A composition and method of preparing the same

Abstract

The present disclosure relates to a composition comprising: a) clay modified with a polysaccharide and b) a plant protein polymeric matrix, wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix. The present disclosure also relates to a method of preparing the composition, a method of forming a coating comprising the composition and a substrate coated with the composition.

Description

[0001] A COMPOSITION AND METHOD OF PREPARING THE SAME CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Singapore application number 10202500126V filed with the Intellectual Property Office of Singapore on 15 January 2025, the contents of which is hereby incorporated by reference in its entirety for all purposes.

[0002] FIELD OF THE INVENTION

[0003] The present disclosure relates generally to the field of food packaging. The present disclosure relates to a composition, a method of preparing the composition, a method of forming a coating comprising the composition and a substrate coated with the composition.

[0004] BACKGROUND OF THE INVENTION

[0005] Food packaging is used to protect the food packaged against the surrounding environment and microbial contamination, thus preserving food quality and prolonging shelf life. Accordingly, it is desired for plastic packaging to possess good barrier properties against permeation of gases and vapors, and also with the ability to retard microbial penetration / growth.

[0006] However, commercially available plastic films such as polyethylene terephthalate (PET), polypropylene (PP) and polyethylene (PE) exhibit relatively poor barrier properties as compared to glass, aluminum foil and metalized film. One method to improve the barrier property of a substrate is through coating. Moreover, with the growing public health and environmental awareness, the use of sustainable materials for barrier and antimicrobial coatings is highly desired

[0007] In recent years, biopolymers of protein origin and polysaccharide origin have received great research interests for coating applications owing to their biodegradable, renewable, low cost and non-toxicity properties. Biopolymers such as zein from maize and chitosan readily form a continuous film with good barrier property under specific preparation conditions. In addition, chitosan exhibits antifungal and antibacterial properties due to its polycationic nature.

[0008] Zein is an edible and biodegradable polymer that has been widely used for coating in vast applications, ranging from food, pharmaceutical to adhesive industry. Due to its non-polar hydrophobic amino acid residues, zein is insoluble in water. However, zein is soluble inwater and organic solvent mixture when the organic solvent percentage is higher than 40%. The formation of a zein film is highly dependent on the concentration, pH and types of solvent At low concentration, zein tends to self-assemble and forms nanoparticles in sphere, which may result in poor barrier property. Although the fabrication of zein film as an oxygen barrier layer has been extensively studied, the brittleness of film remains one of the most challenging issues. To date, plasticizers such as glycerol have been employed to improve zein’s mechanical strength.

[0009] For instance, the process of preparing a non-aqueous solution coating of zein has been previously reported to comprise a mixture of solvents and plasticizers. The effect of solvent, plasticizer, zein concentration and heating temperature on the gelling property of zein to form a transparent, flexible and hard film have also been studied and reported. Another previous finding disclosed a process for producing a biodegradable water-resistant wrapping film for food packaging comprising zein dispersion in an aqueous acetone solution, casting zein film at a thickness of about 60 to 70 pm, followed by film drying. Still further, another finding disclosed a method of making water-based zein (prolamin) solution or emulsion with low co-solvent percentage of 9 to 40 %, which the steps comprised of (1) providing a zein solution comprising zein, water, alcohol or ketone and cold-water insoluble polymer with heating, (2) mixing the zein solution with stabilizer water solution under stirring, (3) removing at least a portion of the alcohol or ketone from the solution to form the water-based zein composition. In this finding, both the cold-water insoluble polymer and stabilizer helped to stabilize the zein dispersion. Another finding disclosed a method of preparing an aqueous zein coating solution with an amphiphilic solvent, surfactant and plasticizer dissolved in water. Water-based zein solutions are useful in a variety of coating applications and water-based polymeric materials have been typically used. It can be applied onto fruits to keep the fruit fresh for longer.

[0010] However, plasticizers may reduce the oxygen barrier performance due to increased mobility of chain segments of zein and free volume in the coating. In addition, migration of plasticizers to packaged food leads to food contamination, which is a pressing problem for consumers. Furthermore, the high percentage of organic solvents used in the method of production has a negative impact on the environment and also raises concerns for food safety.

[0011] Most of the studies in the literature for chitosan and its derivative compounds are related to the antimicrobial coatings. For instance, one study provided antimicrobial barriers, systemsand methods formed from a structure including a chitosan biomaterial Another study disclosed a method for making an antimicrobial structure comprising coating a hydrophobic solid substrate with a chitosan material. In this study, some crosslinking agents may be added to insolubilize or bind to the chitosan material. Yet another study described a method of producing the antimicrobial chitosan thermoplastic polymer blends, wherein the composition comprised of a water insoluble polymer that contained amino-reactive functional groups and a chitosan acid salt solution.

