Patent Application
20230331932
The present invention relates to a method for preparing a plant-based protein hydrogel slurry, and to a method for preparing a plant-based structured material (e.g. a film, a casting, a moulding etc.) from the plant-based protein hydrogel slurry. The present invention also relates to the plant-based protein hydrogel slurries and the plant-based structured materials per se, and to uses thereof.
There is an increasingly urgent need to reduce the environmental impact of many day-to-day activities and to reduce the amounts of non-renewable resources involved in these activities. An example of this is the increasing use of biodegradable or renewable packaging to replace conventional plastics such as polyethylene and polypropylene (e.g. edible films for use in foodstuffs).
Consequentially, efforts have been focussed on the use of natural or naturally-derived materials, such as celluloses, alginates, starches, collagen and collagen-derived proteins, as film and packaging forming materials. However, many of these naturally-derived films often have issues such as limited tensile strength or susceptibility to moisture or limited barrier properties which limit the range of applications for which they are suitable. One option is to chemically modify the film-forming material, typically by using a cross-linking chemical which can cross-link long-chain polymers, but this introduces complexity and additional chemistries which may not be suitable for the end-use, e.g. in an edible film or product having high biodegradability. Similarly, a composite material that combines natural and synthetic materials so as to overcome any limitations of one material will also be more complicated to produce and may not be edible or recyclable.
Amongst the different types of biopolymers that could serve as building blocks to generate new functional materials such as films, proteins are interesting candidates given their ability to self-assemble into functional structures.
Currently, the use of these materials for commercial application is restricted to highly soluble, animal-derived proteins. Commonly used animal-based proteins in food products, such as whey protein, exhibit good biocompatibility, biodegradability, amphiphilic and functional properties such as water solubility, emulsifying and foaming capacity. However, there is an increasing demand for replacing animal-derived proteins for plant-based ones, not only due to their lower environmental impact but also due to their lower allergenicity and reduced cost.
The formation of self-assembled hydrogel materials such as films from plant-based proteins has been reported, where hydrogels can be obtained from soy and pea proteins under a range of experimental conditions. However, the mechanical properties obtained from current plant-based materials are generally lower in comparison to the ones obtained from animal-derived ones as the plant proteins are more difficult to process, at least in part due to their inherent low solubility in water. The same can be said for the optical and barrier properties of current plant-based materials.
Thus, there exists a need to develop simple routes to plant-based material products having improved physical properties so as to increase the range of applications for which plant-based materials can be used to further replace synthetic materials.
Viewed from a first aspect, the present invention provides a method for the preparation of a plant-based protein hydrogel slurry, the method comprising:
Viewed from a further aspect, the present invention provides a plant-based protein hydrogel slurry prepared according to a method as hereinbefore described.
Viewed from a further aspect, the present invention provides a method for the preparation of a plant-based structured material, the method comprising:
Viewed from a further aspect, the present invention provides a plant-based structured material prepared according to a method as hereinbefore described.
Viewed from a further aspect, the present invention provides the use of a plant-based protein hydrogel slurry as hereinbefore described to produce a plant-based structured material.
Viewed from a further aspect, the present invention provides a plant-based protein hydrogel slurry having a protein solids content of 5 wt % to 25 wt % based upon the total weight of the plant-based protein hydrogel slurry and a viscosity in the range 10 to 10,000 cps at 50 s−1 and 20° C., wherein the plant-based protein hydrogel slurry comprises fragments having a d50 particle size as determined by laser diffraction of 0.5 to 150 microns.
Viewed from a further aspect, the present invention provides a plant-based protein hydrogel slurry having a protein solids content of 5 wt % to 25 wt % based upon the total weight of the plant-based protein hydrogel slurry and a viscosity in the range 10 to 10,000 cps at 50 s−1 and 20° C., wherein the plant-based protein hydrogel slurry comprises fragments having a d50 particle size as determined by Dynamic Light Scattering of less than 500 nm.
Viewed from a further aspect, the present invention provides a film comprising a plant-based protein hydrogel slurry as hereinbefore described.
As used herein, the term “low shear step” may refer to a process step in which low levels of mechanical energy are applied to a material, preferably by a cutting action, to cause it to break or fragment primarily into large discrete fragments. “Low-shear” does not typically include any milling step that shatters or fragments a material by high-speed impact, for example impacts at a differential velocity of greater than 2 ms−1. Nor does it typically include milling processes based on cavitation. In a particular embodiment, during the low shear step, a hydrogel is fragmented to give fragments such that at least 80% by weight of the hydrogel fragments have a maximum size as determined by sieving, of between 1 mm and 50 mm. Sieving of the hydrogel slurry can be performed according to the method described herein.
As used herein, the term “high shear step” may refer to a process step which applies energy to reduce the hydrogel to small fragments, such as to form e.g. a colloidal dispersion. During the high shear step, a hydrogel may be fragmented to give fragments having a d50 particle size as determined by Dynamic Light Scattering (DLS) or laser diffraction, as appropriate, of 50 nm to 150 microns. In a particular embodiment, during the high shear step, a hydrogel is fragmented to give fragments having a d50 particle size as determined by Dynamic Light Scattering (DLS) of less than 500 nm. In an alternative embodiment, during the high shear step, a hydrogel is fragmented to give fragments having a d50 particle size as determined by laser diffraction of 0.5 to 150 microns. DLS and laser diffraction can be performed according to the methods defined herein.
For the avoidance of doubt, the high shear step subjects the hydrogel to higher levels of shear than the low shear step. In the instance the method involves both a low shear step and a high shear step, the high shear step must happen after the low shear step (i.e. they are discrete steps occurring in this particular order).
The present application describes a process for making pourable and pumpable hydrogel slurries, which can be dried to form robust films, coatings, mouldings and other structured objects. Thus, the present invention provides a method for the preparation of a plant-based protein hydrogel slurry, the method comprising:
In embodiments, prior to step (b), it may be preferred to remove solvent(s) from the protein solution so as to form a more concentrated protein solution prior to step (b). This can be done by the application of heat and/or vacuum amongst other techniques. This initial solvent reduction may offer advantages such as simplifying subsequent drying. Suitable equipment could include scraped-wall evaporators or twin-screw extruders with applied vacuum.
Any suitable plant-based proteins may be used in the present invention. Different plant-based proteins can give hydrogel slurries giving structured objects with different properties. For example, soy proteins may give hydrogels (and materials formed from these hydrogels) that are more robust than pea proteins and may need to be processed differently for optimum performance. However, suitability for the present invention is determined by more than just the hydrogel properties, this being balanced with other factors such as availability of the protein raw material, lack of competition with food supply, protein allergenicity and so on. In preferred methods of the present invention, the plant-based protein(s) is selected from soybean protein, pea protein, rice protein, potato protein, wheat protein, corn zein protein or sorghum protein. Preferably, the plant protein(s) is selected from soy protein, pea protein, potato protein, and/or rice protein. More preferably, the plant-based protein(s) is selected from soy protein and/or pea protein.
In preferred methods of the present invention, the plant-based protein(s) is selected from soybean protein, pea protein, rice protein, potato protein, wheat protein, corn zein protein, rapeseed protein or sorghum protein. Preferably, the plant protein(s) is selected from soy protein, pea protein, potato protein, rapeseed protein and/or rice protein. More preferably, the plant-based protein(s) is selected from soy protein and/or pea protein.
Suitable plant-based proteins further include:
For the avoidance of doubt, the plant-based hydrogels and structured materials according to the present invention do not encompass plants in their natural state, e.g. naturally formed plant cells, organelles or vesicles are not plant-based hydrogels or structured materials of the present invention.
