Ultra-high shear (UHS) high-capacity method for the preparation of an aqueous coating composition

Abstract

The present invention relates to an ultra-high shear (UHS) high-capacity method for the preparation of an aqueous coating composition comprising one or more plant proteins, to the coating composition thus obtained and to the use of said coating composition to coat a cellulosic fibrous substrate or other substrates / materials. In particular, this invention relates to a composition suitable for coating paper and cardboard for packaging purposes, especially for food packaging and a process for preparing the composition. The invention also relates to aqueous coating compositions suitable for other coating applications, such as the coating or encapsulation of actives or even the coating of foods such as fruits to extend their period of use. The aqueous coating compositions of the present invention can also be used in some non-substrate coating applications, for example emulsion stabilizers, where plant protein particles coat the surface of oily droplets dispersed in the emulsion.

Description

[0001] ULTRA-HIGH SHEAR (UHS) HIGH-CAPACITY METHOD FOR THE PREPARATION OF AN AQUEOUS COATING COMPOSITION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an ultra-high shear (UHS) high-capacity method for the preparation of an aqueous coating composition comprising one or more plant proteins, to the coating composition thus obtained and to the use of said coating composition to coat a cellulosic fibrous substrate or other substrates / materials. In particular, this invention relates to a composition suitable for coating paper and cardboard for packaging purposes, especially for food packaging and a process for preparing the composition. Specifically, the invention relates to the manufacture of food containers, such as containers used to hold ready to eat food from shops and stalls. Such examples can include cardboard boxes for holding food such as pasta or curries. Such packaging needs to be able to withstand both water and oilcontaining liquids for long enough for the food to be carried and eaten without leakage. The invention also relates to aqueous coating compositions suitable for other coating applications, such as the coating or encapsulation of actives such as vitamins, fragrances, flavours, nutraceuticals and medications or even the coating of foods such as fruits to extend their period of use. The aqueous coating compositions of the present invention can also be used in some non-substrate coating applications, for example emulsion stabilizers, where plant protein particles coat the surface of oily droplets dispersed in the emulsion.

[0004] BACKGROUND OF THE INVENTION

[0005] Traditionally, the necessary liquid resistance for cardboard food packaging has been provided by a thin layer of plastic laminated to the inner surface of the cardboard. This is undesirable because it limits the biodegradability and / or recyclability of the package and there has been extensive research into the use of biodegradable alternatives.

[0006] The inventors have previously discovered that a dispersion containing plant protein and additives such as e.g. organic acids can be used as a coating for cardboard or paper to increase its ability to resist both water and oils for use as food packaging. The use of plant proteins, such as pea, soy or bean proteins can have technical and environmental advantages whilst avoiding the use of animal products, which can be problematic to some people on moral or ethical grounds. Typically plant proteins are larger and less soluble than animal proteins and are globular in form. There are many processes for preparing such mixes. Typically, these processes will involve a step to unfold or denature the globular protein or to shear the protein to mechanically break open the protein particles.

[0007] A necessary step in reported methods for preparation of a plant protein containing composition for use as a coating is to shear the plant protein slurry in the presence of heat and high levels of organic acid to cause the globular plant proteins to denature and unfold and form a hydrogel. The organic acid typically acts as a solvent for the globular plant protein rather than being added solely for the purpose of pH control. This hydrogel can then be sheared to form a flowable slurry and formed into a film. However, the reported methods typically involve the use of high levels of organic acids, such as acetic acid, and this makes the process of forming a film or coating layer more complex, or coating layer more complex.

[0008] The inventive composition and process can use lower levels of organic acid as compared to the art and a simpler process and equipment which is better suited to large-scale production.

[0009] The proteins are dispersed in known methods by the use of high shear equipment such as an ultrasonic sonicator. However, sonicators are energy intensive and more difficult to scale up to large scale production. There is therefore an interest in finding processes and compositions that are suitable for large-scale production. A particular issue specifically relating to large industrial-scale production, as compared to lab-scale work, is that of temperature control. Heating and cooling large quantities and large containers of a material is much harder at industrial scale due to the reduced surface area to volume ratio. Ease of handling on a large scale also means that lower viscosity mixes are preferable. Industrial scale is herein defined as production rates of greater than 0.5 litres / minute, such as greater than 1 litres / minute or greater than 2 litters / minute, as this rate would produce larger quantities of composition and is much greater than the rates typical of lab-scale equipment.

[0010] There is also an interest in ensuring that all of the ingredients or materials used in such food packaging are food grade and / or food-contact safe for consumption in case some of the coating, or indeed even part of the package itself are accidentally ingested. Plant-protein containing compositions for coating substrates such as paper and cardboard are known in the art. Examples include compositions for use in paper sizing, in ink and paint compositions and as adhesives.

[0011] As stated earlier, the plant protein coating composition needs to provide resistance to watercontaining foods. Therefor plant proteins with higher aqueous solubilities are typically less suited for such compositions. Zhang et al (Food Science and Technology 153(2022) 112542 processed Tigernut Sedge to form a protein concentrate at 71%. A 2% suspension of the protein isolate was dispersed in phosphate buffer at pH 7 and batches passed through a H PH at pressures of 0, 40, 60, 80, 100, 120 and 140 MPa with cooling afterwards. The secondary structure began to be affected at processing pressures above 40 mPa.

[0012] Moll et al (J. Food Sci. 2022; 87: 4623-4635) passed a 5% insoluble pea protein suspension (prepared from protein isolate) at pH 3 and pH 5 through a HPH at pressures of 50 MPa, 100 MPa and 150 MPa. The pH had been adjusted using HCI and the temperature was less than 25 °C at the outlet. The homogenized suspension had improved foaming properties.

[0013] Song et al (Industrial Crops and Products 43 (2013) 538-544) prepared a 7% suspension of soy protein isolate in water and passed it through a HPH after stirring and ultrasonic treatment. The homogenized suspension was passed through a cooling coil in ice after the HPH. The homogenized suspension was then mixed with glycerol (30% of the protein solids) and cast into films at 30 °C.

[0014] Ong et al (Food Structure 34 (2022) 100298) homogenized 4% samples of pea protein isolate in water at 10 °C at 60, 120 and 180 MPa. The homogenized mixes were cooled to 20 °C after each pass in an ice bath. The highest recorded temperature after the homogenizer was 48 °C.

[0015] US 2024 / 0196928 discloses a process of passing plant proteins, specifically claiming chickpea, through a high-pressure homogenizer at concentrations of > 10 wt% in water. The sheared suspensions are to be added in drinks as a nutritional supplement. In US 2024 / 0196928 the chickpea suspensions were pre-sheared in an Ultraturrax mixer to form a lower viscosity mix which could be processed through the HPH. Interestingly, pre-shearing a sample of pea protein isolate in water (7.5% solids) in the Ultraturrax did not give any benefit in reducing the viscosity of the mix. If anything, it marginally increased viscosity. Higher concentrations could not be processed. The examples and application all show that chickpea protein is uniquely able to be processed at these high concentrations and behaves quite differently to other plant proteins. This is likely due to its higher inherent aqueous solubility. There is no information on temperatures during processing and the suspensions are simply plant protein and water. US 2023 / 331932 discloses a multi-step process for the production of an aqueous slurry comprising small fragments of protein hydrogel dispersed in water. A plant protein is solubilised in an initial aqueous solvent / additive mix at high temperature with some shear. The exemplary examples use extended heating at temperatures of 80 °C to 85 °C followed by a limited sonication shear step. The sonication step is described as “a short sonication step to disrupt large colloidal aggregates”. The resulting hot transparent protein solution is then cooled, which forms a solid hydrogel in preparation for further processing. The solid hydrogel is broken or cut into larger fragments, washed to remove non-aqueous solvent and then further sheared to form the desired slurry of small hydrogel fragments.

[0016] The protein slurry can be mixed with further additives, such as plasticisers, and can be used for coatings or film-forming. The initial protein compositions disclosed in US 2023 / 331932 contain additives (the non-aqueous co-solvents) at levels between -280% and -400% of the level of protein. The formation of a solid protein hydrogel after the heating / shearing step is an integral requirement of US 2023 / 331932 as it would not otherwise be possible to subject the protein composition to the required subsequent processing steps. This is fundamentally different to the inventive process where the desired result after the shearing step is a stable, flowable aqueous protein dispersion and where there are no subsequent processing steps needed to change the composition of the dispersion.

[0017] The present invention provides practical advantages over the process described in US 2023 / 331932. It is considerably less complex, does not require high levels of additives and is more easily scaled to industrial production. This comes from the inventive combination of compositions, specified levels of applied shear and the use of viscosity reduction steps (such as the rapid reduction of post-shear temperature) at different stages of the process. US 2023 / 331932 can be regarded as a process that fully solubilises plant proteins first and then modifies the solubilised plant proteins to have a required level of insolubility whereas the inventive process modifies mostly insoluble plant protein dispersions to have a required level of solubility. This is more efficient. The inventors have discovered that subjecting a plant protein dispersion containing a lower level of additives to a high level of shear is sufficient to reduce particle size and partially denature the plant protein particles, making then better coating agents. The use of a lower level of additives, such that the additives do not need to be removed from the protein coating mix prior to use as happens in US 2023 / 331932, is particularly attractive due to cost and simplification reasons. The disclosed levels of additives in US 2023 / 331932 are between -280% and -400% of the level of protein, which is very different to the 25%-150% described in the present invention. The partially denatured nature of the sheared and milled plant protein particles makes them liable to aggregate on storage resulting in increases in viscosity and consequent handling issues.

[0018] The inventors have seen that it is necessary to combine viscosity reduction / control steps with the compositional requirements and the minimum level of shear to have a viable process. A particularly effective viscosity control step is control of the temperature in the HPH combined with a very rapid reduction in mix temperature afterwards. US 2023 / 331932 does not disclose information about required levels of shear, required temperatures after shearing, the impact of the rate of cooling on the properties of the mix and requires the protein compositions being processed to have high levels of additives.

