Natural Dyes

Abstract

A method for producing a powdered natural colourant comprises heating organic matter in a solvent under reduced pressure, separating the resulting coloured solution and residual solid matter, and spra

Description

01 04 25 Field of Invention The present invention relates to natural colourants and to methods for preparing natural colourants. In particular, the present invention relates to powdered colourants dyes derived from organic matter such as food waste. The powdered natural colourants are particularly suitable for use as a textile dye. Background Synthetic dyes have dominated the textile manufacturing industry since their discovery in the mid-19th century. Synthetic dyes have many advantages over the previously used natural colourings that were accessible at the time, such as their ability to stick to fabrics more easily, their colourfastness and the varied palette of colours available synthetically. This allowed manufacturers and dye houses to function and produce in much larger quantities as well as being able to offer more vivid and richer colours. However, there are many disadvantages associated with the use of synthetic dyes. For example, the chemicals which are used to produce these synthetic dyes are often toxic, carcinogenic, and sometimes even explosive - such as the chemical aniline which is the base component for azo dyes. These chemicals are dangerous to work with and sometimes even the dyes themselves are considered lethal poisons. Furthermore, the process of using synthetic dyes comprises multiple chemicals, many of which provide further hazards. For example, dioxin, which is carcinogenic and a probable hormone disrupter, many noxious heavy metals, for example chrome, copper and zinc which are recognised carcinogens, and formaldehyde, an assumed carcinogen are all chemicals which play essential roles in conventional synthetic dyeing processes. The fashion industry is recognised as the second largest polluting industry in the world and relies heavily on the use of synthetic dyes. 80% of the fashion industries emissions are caused by the liquid waste made as a by-product of the dyeing processes used and synthetic dyes are responsible for 20% of global wastewater pollution. Chemical dye effluent is dumped into waterways causing contamination, killing aquatic biota, damaging soil, and contaminating the food chain and drinking water. Local populations have been shown to experience effects such 01 04 25 as bladder cancer, infertility, nervous-system disorders and rashes amongst many other side effects. Thus, a further disadvantage associated with synthetic dyes is their environmental and health impact. There is therefore a need in the art for safe and environmentally friendly alternatives to conventional synthetic dyes and dyeing processes. Natural dyes encompass any dyes derived from plants, invertebrates, or minerals; however, the majority of natural dyes are vegetable dyes. Natural dyes have many inherent advantages, including high sustainability, fewer health hazards and they are more environmentally friendly. As the dyes are made only from naturally sourced ingredients, the dyes themselves are biodegradable and therefore their disposal is not polluting. This means that waste products formed in the dyeing process are also environmentally safe. Traditionally, natural dyes have been made by grinding up organic materials, and then applying them to a substrate such as a textile. However, dyes made in this way cannot be used directly in conventional industrial dyeing process as they tend to clog up the machinery, thereby reducing the efficacy of the dyeing process. Furthermore, these natural dyes lack consistency in colour and fail to achieve an intense colour in use. Methods for producing natural dyes using solvent extraction dyes followed by spray drying are known in the art. However, these methods often produce dyes which are lacking in vibrancy. Furthermore, high energy levels and / or polluting chemicals have often been used in such methods, thereby reducing the environmental credentials of the natural dye. Thus, there remains a need for natural dyes which are easy to integrate in conventional dyeing processes, and improved methods for making the same. Summary of the Invention The present invention is based on the discovery that, by extracting natural dyes from organic matter under reduced pressure, a powdered pigment with high levels of colour intensity may be produced. By carrying out extraction under reduced pressure, milder conditions may be used in step (a) thereby reducing degradation of the dye during extraction. Thus, the present invention provides a method for producing a powdered natural colourant. 01 04 25 The method comprises: (a) heating organic matter in a solvent under reduced pressure to provide a coloured solution and residual solid matter; (b) separating the coloured solution from the residual solid matter; and (c) spray drying the coloured solution to provide a powdered natural colourant wherein: the organic matter is plant material, and the solvent comprises an organic solvent or a mixture of water and an organic solvent, wherein the organic solvent is an alcohol. Detailed Description The present invention relates to a powdered natural colourant. The powder that is produced by the method of the present invention may be used as a “dye” or a “pigment”. It will be appreciated that, when used, a “dye” is in solution whereas a “pigment” is in a solid, typically particulate, form. Whether the powders of the present invention act as “dyes” or “pigments” will therefore depend on the medium in which they are eventually used. The colourants of the present invention are soluble in water but can be converted into insoluble pigments by adding alum and soda ash in equal quantities to an aqueous solution of the colourant and then adjusting the pH of the solution to 7. The colourants will react with the alum and soda ash, which causes the colourants to precipitate out to form an insoluble pigment that can then be filtered from the solution and dried. Method for producing a powdered natural colourant The present invention provides a method for producing a powdered natural colourant from organic matter. The organic matter that is used in the present invention is plant material. The plant material may be selected from fruits, vegetables, flower petals, grasses, leaves and spices. For example, fruits may include blueberries, avocados, blackberries, elderberries, grapes, huckleberries, mulberries, raspberries, pomegranates, sumac fruits, cherries, and strawberries. Vegetables may include beetroots, onions, red onions, red cabbages, artichokes, and carrots. 