In methods according to the present invention, the plant-based protein hydrogel is formed by adding the plant-based protein into a solvent system, wherein the solvent system comprises two or more miscible co-solvents as defined herein. By selecting a solvent system that comprises miscible co-solvents, wherein a first co-solvent increases solubility of the plant-based protein(s), and a second co-solvent decreases solubility of the plant-based protein(s), it is possible to control the properties of the hydrogel and related sol-gel conditions.
The first co-solvent increases solubility of the plant-based protein(s). The first co-solvent may be considered a solubilising co-solvent. There may be one or more solubilising co-solvent(s) and the solubilising co-solvent(s) may fully or partially solubilise the plant-based protein(s).
Examples of solubilising co-solvents are organic acids. An organic acid is an organic compound with acidic properties. Suitable organic acids include acetic acid, formic acid, propionic acid or an α-hydroxy acid. Suitable organic acids include acetic acid, formic acid, propionic acid, an α-hydroxy acid, or a β-hydroxy acid. Suitable α-hydroxy acids include glycolic acid, lactic acid, malic acid, citric acid and tartaric acid. Suitable β-hydroxy acids include β-hydroxpropionic acid, β-hydroxybutyric acid, β-hydroxy β-methylbutyric acid, 2-hydroxybenzoic acid and carnitine. Particularly preferred organic acids are volatile organic acids, i.e. those having a boiling point of less than 130° C. This is because volatile organic acids can be easily removed from a plant-based protein hydrogen slurry during a subsequent drying step, such that the final plant-based structural material contains little, if any, residual organic acid. Examples of volatile organic acids include acetic acid and formic acid. Preferred organic acids are acetic acid and lactic acid. Using an organic acid enables solubilisation of the plant protein and also allows for mild hydrolysis of the protein. For example, without wishing to be bound by theory, the solubility of plant-based proteins in organic acid is possible due to: i) the protonation of proteins and ii) the presence of an anion solvation layer which contributes to a reduction of hydrophobic interactions.
In preferred methods of the present invention, the first co-solvent is an organic acid.
In preferred methods of the present invention, the first co-solvent has a boiling point of less than 130° C., more preferably less than 120° C.
The second co-solvent has decreased solubility of the plant-based protein(s), as compared to the first co-solvent. The second co-solvent may be considered a de-solubilising co-solvent. There may be one or more de-solubilising co-solvent(s).
Examples of de-solubilising second co-solvent(s) are an aqueous buffer solution. Preferably, the second co-solvent may be water, ethanol, methanol, acetone, acetonitrile, dimethylsulfoxide, dimethylformamide, formamide, 2-propanol, 1-butanol, 1-propanol, hexanol, t-butanol, ethyl acetate or hexafluoroisopropanol. Particularly preferably, the second co-solvent is water and/or ethanol. Most preferably, the second co-solvent is water.
In preferred methods of the present invention, the second co-solvent has a boiling point of less than 130° C., more preferably less than 120° C.
In preferred methods of the present invention, the concentration of plant-based protein(s) in the solvent system in step (a) is 50-250 mg/ml, preferably 50-150 mg/ml. The ratio of the solubilising co-solvent (typically an organic acid) may be varied depending on protein concentration, e.g. using a higher organic acid ratio with increasing protein concentration.
In preferred methods of the present invention, the solvent system has a co-solvent ratio of first co-solvent to second co-solvent from about 20-80% v/v, about 20-60% v/v, about 25-55% v/v, about 30-50% v/v, about 20%, about 30%, about 40% about 50% or about 60% v/v, most preferably about 30-50% v/v. Such ratios lead to functionally useful materials.
In preferred methods of the present invention, the protein solution is heated to a first temperature above the sol-gel temperature of the one or more plant-based protein(s) solution, then reduced to a second temperature below the sol-gel temperature of the one or more plant-based protein(s) solution so as to form a hydrogel.
In preferred methods of the present invention, the degree of protein hydrolysis (i.e. the percentage of cleaved peptide bonds in a protein hydrolysate) is controlled to modify the properties of the resultant hydrogel. For example, increasing the organic acid concentration present during formation will increase the degree of protein hydrolysis. A higher degree of protein hydrolysis leads to the formation of less rigid hydrogels.
In preferred methods of the present invention, the degree of protein hydrolysis is 0.1 to 10%, preferably 0.1 to 5%, even more preferably 0.1 to 2.5%.
In order to form the solution comprising one or more plant-based protein(s), it may be necessary to apply physical stimulus to the protein/solvent system mixture to enable dissolution of the protein. Suitable physical stimuli include heating, ultrasonication, agitation, high-shear mixing or other physical techniques. A preferred technique is heating, optionally with simultaneous or subsequent ultrasonication.
Preferably, the protein/solvent system mixture is subjected to a physical stimulus which is heating, wherein the solution is heated to about or above 70° C. More preferably, the protein/solvent system mixture is heated to about or above 75° C., about or above 80° C., about or above 85° C. or about 90° C. Even more preferably, the protein/solvent system mixture is heated to 85° C.
Preferably, the protein/solvent system mixture is subjected to a physical stimulus which comprises heating for a period of about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, or greater than 30 minutes. A preferred heating time period is about 30 minutes. The heated protein/solvent system mixture is optionally subjected to simultaneous or subsequent ultrasonication.
The resulting protein solution is heated such that the protein solution is then held above the sol-gel transition for the protein solution. By modifying the solvent system (for example through selection of the choice of organic acid, the ratio of organic acid to further solvent or through further means) it is possible to modify the sol-gel transition temperature for the protein(s). Through appropriate selection of conditions, it is possible to carefully control the sol-gel transition of the protein thereby controlling the formation of the hydrogel.
Preferably, the protein solution is heated to about or above 70° C. More preferably, the protein solution is heated to about or above 75° C., about or above 80° C., about or above 85° C. or about 90° C. Even more preferably, the protein solution is heated to about 85° C.
The protein solution may be held at elevated temperature for a time period of about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 45 minutes or 1 hour. A preferred time period is at least 30 minutes to enable the proteins to fully solubilise. It is possible to hold the protein solution at an elevated temperature for a longer period of time. This may be useful for a commercial batch process or for use in a fluidic processing step where it is necessary to retain the protein solution in liquid form for higher periods of time.
Having heated the protein solution to above the sol-gel transition temperature, the temperature of the protein solution can be reduced to a second temperature below the sol-gel transition temperature to facilitate formation of the hydrogel. The second temperature may be room temperature. The second temperature may be in the range 5 to 25° C., preferably 10 to 20° C. The protein solution may be held at the reduced temperature for long periods of time, e.g. days, weeks. The protein solution may be held at the reduced temperature for a time period of about 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or about 30 minutes. A particular reduced time period is about 5 minutes. However, the method of the present invention allows the protein to remain in solution for long periods of time. As such, depending on need, the protein solution can be kept above the sol-gel transition temperature for as long as required to retain the protein in liquid form. This could be hours, days or more but is preferably of the order of minutes or hours. Also, since the process is reversible, a solution could, for example be kept at a lower temperature (for example room temperature) where a hydrogel will form but thereafter heated to above the sol-gel transition temperature to return the solution to a liquid state for further processing. Protein hydrogels in this way could be stored for hours, days, weeks, months or years as the hydrogel remains stable for a long time.
The particular temperatures will depend on the properties of the protein source, the solvent conditions used and therefore the sol-gel transition temperature. Alternatively, the elevated and reduced temperatures may be relatively fixed (for example about 85° C. then about room temperature) and the co-solvent mixture conditions are adjusted to ensure a suitable sol-gel transition temperature for the selected plant-based protein.