[0019] The inventors have seen that the use of high-pressure homogenizers (HPHs) is suitable for preparing the inventive plant protein containing compositions provided that the dispersions are processed at a suitably high pressure to ensure that the protein particles are reduced sufficiently in size to form a suitably coherent, high-quality coating on a substrate that has sufficient barrier properties. Without wishing to be bound by theory, it is believed that the presence of some organic acid in the inventive plant protein containing compositions can partially solvate and soften the protein particles and make them easier to disrupt and break up when passing through the high-pressure homogenizer. It can also be beneficial for mixtures fed to the homogenizer to have a pre-treatment step to assist the performance of the HPH.

[0020] A high-pressure homogenizer comprises a small nozzle through which the liquid is forced. The design of the nozzle and the very high shear at this point disrupts the protein particles, reducing their size and forming the desired dispersion. High-pressure homogenization refers to the process of pumping a stream of liquid through a constriction, e.g. valve, impact surface, narrow pipe or slits causing various degrees of shearing, turbulence and / or cavitation which homogenize the sample, i.e. mix and / or reduce the particle size of any components of the liquid. The high shear forces cause friction between fluid elements and can increase the temperature of the mixture. Optionally high-pressure steam can also be used resulting in additional heating of the liquid. High pressure homogenization can also pasteurize the liquid prolonging the shelf-life of the mixture obtained. The liquid may be passed through the homogenizer at various levels of pressure and / or kinetic energy once or multiple times to achieve the desired mixture properties. The intensity of the shear in a HPH is related to the pressure involved and the operation of a HPH is typically defined and characterized by the pressure at the nozzle. Higher pressures mean higher shear. The inventors have seen that the viscosity and tendency to gel of aged, sheared plant protein compositions can be high, making general handling and pumping more difficult, especially at industrial scale. This can be avoided by the use of lower concentrations of plant protein in the compositions. However, this then can make the subsequent coating process more difficult due to the higher levels of aqueous coating composition that will then need to be applied to a substrate and dried to get a required coating thickness and level.

[0021] Hence it is beneficial to be able to make suitable plant protein-based aqueous coating compositions at higher solids levels and with lower coating composition viscosities after processing. The inventors have seen that application of one or more viscosity adjustment steps during the processing reduces the viscosity of suitable aqueous coating compositions after processing compared to the same process without applying the one or more viscosity adjustment steps. The viscosity adjustment step can take place at different points in the process. Without wishing to be bound by theory it is believed that the mechanism is specific to each processing step but all result in the same effect of reducing the viscosity of the final aged aqueous coating composition.

[0022] SUMMARY OF THE INVENTION

[0023] Therefore, in a first aspect, the present invention relates to an ultra-high shear (UHS) high- capacity method for the preparation of an aqueous coating composition comprising one or more plant protein-containing materials having plant proteins at a total level of between 7 % and 25 % of the weight of the coating composition and one or more additives selected from the group consisting of organic acids, plasticisers, surfactants, pH-adjustment materials and mixtures thereof at a total solids level of between 25 % and 150 % of the total weight of the one or more plant proteins, said method comprising the following steps:

[0024] (a) mixing together the one or more plant protein-containing materials and the one or more additives with water to form an initial dispersion of pH 10 or less;

[0025] (b) passing the initial dispersion at least once through a High-Pressure Homogenizer at a pressure of greater than 40 MPa and at a rate of greater than 0.5 litre / minutes to form a sheared dispersion;

[0026] (c) actively cooling the sheared dispersion to form an aqueous coating dispersion;

[0027] (d) ageing the aqueous coating dispersion to form the aqueous coating composition; wherein at least step (c) is a viscosity adjustment step that results in reducing the viscosity of the aged aqueous coating composition compared to the method wherein step (c) is not a viscosity adjustment step. In another aspect, the present invention relates to an aqueous coating composition obtained or obtainable by said method.

[0028] In a further aspect, the present invention relates to the use of said aqueous coating composition to coat a substrate or as an emulsion stabilizer.

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] In a first aspect, the present invention relates to an ultra-high shear (UHS) high-capacity method for the preparation of an aqueous coating composition comprising one or more plant protein-containing materials having plant proteins at a total level of between 7 % and 25 % of the weight of the coating composition and one or more additives selected from the group consisting of organic acids, plasticisers, surfactants, pH-adjustment materials and mixtures thereof at a total solids level of between 25 % and 150 % of the total weight of the one or more plant proteins, said method comprising the following steps:

[0031] (a) mixing together the one or more plant protein-containing materials and the one or more additives with water to form an initial dispersion of pH 10 or less;

[0032] (b) passing the initial dispersion at least once through a High-Pressure Homogenizer at a pressure of greater than 40 MPa and at a rate of greater than 0.5 litre / minutes to form a sheared dispersion;

[0033] (c) actively cooling the sheared dispersion to form an aqueous coating dispersion;

[0034] (d) ageing the aqueous coating dispersion to form the aqueous coating composition; wherein at least step (c) is a viscosity adjustment step that results in reducing the viscosity of the aged aqueous coating composition compared to the method wherein step (c) is not a viscosity adjustment step.

[0035] The term “total solids level” refers to the combined weight of the additives minus any solvents or carriers they may be dispersed or dissolved in and any impurities and adjuncts associated with them.

[0036] “Actively cooling” refers to a process where energy is used to forcibly and quickly remove heat from a system. This can include forced convection and conduction. For example, liquid cooling can be used where pumps circulate coolant, such as very cold water or a refrigerant, through a cold plate, such as in a heat exchanger, in order to forcibly remove heat from a material. Alternatively, a fan or blower can be used to move air over a material at high speed to increase heat transfer, relative to a system where the air is still. This compares to “passively cooling” which refers to a process which relies on natural processes of convection, conduction or radiation where there is no use of external energy to increase the rate of heat removal.

[0037] In a preferred aspect of the present invention, at least one of steps (a), (b) and (d) includes a viscosity adjustment step that results in reducing the viscosity of the aged aqueous coating composition compared to the method wherein the viscosity adjustment step is not included.

[0038] In a preferred aspect of the present invention, the viscosity adjustment step comprises taking the temperature of the sheared dispersion at the nozzle of the High-Pressure Homogenizer in step (b) above 35 °C, more preferably above 40 °C, most preferably above 50 °C. The temperature of the sheared dispersion at the nozzle of the High-Pressure Homogenizer is preferably kept below 95 °C, preferably below 90 °C and more preferably below 85 °C. A preferred feature is to use in-line cooling of the HPH nozzle to keep temperatures from rising excessively.

[0039] In another preferred aspect of the present invention, the viscosity adjustment step comprises actively cooling the sheared dispersion in step (c) to less than 40 °C, more preferably less than 35 °C, most preferably less than 30 °C.

[0040] In another preferred aspect of the present invention, the viscosity adjustment step comprises cooling the sheared dispersion in step (c) faster than passively cooling through natural conduction and convection. The time taken to reach less than 40°C is less than 60 minutes, preferably less than 30 minutes, more preferably less than 10 minutes, even more preferably less than 5 minutes, most preferably less than 1 minute.

[0041] In a further preferred aspect of the present invention, the viscosity adjustment step comprises mixing the initial dispersion and optionally heating the initial dispersion in step (a) to above 30 °C, preferably to above 35 °C, more preferably to above 40 °C.

[0042] The degree of heating or cooling that is required to control the temperatures of different compositions can be variable. One reason for this is the difference between the heat capacities of different compositions due to the different levels of the various non-aqueous components. Materials such as plant proteins or organic acids have significantly lower heat capacities. One consequence is that the industrially preferred more concentrated coating dispersions can be over-heated more easily during standard processing due to their lower heat capacities. In another preferred aspect of the present invention, the viscosity adjustment step comprises ageing the initial dispersion in step (a) for more than 1 hour prior to step (b), more preferably more than 6 hours, most preferably more than 12 hours. The ageing of the initial dispersion can be carried out as part of the preparation of a large batch of initial dispersion. It can also be advantageous to prepare the initial dispersion in a different location to where it is processed by the inventive process. The use of an ageing step can allow the larger protein particles in the initial dispersion to become at least partially solvated prior to the High- Pressure Homogenizer step. This is believed to further help the denaturing of the protein in the HPH to further expose the more hydrophobic regions of the protein structure.

[0043] In a further preferred aspect of the present invention, the viscosity adjustment step comprises ageing the aqueous coating composition in step (d), preferably under shear. The plant protein particles or fragments formed after step (b) can aggregate to form larger aggregates and macrostructures in the dispersion. This is the mechanism of the unwanted gelling and viscosity increase. Without wishing to be bound by theory, it is believed that the aggregation of the sheared protein fragments is similar in behaviour to a first order chemical reaction with the temperature affecting the rate of aggregation in an analogous manner to how temperature typically affects chemical reactions, where a 10 °C temperature increase can often result in a doubling of the reaction constant according to the Arrhenius equation.

[0044] Preferably, ageing the aqueous coating composition in step (d) is done at a temperature between 40°C and 5 °C, more preferably between 35°C and 10°C, even more preferably between 30°C and 15°C, and most preferably between 25°C and 17°C.

[0045] Preferably, ageing the aqueous coating composition in step (d) includes cooling over the ageing period from the temperature achieved in step (c) to a long-term storage temperature, usually ambient. Preferably this cooling is achieved through passively cooling the composition. For the avoidance of doubt stirring the ageing composition in step (d) is not considered active cooling.

[0046] In a preferred aspect of the present invention, the initial dispersion is passed through the High-Pressure Homogenizer in step (b) at a rate of greater than 0.5 litre / minute, more preferably greater than 1.0 litre / minute, most preferably greater than 2.0 litre / minute.

[0047] The terms "mixing" and "shearing" have different meanings in the context of this invention even though mixing will involve some shearing. Mixing - even high-shear mixing - describes a process of agitating and stirring a bulk mass of material so as to mix and homogenise materials on a larger macro-scale to form a bulk homogenous mixture. Ultra-High-Shearing (UHS) refers to a process where a material is subjected to a very intense, but very localised, shear field. The high degree of localisation, for example at the nozzle of a High Pressure Homogenizer, is required to create the very intense shear field needed change the form and nature of the material being sheared. However, this also means that a High Pressure Homogenizer is incapable of homogenising mixtures on a bulk, macro-scale. "Shearing" needs to happen on a micro-scale. Hence mixtures need to be mixed, e.g. by stirring, to form a homogenous mix before they are sheared.