01 04 25 The organic matter is preferably selected from turmeric, blue pea flowers, beetroots, onions, red cabbages, blueberries, spinach, avocados, celery leaves, bay leaves, peach tree leaves, basil, blackberries, elderberries, grapes, huckleberries, mulberries, honey berries raspberries, coffee grounds, fennel leaves and flowers, juniper, oak acorns, sumac leaves, walnut husks, artichokes, grass, mint, nettles, red onions, sorrel, tarragon, carrots, paprika, pomegranates, carob pods, oak gals, sumac fruits, cherries, strawberries, and combinations thereof. The colourants that may be extracted from the organic matter in step (a) of the method include anthocyanin compounds, curcuminoid compounds, betalain compounds, chlorophyll compounds, tannin compounds, carotenoid compounds or anthraquinone compounds. The organic matter may comprise food waste that has been scheduled for disposal at landfill. It is estimated that one-third of all the food produced in the world goes to food waste. The food waste used in the present invention may be inedible food waste, such as onion skins or avocado pits, or it may be discarded food. A key issue of using synthetic dyes is that they are commonly derived from petrochemicals and therefore there are sustainability issues associated with their long-term use. By using food waste that has been scheduled for disposal at landfill as the organic matter, the colourants produced by the method of the invention may provide sustainable alternatives. In step (a) of the method, the organic matter is heated in a solvent under reduced pressure to provide a coloured solution and residual solid matter. By heating the organic matter in a solvent, soluble colourants that are present in the organic matter are extracted into the solvent. The solvent that is used in the present invention will typically be a liquid solvent. In some instances, the solvent that is used in extraction step (a) comprises or is the solvent that is used in the dyeing process in which the natural colourant will eventually be used. This ensures that the colourants that are extracted will be soluble during their use. The solvent that is used in step (a) comprises an organic solvent or a mixture of water and an organic solvent. According to the present invention, the organic solvent is an alcohol. The use of an organic solvent during step (a) gives superior extraction than the use of water alone due to enhanced selectivity and / or ability to penetrate cell walls. For instance, ethanol and similar solvents may penetrate cell walls to selectively dissolve pigments but not sugars, thereby leading to a purer powdered colourant product. 01 04 25 Unfortunately, spray drying with an organic solvent can be challenging and often requires the use of an inert atmosphere due to the risk of the explosion associated with organic solvents at the high temperatures used in the spray drier. It is therefore preferable to use a mixture of water and organic solvent in step (a) with the organic solvent removed before spray drying, or to use an organic solvent in step (a) with water added and the organic solvent removed after step (a) but before spray drying step (c). The solvent that is used in step (a) may comprise the organic solvent in an amount of at least 30 %, preferably at least 40 %, and more preferably at least 50 %, by volume. The solvent that is used in step (a) may comprise the organic solvent in an amount of up to 100 %, by volume. Thus, the solvent that is used in step (a) may comprise the organic solvent in an amount of from 30 to 100 %, preferably from 40 to 100 %, and more preferably from 50 to 100 %, by volume. Where more than one organic solvent is used, these amounts represent the total amount of organic solvent present. Where a combination of water and organic solvent is used in step (a), the solvent may comprise water in an amount of at least 20 %, preferably at least 30 %, and more preferably at least 35 %, by volume. The solvent that is used in step (a) may comprise water in an amount of up to 60 %, preferably up to 50 %, and more preferably up to 45 %, by volume. Thus, the solvent that is used in step (a) may comprise water in an amount of from 20 to 60 %, preferably from 30 to 50 %, and more preferably from 35 to 45 %, by volume. Where a combination of water and organic solvent is used in step (a), the solvent that is used in step (a) may comprise the organic solvent in an amount of at least 30 %, preferably at least 40 %, and more preferably at least 50 %, by volume. The solvent that is used in step (a) may comprise the organic solvent in an amount of up to 80 %, preferably up to 70 %, and more preferably up to 65 %, by volume. Thus, the solvent that is used in step (a) may comprise the organic solvent in an amount of from 30 to 80 %, preferably from 40 to 70 %, and more preferably from 50 to 65 %, by volume. Where more than one organic solvent is used, these amounts represent the total amount of organic solvent present. Where an organic solvent is used in step (a) and water is added to the coloured solution after step (a) but before step (c), the solvent that is used in step (a) may comprise the organic solvent in an amount of at least 80 %, preferably at least 90 %, and more preferably at least 95 %, by volume. The solvent that is used in step (a) may comprise the organic solvent in an amount of up to 100 %, by volume. Thus, the solvent that is used in step (a) may comprise 15 04 25 the organic solvent in an amount of from 80 to 100 %, preferably from 90 to 100 %, and more preferably from 95 to 100 %, by volume. Where more than one organic solvent is used, these amounts represent the total amount of organic solvent present. Water may then be added to the coloured after step (a) but before step (c). For instance, water is preferably added after step (a) but before the concentration step (mentioned below). For instance, water may be added in ratio of water to organic solvent used in step (a) of at least 0.3:1, preferably at least 0.5:1, and more preferably at least 0.6:1, by volume. Water may be added in a ratio of water to organic solvent used in step (a) of upto 1:1, preferably up to 0.8:1, and more preferably up to 0.7:1, by volume. Thus, water may be added in a ratio of water to organic solvent used in step (a) of from 0.3:1 to 1:1, preferably from 0.5:1 to 0.8:1, and more preferably from 0.6:1 to 0.7:1, by volume. Where more than one organic solvent is used, these amounts represent the total amount of organic solvent present. The organic solvent preferably has a boiling point which is lower than water. This allows for its selective withdrawal before spray drying step (c). The organic solvent is an alcohol (e.g., methanol, ethanol, propanol or butanol), however combinations of an alcohol with other solvents may be suitable such as acetone, DMSO, and ethyl acetate. Generally, it is preferred for a single organic solvent, such as ethanol, to be used. In some preferred embodiments, the solvent comprises water and ethanol. In these instances, the solvent that is