Thus, a preferred method of the present invention comprises:
The protein solution may be held at an elevated temperature in step (bi) while it is shaped in a suitable mould where after the temperature is reduced in step (bii) allowing the proteins to form into a hydrogel.
Without wishing to be bound by theory, it is believed that when the plant protein is added to the solvent system and subjected to a physical stimulus such as heating and/or sonication, the plant proteins partially unfold, resulting in the exposure of hydrophobic amino acids initially buried within the protein native structure. Once partially unfolded, the co-solvents are able to interact with the unfolded protein molecules. For example, an organic acid has greater access to protonate amino acid residues, as well as enabling the formation of anion salt bridges that stabilise hydrophobic interactions. Also, upon heating at elevated temperatures, protein-protein non-covalent intermolecular contacts are disrupted.
Further, it is believed that upon cooling the protein solution to below the sol-gel temperature, protein-protein non-covalent intermolecular contacts are enabled, thus promoting the self-assembly of plant protein molecules into a hydrogel of inter-connected protein aggregates.
Further, it is believed that the application of mechanical agitation, for example ultrasonication, disrupts large colloidal protein aggregates into smaller ones, as well as disrupting protein intermolecular interactions. Using this approach, the size of the protein aggregates can be significantly reduced to particle sizes below 100 nm.
Preferably, the method of the present invention produces a plant-based protein solution comprising protein aggregates with an average size less than 200 nm, preferably less than 150 nm, less than 125 nm, less than 100 nm, less than 90 nm, less than 80 nm, less than 70 nm, less than 60 nm, less than 50 nm, less than 40 nm, or less than 30 nm.
It is believed that the method of the present invention allows the plant proteins to aggregate into supramolecular structures held by intermolecular hydrogen bonding interactions, and in particular between the β-strands. The method of the present invention enables materials to be formed in which there are high levels of β-sheet intermolecular interactions.
A feature of the method of the present invention is that it is not necessary to use cross-linking agents as the plant-based proteins will self-form hydrogels. Thus, in preferred methods of the present invention, the plant-based protein hydrogel does not contain or does not substantially contain a cross-linking agent.
However, in alternative preferred methods of the present invention, the plant-based protein hydrogel may comprise a cross-linking agent. Suitable cross-linking agents include microbial transglutaminase, glutaraldehyde, formaldehyde, glyoxal, phenolic compounds, epoxy compounds, genipin or dialdehyde starch.
In the methods of the present invention, the plant-based protein hydrogel is subjected to a shear treatment to form a plant-based protein hydrogel slurry. As would be understood by a skilled person, a shear treatment does not include centrifugation. Without wishing to be bound by theory, it is thought that the shear treatment modifies the composition of the hydrogel such that the resultant slurry is comprised of small fragments of controlled size. This means the plant-based protein hydrogel slurries can be poured, pumped and handled. Additionally, the small fragments are then able to bond together well during subsequent processing, e.g., to form a film. The inventors of the present invention have surprisingly found that, in general, the smaller the fragments of the hydrogel slurry, the better the tensile strength and optical properties of the resulting film.
The inventors have also found that the rheological properties of the hydrogel ideally need to be controlled with certain limits to aid processing of the hydrogel and the properties of the final film.
In preferred methods of the present invention, said shear treatment comprises a high-shear step. Preferably, said high-shear step involves fragmenting the plant-based protein hydrogel into fragments.
In preferred methods of the present invention, said fragments produced in said high-shear step have a d50 as determined by Dynamic Light Scattering (DLS) of less than 500 nm, preferably less than 300 nm, more preferably less than 200 nm, even more preferably less than 50 nm.
In alternative preferred methods of the present invention, said fragments produced in said high-shear step have a d50 as determined by laser diffraction of 0.5 to 150 microns, preferably 0.6 to 100 microns, more preferably 0.7 to 70 microns, even more preferably 0.8 to 50 microns, more preferably 0.9 to 25 microns, more preferably 1 to 20 microns, more preferably 1 to 10 microns, even more preferably 1 to 5 microns. The inventors have surprisingly found that if the fragments are within these particle size ranges, the hydrogel slurry can be used to form films having improved properties, such as tensile strength or transparency.
In preferred methods of the present invention, said fragments produced in said high-shear step have a d10 as determined by laser diffraction of less than 10 microns, more preferably less than 8 microns, more preferably less than 6 microns, more preferably less than 4 microns, more preferably less than 2 microns, even more preferably less than 1 micron. In preferred methods of the present invention, said fragments produced in said high-shear step have a do as determined by laser diffraction of 0.05 to 10 microns, more preferably 0.1 to 8 microns, more preferably 0.2 to 6 microns. Without wishing to be bound by theory, it is thought that the presence of a proportion of relatively smaller sized fragments within the hydrogel slurry can help to bind the relatively larger sized fragments also present therein together, meaning that any final structured material made using the plant-based protein hydrogel slurry (e.g. a film) has better mechanical properties.
Thus, in preferred methods of the present invention, said fragments produced in said high-shear step have a d50 as determined by laser diffraction of 0.5 to 150 microns and a do as determined by laser diffraction of 0.05 to 10 microns, preferably a d50 of 0.6 to 100 microns and a d10 of 0.1 to 8 microns, more preferably a d50 of 0.7 to 70 microns and a do of 0.2 to 6 microns.
In preferred methods of the present invention, said fragments produced in said high-shear step have a d5 as determined by laser diffraction of less than 3 microns, more preferably less than 1 micron, even more preferably less than 0.15 microns.
In preferred methods of the present invention, said high-shear step involves ultrasonication (e.g. using equipment such as a Bandelin HD4200, TS 113 probe or a Hielscher UIP1000hdT), high-shear mechanical stirring (e.g. using equipment such as a Silverson rotor-stator high-shear mixer), or cavitation, preferably ultrasonication.
In preferred methods of the present invention, said high-shear step involves ultrasonication (e.g. using equipment such as a Bandelin HD4200, TS 113 probe or a Hielscher UIP1000hdT), high-shear mechanical stirring (e.g. using equipment such as a Silverson rotor-stator high-shear mixer), high pressure homogenisation, or cavitation, preferably ultrasonication.
In preferred methods of the present invention, the high-shear step is conducted at a temperature that is below the sol-gel temperature of the plant-based protein solution. In preferred methods of the present invention, said high-shear step is conducted for a duration of at least 5 minutes, more preferably at least 1 minute.
In preferred methods of the present invention, said shear treatment comprises two steps. Preferably, said shear treatment comprises a low-shear step followed by a high-shear step.
In preferred methods of the present invention, said low-shear step involves fragmenting the plant-based protein hydrogel into fragments. Preferably, at least 50 wt % of said fragments produced in said low-shear step have a particle size in the range 1 mm to 50 mm, preferably 5 mm to 30 mm, more preferably 10 mm to 30 mm. More preferably, at least 80 wt % of said fragments produced in said low-shear step have a particle size in the range 1 mm to 50 mm, preferably 5 mm to 30 mm, more preferably 10 mm to 30 mm. This can be measured by collecting the fragments on a series of sieves of decreasing mesh size and weighing the amounts on the different meshes.
The low-shear step is conducted at a temperature that is below the sol-gel temperature of the plant-based protein solution.
In preferred methods of the present invention, said low-shear step involves mechanical cutting. By mechanical cutting, we mean cutting using a knife edge (e.g. a knife, an extruder blade etc.)