[0048] The mixing in step (a) must be sufficient to create a homogeneous mixture on a macro-scale. The level of shear in step (a) is significantly lower than in step (b) and does result in changes in the micro-structure of the protein-containing material or the additives and auxiliary agents. In accordance with the present invention in step (b) the High Pressure Homogeniser must operate at a pressure greater than 40 MPa in order to create sufficiently high shear, referred to as Ultra-High Shear (UHS), to result in changes in microstructure. In a preferred aspect of the present invention, step (a) is carried out using a low shear mixer such as an agitator with a rotating blade. Alternatively, step (a) is carried out using a high shear mixer such as a rotor / stator mixer, for example a Silverson mixer.

[0049] Preferably, step (b) is carried out in a High-Pressure Homogenizer having a piston-gap nozzle.

[0050] Usually, it is sufficient to carry out step (b) once, but it may also be desirable to carry out step (b) more than once.

[0051] In one aspect of the present invention the additives in step (a) are mixed with water before the plant protein-containing material.

[0052] In an alternative aspect of the present invention the plant protein-containing material in step (a) is mixed with water before the additives.

[0053] Plant-based proteins are mainly comprised of globular proteins which are storage proteins and can be classified as albumins (soluble in water), globulins (soluble in dilute salt solutions), prolamins (soluble in aqueous ethanol solutions), and glutelins (soluble in dilute acid / alkaline solutions or insoluble in water). Albumins and globulins are predominately present in all pulses (at greater than 50%) and some pseudo cereals (such as quinoa and amaranth). Globulins represent between about 70 and 78 wt% of the protein found in legume seeds, whereas albumins constitute between about 10 and 20 wt% of the protein. Globulins are the storage proteins of most legume seeds. Globulins have higher molecular weights than albumins and are insoluble in pure water but dissolve in dilute salt solutions. Globulins are typically more water soluble than prolamins.

[0054] The storage proteins from different plants can be classified by their sedimentation coefficient in Svedberg units (S). This coefficient indicates the speed of sedimentation of a macromolecule in a centrifugal field. It should be noted however that some small variations of sedimentations are expected depending on the type of plant and / or the extraction protocol employed. Therefore, the sedimentation coefficient is not intended to be restrictive, but rather serve as a useful guide for the classification of the storage proteins.

[0055] The major globulins found in pulses are vicilin (7S) and legumin (11S). The vicilin (7S) has a trimeric structure with molecular mass (MM) of -175-180 kDa and lacks disulfide bridging. In contrast, the legumin (11 S) has a hexameric (MM of -340-360 kDa) quaternary structure composed of 6 subunits (MM of ~60kDa) linked by non-covalent interactions. Each subunit pair is comprised of an acidic (MM -40 kDa) and basic (MM -20 kDa) chain joined by a disulfide bond. The ratio of the legumin:vicilin (L / V) is not fixed and may vary among different pulse varieties and species. A third globulin pulse protein is convicilin with 3 or 4 subunits each having a MM of -70 kDa and a sedimentation coefficient of -8S. Convicilin is present in lesser amounts as compared to other globulins. Other globulins include for example 2S globulins, conglutin, sfa, edestin, amandin, concanvalin, cruciferin, helianthinin.

[0056] The albumins found in pulse proteins are soluble proteins with a variable molecular mass (-12-28 kDa). Albumin proteins include for example 2S albumins, napins, barley trypsin inhibitor and wheat a-amylase inhibitor. In typical commercial protein isolates, there are generally only residual amounts of albumins present as they are generally removed during the protein extraction process.

[0057] Globulins are typically obtained from soybean, pea, rice, potato, rapeseed, sunflower, lentil, bean, fava bean, mung bean, sunflower seed, pumpkin seed, flax, chia, canola, lupine, alfalfa, moringa, borage, hemp seed, and cotton seed; preferably obtained from pea protein, potato protein, rapeseed protein, and / or sunflower protein. Prolamins and glutelins make up 85% of protein in the cereal and pseudo cereal families. Prolamins are typically found in wheat, corn, barley and rye whilst glutelins are typically only found in wheat and rice.

[0058] Prolamins are high in proline and glutamine amino acid content. They have a relatively high fraction of non-polar functionalities. They are less abundant than globulins and are found across fewer plant species. They include gliadin from wheat, hordein from barley, secalin from rye, zein (alpha, beta, gamma) from corn, kafirin from sorghum, avenin from oats. Prolamins are typically much less water soluble than Globulins.

[0059] Within the scope of the present invention plant-based proteins may comprise albumins, globulins, prolamins and glutelins and mixtures thereof. The plant-based protein containing materials have preferably higher levels of globulins, prolamins and glutelins, more preferably higher levels of globulins and glutelins, most preferably higher levels of prolamins..

[0060] In a preferred aspect of the present invention, the plant protein-containing material is selected from the group consisting of soybean protein, pea protein, rice protein, potato protein, rapeseed protein, sunflower protein, lentil protein, bean protein, fava bean protein, mung bean protein, sunflower seed protein, pumpkin seed protein, flax protein, chia protein, canola protein, lupine protein, alfalfa protein, moringa protein, borage protein, hemp seed protein, cotton seed protein, wheat protein, barley protein, rye protein, corn protein, sorghum protein, oats protein and mixtures thereof.

[0061] Mixtures of plant protein-containing materials may be selected so as to optimize the viscosity of the aqueous coating compositions. Without wishing to be bound by theory it is believed that different plant proteins swell to different degrees in water, thereby resulting in different aqueous coating composition viscosities. For example, rice protein which contains high levels of more hydrophobic glutelins, can swell less result in lower viscosities. This can be mixed with pea protein which contains higher levels of more hydrophilic globulins and can swell more resulting in higher aqueous composition viscosities.

[0062] In a preferred aspect of the present invention, the plant protein-containing material is selected from protein isolates, protein concentrates, and flours which have been processed to increase the protein content of the plant-containing material.

[0063] Plant protein-containing materials can be extracted from plants by a variety of processes that can determine the concentration of protein in such plant protein-containing materials. Plant protein isolates have a higher concentration of protein, typically 80%. Plant protein concentrates have a lower concentration of protein, typically 65%, and plant protein flours have the lowest concentration of protein, typically 55%. The amount of plant protein in the plant protein-containing material is preferably greater than 25%.

[0064] Plant proteins are typically isolated from plants or plant material that is a by-product from their processing for other uses, such as plant meal or cake from seed oil extraction processes, or spent grain from the brewing and distilling industry, for example for rapeseed oil extraction as described by Ahlstrom et al in Molecules 2022, 27(9), 2957. Typically the plant protein-containing material goes through a process of alkaline wet extraction at high pH, for example with sodium hydroxide, where the protein is solubilized and then separated from the insoluble fibres and starches through centrifugation. Alternatively the plant proteincontaining material goes through a process of neutral salt wet extraction. The extracted protein can then be precipitated by isoelectric precipitation through addition of an acid, for example citric, hydrochloric or sulphuric acid, and separated from the liquid by centrifugation or filtration. The resulting wet material can be further purified and is often spray dried into a powder. The degree of separation and purification in the process results in different protein concentrations in the plant protein-containing material and whether the material is an isolate, a concentrate or a flour.

[0065] Suitable by-product plant-protein containing materials include corn gluten meal, soybean meal, cottonseed meal, hemp meal, brewer’s spent grain and distiller’s spent grain.

[0066] In one aspect of the present invention the plant protein-containing material in step (a) is a dry powder. In an alternative aspect of the present invention the plant protein-containing material in step (a) is an aqueous mixture. In the later it is simply necessary to take account of the water coming with this mixture, with less water added directly to the formulation. Therefore wherein step (a) of the claimed process involves the mixing together the one or more plant protein-containing materials and the one or more additives with water to form an initial dispersion, such water may be introduced as part of the wet plant protein-containing materials or be added directly.

[0067] The remaining plant material is composed of carbohydrates. The level of carbohydrate can be analysed by readily available methods, such as the phenol-sulfuric acid method, in which polysaccharides are hydrolysed and then converted to furfural or 5-hydroxymethyllfurfural. These compounds react with a developer to generate a chromogen, which can be detected spectrophotometrically. Even more preferably the plant-protein containing material is selected from the group consisting of pea protein, potato protein, rapeseed protein, rice protein, cottonseed protein and / or sunflower protein. Most preferably the plant-protein containing material comprises pea protein.

[0068] According to the present invention additives are essential for the formation of a coherent coating when the coating composition is applied to a substrate. In accordance with the present invention, the one or more additives are selected from the group consisting of organic acids, plasticisers, surfactants, pH-adjustment materials and mixtures thereof.

[0069] In a preferred aspect of the invention, the aqueous coating composition comprises one or more organic acids selected from the group consisting of acetic acid, an a-hydroxy acid, or a P-hydroxy acid. More preferably, the organic acid is selected from acetic acid, lactic acid, citric acid, oleic acid, malic acid, maleic acid, glycolic acid, gluconic acid, tartaric acid, - hydroxypropionic acid, p-hydroxybutyric acid, p-hydroxy p-methylbutyric acid, 2- hydroxybenzoic acid, carnitine and mixtures thereof. Even more preferably, the organic acid is selected from acetic acid, oleic acid and / or lactic acid. Most preferably the organic acid is lactic acid.

[0070] An acid is a compound which dissociates in water to produce an acidic environment. Organic acids usually are considered as weak acids dissociating partially in water.

[0071] In preferred coatings of the present invention, the organic acid is a volatile organic acid (i.e. those having a boiling point of less than 120 °C at atmospheric pressure), preferably acetic acid. This is because volatile organic acids can be easily removed from a coating mixture during the drying step, such that the final coating contains little, if any, residual organic acid.

[0072] In alternatively preferred coatings of the present invention, the organic acid is a low volatility organic acid (i.e. those having a boiling point greater than 120 °C at atmospheric pressure), preferably lactic acid. This is because less volatile organic acids are less easily removed from a coating mixture during a drying step, enabling them to have a dual function as a plasticiser.