used in step (a) may comprise ethanol in an amount of greater than 30 %, preferably at least 40 %, and more preferably at least 50 %, by volume. The solvent that is used in step (a) may comprise ethanol in an amount of up to 80 %, preferably up to 70 %, and more preferably up to 65 %, by volume. Thus, the solvent that is used in step (a) may comprise ethanol in an amount of from 30 to 80 %, preferably from 40 to 70 %, and more preferably from 50 to 65 %, by volume. The choice of solvent may be dependent on the intended use of the natural colourant product. For example, ethanol or acetone in combination with ethanol may be suitable choices for natural dye products that are intended for dyeing metals. Where the product is used in a cosmetic, it is preferably extracted using solely an organic solvent to ensure its purity. Where the solvent comprises a mixture of water and ethanol, preferably the ratio of water to ethanol is at least 0.3:1, preferably at least 0.5:1, and more preferably at least 0.6:1, by volume. The ratio of water to ethanol may be upto 1:1, preferably upto 0.8:1, and more 01 04 25 preferably up to 0.7:1, by volume. Thus, the ratio of waterto ethanol may be from 0.3:1 to 1:1, preferably from 0.5:1 to 0.8:1, and more preferably from 0.6 :1 to 0.7:1, by volume. Where more than one organic solvent is used, these amounts represent the total amount of organic solvent present. In preferred embodiments, a hydroxy acid, such as an alpha-hydroxycarboxylic acid, is present in step (a) in addition to the organic matter and solvent. These acids have been found to be particularly effective at enhancing the solubility and / or stability of certain colourants, yet are themselves advantageously biodegradable. Hydroxy acids are typically solids at room temperature and are therefore dissolved in the solvent. Examples of suitable alphahydroxycarboxylic acids include glycolic acid, lactic acid, malic acid, tartaric acid and citric acid. Preferably, citric acid is present in step (a). The hydroxy acid may be present in an amount of at least 0.5 g, preferably at least 1 g, and more preferably at least 1.5 g, per 100 mL of solvent. The hydroxy acid may be present in an amount up to 10 g, preferably up to 5 g, and more preferably up to 3 g, per 100 mL of solvent.. Thus, the hydroxy acid may be present in an amount from 0.5 to 10 g, preferably from 1 to 5 g, and more preferably from 1.5 to 3 g, per 100 mL of solvent. Where a mixture of hydroxy acids is used, these values represent the total amounts of hydroxy acids used. A key feature of the present invention is that step (a) is performed under reduced pressure. This means that the pressure is lower than atmospheric pressure, which is around 101.3 kPa, for instance at least 10 kPa lower than atmospheric pressure. In some instances, the reaction may be performed in a sealed vessel with steps taken to withdraw pressure. Step (a) may be carried out at a pressure of at least 18 kPa, preferably at least 20 kPa, and more preferably 25 kPa. Step (a) may be carried out at a pressure of up to 50 kPa, preferably up to 40 kPa, and more preferably up to 30 kPa. Thus, step (a) may be carried out at a pressure from 18 to 50 kPa, preferably from 20 to 40 kPa, and more preferably from 25 to 30 kPa. Since step (a) involves heating the organic matter in the solvent, itis carried out at elevated temperatures. In some instances, step (a) is carried out with at the boiling point of the solvent plus or minus 10 °C, preferably plus or minus 5 °C, and more preferably plus or minus 2 °C. 01 04 25 In preferred embodiments, step (a) is carried out with the solvent boiling. The skilled person will appreciate that the boiling point of a solvent decreases under reduced pressure. Thus, performing the extraction under reduced pressure allows a reaction to be carried out at a lower temperature than would be used if the solvent was heated to boiling point at atmospheric pressure. This reduces the levels of heat degradation observed in the colourants that are extracted, thus providing a greater yield of powdered natural colourant at the end of the process and also allowing for a greater range of raw material to be used, providing a fuller range of colours. Furthermore, it is easier to maintain a consistent temperature in a reaction that is carried out at the boiling point of a solvent than in a reaction that is carried out below the boiling point of a solvent. It will be appreciated that, although step (a) is preferably carried out with the solvent boiling, any solvent that evaporates is returned to the extraction mixture, for instance due to a condenser. In some embodiments, step (a) may be carried out under reflux. Step (a) of the method may be carried out at a temperature of at least 30 °C, preferably at least 35 °C, and more preferably at least 40°C. Step (a) may be carried out at a temperature up to 80 °C, preferably up to 65°C, and more preferably up to 50 °C. Thus, step (a) may be carried out from 30 to 80 °C, preferably from 35 to 65 °C, and more preferably from 40 to 50 °C. Step (a) of the method may be performed for a period of at least 0.5 hours, preferably at least 1 hour, and more preferably at least 1.5 hours. Step (a) may be carried out for a period of up to 5 hours, preferably up to 4.5 hours, and more preferably up to 3 hours. Thus, step (a) may be carried out for a period of from 0.5 to 5 hours, preferably from 1 to 4.5 hours, and more preferably from 1.5 to 3 hours. The organic matter may be added in step (a) in an amount of at least 10 g, preferably at least 25 g, and more preferably at least 50 g per litre of solvent. The organic matter may be added in amount up to 500 g, preferably up to 250 g, and more preferably up to 150 g per litre of solvent. Thus, the organic matter may be added in step (a) in an amount of from 10 to 500 g, preferably from 25 g to 250 g, and more preferably from 50 to 150 g per litre of solvent. As an example protocol, step (a) may be carried out by placing from 5 g to 500 g of food waste in a sealable vessel per litre of solvent, where the solvent is preferably a mixture of water and ethanol and citric acid is preferably also present. The pot is heated to maintain a temperature 01 04 25 between 30 and 80 °C at a pressure of from 18 to 50 kPa. This is left for between 0.5 and 5 hours before moving onto step (b). In preferred embodiments, the method further comprises a step of dehydrating the organic matter before step (a). Drying the organic matter means that natural variation in water content is removed, thereby improving the consistency of the process. It also allows for storage of the feedstock without risk of degradation through rotting. Dehydration may be carried out by drying the organic matter in an oven, e.g. at a temperature between 50 and 65 °C for approximately 10 to 16 hours. Preferably the moisture content of the