In alternative preferred methods of the present invention, said low-shear step involves extrusion. For example, the plant-based protein solution formed in step (a) can be extruded into a non-solubilising solvent (e.g. water) to form the plant-based protein hydrogel in large discrete fragments, e.g. the large discrete fragments may take the form of extrudates having a thread or string form. In this way, the fragments can be directly subjected to a solvent reduction step, as described in more detail below. A low-shear step of this nature is more amenable to large scale processing. In this case, the low-shear step may reduce the at least one dimension of the large fragment to between 1 mm and 50 mm, for example a diameter of the extrudate. Preferably, at least 50 wt % of said fragments produced in said low-shear step have at least one internal dimension in the range 1 mm to 50 mm, preferably 5 mm to 30 mm, more preferably 10 mm to 30 mm. More preferably, at least 80 wt % of said fragments produced in said low-shear step have at least one internal dimension in the range 1 mm to 50 mm, preferably 5 mm to 30 mm, more preferably 10 mm to 30 mm.
In preferred methods of the present invention, said high-shear step involves further fragmenting the plant-based protein hydrogel. Preferably, said fragments produced in said high-shear step have a d50 as determined by Dynamic Light Scattering of less than 500 nm, preferably less than 300 nm, more preferably less than 200 nm, even more preferably less than 50 nm. Alternatively, said fragments produced in said high-shear step have a d50 as determined by laser diffraction of 0.5 to 150 microns, preferably 0.6 to 100 microns, more preferably 0.7 to 70 microns, even more preferably 0.8 to 50 microns, more preferably 0.9 to 25 microns, more preferably 1 to 20 microns, more preferably 1 to 10 microns, even more preferably 1 to 5 microns. The inventors have surprisingly found that if the fragments are within these particle size ranges, the hydrogel slurry can be used to form films having improved properties, such as tensile strength
In preferred methods of the present invention, said fragments produced in said high-shear step have a d10 as determined by laser diffraction of less than 10 microns, more preferably less than 8 microns, more preferably less than 6 microns, more preferably less than 4 microns, more preferably less than 2 microns, even more preferably less than 1 micron. In preferred methods of the present invention, said fragments produced in said high-shear step have a d10 as determined by laser diffraction of 0.05 to 10 microns, more preferably 0.1 to 8 microns, more preferably 0.2 to 6 microns. Without wishing to be bound by theory, it is thought that the presence of a proportion of relatively smaller sized fragments within the hydrogel slurry can help to bind the relatively larger sized fragments also present therein together, meaning that any final structured material made using the plant-based protein hydrogel slurry (e.g. a film) has better mechanical properties.
Thus, in preferred methods of the present invention, said fragments produced in said high-shear step have a d50 as determined by laser diffraction of 0.5 to 150 microns and a d10 as determined by laser diffraction of 0.05 to 10 microns, preferably a d50 of 0.6 to 100 microns and a d10 of 0.1 to 8 microns, more preferably a d50 of 0.7 to 70 microns and a d10 of 0.2 to 6 microns.
In preferred methods of the present invention, said fragments produced in said high-shear step have a d5 as determined by laser diffraction of less than 3 microns, more preferably less than 1 microns, even more preferably less than 0.15 microns.
In preferred methods of the present invention, the particle size distribution of the hydrogel fragments in the plant-based protein hydrogel slurry can be adjusted by varying the nature and the intensity of the high shear step. In another preferred method, the particle size distribution of the hydrogel fragments in the plant-based protein hydrogel slurry can be adjusted by blending or combining two or more different hydrogel slurries that have been subjected to different high-shear steps and having different particle size distributions.
In preferred methods of the present invention, said high-shear step is conducted at a temperature that is below the sol-gel temperature of the plant-based protein solution.
In preferred methods of the present invention, said high-shear step is conducted at a temperature that is below the protein denaturation temperature of the plant-based protein solution.
Said high-shear step is conducted for a duration of at least 5 minutes, more preferably at least 1 minute.
In preferred methods of the present invention, said high-shear step involves ultrasonication (e.g. using equipment such as a Bandelin HD4200, TS 113 probe or a Hielscher UIP1000hdT), high-shear mechanical stirring (e.g. using equipment such as a Silverson rotor-stator high-shear mixer), or cavitation, preferably ultrasonication.
In preferred methods of the present invention, said high-shear step involves ultrasonication (e.g. using equipment such as a Bandelin HD4200, TS 113 probe or a Hielscher UIP1000hdT), high-shear mechanical stirring (e.g. using equipment such as a Silverson rotor-stator high-shear mixer), high pressure homogenisation, or cavitation, preferably ultrasonication.
In preferred methods of the present invention, step (c) further comprises subjecting the plant-based protein hydrogel slurry to a solvent reduction step, most preferably a solubilising solvent reduction step, between said low-shear step and said high-shear step.
By solubilising solvent, we mean a solvent or mixture of solvents in which the plant-based protein hydrogel slurry dissolves. Examples include organic acids: such as acetic acid, formic acid, propionic acid and/or an α-hydroxy acid; Examples include organic acids: such as acetic acid, formic acid, propionic acid, an α-hydroxy acid and/or a β-hydroxy acid. The α-hydroxy acid may preferably be selected from glycolic acid, lactic acid, malic acid, citric acid and/or tartaric acid. The β-hydroxy acid may preferably be selected from β-hydroxypropionic acid, β-hydroxybutyric acid, β-hydroxy β-methylbutyric acid, 2-hydroxybenzoic acid and carnitine.
In preferred methods of the present invention, wherein said solvent reduction step comprises the steps of:
Step (i) involves contacting the fragments of the plant-based protein hydrogel slurry with a non-solubilising solvent. By non-solubilising solvent, we mean a solvent or mixture of solvents in which the plant-based protein hydrogel slurry does not dissolve. Examples include water or a mixture of water and ethanol.
In preferred methods of the present invention, step (ii) involves mesh filtration. More preferably, the mesh filtration involves using multiple meshes of decreasing size.
As would be understood by a skilled person, if the fragments produced in the low-shear step are too small the solvent reduction step can prove difficult as the fragments can end up blocking the meshes. However, if the fragments produced in the low-shear step are too large, the solvent reduction step can take excessive amounts of time due to the slow mass transport of solvent from the core of the fragments.
Without wishing to be bound by theory, it is thought that due to the porous nature of the hydrogel, the solvent reduction step can remove some or all of the solvent (e.g. organic acid) from the hydrogel via a solvent exchange.
It is important for the hydrogel fragments to be weak and deformable enough, and small enough, to combine together well to form the final film or other structured material during subsequent processing. If the hydrogel fragments are not deformable enough, the strength and integrity of any film or structured material will be reduced. In addition, strong hydrogels are harder to disperse to form a slurry.
It is also important for the hydrogel fragments not to be too soft and deformable. Being too soft can make any intermediate processing steps (e.g. washing and solvent exchange) difficult. Excessively soft hydrogel fragments typically arise from insufficient levels of pre-formed macro-structures in the hydrogel, which will typically result in weaker films or structured materials.
The strength of a protein hydrogel can be altered by varying the concentration of protein and organic acid, amongst other variables.
It is therefore important for the strength of the hydrogel used to form the hydrogel slurries to be within certain limits. This can be measured by oscillatory rheometry. A suitable measure of hydrogel strength is the storage modulus, G′, of the hydrogel. Suitable test conditions are 1% strain at an oscillatory frequency of 1 Hz at 20° C. Suitable equipment is an Anton Paar MCR 92 Rheometer with a 50 mm diameter, 1 degree angle cone and plate measurement geometry.