[0073] In alternative preferred coatings of the present invention, the organic acid is a fatty acid, wherein the fatty acids include, but are not limited to, fatty acids having carbon chain lengths of six to twenty-two, preferable ten to twenty-two, more preferably from 18 to about 20 carbon atoms. Both saturated and unsaturated carbon chains are equally suitable. Oleic acid is a monounsaturated 18 carbon chain. The fatty acid can be extracted from animal or plant fats and oils. It can be used in the inventive mixtures as a pure compound or as part of a natural oil, for example rapeseed oil has a high content of oleic acid. Preferably oleic acid is extracted from plant sources.

[0074] Mixing of the plant-based protein with organic acid can be done with pure or highly concentrated acids, such as glacial acetic acid. However, concentrated acid solutions can be dangerous to be handled at large scale. Preferably, the mixing of the plant-based protein with organic acid involves the use of an aqueous organic acid solution. The concentration of the organic acid is not particularly limiting provided that the desired end concentration is achievable.

[0075] When the substrates that are to be coated are flexible it is important to avoid them cracking when handled, for example when card is folded into boxes, so as not to expose the underlying original uncoated substrate. Plasticisers maybe hydrophobic or hydrophilic. Hydrophilic plasticisers can negatively affect the coatings moisture resistance whilst hydrophobic plasticisers can negatively affect the coatings oil resistance, so the levels need to be controlled to balance these features.

[0076] In preferred coatings of the present invention, the one or more hydrophilic plasticisers are independently selected from the group consisting of: a) polyols formed by from 1 to 20 repeating hydroxylated units each unit including from 2 to 6 carbon atoms, provided that when the polyol is formed by only one repeating unit it has at least 4 carbon atoms, with the exclusion of sorbitol, b) ethers, thioethers, inorganic and organic esters, acetals and amino-derivatives of polyols formed by from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms with the exclusion of acetic esters of glycerine, triethyl citrate and tributyl citrate, c) polyol reaction products having from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms with chain extenders, d) polyol oxidation products having from 1 to 20 repeating hydroxylated units each including from 2 to 6 carbon atoms including at least one aldehydic or carboxylic functional group or mixtures thereof.

[0077] In preferred coatings of the present invention a hydrophobic plasticiser can be a water insoluble vegetable oil or wax. Preferred waxes are made from natural waxes passing the OECD301B biodegradation screening test, such as bees wax, rapeseed wax, castor wax, candelilla wax, soy wax, palm oil wax, carnauba wax, rice bran wax, or another natural wax, provided that the temperature of exposure does not exceed the wax melting point. In some cases, some paraffin oil-based waxes may also pass OECD301B.

[0078] Preferred plasticisers are selected from the group consisting of glycerol, propylene glycol, polyethylene glycol, sorbitol, erythritol, mannitol, xylitol, triethyl citrate, monoglycerides, diglycerides, triglycerides, glucose, mannose, fructose, sucrose, urea, lecithin, waxes, and amino acids and mixtures thereof.

[0079] Preferably, the plasticisers are bio-based and even more preferably plant-derived. Plasticisers can also be added in the form of a mixture with other components, preferably a bio-based and even more preferably a plant-derived mixture.

[0080] The aqueous coating composition may include surfactants. Suitable surfactants may include, but are not limited to, the nonionic, cationic, anionic and zwitterionic classes. Suitable surfactants may include, but are not limited to, polyoxyethylenated polyoxypropylene glycols, alcohol ethoxylates, alkylphenol ethoxylates, tertiary acetylenic glycols and alkanolamides (nonionics), polyoxyethylenated amines, quaternary ammonium salts and quaternised polyoxyethylenated amines (cationics), and amine oxides, N-alkylbetaines and sulfobetaines (zwitterionics). Other suitable surfactants may include, but are not limited to, dioctyl sodium sulfosuccinate, lactylated fatty acid esters of glycerol and propylene glycol, lactylic esters of fatty acids, sodium alkyl sulfates, polysorbate 20, polysorbate 60, polysorbate 65, polysorbate 80, lecithin, acetylated fatty acid esters of glycerol and propylene glycol, and acetylated esters of fatty acids, and combinations thereof. The amount of surfactant in the dry coating may be in a range of from about 0.1 wt.% to about 2.5 wt %, preferably from about 1.0 wt.% to 2.0 wt.% by weight of the dry coating. The pH of the aqueous composition can be adjusted so that it is either acidic, neutral or alkaline. In a preferred aspect of the present invention, the pH of the aqueous coating composition is less than 10.

[0081] The pH of the aqueous composition can be adjusted so that it is either acidic, neutral or alkaline. In accordance with the present invention the pH of the aqueous coating composition is alkaline with a pH of 10 or less. In a preferred aspect of the present invention the pH of the aqueous coating composition is alkaline with a pH of less than 9.5, such as pH 9 or pH 8.5. Without wishing to be bound by theory it is believed that limiting the pH to 10 or less will limit any alkaline hydrolysis of the plant protein to an insignificant level. Typically, alkaline hydrolysis of plant protein, which is not a desired feature of the present invention, will only happen at pH values greater than 10, such as around pH 11 or pH 12. Controlling the pH to 10 or less allows for the use of chemistries and additives that may work best under alkaline conditions without risk of unwanted alkaline hydrolysis of the plant protein.

[0082] The aqueous coating composition may include pH-adjusting materials other than organic acids. pH-adjusting agents of this invention that reduce pH include inorganic acids, including hydrochloric acid, sulphuric acid, nitric acid, phosphoric acid, hydrofluoric acid and carbonic acid. pH-adjusting agents of this invention that increase pH include alkalis, bases that are water soluble, include sodium hydroxide, potassium hydroxide, calcium hydroxide and ammonia. For avoidance of doubt materials such as silanes and metasilicates are classed as auxiliary agents for the purpose of this invention.

[0083] In a preferred aspect of the present invention the pH of the aqueous coating composition is more than 0.5 units, more preferably more than 1.0 unit away from the isoelectric point of the plant protein. Without wishing to be bound by theory it is believed that this can reduce the likelihood of unwanted plant protein aggregation.

[0084] The aqueous composition may additionally comprise one or more auxiliary agents. An auxiliary agent may be a processing aid or may be a material that can enhance or modify the properties of the coating once it is formed on the substrate.

[0085] The aqueous coating composition may additionally comprise an auxiliary agent such as titanium dioxide. This can provide both a whitening effect for paper substrates but also can act as a processing aid by reducing the viscosity of the protein mixture.

[0086] The aqueous coating composition may additionally comprise an auxiliary agent such as a phyllosilicate. Preferably, said phyllosilicate is a serpentine mineral, a clay mineral, a chlorite mineral or a mica mineral, or mixtures thereof. Preferably, said clay mineral is selected from bentonite, kaolinite, pyrophyllite, vermiculite and a smectite (e.g. montmorillonite, cloisite, laponite, hectorite etc.), or mixtures thereof. Phyllosilicates can improve the barrier properties of the coating formed by applying the aqueous coating composition to a substrate.

[0087] The aqueous coating composition may additionally comprise an auxiliary agent such as a silicon-containing compound, e.g. selected from silica sol, silica powders, hydrolysable silanes, sodium silicates such as sodium metasilicate, sodium orthosilicate and sodium pyrosilicate, tetra ethoxy silane (commonly known as tetraethyl orthosilicate, TEOS), tetrapropyl orthosilicate, dimethyl diethoxysilane, methyltriethoxysilane and tetramethyl orthosilicate, or combinations thereof. Silicon-containing compounds can improve the barrier properties of the coating formed by applying the aqueous coating composition to a substrate. The aqueous coating composition may additionally comprise auxiliary agents such as biodegradable polymers. Preferably additional biodegradable polymers are selected from plant derived polysaccharides such as pectins, starches, konjac glucomannan and gums such as guar gum, gum Arabic, locust bean gum or xanthan gum, algae derived polysaccharides such as alginates, carrageenan, agar, fucoidan, fungi derived polysaccharides, microbial derived polysaccharides (such as gellan gum and bacterial cellulose), microbial derived polyesters (such as polyhydroxyalkanoates, PHA), biodegradable polyesters (such as polylactic acid, PLA), chitosan, shellac, cutin, lignin, cellulose, microfibri Hated cellulose (MFC), nanofibrillated cellulose (NFC), microcrystalline cellulose, microbial nanocellulose or cellulose nanocrystals (CNC). Preferably the additional biodegradable polymers are naturally sourced. Preferably the additional biodegradable polymers are not animal derived.

[0088] The aqueous coating composition may additionally comprise auxiliary agents such as synthetic polymers. Preferably additional synthetic polymers are selected from polyvinyl alcohol, styrene-butadiene rubber (SBR) latex, silicone-based polymers, vinyl polymers, polyesters, polyethers, polycarbonates, and acrylic-based polymers. The acrylic-based polymer latex may include an acrylate homo- or co-polymer that is the polymerization product of one or more acrylate monomers, such as alkyl, aryl, alkaryl (meth)acrylates, esters of acrylic and methacrylic acid with alcohols which contain at least one further hetero atom in addition to the oxygen atom in the alcohol group and / or which contain an aliphatic or aromatic ring. Exemplary acrylate monomers include, for example, methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, cyclohexyl (meth)acrylate, phenylethyl (meth)acrylate, phenylpropyl (meth)acrylate, acrylates of heterocyclic alcohols, e,g., furfuryl (meth)acrylate, and combinations thereof. The acrylate homo- or co-polymers in the acrylic-based polymer latex may also include other polymerized monomers such as those having olefinic double bond(s) capable of undergoing free radical polymerization, including but not limited to vinyl esters, vinylaromatic compounds, nitriles, vinyl halides, hydrocarbons, and the like, such as vinyl laurate, vinyl stearate, vinyl propionate, vinyl acetate, vinyltoluene, a- and p-styrene, a- butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, styrene, chlorine-, fluorine- or brominesubstituted ethylenically unsaturated compounds, vinyl chloride, vinylidene chloride, butadiene, isoprene, chloroprene, and combinations thereof. The aqueous coating composition may additionally comprise auxiliary agents such as colorants. Suitable colorants include, but are not limited to, organic or inorganic pigments and dyes. Suitable dyes include, for example, fluorescent dyes, azo dyes, anthraquinone dyes, xanthene dyes, azine dyes, and combinations thereof. Organic pigments may be one pigment or a combination of pigments, such as for instance Pigment Yellow Numbers 12, 13, 14, 17, 74, 83, 114, 126, 127, 174, 188; Pigment Red Numbers 2, 22, 23, 48:1, 48:2, 52, 52:1, 53, 57:1, 112, 122, 166, 170, 184, 202, 266, 269; Pigment Orange Numbers 5, 16, 34, 36; Pigment Blue Numbers 15, 15:3, 15:4; Pigment Violet Numbers 3, 23, 27; and / or Pigment Green Number 7. Suitable inorganic pigments that may be included in the compositions are, for example: iron oxides, titanium dioxides, chromium oxides, ferric ammonium ferrocyanides, ferric oxide blacks, Pigment Black Number 7 and / or Pigment White Numbers 6 and 7.