organic matter is reduced to less than 10 % by weight. In preferred embodiments, the method further comprises a step of grinding the organic matter before step (a). By grinding the organic matter, the surface area of the particles increases, which allows for a more efficient extraction process. Other forms of increasing the surface area, such as slicing the organic matter into smaller pieces may also be suitable. In step (b) of the method, the coloured solution is separated from the residual solid matter. Step (b) may be carried out using commonly known separation techniques, such as filtration. Generally, filtration may be carried out using a sieve or filter paper, depending on the size of the residual solid matter. The residual solid matter is removed so that the coloured solution used in step (c) is substantially free from solid organic matter. This means that the waste-derived colourants that are present in the powdered product are soluble. Preferably, the separation step involves two filtration steps to provide a more refined end product. In a first step, the larger particles are removed. Then smaller particles are removed in a second step by passing the mixture through a finer filter. The filter used in the first filtration step may have an opening size of from 0.1 mm, preferably 0.2 mm, and more preferably 0.25 mm. The filter used in the first filtration step may have an opening size up to 1 mm, preferably up to 0.8 mm, and more preferably up to 0.5 mm. Thus, the filter used in the first filtration step may have an opening size from 0.1 to 1 mm, preferably from 0.2 to 0.8 mm, and more preferably from 0.25 to 0.5 mm. The filter used in the first filtration step may be a mesh filter. The filter used in the second filtration step has a smaller opening size to further remove finer particles. Optionally, the filter used in the second filtration step may have an opening size of 01 04 25 from 50 pm, preferably 60 pm, and more preferably 70 pm. The filter used in the second filtration step may have an opening size up to 150 pm, preferably up to 100 pm, and more preferably up to 80 pm. Thus, the filter used in the second filtration step may have an opening size from 50 to 150 pm, preferably from 60 to 100 pm, and more preferably from 70 to 80 pm. In some embodiments, the second filtration step is carried out using microfiltration or ultrafiltration. The separated residual solid matter may simply be passed to landfill, but preferably it is further used. For instance, it may be composted or used in animal feed. In other embodiments, the residual organic matter may be passed to a biomass processing facility. In some embodiments, the method of the present invention further comprises a concentration step before step (c), and preferably between steps (a) and (b). During this step, the concentration of the coloured solution is increased, preferably by evaporation of the solvent, to form a concentrated coloured solution. By using a concentrated solution during spray drying step (c), the residual solvent may be rapidly removed thus limiting the time that the colourants are exposed to temperatures which have the potential to degrade the colourants. The concentrated coloured solution that is present after the concentration step may comprise residual solid matter in an amount from 15 %, preferably from 20 %, and more preferably from 25 % by weight. The concentrated coloured solution may comprise residual solid matter in an amount up to 50 %, preferably up to 40 %, and more preferably up to 35 % by weight. Thus, the concentrated coloured solution may comprise residual solid matter in an amount from 15 to 50 %, preferably from 20 to 40 %, and more preferably from 25 to 35 % by weight. As with extraction step (a), the concentration step may also be performed under reduced pressure. As the boiling point of the solvent will decrease with reduced pressure, this allows for the concentration step to be performed at lower temperatures, and thus reducing heat degradation of the extracted colourants within the coloured solution. The concentration step may be carried out at a temperature of at least 30 °C, preferably at least 35 °C, and more preferably at least 40°C. Step (a) may be carried out at a temperature up to 80 °C, preferably up to 65°C, and more preferably up to 50 °C. Thus, step (a) may be carried out from 30 to 80 °C, preferably from 35 to 65 °C, and more preferably from 40 to 50 °C. 01 04 25 The concentration step may be carried out at a pressure of at least 5 kPa, preferably at least 10 kPa, and more preferably 12 kPa. The concentration step may be carried out at a pressure of up to 50 kPa, preferably up to 35 kPa, and more preferably up to 25 kPa. Thus, the concentration step may be carried out at a pressure from 5 to 50 kPa, preferably from 10 to 35 kPa, and more preferably from 12 to 25 kPa. In preferred embodiments, the solvent that is removed during the concentration step is recycled for use in step (a). This reduces the amount of waste that is produced during production of the natural colourants. Where the solvent system contains a mixture of solvents, these solvents are preferably separated during this step. Typically, solvents will have different boiling points and thus can be separated by evaporating the solvents at different temperatures. This is particularly preferred for solvent mixtures of water and an organic solvent, where the organic solvent has a lower boiling point than water because the concentration step can remove substantially all of the organic solvent (e.g. greater than 95 % and preferably greater than 99 %, by volume) to leave an aqueous coloured solution. This aqueous solution is then saferand easier to spray dry. Even more preferably, some of the water is also removed during the concentration step to further increase the concentration of the coloured solution. As will be explained in further detail below, the concentration of the coloured solution that is used in step (c) may influence the size of the powdered natural colourant that is formed during the spray drying process. The colourants extracted from the organic matter in step (a) may be pH sensitive, for example, anthocyanins extracted from red cabbage. Therefore, the colour of the compounds and thus the colour of the resulting natural colourant product may be adjusted by modifying the acidity or basicity of the coloured solution. In some embodiments, the method therefore further comprises the step of adding pH modifiers to the coloured solution before step (c), and preferably between steps (a) and (b). In some embodiments, the method further comprises the step of adding pH modifiers to the powdered natural colourant formed after step (c). This ensures that the pH of the colourants is appropriate during their use. Thus, the amount of pH modifier is selected to ensure that the pH of the colourant in use in