[0012] One reported study described a method of preparation of duck egg coating preservative based on zein water-based nanoparticle dispersion. Zein solution in water ethanol mixture was added into acidified chitosan solution slowly under stirring. The prepared zein nanoparticle suspension was then filtered to produce zein / chitosan nanoparticles. The zein water-based nanoparticle dispersion was finally prepared by redispersing the zein / chitosan nanoparticles in water. The nanoparticle dispersion was applied onto duck egg to prolong its shelf life. However, no enhancement to the mechanical property was reported. Furthermore, the gas barrier of the nanoparticle coating is not high due to the interfacial gas leakage between zein / chitosan particles.

[0013] In another study, a method of preparation of stable zein / silicate / chitosan dispersion was disclosed, where silicate was modified with silane coupling agent via solvent exchange. In the presence of modified silicate, hydrophobic zein was dispersed into water to produce stable zein / silicate / chitosan dispersion. The obtained dispersion was applied onto plastic substrate or food to produce uniform coating with high oxygen barrier and antimicrobial property to prolong the shelf life of foods. The modified silicate, working as a solid surfactant, was able to stabilize zein dispersion in water and keep the zein molecules in extended configuration for uniform coating. However, the silicate modification involved using a large amount of organic solvent through a complicated solvent exchange process. Consequently, these will lead to high production cost, high negative environmental impact as well as food safety concern due to the silane residue in the coating.

[0014] Therefore, there is a need for a composition that at least ameliorates the disadvantages mentioned above.SUMMARY

[0015] In an aspect, there is provided a composition comprising: a) clay modified with a polysaccharide and b) a plant protein polymeric matrix, wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

[0016] In the composition, the clay may chemically couple to the polysaccharide, where it is envisaged that the clay is enveloped within the polysaccharide through chemical bonding. The clay when coupled to the polysaccharide or when modified with the polysaccharide may be termed as modified clay . The modified clay may then be coupled to the plant protein matrix via intermolecular forces of attraction. Advantageously, the intermolecular forces of attraction (such as hydrogen bonding) formed between the polysaccharide and the plant protein polymeric matrix increases the miscibility between the modified clay and the plant protein polymeric matrix and thereby forming a more homogenous mixture and a more uniform composition with high barrier properties (such as gas barrier).

[0017] In another aspect, there is provided a method of preparing a composition as defined herein, the method comprising the step of mixing a solution of plant protein polymeric matrix and modified clay to form the composition, wherein the modified clay comprises clay modified with a polysaccharide, and wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

[0018] Advantageously, as the method of preparing the composition as described herein involves negligible use of organic solvent, it is environmentally friendly and provides a safer alternative to produce packaging (such as food packaging). The resulting composition without any organic solvent present is useful for preparing coatings on substrate which may otherwise be sensitive to organic solvent.

[0019] In another aspect, there is also provided a method of forming a coating comprising a composition as defined herein or a composition formed from the method as defined herein on a substrate, comprising the step of applying the composition on a substrate to form the coating thereon.

[0020] In another aspect, there is also provided a substrate coated with the composition as defined herein or a composition formed from the method as defined herein.

[0021] Advantageously, having the composition coated on the substrate allows for production of packaging (such as food packaging) with high gas barrier, enhanced mechanical property and antimicrobial property which increases the shelf-life of the products (such as food).DEFINITIONS

[0022] The terms “chemically couple” or “chemical bonding” when used in association with the clay and the polysaccharide refer to the clay and the polysaccharide as having strong electrostatic forces of attractions such as but not limited to ionic bonding.

[0023] The terms “intermolecular forces of attraction” when used in association with the modified clay and the plant protein polymeric matrix refer to the modified clay and the plant protein polymeric matrix as having forces of attraction such as but not limited to hydrogen bonding, Van der Waals forces and ion-dipole interactions.

[0024] The term “plate-like structured” clay, as used herein refers to layered clay minerals that are structured within the clay as planes of anions, arranged in sheets, which may be tetrahedrally or octahedrally coordinated (with oxygen), which in turn are arranged into layers of tetrahedral and / or octahedral sheets.