[0089] The aqueous coating composition may additionally comprise other auxiliary agents, such as, but not limited to, aversive agents such as antimicrobial preservatives (e.g.: sodium benzoate, potassium sorbate, 1 ,2-benzisothiazolin-3-one), bitterants (e.g., denatonium salts such as denatonium benzoate, denatonium saccharide, and denatonium chloride; sucrose octaacetate; quinine; flavonoids such as quercetin and naringen; and quassinoids such as quassin and brucine) and pungents (e.g., capsaicin, piperine, allyl isothiocyanate, and resinferatoxin), cross-linking agents (e.g. tannic acid, ferulic acid, gallic acid, epigallocatechin gallate), anti-blocking agents, antifoams, antioxidants, bleaching agents (e.g., sodium metabisulfite, sodium bisulfite or others), detackifying agents, extenders, wetting agents, levelling agents, colloidal stabilisers, rheology modifiers, adhesion promoters, light stabilisers, fillers (e.g. talc or calcium carbonate), lubricants, plasticizer compatibilizers, release agents, salts (e.g.: magnesium chloride, calcium chloride), gas-barrier additives (e.g., nanoparticles such as layered silicate-type nanoclays such as sodium montmorillonite), and other functional ingredients, in amounts suitable for their intended purposes.

[0090] The amount of such auxiliary agents can be up to about 60 wt.%, 50 wt.%, 40 wt.%, 30 wt.%, 20 wt.%, 15 wt.%, 10 wt.%, 5 wt.%, 4 wt.% and / or at least 0.01 wt.%, 0.1 wt.%, 1 wt.%, or 5 wt.%, individually or collectively, by weight of the dry coating.

[0091] The amount of such auxiliary agents can be between 25 wt.% and 100 wt.% individually or collectively, by weight of the one or more plant proteins.

[0092] Additives and auxiliary agents may be added to the composition at any step in the process or after completion of step (d), preferably in step (a). In a preferred aqueous coating composition of the present invention, the plant protein has a dso by volume distribution particle size between 0.1 microns and 50 microns, more preferably between 1 and 40 microns, most preferably between 10 and 30 microns.

[0093] In another aspect, the present invention relates to an aqueous coating composition obtained or obtainable by the inventive method as described hereinbefore.

[0094] The substrate suitable for coating may be any substrate that requires protection. The substrate may have been previously coated with other coating compositions and so result in a multi-layer coating. The substrate coated with the inventive aqueous coating composition may also itself be further over-coated by another coating composition to form a multi-layer coating. The substrate could even be the surface of a droplet of one immiscible liquid dispersed in another liquid.

[0095] The substrate material may be a crystalline material, an amorphous material or a fibre-based material. The material may be natural or synthetic; alternatively, it may be plant-based, animal-based or inorganic. Typical crystalline materials include metals, typical amorphous materials include glass, fibre optics and synthetic or bio-based polymers and typical fibrebased materials include paper, textiles, seeds, fruits and vegetables.

[0096] In one aspect plant-based protein coatings for fibres are preferred due to the opposite charge between the positively charged plant-based protein and the negatively charged fibre material, for example cellulose, resulting in the formation of a strongly bonded coating. These strong electrostatic interactions, typically result in enhanced properties, including mechanical properties such as strength, stiffness, wear resistance, water resistance, and elasticity. Polycations normally used for electrostatically binding to negatively charged cellulose fibres are animal derived (for example chitosan) or are non-biodegradable (i.e. polyvinylamines).

[0097] Fibre-based materials maybe be cellulosic in origin and can be selected from paper and cardboard (bleached, unbleached, coated in which pores still remain, sized, printed, uncoated, super-calendered), wood, fabric or textile, seeds, fruits and vegetables.

[0098] Examples of paper materials can include generally thinner, flexible papers, for example useful as wrapping materials, or in making sachets, as well as generally thicker, rigid papers or cardboard (e.g., corrugated cardboard, paperboards, moulded fibreboard), for example useful as boxes, containers, plates, cups, or other storage or food-service items. In this case it is highly desirable that the coating is biodegradable and / or does not affect the recyclability of the paper or cardboard. Test methods commonly used to assess the effect of materials on recyclability include PTS-RH 021:2012 Cat 1 and Cat 2.

[0099] It can also be advantageous that the coating can be heat sealed to enable sachets and boxes to be closed and sealed.

[0100] Natural fibres include non-woody fibres, such as cotton, abaca, kenaf, sabai grass, flax, esparto grass, straw, jute, hemp, bagasse, milkweed floss fibres, and pineapple leaf fibres; and woody fibres, such as wood or pulp fibres such as those obtained from deciduous and coniferous trees, including softwood fibres, such as northern and southern softwood kraft fibres, hardwood fibres, such as eucalyptus, maple, birch, and aspen. Pulp fibres may be prepared in high-yield or low-yield forms and may be pulped in any known method, including kraft, sulphite, high-yield pulping methods and other known pulping methods.

[0101] The natural fibres to be used in accordance with the present invention may be recycled natural fibres, virgin natural fibres or mixes thereof. Additionally, for good mechanical properties, it may be desirable that the natural fibres be relatively undamaged and largely unrefined or only lightly refined.

[0102] Suitable wood materials can be any type of wood commonly used in home, office, and outdoor settings and the material can include furnishings and construction materials. In such cases it is desirable that the coating does not alter negatively the aesthetics and physical properties of the items.

[0103] In a particular aspect, the material comprises a porous cellulosic material. A cellulosic material generally includes at least one of cellulose and hemicellulose, and it can further include lignin (e.g., as a lignocellulosic material).

[0104] Cellulose-based fibres may include regenerated cellulose fibre such rayon or Cuprammonium rayon, and high pulping yield fibres, unless specified differently. The term “cellulose-based fibres” also includes chemically treated natural fibres, such as mercerized pulps, chemically stiffened or cross-linked fibres, or sulfonated fibres. Also included are mercerized natural fibres, regenerated natural cellulosic fibres, cellulose produced by microbes, the rayon process, cellulose dissolution and coagulation spinning processes, and other cellulosic material or cellulosic derivatives. Other cellulose-based fibres included are paper broke or recycled fibres and high yield pulp fibres including bleached chemo-thermomechanical pulp (BCTMP), chemo-thermomechanical pulp (CTMP), pressure / pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), high yield sulphite pulps, and high yield Kraft pulps, all of which leave the resulting fibres with high levels of lignin but are still considered to be natural fibres. High yield fibres are well known for their stiffness in both dry and wet states relative to typical chemically pulped fibres.

[0105] Suitable fabric or textile substrates can include any cellulosic materials commonly used in garments or upholstery or otherwise, such as cotton, jute, flax, sisal, hemp, etc.

[0106] Suitable seed substrates include those which can be used in domestic, horticultural, or agricultural settings. In this case it is highly desirable that the coating is biodegradable so as not to pollute the environment.

[0107] Fruit and vegetable substrates may be fresh or dried or frozen and will benefit from a coating to provide protection during storage and transports to increase their shelf life and reduce spoilage. Fruit and vegetables also benefit from the coating providing a gas barrier to reduce the ripening effects of ethanol produced by other produce stored in close proximity. In this case it is necessary that the coating is edible and highly desirable that it is digestible.

[0108] Inorganic fibres are often fragile and require protection from the environment. Common examples of such fibres are silica-based fibres such as fibre optics which is very pure and has a very low index of refraction, however they are fragile. Alternatively, plastic fibre optic cables are made from acrylate and polyimides, can be used but these eventually breakup in the environment into harmful micro plastic. Glass fibres also include those used in Fibreglass or mineral wool and Rockwool.

[0109] In a preferred aspect of the invention, the substrate material is a fibre-based material. In another preferred aspect of the invention, the substrate material is a cellulosic material.

[0110] More preferably, the substrate material is selected from the group consisting of wood, wood pulp, cotton fibres, hemp fibres, jute fibres, sisal fibres, flax fibres, cellulose-based fibres, silica-based fibres, fruits, vegetables, and seeds.

[0111] More preferably, the substrate material is selected from the group consisting of paper, cardboard, corrugated board.

[0112] A variety of coating methods can be employed depending on the substrate to be coated. For physically fragile and / or heat-sensitive substrates, such as fruits and vegetables, coating is typically achieved by dip coating or spray coating, with drying at temperatures between 4°C and 50°C, preferably between ambient and 30°C, more preferably at ambient. For drying at lower temperatures this may need to take place over several hours.

[0113] For seeds the coating is typically applied in a drum coater, spray coater, rotary coater, fluid bed or extruder. Drying typically is carried out at ambient temperature.

[0114] In a preferred aspect of the invention, applying the coating to the substrate is achieved by roller coating, dip coating, slot dies, air knives, or spray coating. Alternatively droplets could be coated as part of an emulsification process or spray drying process.