correct. Any suitable pH modifier may be used. Particularly suitable are pH modifiers selected from 01 04 25 12 sodium hydrogen carbonate, potassium aluminium sulfate, sodium carbonate, ascorbic acid, citric acid and combinations thereof. The solution may be allowed to cool, for instance to room temperature (e.g. to a temperature of from 18 to 25 °C) before the pH modifier is added. This allows for the colour change to be more accurately controlled, as the chemical reaction that occurs upon addition of the pH modifier reacts more slowly at a cooler temperature. Step (c) of the method involves spray drying the coloured solution to provide a powdered natural colourant. Spray drying is a method of producing a dry powder from a liquid solution by rapidly drying the atomised solution with a hot gas. Thus, in the present case, spray drying step (c) comprises the sub-steps of: atomising the coloured solution, and drying the atomised coloured solution using a drying gas to form the powdered natural colourant. The properties of a powderthat is produced using a spray drying process may be dependent on the conditions used during the spray drying step. In order to atomise the coloured solution, the coloured solution is preferably passed through an atomiser e.g. into a spray drying chamber. Suitable atomisers include rotary atomisers and nozzle atomisers. Nozzle atomisers may be selected from single fluid nozzle atomisers and multi-fluid nozzle atomisers. As the skilled person will be aware, in single fluid atomisers the liquid which is to be spray dried is passed under hydraulic pressure from the liquid itself through a nozzle, whereas, in multi-fluid nozzle atomisers, pneumatic pressure from a compressed gas stream helps to atomise the liquid. In the present case, the coloured solution is preferably atomised using a two-fluid nozzle atomiser. The nozzle atomiser may have a diameter - i.e. diameter at the point the coloured solution exits the nozzle - of at least 0.5 mm, preferably at least 0.7 mm, and more preferably at least 1 mm. The nozzle atomiser may have a diameter of up to 2 mm, preferably up to 1.8 mm, and more preferably up to 1.5 mm. Therefore, the nozzle atomiser may have a diameter of from 0.5 to 2 mm, preferably from 0.7 to 1.8 mm, and more preferably from 1 to 1.5 mm. Particularly preferred are nozzle atomisers having a diameter of from 1.3 to 1.5 mm. The coloured solution is preferably sprayed - i.e. exits the atomiser - at a pressure of at least 160 kg / cm2, preferably at least 165 kg / cm2, and more preferably at least 170 kg / cm2. A 01 04 25 spraying pressure of up to 200 kg / cm2 may be used, preferably up to 190 kg / cm2 and more preferably up to 180 kg / cm2. Therefore, step (c) may be performed using a spraying pressure of from 160 to 200 kg / cm2, preferably from 165 to 190 kg / cm2 and more preferably from 170 to 180 kg / cm2. Particularly preferred are spraying pressures of from 170 to 175 kg / cm2. It will be appreciated that, while the pressure settings on some spray dryers are expressed in terms of the units “kg / cm2”, other spray dryers may use the SI units “Pa”. The person of skill in the art will be aware that the conversion between these units is 1 kg / cm2 = 98.0665 kPa. The coloured solution is preferably sprayed - i.e. passed through the atomised - at a flow rate of at least 1300 mL / hour, preferably at least 1500 mL / hour, and more preferably at least 1800 mL / hour. The coloured solution is preferably sprayed at a rate of up to 2500 mL / hour, preferably up to 2300 mL / hour, and more preferably up to 2100 mL / hour. Therefore, the coloured solution may be sprayed at a rate of from 1300 to 2500 mL / hour, preferably from 1500 to 2300 mL / hour, and more preferably from a speed of 1800 to 2100 mL / hour. However, it will be appreciated that the larger the spray drying apparatus, the greater the flow rate. Thus higher flow rates than those mentioned above may also be used. For example, industrial spray dryers can have flow rates from 50 to greater than 1500 L / hour. The coloured solution may be passed through a single atomiser, orthrough multiple atomisers, e.g. into the spray drying chamber. For instance, where a nozzle atomiser is used, the coloured solution may be passed through two or more nozzles. A wide range of gases may be used as the drying gas in step (c) though, this will typically be air. The drying gas is preferably used -i.e. introduced into the spray drying chamber-co-currently with the atomised coloured solution, though counter-current or mixed flows may also be used. It will be understood by the skilled person that co-current flow denotes a system in which the drying gas and atomised liquid are introduced in the spray drying chamber in the same direction, typically by introducing the atomised liquid and drying gas at the top of the chamber and withdrawing the dried product and drying gas at the bottom of the chamber. Countercurrent flow denotes a system in which the drying gas and atomised liquid are introduced into opposite ends of the spray drying chamber, typically by introducing the atomised liquid at the top of the chamber and withdrawing the dried product at the bottom of the chamber while introducing the drying gas at the bottom of the chamber and withdrawing it at the top of the chamber. A mixed system involves both co-current and counter-current flows, typically by 01 04 25 14 introducing the atomised feed at the bottom of the chamber and the drying gas at the top of the chamber while withdrawing both the dried product and the drying gas at the bottom of the chamber. The temperature of the drying gas - i.e. at its inlet into the spray dryer - may be at least 140 °C, preferably at least 145 °C, and more preferably at least 150 °C. The temperature of the drying gas may be up to 200 °C, preferably up to 190 °C and more preferably up to 180 °C. Therefore, the temperature of the drying gas may be between 140 and 200 °C, preferably between 145 and 190 °C, and more preferably between 150 and 180 °C. The outlet temperature of the spray dryer - i.e. the temperature of the drying gas stream removed from the drying chamber - may be at least 50 °C, preferably at least 60 °C, and more preferably at least 70 °C. The outlet temperature may be up to 100 °C, preferably up to 95 °C, and more preferably up to 90 °C. Thus, the outlet temperature may be between 50 and 100 °C, preferably from 60 to 95 °C, and more preferably between 70 and 90 °C. The outlet temperature may be measured after 60 minutes of operation of the spray drier. It has surprisingly been found that the level of colourant degradation is low even at these high temperatures, particularly where a concentrated coloured solution is used. In these instances, there is less solvent to remove and so the residence time of the colourant in the spray dryer is less. This means that high