[0025] The invention illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising", "including", "containing", etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

[0026] As used in this application, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a genetic marker” includes a plurality of genetic markers, including mixtures and combinations thereof. As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0027] The invention has been described broadly and generically herein Each of the narrower species and sub-generic groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0028] DETAILED DESCRIPTION OF OPTIONAL EMBODIMENTS

[0029] Exemplary, non-limiting embodiments of a composition will now be disclosed. There is provided a composition comprising: a) clay modified with a polysaccharide and b) a plant protein polymeric matrix, wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

[0030] In one embodiment, the present disclosure provides a composition consisting essentially of: a) clay modified with a polysaccharide and b) a plant protein polymeric matrix, wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

[0031] The composition may not comprise a silane coupling agent. The composition may not comprise a plasticizer (such as glycerol) as plasticizers reduce the barrier performance (such as oxygen barrier) and migration of plasticizer in packaging (such as food packaging) leads to contamination of the product (such as food).

[0032] In the composition, the clay may chemically couple to the polysaccharide, where it is envisaged that the clay is enveloped within the polysaccharide through chemical bonding.The clay when coupled to the polysaccharide or when modified with the polysaccharide may be termed as modified clay.

[0033] The modified clay may then be coupled to the plant protein matrix via intermolecular forces of attraction. Advantageously, the intermolecular forces of attraction (such as hydrogen bonding) formed between the polysaccharide and the plant protein polymeric matrix increases the miscibility between the modified clay and the plant protein polymeric matrix and thereby forming a more homogenous mixture and a more uniform composition with high barrier properties (such as gas barrier).

[0034] The clay may be any clay that has a plate-like structure and a high aspect ratio. Where the clay has a plate-like structured, the clay may be termed as a “plate-like structured clay”. The plate-like structured clay may allow for enhanced exfoliation and dispersion of the plate-like structured clay within the composition, which consequently increases the distance that molecules (such as gas molecules) may travel to permeate the composition and thus enhances the barrier property (such as gas barrier property) of the composition. The aspect ratio of the clay or the plate-like structured clay may be in the range of about 5 to about 1000, about 200 to about 1000, about 400 to about 1000, about 600 to about 1000, or about 800 to about 1000.

[0035] The plate-like structured clay may be pristine clay silicates selected from the group consisting of montmorillonite, halloysite, bentonite, laponite, kaolinite, saponite, vermiculite and combinations thereof. Advantageously, having the plate-like structured clay allows for the composition to have enhanced mechanical property, where the platelike structured clay may form hierarchical structure in the composition when it is exfoliated and dispersed within the composition, which consequently enhances punch strength in the perpendicular direction.

[0036] In the composition, the weight percentage of the clay may be in the range of about 10 wt% to about 80 wt%, about 40 wt% to about 50 wt%, about 44 wt% to about 50 wt%, about 46 wt% to about 50 wt% or about 48 wt% to about 50 wt% based on the total weight of the composition.

[0037] The polysaccharide may be an amino polysaccharide. The amino polysaccharide may be selected from the group consisting of chitosan, chitosan derivatives, and combinations thereof. The chitosan derivatives may be a chitosan-arginine compound, a chitosanguanidine compound, a methyl-thiocarbamoyl chitosan derivative, a phenylthiocarbamoyl chitosan derivative or a chitosan-lysine compound. The polysaccharide may be positivelycharged. Advantageously, the polysaccharide (when positively charged) may interact strongly through electrostatic interaction (such as ionic bonding) with the clay (which tends to be negatively charged), allowing for optimum attraction between the polysaccharide on the surface of the clay. Advantageously, the polysaccharide (such as chitosan / chitosan derivatives) may confer antimicrobial property to the composition.

[0038] In the composition, the weight percentage of the polysaccharide may be in the range of about 10 wt% to about 80 wt%, about 40 wt% to about 50 wt%, about 42 wt% to about 50 wt%, about 46 wt% to about 50 wt% or about 48 wt% to about 50 wt% based on the total weight of the composition.

[0039] The plant protein polymeric matrix may be plant storage proteins (prolamins) selected from the group consisting of com (zein), wheat (gliadin), rye (secalin), barley (hordein), rice (glutelin), sorghum (kafirin), oats (avenin), derivatives thereof and combinations thereof. The plant protein polymeric matrix may be corn (zein).

[0040] In the composition, the weight percentage of the plant protein polymeric matrix may be in the range of about 10 wt% to about 80 wt%, about 10 wt% to about 20 wt%, about 12 wt% to about 20 wt%, about 16 wt% to about 20 wt% or about 18 wt% to about 20 wt% based on the total weight of the composition.