[0115] For materials that are not sensitive to heat, pressure or shear, for example paper or fabrics, coating can be undertaken using a variety of equipment including reverse rollers, direct rollers, gravure rollers (direct and reverse), blade over rollers, flexographic equipment, lithographic equipment, slot dies, air knives, spray coating or dip coating. Once the coating has been applied, the wet coated sample is exposed to temperatures between 50°C and 200°C, preferably 70°C and 150°C, more preferably 80°C and 130°C in order to dry it including equipment such as steam cylinders, Yankee Dryers, Flakt Dryers, Infra-red dryers, non-contact dryers (fans) or air flotation dryers.

[0116] In a further preferred aspect of the invention, drying of the coating is achieved by exposure to air at temperatures between 50°C and 250°C for between 0.1 seconds and 10 minutes, more preferably 60°C and 200°C for between 2 seconds and 5 minutes, most preferably between 80 °C and 150°C for between of 6 seconds and 3 minutes. Preferably, drying of the coating is achieved by non-contact, preferably by using a fan.

[0117] When the substrate is paper or cardboard, drying of the coating is preferably achieved by exposure to elevated temperatures for a period of time of 10 seconds or less, more preferably 5 seconds or less, most preferably 2 seconds or less.

[0118] Many substrates such as paper, cardboard, fabrics or textiles have print applied for background colour, branding or packaging information. For examples industrially Offset Printing, Lithography, Digital Printing, Gravure, Screen Printing or Flexography can be used to apply print to paper. All of these methods use roller technology to apply single-colour inks or pigments to the substrate one at a time. Therefore, there needs to be minimal bleed between the layers of colour to prevent smudging and warping of the printed image. The inventive coatings can prevent bleeding of inks or pigments, particularly when used on low density substrate materials such as tissue, blotting or porous paper by providing a less permeable printing surface. The inventive coatings can be used in conjunction with overprint varnishes (OPVs) to give a gloss, satin or matt finish to printing. The inventive coating can be applied over the inks or the inks could be applied on top of the inventive coatings.

[0119] In a preferred aspect of the invention, the average thickness of the coating is between 1 and 40 microns, more preferably between 2 and 30 microns.

[0120] In an alternatively preferred aspect of the invention, the average density of the coating is between 0.1 and 40 g / m2.

[0121] In a further aspect, the present invention relates to the use of an inventive aqueous coating composition as described hereinbefore to coat a cellulosic fibrous substrate.

[0122] In a further aspect, the aqueous coating compositions of the present invention may also find use as a means of coating liquid droplets or solid particles of actives. Such actives can comprise hydrophobic materials such as fragrances, flavours, nutraceuticals including vitamins, various oils and waxes as well as medications. Such actives can comprise hydrophilic materials that have been pre-emulsified in a water-in-oil emulsion. The actives can include solid materials dispersed or dissolved in the coating composition including bacteria, bacterial spores and other materials useful as probiotics. In these situations, the liquid droplet or particle coating can typically be carried out by a process of emulsification and this can be followed by further processes to form a hard shell such as spray-drying, or cross-linking by physical or chemical or covalent means. The coating compositions can also be used to coat pre-formed particles to provide an extra level of protection, for example by spraying onto already spray-dried particles made from starch. The coating compositions can be used in any application where the ability to form a coherent film from plant protein material is useful.

[0123] The coating compositions can also be used just as emulsion stabilisers ,e.g. for hydrophobic actives dispersed in water. The protein particles of the coating compositions can coat the oil droplets and hence stabilise the emulsion.

[0124] FIGURES Figure 1 - Viscosity profile with and without post-HPH viscosity adjustment for aqueous coating composition C after ageing for 16 days

[0125] Figure 2 - Viscosity profile with and without post-HPH viscosity adjustment for aqueous coating composition F after ageing for 1 day

[0126] EXAMPLES

[0127] Ingredients and Materials

[0128] Pea Protein Isolate (PPI) (83 wt.% protein, 4 wt.% carbohydrate) (ProEarth P16109) was purchased from Cambridge Commodities Ltd.

[0129] Soy Protein Isolate (SPI) (90 wt.% protein) was purchased from Bakerite.

[0130] Rice Protein (79 wt.% protein) was purchased from Bakerite.

[0131] Acetic acid (80 wt.% solids) was purchased from Univar Solutions.

[0132] Lactic acid (88 wt.% solids) was purchased from Surfachem.

[0133] Oleic acid (90.2 wt.% C18, solids) was obtained from The White Sea and Baltic Company Ltd.

[0134] Sodium hydroxide pellets (>99 wt.% solids) were purchased from ReAgent, UK.

[0135] Glycerol (>99.9 wt.% solids) was purchased from APC Pure.

[0136] Innospers CWF, a nonionic Carnauba wax emulsion (30 wt% solids) was purchased from Allinova.

[0137] ASP NCX-9 hydrous Kaolin (hydrous aluminium silicate) (96-99 wt.% solids) was purchased from KaMin.

[0138] Tween20 (>95 wt.% solids) was purchased from Thermo Fisher Scientific.

[0139] Guar gum powder was purchased from Sigma Aldrich.

[0140] Magnesium chloride (100 wt.% solids), sodium benzoate (99 wt.% solids) and methyl paraben (100 wt.% solids) were purchased from Thermo Fisher Scientific.

[0141] Antifoam B 1(0 wt% solids) aqueous emulsion of polydimethylsiloxane, was purchased from Sigma-Aldrich

[0142] 50 gsm G Kraft Brown Euca was obtained from Sterling Paper Services Ltd.

[0143] Castor oil, Thermo Scientific Chemicals was purchased from Fisher Scientific.

[0144] Toluene, 99.85 wt.%, Extra Dry over Molecular Sieve, AcroSeal™, Thermo Scientific Chemicals was purchased from Fisher Scientific. n-Heptane, 99 wt.%, Thermo Scientific Chemicals was purchased from Fisher Scientific.

[0145] In the Examples that follow, all references to “ambient temperature” are to a temperature of approximately 20°C. In addition, the weight percentages of ingredients and materials used in the preparation of the examples refer to the ingredients and materials as purchased and do not take account of their purity.

[0146] Measurement methods

[0147] Protein weight%

[0148] The protein weight % of a sample was measured according to the method in ISO 16634 - 2:2016 Food products (Edition 1 May 2016) - Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content, Part 2: Cereals, pulses and milled cereal products

[0149] This method measures the nitrogen content of the plant protein containing sample by combusting the sample and analysing the mixture of gases produced. The plant protein content is calculated by multiplying the nitrogen content by a factor, usually 5.7 for wheat, rye and their milled products and 6.25 for other products falling within the scope. For the plant proteins of this invention the calculation factor is 6.25.

[0150] A dry powdered sample of the product was required, therefore samples, such as a dispersion coating composition, needed to first be dried. For samples which only contain materials, other than water, that do not evaporate close to 100°C, the samples can be dried in an oven, for example at 120 °C, until the sample weight remains steady, defined as less that 1mg reduction in weight over 60 seconds. For samples which contain materials, other than water, that might evaporate close to 100°C, the samples can be freeze dried. The sample tube is either immersed in liquid nitrogen for 5 minutes, or left in a -20°C freezer overnight, to freeze completely. The frozen sample was then left in a lyophiliser to dry for 2 days.

[0151] Total dry weight % measurement

[0152] The sample to be tested should be well-mixed, free-moving and homogenous. If the sample appears inhomogeneous then it should be mixed before measuring. a) Moisture Analyser method

[0153] This method is appropriate for samples which only contain materials, other than water, that do not evaporate close to 100°C. Approximately 5g of sample was added to an aluminium pan and the mass recorded. The pan was placed in a moisture analyser, such as a Sartorius MA100 Moisture Analyzer. The temperature was set to 120 °C and the sample is heated until a constant mass achieved - defined as less thanl mg mass change over 60 seconds. The final mass of the sample was recorded. Measurements can be repeated to obtain an average, generally of at least 3 measurements. The total dry content was calculated as follows:

[0154] Dry content weight % = 100 x (mass sample after heating I mass sample before heating) b) Freeze drying method

[0155] This method is appropriate for samples which contain materials, other than water, that might evaporate close to 100°C. Approximately 5 g of sample was added to a 15 mL Falcon tube and the mass was recorded precisely. The sample tube was then immersed in liquid nitrogen for 5 minutes, or left in a -20°C freezer overnight, to freeze completely. The frozen sample was then left in a lyophiliser to dry completely for 2 days. After that, the dried sample was collected and the mass was measured precisely. Measurements can be repeated to obtain an average, generally of at least 3 measurements. The total dry content was calculated as follows:

[0156] Dry content weight % = 100 x (mass sample after freeze drying I mass sample before freeze drying)

[0157] Kit test

[0158] Following a TAPPI standard T 559 (Technical Association of the Paper and Pulp Industry), test solutions comprising of castor oil, toluene and n-heptane were blended as follows:

[0159] Table 1: Kit test standard solutions

[0160] A sample of test paper specimen was selected and conditioned for a minimum of 24 hours at 50% relative humidity and 23°C. Under extraction in a fume cupboard, a drop of test solution 6 was added to the paper. After 15 seconds, excess test solution was wiped off and the sample examined for dark patches which show coating failure. This was repeated 5 times for each test solution. If the sample shows no dark patches it passes, the solution with the higher number is tested until samples fail, or the highest number test solution is reached. If the sample fails, the solution with a lower number is then tested until samples pass, or the lowest number test solution is reached. Once the highest value test solution that does not cause failure is identified, then this is the kit rating of the specimen.

[0161] The lowest rating is 0 and indicates the test paper specimen has no oil resistance under these test conditions. The maximum rating is 12 indicating the test paper specimen has very good oil resistance under these test conditions.

[0162] Dry Paper GSM

[0163] 125x125mm samples were cut from paper specimens, equilibrated for a minimum of 24h at 50% RH and 23°C and weighed to 0.001g. The GSM was calculated as follows:

[0164] GSM = Weight, g x 10,0001 [length, cm x Width, cm]

[0165] Dry Coating GSM

[0166] The same procedure as above was used as for Dry Paper GSM after it was coated. The Coating GSM was calculated as the Coated Paper GSM minus the Uncoated Paper GSM.

[0167] Dry Paper Thickness

[0168] 125x125mm samples were cut from paper specimens, equilibrated for a minimum of 24h at 50% RH and 23°C and thickness was measured using a micrometre accurate to 0.001mm. 5 values were taken and averaged to give a sample thickness. The paper specimen may be coated or uncoated.