temperatures may be used without harming the colourant, with the powdered colourant leaving the spray drying chamber still at a temperature which is approximately 15 °C lower than the outlet temperature. Where a concentrated solution is not used in step (c), then a lower temperature and therefore slower spray drying process may be preferred to avoid pigment degradation. The spray drying may be performed using a drying gas velocity of at least 4 m / sec, preferably at least 5 m / sec, and more preferably at least 6 m / sec. The drying gas velocity may be up to 10 m / sec, preferably up to 9 m / sec, and more preferably up to 8 m / sec. Therefore, the drying gas velocity may be from 4 to 10 m / sec, preferably from 5 to 9 m / sec, and more preferably from 6 to 8 m / sec. During spray drying step (c), the solvent that is present in the coloured solution is evaporated to give the powdered natural colourant. In some embodiments, the method of the present invention comprises the step of collecting the solvent, e.g. by condensing the vapour, in order 01 04 25 that it may be discarded or reused. Due to the steps of evaporating and collecting the solvent, the solvent will be purified and, as such, is particularly suited for reuse. In some embodiments, the solvent may be recycled for use in an earlier step - for instance as (at least part of) the extraction solvent in step (a) or it could be added before the concentration step. Where a hydroxy acid, such as citric acid, is used in step (a), the acid will be removed with the solvent at this stage. A large problem associated with the use of synthetic dyes is the large amount of wastewater that is produced through the formation and use of the dyes. Furthermore, as these dyes are not naturally occurring, the wastewater formed can be toxic and environmentally damaging. A benefit of the method of the invention is therefore that the solvent used in step (a) may be collected during the spray drying step and reused. The method is particularly advantageous when a mixture of water and ethanol is used as the solvent in combination with a condensing step, as purified, and separated, ethanol and water streams may be collected during the condensing and spray drying steps. The powdered natural colourant that is formed during step (c) may have an average diameter (D50) of at least 10 pm, preferably at least 20 pm, and more preferably at least 30 pm. The powdered natural colourant that is formed during step (c) may have an average diameter of up to 50 pm, preferably up to 40 pm, and more preferably up to 35 pm. Therefore, the powdered natural colourant may have an average diameter of from 10 to 50 pm, preferably from 20 to 40 pm, and more preferably from 30 to 35 pm. A powdered natural colourant of this size is believed to be particularly effective in a dyeing process. The size of the powdered natural colourant may be determined using laser diffraction, preferably according to ISO 13320:2020. The skilled person will be aware that laser diffraction determines volume-based particle size, and that the average diameter (D50) represents the median diameter. The size of the powdered natural colourant can be controlled in a number of different ways. For instance, as mentioned above, by increasing the concentration of the colourant molecules in the coloured solution before spray drying, the size of the resultant powder natural colourant may also be increased. Similarly, the settings on the spray drying machine can be used to control particle size. In some instances, the particle size may be increased by adding a soluble mineral to the 01 04 25 coloured solution before spray drying step (c). The colourant can bind to this mineral during the spray drying process, thereby increasing the particle size of the powdered natural colourant. Suitable minerals may include sodium chloride, potassium aluminium sulfate, sodium carbonate, ascorbic acid, riboflavin, and combinations thereof. It will be appreciated that methods of controlling particle size may be combined, for instance the coloured solution may be concentrated and a mineral may be added to the coloured solution before spray drying. In preferred embodiments, an antioxidant is added to the coloured solution before spray drying step (c). This reduces the risk of the natural powdered colourant undergoing an oxidation reaction during storage or use, and therefore increases the shelf life of the powdered natural colourant and also reduces changes in colour of the colourant due to a change in oxidation state. Preferably, the antioxidant is ascorbic acid as this has the dual function as an antioxidant and particle size enhancer (see above). In some embodiments, an anti-caking agent may be added to the powdered natural colourant after spray drying step (c). Preferably, the anti-caking agent is silica to avoid reabsorption of water from the air and thus prevent clumping of the powdered natural colourant during storage and handling before use. Natural colourant compositions The natural colourant powder that is prepared using the method described above is a natural powdered colourant obtainable from organic matter. The natural colourant is preferably free from insoluble matter. The natural colourants of the present invention have a number of advantageous properties as compared to existing natural dyes, including ease of use, consistency and colour intensity. Method of dyeing textiles The natural colourants of the present invention may be used in a method of dyeing textiles. The method comprises contacting the textile with the natural colourant, in the presence of a solvent, to form a dyed textile. 01 04 25 The textile is preferably a natural textile. The natural textile may be selected from wool, cotton, linen and silk, or it may contain a blend of these materials. However, semi-synthetic textiles may also be dyed, for instance rayon materials such as viscose or lyocell. Furthermore, blends of natural, semi-synthetic and / or synthetic fibres, such as those mentioned previously, may also be dyed using the natural dyes of the present invention. Examples of synthetic fibres suitable for use in blends include nylon, polyester or blends thereof. The solvent is preferably selected from water, ethanol, acetone and ethyl acetate and is preferably water. The textile may be contacted with the dye for a period of at least 5 minutes, preferably at least 8 minutes, and more preferably at least 10 minutes. The textile may be contacted with the dye for a period of up to 20 minutes, preferably up to 18 minutes, and more preferably up to 15 minutes. Thus, the textile may be contacted with the dye for a period of from 5 to 20 minutes, preferably from 8 to 18 minutes, and more preferably from 10 to 15 minutes. The natural colourant may be used in an amount of at least 1 g, preferably at least 3 g, and more preferably at least 5 g per litre of solvent. The natural dye may be used in an amount of up to 20 g, preferably up to 15 g, and more preferably up to 10 g per litre of solvent. Thus, the natural dye may be used in an amount of from 1 to 20 g, preferably from 3 to 15 g, and more preferably from 5 to 10 g per litre of solvent. Another environmental factorto consider is liquid waste emissions produced during the dyeing process. 