mug at 30° C., periodically removed, dried and weighed to monitor the oil loss to the water undemeath and the air above. After 30 minutes, the water was replaced with freshly boiled water and the temperature was monitored as it cooled over the next 10 minutes. The membrane was floated on the hot water and its weight measured after 5 minutes and then after 10 minutes.
Mesoporous silicon membrane segments of silicon (C-E), possessing a porosity of 65 vol % and a thickness of 158 μm, were immersed in pure linseed oil. The fatty acid component of linseed oil contains more than 50 wt % alpha linoleic acid (ALA) and is an essential fatty acid. ALA is known to be sensitive to both heat and light. The linseed oil was purchased from Aldrich (catalogue number 430021, contains 0.5 wt % lead napthenate).
Incorporation of the linseed oil, which is of low viscosity and low volatility, was assessed gravimetrically. The results are presented in Table 3. The density of the linseed oil in the pores was assumed to be that of the bulk liquid (0.93 g/cm3). Cross sectional Energy Dispersive X-Ray analysis was used to confirm incorporation of the linseed oil throughout the material.
Mesoporous silicon membrane segments of silicon (F—H), possessing a porosity of 65 vol % and a thickness of 158 μm, were immersed in a high viscosity liquid form of vitamin E (Aldrich Cat 25,802-4) for different periods of time at room temperature. Vitamin E is sensitive to light, heat and oxygen. Its stability can be affected when stored in food for relatively short periods of time. Natural sources of vitamin E include vegetable and soybean oils. Synthetic versions tend to be cheaper but have lower biological activity. Table 4 illustrates the effects of immersion times on the degree of loading.
Mesoporous silicon membrane segments of silicon, possessing a porosity of 65 vol % and a thickness of 158 μm, were immersed In a plant/vegetable oil blend (Vertese™ Omega 3&6&9 formulation). The oil, blend includes sunflower oil, pumpkinseed oil, wheatgerm oil, rosemary oil, rice bran oil and evening primrose oil. These oils contribute alpha-linolenic acid, linoleic acid, oleic acid palmitic acid and stearic acid. The capsules were broken and the oil blend extracted and pooled. Immersion of the silicon sample was carried out for 1 hour and at room temperature. The sample was removed and excess oil removed by filter paper. The weight increase was equivalent to an average of 41 wt % loading throughout the silicon. Cross sectional EDX measurements confirmed the high loading levels with only slightly higher incorporation near the external surfaces of the porous silicon. The very high carbon to oxygen ratio was consistent with the chemical composition of such oils.
Lycopene (C40H56) belongs to the carotenoid family and is a natural red pigment which is synthesised by plants but not by animals. Lycopene is often not lost through cooking or food processing although it is easily oxidised. However, lycopene is very hydrophobic and this limits its bioavailability.
The liquid contents of Lyc-O-Mato™ (6% strength oily dispersion) from Lycored Natural Products Industries Ltd, Israel were pooled. A 69% porosity membrane segment of a 164 μm thickness sample of porous silicon was immersed for 18 hours at room temperature in the pooled liquid contents.
Cross sectional EDX measurements confirm the high loading levels of the lycopene in the porous silicon. Only slightly higher loading levels were detected near the external surfaces of the porous silicon. The detected levels of oxygen are indicative of carrier fluid penetration, since unoxidised lycopene contains no oxygen.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0515353.1 | Jul 2005 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2006/002785 | 7/27/2006 | WO | 00 | 1/23/2009 |