[0169] Dry Coating thickness The Total Coating thickness was calculated as the Dry Total Coated Paper thickness minus the Dry Uncoated Paper thickness with the paper conditioned and the thickness measured as above. This can be undertaken for the paper after only the first coating has been applied and dried to obtain the Dry First Coating thickness. To obtain the Dry Second Coating thickness the Dry First Coating thickness is subtracted from the Total Coating thickness.

[0170] Viscosity

[0171] Viscosity measurements were made using an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50mm plate and 1 degree angle. The sample was tested on a shear sweep from 0.1 s-1to 1000 s-1at 20°C. The viscosity at 1 .13 s-1shear rate and 5.46 s-1shear rate at 20 °C can be reported, for simplicity in the data tables and text they are referred to as 1 s-1and 55s-1respectively. It is important that the sample is left for a suitable rest period, such as 2 minutes, prior to testing so that the viscosity is not disturbed by shear introduced by pipetting or spooning the sample into the measurement equipment.

[0172] Particle size

[0173] Particle size measurements were carried out using a laser diffraction technique with an Anton Paar PSA 1190. The sample was diluted with an aqueous solution of 2% acetic acid. It is important that the pH of a sample is away from the isoelectric point of that sample to avoid misleading results due to coagulation. For example, Pea Protein Isolate has an isoelectric point of 4.5 and the pH of the mixtures was adjusted to below that prior to measurement.

[0174] The sample was diluted to the required concentration in order to have the desired optical density (normally 2-8% obscuration) for the measurement.

[0175] The particle size distribution was measured after sonication for 5 minutes. In order to ensure that there were no aggregates remaining the sample was sonicated for another minute and the particle size distribution measured again. If there was less than a 0.15 micron reduction in d50 it was deemed that there were no remaining aggregates. The sonication and measuring was repeated until there was less than a 0.15 micron reduction in d50.

[0176] The d50 quoted is for the volume distribution. d10 and d5 values for the volume distribution can also be obtained in this way using laser diffraction.

[0177] Example 1 : Preparation of initial dispersion A An initial dispersion A for the preparation of aqueous coating composition A was mixed according to the procedure described below.

[0178] In a mixing vessel containing an overhead stirrer attached to an in-line Silverson powder / liquid mixer (FMX5 model) with a general purpose head, 33.3 kg of Reverse Osmosis water was mixed with 40 g of Sodium benzoate with the overhead stirrer at 150 rpm and the Silverson mixer at 2000 rpm at 17°C for 30 seconds. 3.96 kg of Pea Protein Isolate (PPI) was added gradually with the overhead stirrer at 180 rpm and the Silverson mixer initially at 6000 rpm. As the PPI was added the Silverson mixer speed was increased stepwise to 8000 rpm over 15 minutes with the temperature at 19°C. The mixture was then mixed with the overhead stirrer at 200 rpm and the Silverson at 8200 rpm for 5 minutes until homogenous. The Silverson speed was returned to 8000 rpm and 2.7 kg of Lactic Acid (88% solids) was added to the mixture at around 21 °C. The mixture was then mixed using the Silverson for another 30 minutes where the temperature reached 24 °C. A first batch of initial dispersion A was collected in buckets and stored for further processing and the process was repeated to collect a second batch.

[0179] The first batch of initial dispersion A had a viscosity of 118 mPas at 55 s-1shear rate, a particle size dso by volume distribution of 70 microns and a dry solids content, measured by Moisture Analyser, of 12.7 wt%.

[0180] The second batch of initial dispersion A had a viscosity of 95 mPas at 55 s-1shear rate, a particle size dso by volume distribution of 58 microns and a dry solids content, measured by Moisture Analyser, of 12.9 wt%.

[0181] Example 2: Preparation of coating composition A

[0182] Approximately 24 hours later, 10 litres of the first batch of initial dispersion A at 18.9 °C was pumped through a High-Pressure Homogenizer (nominal maximum working pressure 270 MPa) from Stansted Homogenising Systems Ltd with a piston-gap nozzle, at 200 MPa of pressure, at 70 litters / hour, with an average temperature at the nozzle of 67.9 °C. The sheared dispersion exited the nozzle and within 1 second immediately passed through a coil in tube heat exchanger with cooling fluid set at 5°C, taking around 12 seconds, so that the average outlet temperature of the sheared dispersion was 30.5 °C. This was stored in a bucket at ambient temperature to cool passively overnight with no stirring resulting in the aqueous coating composition. The average temperature recorded over the first hour was 25.3 °C.

[0183] Comparative Example 3: Preparation of comparative coating composition A

[0184] Approximately 8 days later, 10 liters of the initial dispersion of Example 1 at 17.5 °C was pumped through a High-Pressure Homogenizer (nominal maximum working pressure 270 MPa) from Stansted Homogenising Systems Ltd with a piston-gap nozzle, at 100 MPa of pressure, at 70 liters / hour, with an average temperature at the nozzle of 40.4 °C. The sheared dispersion exited the nozzle and within 1 second immediately passed through a coil in tube heat exchanger which was not operating, taking about 12 seconds, so that the average outlet temperature of the sheared dispersion was 39.6 °C.

[0185] This was stored in a bucket with an immersion coil with recirculating fluid set at 43°C and slowly agitated at low shear overhead stirrer for 90 minutes. The average temperature recorded over the first hour was 43.7 °C. After that time the coil was removed and the aqueous coating composition was stored in a bucket at ambient temperature to cool passively overnight.

[0186] Effect of aqueous coating composition post-HPH temperature and shear on aged viscosity and particle size distribution

[0187] The aqueous coating compositions’ viscosity and particle size distribution were measured after 24 hours ageing according to the method herein described.

[0188] Table 2: Effect of post-HPH processing In Example 2 the mixture immediately after the HPH nozzle outlet was at 30.5°C and had an average temperature of 25.3°C over the next hour, and a viscosity at 1s-1of 2312 mPas 24 hours later. This demonstrated that cooling the sheared dispersion quickly after High- Pressure Homogenizing at 200 MPa and maintaining the temperature below 40°C for at least an hour after, and allowing it to cool passively to ambient temperature resulted in a lower aqueous coating composition viscosity.

[0189] In Comparative Example 3 the mixture immediately after the HPH nozzle outlet was higher at 39.6°C and had an average temperature of 43.7°C over the next hour, and a viscosity at 1s-1of 3039 mPas 24 hours later after allowing to cool passively to ambient temperature. This demonstrated that without cooling the sheared dispersion quickly after High-Pressure Homogenizing at 100 MPa resulted in a higher viscosity aqueous coating composition.

[0190] Example 4: Preparation of initial dispersions

[0191] The initial dispersions of Table 3 were prepared according to the procedure described below.

[0192]

[0193] Table 3 - dispersion components, qs water

[0194] For Initial Dispersions B, F and G, in a mixing vessel, containing an overhead stirrer attached to an in-line Silverson powder / liquid mixer (FMX5 model) with a Square Hole High Shear Screen head, Reverse Osmosis water was mixed with the preservative with the overhead stirrer at around 100-120 rpm and the Silverson mixer at around 4000-4500 rpm starting at around 20°C for 30 seconds. Oleic acid, if present, was then added to the mixture, followed by the protein-containing material added gradually with continuous mixing and the mixer speed increased stepwise to 7000 rpm over 15 minutes. Next the Lactic or Acetic acid, if present, was then added and mixed with the overhead stirrer at 110 rpm and the Silverson at 8000 rpm for 5 minutes until homogenous. Finally the remaining materials were added and mixed for another 2 minutes. The shear resulted in an increase in temperature as given in Table 4.

[0195] For Initial Dispersion D the same process was followed however the wax mixture was added to the water and preservative mixture prior to the protein.

[0196] For Initial Dispersion C the same process was followed however the Glycerol and Anti-foam B were added to the water and preservative mixture prior to the protein. After the protein the Kaolin was added and the overhead stirrer impeller was changed to a turbine blade to allow the speed to be increased to 750 rpm due the increased viscosity. Finally the sodium hydroxide solution was added and the speed increased to 850 rpm and mixing carried on for 1 hour 35 minutes. The Silverson was then run at up to 8000 rpm for up to 30 minutes. For Initial Dispersion E the higher viscosity required a general-purpose head and an anchor type impeller, instead of the previous pitched blade. The Silverson mixer was only used at the later stages of mixing after the lactic acid was added, and the speed was turned up to 1100 rpm for the last 6.5 minutes of mixing, and the Silverson was at 4000 rpm for 1 minutes and then 8000 rpm for 5.5 minutes.

[0197] Table 4: initial dispersion processing conditions and characteristics

[0198] Table 4 shows that the final viscosity of the initial dispersions after 24 hours varied depending on its composition. The acidic dispersion with the highest level of protein, Dispersion E, had the highest viscosity. However, the alkali dispersion with a similar level of protein, Dispersion D, had a much lower viscosity. Dispersion G, containing rice protein had the lowest viscosity. Without wishing to be bound by theory it is believed that rice protein, which contains glutelin which is more hydrophobic, swells less than more soluble proteins such as pea, which are high in globulins. Therefore this resulted in a dispersion with a lower viscosity.

[0199] From Table 4 it can be seen that the particle size d50 of the initial dispersion also varied depending on its composition. The dispersion with the lowest d50 of 14 microns, Dispersion D, had an alkali pH. The two dispersions with the highest particle size d50 of 63-64 microns, Dispersions C and F, contained materials which, without wishing to be bound by theory, could result in solids aggregation.

[0200] Example 5: Preparation and assessment of aqueous coating compositions All the initial dispersions were left overnight at ambient temperature and then were pumped through a High-Pressure Homogenizer (nominal maximum working pressure 270 MPa) from Stansted Homogenising Systems Ltd with a piston-gap nozzle at 70 litres / hour. The sheared dispersion exited the nozzle and within 1 second immediately passed to a coil in tube heat exchanger with a residence time of around 12 seconds. For the inventive examples the cooling fluid was set at 5°C, so that there was a post-HPH viscosity adjustment step as the high sheared coating was actively and rapidly cooled to form the coating dispersion. For the comparative examples the heat exchanger was turned off, so there was no post-HPH viscosity adjustment step as there was no additional active cooling provided in this step.