80 % of the emissions caused by the textiles industry are due to liquid waste produced from dyeing processes. An advantage of the textile dyes produced and the method of dyeing textiles according to the present invention is that there may be no harmful liquid waste. As the natural colourants are naturally derived and water soluble, there may be minimal environmental impact associated with any liquid disposal. Natural colourant compositions and use in natural colourant compositions Although the natural colourants of the present invention are preferably used as a textile dye, they may also be used in compositions having other applications. Thus, the present invention provides a composition comprising a natural colourant of the present invention, and the use of a natural colourant of the present invention in a composition. The composition may be selected from a paint, an ink, a food colouring, a textile dye, a leather 01 04 25 tan, a wood stain, and a makeup composition. It will be appreciated that, in some instances, the natural colourant may be present as a pigment (e.g. in a paint or a cosmetic such as a lipstick or compressed powder) or as a dye (e.g. in an ink, a food colouring, a textile dye, a leather tan or a stain such as a wood stain or cosmetic stain). The invention will now be illustrated with the following non-limiting examples. Examples Example 1: General colourant preparation method Different food waste was recovered and cleaned. In some cases, the food waste was merely chopped or squashed before extraction. In other cases, the food waste was dried generally to a water content of less than 10 % by weight, then ground. The food waste was added to a solvent system comprising 55 to 70% ethanol and 30 to 45 % water, by volume, and approximately 2 g of citric acid added per 100 ml solvent. In some instances, citric acid was added until a target pH was reached. The food waste was used in an amount of 35 to 100 g of food waste per litre of solvent mixture. Extraction step (a) was carried out by heating the mixture to boiling point. This was achieved with a temperature of from 40 to 70 °C and a pressure of from 20 to 40 kPa. When lower temperatures were used, a greater vacuum was applied to ensure that the solvent was boiling during extraction. The extraction was carried out for between 2 and 4 hours. The exact conditions that were used varied depending on the food waste in question. The extraction mixture was then heated under reduced pressure to remove ethanol and some of the water until a concentrated coloured solution was obtained containing solids in an amount of from 25 to 35 % by weight. The coloured solution was then pH adjusted, if desired, and separated from the residual food waste by passing the extraction mixture through a mesh filter followed by a microfiltration process. The concentrated coloured solution was atomised using a two-fluid nozzle atomiser, at a flow rate 1800 to 2100 mL / hour, with an inlet temperature of from 160 and 180 °C and an outlet temperature of from 70 and 90 °C. Once again, the exact conditions varied with different food waste streams. If desired, further pH adjustments were made following spray drying. 01 04 25 Example 2: Comparison of extraction step (a) Experimental Samples of blueberries; yellow onion skins; red onion skins; avocado pits; and red cabbage were gathered. The samples were dried to a moisture content of less than 10% by weight. The samples were then processed according to either Method A or Method B, outlined below. • Method A: For extraction, 100g of each of the samples was added to a solvent mixture containing 1000 mL of ethanol and 20g of citric acid. Extraction step (a) was performed for 2 hours using a rotary evaporator providing a pressure of 27 kPa. The extraction temperature was maintained at 40 °C. After extraction, 500g of water was added to the extraction mixtures and the extraction mixtures were concentrated. Concentration was carried out by heating the extraction mixtures back up to the extraction temperature of 40 °C. The pressure was reduced to 13 kPa. The concentrating step was carried out for approximately 2 hours to remove the ethanol and some of the water to form concentrated coloured solutions. The residual food waste was then separated from the mixture by passing the concentrated coloured solutions through a filter. • Method B: For extraction, 100g of each of the samples was added to a solvent mixture containing 1000 of water and 20g of citric acid. Extraction step (a) was performed for 2 hours at atmospheric pressure at a temperature of between 80 and 100 °C. After extraction, the extraction mixtures were concentrated. Concentration was carried out by heating the extraction mixtures to a temperature of from 80 and 120 °C, i.e. close to the extraction temperature. The concentrating step was carried out for approximately 3 hours at atmospheric pressure in orderto reduce the volume of the solvent mixture to form concentrated coloured solutions. The residual food waste was then separated from the mixture by passing the concentrated coloured solutions through a filter. All the of samples were atomised using a two-fluid nozzle atomiser with an inlet temperature between 150 to 190 °C and an outlet temperature between 60 and 95 °C, depending on the food waste product. The formed powdered natural colourant was then collected and weighed for each of the samples. Results The yields of the powdered natural colourant forthe samples processed using Method A were significantly higher than those processed using Method B. The percentage increase in yield was calculated using equation:------------------------------x 100. The results are shown Yield of Method B in the following table: 01 04 25 Sample Increase in yield from Method A compared with Method B (%) Blueberries 36 Yellow onion skins 41 Red onion skins 40 Avocado pits 140 Red cabbage 50 It can be seen that significantly greater yields were obtained using reduced pressure method A. The powdered colorants also exhibited a strong colour, and were more vivid that powders produced using methods in which extraction is not carried out under vacuum. Example 3: Use of colourant as textile dyes The general method outlined above was carried out to provide powdered colourants in seven different colours: orange, sage green, yellow, peach, hot pink, green and deep blue. The colourants were successfully used to dye fabrics. High levels of colour intensity were obtained. 01 04 25