Thus, in preferred methods of the present invention, prior to washing said plant-based protein hydrogel has a storage modulus (G′) at 10 rad/s of greater than 1000 Pa, preferably greater than 2000 Pa, more preferably greater than 5000 Pa, even more preferably greater than 6000 Pa, most preferably greater than 8000 Pa. As would be understood by a skilled person, 2π rad/s is equivalent to 1 Hz.
In preferred methods of the present invention, prior to washing said plant-based protein hydrogel has a storage modulus (G′) at 10 rad/s of less than 20,000 Pa, preferably less than 15,000 Pa, more preferably less than 10,000 Pa.
Further, in preferred methods of the present invention, the washed plant-based protein hydrogel has a storage modulus (G′) at 10 rad/s of greater than 500 Pa, preferably greater than 1000 Pa, more preferably greater than 2500 Pa, even more preferably greater than 3000 Pa, most preferably greater than 4000 Pa.
In preferred methods of the present invention, the washed plant-based protein hydrogel has a storage modulus (G′) at 10 rad/s of less than 20,000 Pa, preferably less than 15,000 Pa, more preferably less than 10,000 Pa.
Preferred methods of the present invention, further comprise the step of:
In preferred methods of the present invention, step (d) is carried out after step (c). In alternative preferred methods of the present invention, step (d) is carried out sequentially with step (c).
During adjustment of the pH of the plant-based protein hydrogel slurry, it is possible for the slurry to pass through the isoelectric point of the protein. Due to the lack of charge repulsion at the isoelectric point, the dispersed protein fragments in the plant-based protein hydrogel slurry can quickly coagulate. To avoid this, pH modification materials can be used to rapidly change the pH and therefore minimise the time that the slurry is at the isoelectric point.
Thus, in preferred methods of the present invention, step (d) involves adding a pH-modification material to the plant-based protein hydrogel slurry. Preferably, said pH-modification material is an aqueous solution comprising monovalent metal ions, divalent metal ions such as calcium, or ammonium ions, preferably an alkaline aqueous solution comprising monovalent metal ions, divalent metal ions, or ammonium ions. More preferably, said pH-modification material is an aqueous hydroxide solution, such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide.
In preferred methods of the present invention, the pH of the plant-based protein hydrogel slurry after step (d) is below the isoelectric point of the plant-based protein by at least 1 pH unit.
In preferred methods of the present invention, the pH of the plant-based protein hydrogel slurry after step (d) is above the isoelectric point of the plant-based protein by at least 1 pH unit. Preferred methods of the present invention further comprise adding an additional ingredient(s) to the plant-based protein hydrogel slurry. Preferably, said additional ingredient(s) is selected from plasticisers, opacifiers, preservatives, pigments and other inorganic nanoparticles (such as clays), or mixtures thereof.
Particularly preferably, said additional ingredient(s) is a plasticiser. In preferred methods of the present invention, said plasticiser is selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, sorbitol, mannitol, xylitol, lactic acid, glycolic acid, triethyl citrate, fatty acids, glucose, mannose, fructose, sucrose, ethanolamine, urea, triethanolamine, vegetable oils, lecithin, waxes and amino acids.
Particularly preferably, said additional ingredient(s) is a plasticiser. In preferred methods of the present invention, said plasticiser is selected from glycerol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, sorbitol, mannitol, xylitol, lactic acid, citric acid, glycolic acid, triethyl citrate, fatty acids, glucose, mannose, fructose, sucrose, ethanolamine, urea, triethanolamine, vegetable oils, lecithin, waxes and amino acids.
The amount of plasticizer to be incorporated will depend on the use of the final material, for example a film. Preferably, the plant-based protein hydrogel slurry may comprise about 1% wt plasticiser based upon the total weight of the protein present in the plant-based protein hydrogel slurry, about 2% wt, about 5% wt, about 10% wt, about 20% wt, about 30% wt, about 40% wt, about 50% wt, about 60% wt or more. More preferably, the plant-based protein hydrogel slurry may comprise between about 5-50% wt plasticiser based upon the total weight of the protein present in the plant-based protein hydrogel slurry, about 10-50% wt, about 20-40% wt about 15-35% wt or about 20% wt plasticizer.
Adding a plasticizer can influence the mechanical properties of the material. Typically, adding a plasticiser will increase the elasticity of the material but this typically conversely reduces the strength, for example the tensile strength, of the resultant material.
Composite films having improved physical and/or barrier particles can be formed by the addition of inorganic particles such as clay platelets to the protein hydrogel slurry.
In preferred methods of the present invention, the plant-based protein hydrogel slurry has a viscosity in the range of 10 to 10000 cps at 50 s−1, preferably in the range 10 to 8000 cps, preferably in the range 12 to 6000 cps, preferably in the range 15 to 5000 cps, preferably 20 to 2000 cps as measured by an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50 mm plate and 1° angle at 50 s−1. Control of the viscosity is beneficial for subsequent processing of the plant-based protein hydrogel slurry. For example, if the viscosity is too high, use of the slurry to form films or coatings becomes more difficult, e.g. when spreading the slurry to form a film. If the viscosity is too low, it can also be difficult to form a structured object such as a film as the slurry can spread too easily. Unless otherwise stated, viscosity is measured at 20° C.
In preferred methods of the present invention, the plant-based protein hydrogel slurry has a protein solids content in the range 5 wt % to 25 wt % based upon the total weight of the plant-based protein hydrogel slurry, preferably 6 wt % to 20 wt %, more preferably 7 wt % to 15 wt %, more preferably 7.5 wt % to 12.5 wt % based upon the total weight of the plant-based protein hydrogel slurry. The protein level affects the rheology of the hydrogel. Hydrogels containing less than 5 wt % protein solids content are generally not sufficiently robust to give fragments which can be handled. Whilst hydrogels containing greater than 25 wt % protein solid content are more robust, they are harder to disperse and therefore have been found to form weaker structured materials (e.g. films).
The plant-based hydrogel slurries described herein allow for the formation of a range of useful plant-based biomaterials. Using plant-based materials has a number of advantages over previously used animal or petrochemical sources. Firstly, plant sources are renewable and can be efficiently obtained in an environmentally efficient manner. Secondly, plant sources are biodegradable and are therefore an environmentally sound alternative to other plastics. Thirdly, in contrast to animal derived proteins, plant-based proteins have the significant advantage that they do not introduce animal derived proteins into a human. This has positive impacts both from a pharmacological and pharmaceutical perspective where animal sourced material must undergo stringent checks and processes to ensure no adverse elements are present (for example removing prions and the like); but also because the products are suitable for vegetarian/vegans.
Since plant-based proteins are naturally present in a human (or other animal)'s diet, biomaterials made according to the present invention exhibit a higher degree of digestibility compared to other biopolymers such as polysaccharides (for example, alginates or chitosan). This makes them particularly suitable for pharmaceutical, food and/or cosmetic use.
Preferably, the plant-based hydrogel slurries of the present invention can be used to form films, for example thin films. Plant protein derived films have many applications including forming biodegradable flexible films for food packaging applications.
An advantage of the plant-based materials of the present invention over animal-based materials or starch-based/cellulose materials, is their inherent insolubility in water. Most biopolymer films will readily dissolve in water, thus making them unusable for food packaging applications on their own, necessitating an extra coating layer with a synthetic polymer. These issues can be overcome with the present invention. Films of the present invention may also be soluble in alkaline conditions, or in the presence of proteolytic enzymes, or the presence of chaotropic agents.
The present invention also provides a plant-based protein hydrogel slurry prepared according to the method hereinbefore described.
The present invention also provides a method for the preparation of a plant-based structured material, the method comprising:
In preferred methods of the present invention, the one or more solvent level reduction step(s) reduces the level of the first co-solvent (e.g. an organic acid).