[0201] Processing conditions of the High Pressure Homogenizer (HPH) for various dispersions are given in Table 5. Each dispersion was run first at steady state with the heat exchanger off with samples collected and then run at steady state with the heat exchanger on.

[0202] For all the acidic dispersions run at a pressure of 100 MPa the average nozzle temperatures were quite similar ranging from 41 - 43 °C. For the alkali dispersions run at a pressure of 100 MPa the average nozzle temperature was higher at 55 - 60 °C. For the acidic dispersions at 200 MPa the average nozzle temperature was also higher at 55 - 60 °C.

[0203] For all the dispersions run at a pressure of 100 MPa the average outlet temperatures were quite similar ranging from 39 - 41 °C with the heat exchanger off. For the dispersion at 200 MPa the outlet temperature was higher at 50 °C with the heat exchanger off. When the heat exchanger was on all the outlet temperatures were quite similar ranging from 18 -20 °C.

[0204] Table 5: High Pressure Homogenizer processing conditions

[0205] The inventive coating dispersions were then left to passively cool to ambient temperature without stirring and then left to age at ambient for up to 16 days to form the coating composition.

[0206] The comparative coating dispersions were placed in a water bath at 40°C for 5 days, followed by 30°C for 5 days and then followed by 5 days passively cooling to ambient temperature, without stirring, to form the comparative coating composition. This was so as to mimic the temperature gradient expected when hot material exiting the high pressure homogenizer is stored in a large tank suitable for commercial scale processes.

[0207] The viscosity and particle size distribution of the coating compositions were measured within ageing time frames ranging from 1 to 16 days, and given in Tables 6 and 7.

[0208]

[0209] Table 6: Effect of post-HPH processing able 7: Effect of post-HPH processing

[0210] All coating compositions after 1 day of ageing had a lower viscosity after having undergone rapid active cooling to ambient and ageing by storage at ambient, compared to the same composition without rapid cooling and storage at elevated temperatures. The % reduction in viscosity due to the viscosity adjustment steps ranged from 17% to 66%.

[0211] For coating composition D, after rapid active cooling in step (c) and ageing at ambient for 2 days in step (d) the viscosity was 1855 mPas at 1s-1shear rate, whilst the same composition without rapid active cooling and storage at elevated temperatures had a much higher viscosity of 46781 mPas at 1s-1shear rate. This was a 96% reduction in viscosity due to the viscosity adjustment step.

[0212] Coating compositions B and C, after 16 days of ageing had a lower viscosity after having undergone rapid active cooling to ambient and ageing by storage at ambient, compared to the same compositions without rapid active cooling and storage at elevated temperatures. The % reduction in viscosity due to the viscosity adjustment steps were 99% to 68% respectively. Coating composition E, after 16 days of ageing had a lower viscosity after having undergone rapid active cooling to ambient and ageing by storage at ambient, compared to the same composition without rapid active cooling and storage at elevated temperatures. The % reduction in viscosity due to the viscosity adjustment steps was only 9%. It is believed that the viscosity of the composition without the viscosity adjustment step was so high that it had almost formed a solid gel. In the rheometer the sample was slipping under shear therefore resulting in a lower measured viscosity value than it should have therefore resulting in an apparently lower viscosity reduction than seen for other samples.

[0213] Comparative coating compositions F and G, after 16 days of ageing without rapid active cooling and storage at elevated temperatures had all visibly phase separated. It is not possible to measure a viscosity for the compositions without further processing. This indicates that there has been an excessive level of aggregation likely leading to syneresis where the material has gelled and contracted separating out the water phase. Hence for these compositions the process without a viscosity adjustment step is not a suitable process for preparing such compositions.

[0214] It should also be noted that the viscosity adjustment effect is observed across a wide range of shear rates. In the Examples given, the values in the Tables 6 and 7 are at a shear rate of 1s'1. The viscosity across a range of shear rates is given for Coating Compositions C and F in Figures 1 and 2 and are typical of the compositions. As can be seen the aged coating compositions are shear-thinning. The viscosity of the inventive aged coating compositions is lower than the comparative aged coating compositions at all shear rates.

[0215] Example 6: Coating of paper card

[0216] The test specimen was prepared by tightly taping the paper card (50 gsm G Kraft Brown Euca) to a glass slide to reduce wrinkling. 50 g of the aqueous coating composition was speed mixed at 1500 to 2000 RPM for 3 to 2 minutes under vacuum to shear and de-gas. Approximately 5 ml per A5 sheet of card was then pipetted on to one end of the test specimen and the appropriate Kbar from RK Print Coat Instruments was used to coat the sample in a continuous and smooth motion to the desired thickness according to Table 8, with any excess being spread off the end of the specimen.

[0217] Table 8: K-bar colours

[0218] The sample was then placed in a pre-heated 120°C oven for 3 minutes until dry.

[0219] The thickness of the dry coating is depended on the content of the coating mixture.

[0220] The paper samples were then tested according to the Kit test described herein and the results are shown in Table 9. They had good oil barrier properties with high Kit test scores. able 9: Coated paper performance

Claims

CLAIMS1. An ultra-high shear (UHS) high-capacity method for the preparation of an aqueous coating composition comprising one or more plant protein-containing materials having plant proteins at a total level of between 7 % and 25 % of the weight of the coating composition and one or more additives selected from the group consisting of organic acids, plasticisers, surfactants, pH-adjustment materials and mixtures thereof at a total solids level of between 25 % and 150 % of the total weight of the one or more plant proteins, said method comprising the following steps:(a) mixing together the one or more plant protein-containing materials and the one or more additives with water to form an initial dispersion of pH 10 or less;(b) passing the initial dispersion at least once through a High-Pressure Homogenizer at a pressure of greater than 40 MPa and at a rate of greater than 0.5 litre / minutes to form a sheared dispersion;(c) actively cooling the sheared dispersion to form an aqueous coating dispersion;(d) ageing the aqueous coating dispersion to form the aqueous coating composition; wherein at least step (c) is a viscosity adjustment step that results in reducing the viscosity of the aged aqueous coating composition compared to the method wherein step (c) is not a viscosity adjustment step.

2. The method according to claim 1, wherein the one or more plant protein-containing materials in step (a) are provided as a dry powder or as an aqueous mixture.

3. The method according to claim 1 or claim 2, wherein at least one of steps (a), (b) and (d) includes a viscosity adjustment step that results in reducing the viscosity of the aged aqueous coating composition compared to the method wherein the viscosity adjustment step is not included.

4. The method according to any of claims 1 to 3, wherein the aqueous coating composition comprises one or more auxiliary agents.

5. The method according to any of claims 1 to 4, wherein the viscosity adjustment step comprises taking the temperature of the sheared dispersion at the nozzle of the High- Pressure Homogenizer in step (b) above 35 °C, preferably above 40 °C, more preferably above 50 °C.

6. The method according to any of claims 1 to 5, wherein the viscosity adjustment step comprises actively cooling the sheared dispersion in step (c) to less than 40 °C, preferably less than 35 °C, more preferably less than 30 °C.

7. The method according to any of claims 1 to 6, wherein the viscosity adjustment step comprises mixing the initial dispersion and optionally heating the initial dispersion in step (a) to above 30 °C, preferably to above 35 °C, more preferably to above 40 °C.

8. The method according to any of claims 1 to 7, wherein the viscosity adjustment step comprises ageing the initial dispersion in step (a) for more than 1 hour prior to step (b), preferably more than 6 hours, more preferably more than 12 hours.

9. The method according to any of claims 1 to 8, wherein the viscosity adjustment step comprises ageing the aqueous coating composition in step (d), preferably under shear.

10. The method according to claim 9, wherein ageing the aqueous coating composition in step (d) is done at a temperature between 40°C and 5 °C, preferably between 35°C and 10°C, more preferably between 30°C and 15°C, and most preferably between 25°C and 17°C.

11. The method according to any of claims 1 to 10, wherein step (a) is carried out using a high shear mixer.

12. The method according to any of claims 1 to 11 , wherein step (b) is carried out in a High-Pressure Homogenizer having a piston-gap nozzle.

13. The method according to any of claims 1 to 12, wherein the one or more surfactants are selected from the group consisting of nonionic, cationic, anionic and zwitterionic surfactants and mixtures thereof.

14. The method according to claim 13, wherein the organic acids are selected from the group consisting of lactic acid, acetic acid, citric acid, oleic acid and malic acid, preferably wherein the organic acid is lactic acid.

15. The method according to claim 13 or claim 14, wherein the plasticisers are selected from the group consisting of glycerol, propylene glycol, polyethylene glycol, sorbitol,erythritol, mannitol, xylitol, triethyl citrate, monoglycerides, diglycerides, triglycerides, glucose, mannose, fructose, sucrose, urea, lecithin, waxes, amino acids and mixtures thereof.

16. The method according to any of claims 1 to 15, wherein the amount of plant protein in the plant protein-containing material is greater than 25%, and wherein the plant protein-containing material is selected from protein isolates, protein concentrates, and flours, preferably wherein the one or more plant proteins are selected from the group consisting of soybean protein, pea protein, rice protein, potato protein, rapeseed protein, sunflower protein, lentil protein, bean protein, fava bean protein, mung bean protein, sunflower seed protein, pumpkin seed protein, flax protein, chia protein, canola protein, lupine protein, alfalfa protein, moringa protein, borage protein, hemp seed protein, cotton seed protein, wheat protein, barley protein, rye protein, corn protein, sorghum protein, oats protein and mixtures thereof.

17. An aqueous coating composition obtained or obtainable by the method according to any of claims 1 to 16.

18. The aqueous coating composition according to claim 17, wherein the plant protein has a d50 by volume particle size between 0.1 microns and 50 microns.

19. Use of an aqueous coating composition according to claim 17 or claim 18 to coat a substrate, preferably a cellulosic fibrous substrate.

20. Use of an aqueous coating composition according to claim 17 or claim 18 as an emulsion stabiliser.

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