Claims

1. A method for producing a powdered natural colourant, said method comprising: (a) heating organic matter in a solvent under reduced pressure to provide a coloured solution and residual solid matter;(b) separating the coloured solution from the residual solid matter; and(c) spray drying the coloured solution to provide a powdered natural colourant wherein:the organic matter is plant material, andthe solvent comprises an organic solvent or a mixture of water and an organic solvent, wherein the organic solvent is an alcohol.

2. The method of Claim 1, wherein step (a) is carried out:at a pressure of from 18 to 50 kPa; and / orat a temperature from 30 to 80 °C.

3. The method of Claim 1 or Claim 2, wherein step (a) is carried out at the boiling point of the solvent.

4. The method of any preceding claim, wherein the alcohol is ethanol.

5. The method of any preceding claim, wherein a hydroxy acid is used in step (a).

6. The method of any preceding claim, wherein the organic matter is used in an amountof from 10 to 500 g per litre of solvent.

7. The method of any preceding claim, wherein the method further comprises a step of grinding the organic matter before step (a).

8. The method of any preceding claim, wherein the method further comprises a step of dehydrating the organic matter before step (a).

9. The method of any preceding claim, wherein the method further comprises a concentration step between steps (a) and (b), wherein the concentration step comprises removing solvent from the coloured solution to provide a concentrated coloured solution.01 04 2510. The method of Claim 9, wherein the solvent that is removed during the concentration step is recycled for use in step (a).

11. The method of Claim 9 or 10, wherein:the solvent that is used in step (a) comprises a mixture of water and an organic solvent with a lower boiling point than water; orthe solvent that is used in step (a) comprises an organic solvent with a lower boiling point than water, and water is added to the coloured solution after step (a) but before the concentration step,and the concentration step comprises: removing the organic solvent from the coloured solution.

12. The method of any preceding claim, wherein step (b) comprises filtering the coloured solution to remove residual solid matter.

13. The method of any preceding claim, wherein the method further comprises the step of adding a pH modifier.

14. The method of any preceding claim, wherein step (c) is carried out with a spray drying: inlet temperature of from 140 to 200 °C; and / oroutlet temperature of from 50 to 100 °C.

15. The method of any preceding claim, wherein the method comprises recycling the solvent that is removed during spray drying step (c) for use during step (a).

16. The method of any preceding claim, wherein the powdered natural colourant formed in step (c) has an average diameter (D50) of from 10 to 50 pm.

17. The method of any preceding claim, wherein the method comprises the step of addingan antioxidant.

18. The method of any preceding claim, wherein the method comprises passing the residual solid matter to a biomass processing facility.

19. The method of any preceding claim, wherein the plant material is selected from fruits, vegetables, flower petals, grasses, leaves and spices.LO CXI20. The method of Claim 19, wherein the plant material is selected from turmeric, blue pea flowers, beetroots, onions, red cabbages, blueberries, spinach, avocados, celery leaves, bay leaves, peach tree leaves, basil, blackberries, elderberries, grapes, huckleberries, mulberries, honey berries, raspberries, coffee grounds, fennel leaves and flowers, juniper, oak acorns, sumac leaves, walnut husks, artichokes, grass, mint, nettles, red onions, sorrel, tarragon, carrots, paprika, pomegranates, carob pods, oak gals, sumac fruits, cherries, strawberries, and combinations thereof.