In preferred methods of the present invention, the one or more solvent level reduction step(s) reduces the level of the second co-solvent (e.g. an alcohol such as ethanol).
In preferred methods of the present invention, step (b) involves placing the plant-based protein hydrogel slurry on a surface before performing the one or more solvent level reduction step(s).
In preferred methods of the present invention, said solvent level reduction step involves heating. Preferably, said solvent level reduction step involves heating at a temperature in the range 50 to 100° C., more preferably at a temperature in the range 55 to 95° C. In such a solvent level reduction step, the solvent is therefore removed via evaporation.
In preferred methods of the present invention, said solvent level reduction step involves forced convection of dry air.
In preferred methods of the present invention, the plant-based structured material is a film.
In alternative preferred methods of the present invention, the plant-based structured material is a casting (i.e. a plant-based structured material formed by moulding, preferably non-thermally reversible moulding, more preferably injection moulding).
In alternative preferred methods of the present invention, the plant-based structured material is a coating. Preferably, the coating is a food coating, a seed coating, a pharmaceutical coating, or a surface coating (e.g. a paper coating).
The coatings of the present invention are fully biodegradable and therefore provide environmentally-friendly alternatives to conventional coatings made from synthetic materials (e.g. chemically modified natural polymers or fossil-fuel derived polymers). For example, the food coatings of the present invention offer a fully biodegradable coating that meet food standards and can extend the shelf life of the food item that has been coated. The pharmaceutical coatings of the present invention offer a fully biodegradable coating that can be used to replace conventional enteric coatings and can mask any unpleasant taste associated with the pharmaceutical ingredient(s) that has been coated.
In preferred methods of the present invention, the plant-based structured material comprises a plant-based protein(s) having secondary structure with at least 40% intermolecular β-sheet, at least 50% intermolecular β-sheet, at least 60% intermolecular β-sheet, at least 70% intermolecular β-sheet, at least 80% intermolecular β-sheet, or at least 90% intermolecular β-sheet. Preferably, the % intermolecular β-sheet content is measured by FTIR.
In preferred methods of the present invention, the plant-based structured material has a Young's modulus over 20 MPa; preferably over 50 MPa, over 80 MPa, over 100 MPa, over 200 MPa, over 300 MPa, over 400 MPa, over 500 MPa, or over 600 MPa. The Youngs Modulus is a measure of the strength of the structured article.
In preferred methods of the present invention, the plant-based structured material is a film.
Preferably, the films have a thickness in the range 1 to 1000 μm, preferably 10 to 150 μm, more preferably 20 to 100 μm, even more preferably 30 to 70 μm, most preferably 35 to 60 μm. This can be measured with a micrometer.
Preferably, the films have an elongation break percentage of above 10%, above 20%, above 30%, above 40%, above 50%, above 60%, above 70%, above 80%, above 90%, above 100% or more.
Films produced according to the method of the present invention can be micropatterned with features ranging from 100 nm to 1000 μm, enabling novel functional properties such as: super-hydrophobicity (lotus-leaf effect) or structural colour (attributed to Mie scattering).
Functional composite films can be produced by embedding inorganic nanoparticles, such as gold nanoparticles or silver nanoparticles, into the protein matrix. Applications could include materials suitable for flexible electronics or films with antibacterial properties. Composite films having improved physical and/or barrier particles can be formed by embedding particles such as clay platelets in the protein matrix.
The present invention also provides a plant-based structured material prepared according to the method hereinbefore described.
A preferred plant-based structured material according to the present invention is a film, a casting, or a coating. Preferably, the coating is a food coating, a seed coating, a pharmaceutical coating, or a surface coating (e.g., a paper coating). Preferred properties of the plant-based structured materials of the present invention are described above. The plant-based structured materials of the present invention are useful in a variety of applications, including food, beverages, cosmetics, formulations (e.g. paints), and packaging. The transparency and high strength of the films of the present invention make them particularly well suited to packaging applications.
The present invention also provides the use of a plant-based protein hydrogel slurry as hereinbefore defined to produce a plant-based structured material. Preferably, said plant-based structured material is a film, a casting, moulding or a coating. Preferably, the coating is a food coating, a seed coating, a pharmaceutical coating, or a surface coating (e.g. a paper coating).
The present invention also provides a plant-based protein hydrogel slurry having a protein solids content of 5 wt % to 25 wt % based upon the total weight of the plant-based protein hydrogel slurry and a viscosity in the range 10 to 10,000 cps at 50 s−1 and 20° C., wherein the plant-based protein hydrogel slurry comprises fragments having a d50 particle size as determined by laser diffraction of 0.5 to 150 microns.
Preferred plant-based protein hydrogel slurries of the present invention comprise fragments having a d50 particle size as determined by laser diffraction of 0.6 to 100 microns, more preferably 0.7 to 70 microns, even more preferably 0.8 to 50 microns, more preferably 0.9 to 25 microns, more preferably 1 to 20 microns, more preferably 1 to 10 microns, even more preferably 1 to 5 microns.
Preferred plant-based protein hydrogel slurries of the present invention have a protein solids content of 6 wt % to 20 wt % based upon the total weight of the plant-based protein hydrogel slurry, more preferably 7 wt % to 15 wt %, even more preferably 7.5 wt % to 12.5 wt %.
Preferably, the viscosity of the plant-based protein hydrogel slurry is measured by an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50 mm plate and 1° angle at 50 s−1. Preferred plant-based protein hydrogel slurries of the present invention have a viscosity in the range 10 to 8000 cps at 50 s−1 and 20° C., more preferably 12 to 6000 cps at 50 s−1 and 20° C., more preferably 15 to 5,000 cps at 50 s−1 and 20° C.
The present invention also provides a plant-based protein hydrogel slurry having a protein solids content of 5 wt % to 25 wt % based upon the total weight of the plant-based protein hydrogel slurry and a viscosity in the range 10 to 10,000 cps at 50 s−1 and 20° C., wherein the plant-based protein hydrogel slurry comprises fragments having a d50 particle size as determined by Dynamic Light Scattering of less than 500 nm.
Preferred plant-based protein hydrogel slurries of the present invention comprise fragments having a d50 particle size as determined by Dynamic Light Scattering of less than 300 nm, more preferably less than 200 nm, even more preferably less than 50 nm.
Preferred plant-based protein hydrogel slurries of the present invention have a protein solids content of 6 wt % to 20 wt % based upon the total weight of the plant-based protein hydrogel slurry, more preferably 7 wt % to 15 wt %, even more preferably 7.5 wt % to 12.5 wt %.
Preferably, the viscosity of the plant-based protein hydrogel slurry is measured by an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50 mm plate and 1° angle at 50 s−1. Preferred plant-based protein hydrogel slurries of the present invention have a viscosity in the range 10 to 8000 cps at 50 s−1 and 20° C., more preferably 12 to 6000 cps at 50 s−1 and 20° C., more preferably 15 to 5,000 cps at 50 s−1 and 20° C.
The present invention also provides the use of a plant-based protein hydrogel slurry as hereinbefore defined to produce a plant-based structured material. Preferably, said plant-based structured material is a film, a casting, moulding or a coating. Preferably, the coating is a food coating, a seed coating, a pharmaceutical coating, or a surface coating (e.g. a paper coating).
The present invention also provides a film comprising a plant-based protein hydrogel slurry as hereinbefore described.
Preferred films of the present invention:
The present invention also provides a film obtained from a plant-based protein hydrogel slurry as hereinbefore described. For example, a film can be obtained by subjecting the plant-based protein hydrogel slurry to one or more solvent level reduction step(s). Preferred features of the solvent level reduction step(s) are as described above. Industrial methods for producing structured objects such as films from the hydrogel slurry include casting wherein the hydrogel slurry is poured or extruded in a carefully controlled manner onto a moving surface, such as a belt or drum, and subjected to controlled drying conditions.
Pea Protein Isolate (PPI) (80% protein) was purchased from Cambridge Commodities Ltd.
Soy Protein Isolate was purchased from Cambridge Commodities Ltd.
Lactic acid (food-grade, >80%) was purchased from Cambridge Commodities Ltd. Acetic acid (glacial) was purchased from Fisher Scientific.
Viscosity measurements were made using an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50 mm plate and 1 degree angle and a constant shear of 50 s−1 at 20° C.
Storage Modulus (G′) can be measured using an Anton Paar MCR 92 Rheometer using a plate and cone measurement geometry with a 50 mm plate and 1 degree angle with 1% strain at an oscillatory frequency of 1 Hz.
Particle size measurements were carried out using a Dynamic Light Scattering (DLS) technique or a laser diffraction technique. DLS measurements were taken using using a Zeta Sizer Nano S from Malvern Panalytical and operated according to the manufacturer's instructions. It is important that the slurry is sufficiently diluted so as to avoid misleading results due to particles coagulating during testing. The hydrogel slurries were diluted by a factor of 100 with deionised water. It is also important that the pH of a sample is away from the isoelectric point of that sample so as to avoid misleading results due to coagulation. The isoelectric point of the Pea Protein Isolate material tested here was 4.5 and the pH of the slurries was adjusted to 3 with acetic acid or lactic acid prior to measurement. Typically, several dilutions and/or buffer solutions should be tested to ensure proper dispersion. A 200 μL of the diluted slurry was placed in a cuvette and positioned in the equipment. Testing was then carried out according to the standard equipment procedures. The d50 measured is for the wt/volume distribution. DLS can generally be used to measure particle size up to 500 nm. The upper limit is primarily governed by the onset of sedimentation. For particles greater than this the particle size measurements were carried out using laser diffraction with an Anton Paar PSA 1190. Measurements were carried out by diluting the protein slurry in an aqueous solution with acetic acid or lactic acid adjusted to the same pH. The slurry was diluted to the required concentration in order to have the desired optical density (normally 5-15% obscuration) for the measurement. 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.
Other equipment, such as the NANO-flex II® system from Colloid Metrix, can be used.
The particle sizes of the fragments of hydrogel from the low-shear step can be determined by sieving. A suitable technique is to take 200 g of the hydrogel mixture from the low-shear step and to rapidly disperse it in 1000 mL of DI water. The dispersed mixture is then quickly poured through a series of stacked sieves of decreasing mesh size between 50 mm and 1 mm. Sieves from Endecotts are suitable. The % of the slurry within a specific size rage can be calculated by combining the weights of the fragments on the different meshes and calculating this as a % of the total amount of slurry. Errors caused by any additional solvent exchange are minimal due to the short test period.
Transmission Electron Microscopy (TEM) measurements were taken using a FEI Talos F200X G2 TEM from Thermo Scientific. A suitable technique is to prepare a test sample by diluting the fine plant-based hydrogel slurry to a 1:100 dilution with a 3% acetic acid solution and deposit the sample on a TEM grid (C400Cu, EM resolutions), followed by staining with uranyl acetate. The maximum fragment size is then determined by optical examination of at least 30 fragments chosen at random from within the field of view of a test sample. The maximum length is the maximum length of a line drawn between any two opposing boundaries of a fragment that does not cross any external boundaries.
Scanning Electron Microscopy (SEM) images were taken using MIRA 3 FEG-SEM, TESCAN with a 10 nm coating of platinum.
Structural analysis was performed by using an FTIR-Equinox 55 spectrometer (Bruker). The samples were used without further pre-treatment and were loaded into the FTIR holder. The atmospheric compensation spectrum was subtracted from the original FTIR spectra and a secondary derivative was applied for further analysis. Each FTIR measurement was repeated 3 times. The sensitivity of the instrument was detected to be 5%. To resolve the transformation of the native structure of Pea Protein Isolate into supramolecular aggregates, vibrational changes in amide I, which is strictly correlated with protein secondary structure, were followed. Structural analysis was either performed in solution (e.g. using the plant-based protein hydrogel slurry directly) or on a resultant dried film. In the latter case, film samples were prepared for structural analysis by drying 200 μL of the relevant plant-based protein hydrogel slurry at 37° C. for 6 hours.
The Youngs Modulus and Tensile Strength of structured objects such as films can be measured using a 5ST electromechanical Universal tester from Tinius Olsen. A 10 cm by 1 cm strip is placed between grips and extended at 12.5 mm/min and the forces and extension recorded. The thickness of the film prior to testing can be measured by a micrometer.
Light transmittance of the structured objects such as films can be measured using a Cary 500 UV-vis spectrometer. The measurement was performed at wavelengths ranging from 300 to 800 nm with average time of 0.1 seconds at 600 nm/min scanning speed.
(a) Protein Hydrogel Formation
500 ml of a mixture was prepared consisting of 12.5% (w/v) Pea Protein Isolate in 40% (v/v) lactic acid solution.
The mixture was then heated in a water bath at 80° C. for 30 minutes, followed by a short sonication step to disrupt large colloidal aggregates (Hielscher UIP1000hdT (1000 W, 20 kHz)), after which a transparent solution was obtained. The energy applied was 16 Wh over 7 minutes.
The solution was then poured into a 220 mm petri dish and left to cool down at 10° C. for 72 h to obtain a self-standing protein hydrogel.
(b) Application of Shear to Protein Hydrogel
Shear was then applied to the hydrogel formed in step (a) as follows. The protein hydrogel was cut into ˜1 cm cubes via a low-shear cutting step. The cubes were placed inside a 75 μm filter bag, which was then submerged inside a bucket containing 5 L of deionised water. This formed a coarse protein hydrogel slurry within the filter bag. The hydrogel cubes were left to soak for 1 h, with occasional gentle agitation. This step was performed to reduce to concentration of lactic acid in the hydrogel by diffusion to the continuous aqueous phase and was repeated 5 more times until the final pH of the aqueous solution was 3.28.
The strained gel cubes were transferred into a 500 ml bottle and were exposed to probe sonication in a high shear step for 10 minutes (˜0.2 kJ/ml) so as to form a homogeneous low-viscosity protein dispersion. The viscosity of the slurry was 12 cps. The d50 size of the fine slurry fragments was 90 nm as measured by DLS.
(c) Preparation of a Pea Protein Film
The fine hydrogel slurry prepared in step (b) was adjusted to pH 2.6 by adding a small amount of lactic acid, and was then poured onto a heated surface (which was held at 80° C.) and dried for 1 hour to form a structured object which was a film, with an average thickness of 18.1 μm. The resultant film was transparent and had a Youngs Modulus of 361 MPa and a tensile strength of 14 MPa.
(a) Protein Hydrogel Formation
800 ml of a mixture was prepared consisting of 10% (w/v) Pea Protein Isolate in 40% (v/v) acetic acid solution.
The mixture was then heated in a water bath at 85° C. for 20 minutes, followed by a short sonication step to disrupt large colloidal aggregates (Hielscher UIP500hdT (500 W, 20 kHz)), after which a transparent solution was obtained. The energy applied was 200 kJ over 30 minutes.
The solution was then poured into two 220 mm petri dishes. The dishes were sealed and left to cool down by storage in a fridge at 4° C. for 20 h to obtain a self-standing protein hydrogel. The storage modulus of this hydrogel was 2640 Pa.
(b) Application of Shear to Protein Hydrogel
Shear was then applied to the hydrogel formed in step (a) as follows. The protein hydrogel was cut into ˜1 cm cubes via a low-shear cutting step. The cubes were placed inside a 75 μm filter bag, which was then submerged inside a bucket containing 7 L of deionised water. This formed a coarse protein hydrogel slurry within the filter bag. The hydrogel cubes were left to soak for 1.5 h, with occasional gentle agitation. This step was performed to reduce to concentration of acetic acid in the hydrogel by diffusion to the continuous aqueous phase and was repeated one more time until the final pH of the aqueous solution was 3.1.
The strained gel cubes were transferred into a 1 L bottle and were exposed to high shear with a rotor stator (15,000 rpm for 5 min) and probe sonication on ice for 30 minutes (˜0.5 kJ/ml) so as to form a homogeneous low-viscosity protein dispersion. The viscosity of the slurry was 23 cps. The d50 size of the fine slurry fragments was 103 nm as measured by DLS.
(c) Preparation of a Pea Protein Film
The fine hydrogel slurry prepared in step (b) was mixed with 20 w/w % glycerol and poured onto a plastic petri dish and dried for 24 hours at room temperature to form a structured object which was a film, with an average thickness of 78.5 μm. The PSD and optical properties of the pea protein film of Example 2 was investigated. The results are shown in Table 1. The resultant film was transparent, as demonstrated in
The results show that functional films having high transparency can be formed using the plant-based protein hydrogel slurries of the present invention. Without wishing to be bound by theory, it is thought that achieving a controlled particle size distribution allows for the high levels of transparency observed.
(a) Protein Hydrogel Formation
430 g of a mixture was prepared consisting of 7.0% (w/w) Soy Protein Isolate in 30% (v/v) acetic acid solution.
The mixture was then heated in a water bath at 85° C. for 30 minutes, followed by a short sonication step to disrupt large colloidal aggregates (Bandelin HD4200, TS 113 probe), after which a transparent solution was obtained. The energy applied was 200 kJ over 30 minutes.
The solution was then poured into two 220 mm petri dishes. The dishes were sealed and left to cool down by storage in a fridge at 4° C. for 20 h to obtain a self-standing protein hydrogel.
(b) Application of Shear to Soy Protein Hydrogel
Shear was then applied to the hydrogel formed in step (a) as follows. The protein hydrogel was cut into ˜1 cm cubes via a low-shear cutting step. The cubes were placed inside a 75 μm filter bag, which was then submerged inside a bucket containing 5 L of deionised water. This formed a coarse protein hydrogel slurry within the filter bag. The hydrogel cubes were left to soak for 1.5 h, with occasional gentle agitation. This step was performed to reduce to concentration of acetic acid in the hydrogel by diffusion to the continuous aqueous phase and was repeated one more time until the final pH of the aqueous solution was 3.07.
The strained gel cubes (469 g) were transferred into a 0.5 L bottle and were mixed with 40 g of deionised water. A colloidal suspension of large gel particles was obtained and divided into 50 g aliquots, which were then subjected to different levels of high shear to obtain samples with varying degrees of particle size distribution as detailed in Table 2:
(c) Preparation of a Soy Protein Film
The fine hydrogel slurry of sample B prepared in step (b) was mixed with 20 w/w % glycerol and poured onto a plastic petri dish and dried at room temperature for 24 h to form a structured object which was a film, with an average thickness of 61 μm. The PSD and optical properties of the soy protein film of Example 3 was investigated. The results are shown in Table 3. The resultant film was transparent, as demonstrated in
The results show that functional films having high transparency can be formed using the plant-based protein hydrogel slurries of the present invention. Without wishing to be bound by theory, it is thought that achieving a controlled particle size distribution allows for the high levels of transparency observed.
(a) Protein Hydrogel Formation
450 g of a mixture was prepared consisting of 11.11% (w/w) Pea Protein Isolate in 30% (v/v) acetic acid solution.
The mixture was then heated in a water bath at 85° C. for 30 minutes, followed by a short sonication step to disrupt large colloidal aggregates (Bandelin HD4200, TS 113 probe), after which a transparent solution was obtained. The energy applied was 200 kJ over 30 minutes.
The solution was then poured into two 220 mm petri dishes. The dishes were sealed and left to cool down by storage in a fridge at 4° C. for 20 h to obtain a self-standing protein hydrogel.
(b) Application of Shear to Protein Hydrogel
Shear was then applied to the hydrogel formed in step (a) as follows. The protein hydrogel was cut into ˜1 cm cubes via a low-shear cutting step. The cubes were placed inside a 75 μm filter bag, which was then submerged inside a bucket containing 5 L of deionised water. This formed a coarse protein hydrogel slurry within the filter bag. The hydrogel cubes were left to soak for 1.5 h, with occasional gentle agitation. This step was performed to reduce to concentration of acetic acid in the hydrogel by diffusion to the continuous aqueous phase and was repeated one more time until the final pH of the aqueous solution was 3.02.
The strained gel cubes (400 g) were transferred into a 0.5 L bottle and were mixed with 100 g of deionised water. A colloidal suspension of large gel particles was obtained and divided into 50 g aliquots, which were then subjected to different levels of high shear to obtain samples with varying degrees of particle size distribution as detailed in Table 4:
(c) Preparation of a Pea Protein Film
The fine hydrogel slurries prepared in step (b) were mixed with 20 w/w % glycerol and poured onto a PTFE evaporating dish and dried at room temperature for 24 h to form a structured object which was a film. The characterisation of the resultant films is described in the Table 5:
The results show that the methods of the present invention allow for the preparation of plant-based protein hydrogel slurries having a controlled particle size distribution. The results also show that the plant-based protein hydrogel slurries of the present invention can be used to prepare structured objects, such as films, with superior tensile properties that can be controlled through control of the slurry particle size. The films produced have a secondary structure with a high level of intermolecular β-sheet (e.g. at least 50% intermolecular n-sheet). This high degree of intermolecular interactions is thought to contribute to the enhanced mechanical properties observed.
A colloidal pea protein dispersion obtained from Example 2 was spray-coated on an uncoated cardboard substrate with an airbrush. One layer was first applied followed by drying in the oven for 1 min at 80° C. to evaporate the remaining solvent. This procedure was repeated 15 times until a uniform transparent coating was applied. The results are shown in
A colloidal pea protein dispersion obtained from Example 2 was applied as a coating to a fresh strawberry via a dip-coating step. A strawberry was first submerged into 50 ml of pea protein dispersion for 5 seconds, followed by removal of the excess dispersion by briefly applying compressed air. The coated strawberry was left to dry at room temperature for 10 min. This procedure was repeated 5 times until a uniform transparent coating was applied. The results are shown in
A colloidal pea protein dispersion obtained from Example 2 was spray-coated on a uncoated Paracetamol tablet with an airbrush. One layer was first applied followed by drying in the oven for 1 min at 80° C. to evaporate the remaining solvent. This procedure was repeated 15 times until a uniform transparent coating was applied. The results are shown in
A colloidal pea protein dispersion obtained from Example 2 was applied as a coating to a wheat seed via a dip-coating step. A wheat seed was first submerged into 50 ml of pea protein dispersion for 5 seconds, followed by removal of the excess dispersion by briefly applying compressed air. The coated wheat seed was left to dry at room temperature for 10 min. This procedure was repeated 2 times until a uniform transparent coating was applied. The results are shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 20195384.1 | Sep 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/074796 | 9/9/2021 | WO |