[0041] Exemplary, non-limiting embodiments of a method of preparing a composition as defined herein will now be disclosed. There is provided a method of preparing a composition as defined herein comprising the step of mixing a solution of plant protein polymeric matrix and modified clay to form the composition, wherein the modified clay comprises clay modified with a polysaccharide, and wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

[0042] The method may not comprise the step of adding a plasticizer and / or a silane coupling agent to form the composition.

[0043] The method may further comprise before the mixing step, the step of 1) modifying clay with a polysaccharide by mixing a dispersion of clay with a solution of polysaccharide under aqueous condition to form the modified clay.

[0044] The modifying step may involve stirring at a temperature in the range of about 50 °C to about 90 °C, about 75 °C to about 90 °C and about 80 °C to about 90 °C. Advantageously, mixing the clay dispersion with the solution of polysaccharide is essential to achieve full exfoliation of the clay. Where the clay is the plate-like structured clay, mixing at this temperature exfoliates the plate-like structured clay into sheets which is facilitated by thestrong electrostatic interaction between the plate-like structured clay and the polysaccharide.

[0045] The modifying step may further comprise the step of a) forming the solution of polysaccharide by dissolving the polysaccharide in an aqueous acid solution. The acid may be selected from the group consisting of acetic acid, formic acid, oxalic acid, citric acid, lactic acid, sulfuric acid, phosphoric acid, hydrofluoric acid and combinations thereof. The concentration of the aqueous acid solution may be in the range of about 2% to about 5%, about 3% to about 5% and about 4% to about 5%.

[0046] The forming step a) may involve stirring at a temperature in the range of about 50 °C to about 90 °C, about 75 °C to about 90 °C, 80 °C to about 90 °C and about 85 °C to about 90 °C. The final pH of the solution of polysaccharide formed may be in a range of about 3.5 to 4.5. The concentration of the polysaccharide in the solution may be in the range of about 1 wt% to about 15 wt%, about 2 wt% to about 10 wt% and about 3 wt% to about 6 wt%. The presence of large amounts of protonated groups (such as -NH2 groups) on the polysaccharide (amino polysaccharide) allows for its solubility in the acid.

[0047] The modifying step may further comprise the step of b) forming the clay dispersion by dispersing the clay in an aqueous solution. The aqueous solution may be modified with an acid selected from the group consisting of acetic acid, formic acid, oxalic acid, citric acid, lactic acid, sulfuric acid, phosphoric acid, hydrofluoric acid and combinations thereof. The acid may be added to the aqueous solution prior to the addition of the clay or after the addition of clay. The addition of acid into the aqueous solution aids in enhancing the exfoliation of the clay into sheets in the dispersion and allows for a more uniform distribution of the clay within the dispersion.

[0048] The forming step b) may involve stirring at a temperature in the range of about 20 °C to about 90 °C, about 30 °C to about 80 °C and about 50 °C to about 70 °C at a duration of about 3 hours to about 4 hours. The stirring may be mechanical stirring. The obtained clay dispersion may be subjected to homogenizing at a speed in the range of about 15,000 rpm to about 20,000 rpm, and about 17,000 rpm to about 20,000 rpm for a duration in the range of about 5 minutes to about 20 minutes. The homogenizing may be conducted in a homogenizer well known in the art.

[0049] The final pH of the clay dispersion formed may be in a range of about 3.5 to 4.5. The concentration of the clay in the dispersion may be in the range of about 1 wt% to about 20 wt%, about 3 wt% to about 15 wt%, about 5 wt% to about 10 wt%.The modifying step may further comprise, the step of homogenizing the modified clay obtained at a speed in the range of about 15,000 rpm to about 20,000 rpm, and about 17,000 rpm to about 20,000 rpm for a duration in the range of about 10 minutes to about 25 minutes and about 15 minutes to about 20 minutes. The homogenizing step may be conducted in a homogenizer well known in the art. The homogenizing step may further involve allowing the homogenized modified clay to be further stirred for a duration of about 16 hours to about 18 hours.

[0050] The method may further comprise before the mixing step, the step of 2) forming the solution of plant protein polymeric matrix by dissolving a plant protein polymeric matrix in an organic solution. The organic solution may be a mixture of an organic solvent with water The organic solvent may be selected from the group consisting of alcohol, ethers, ethyl acetate, ethanol, acetone, tetrahydrofuran, isopropanol and combinations thereof. The organic solvent may be ethanol. The volume percentage of organic solvent in water may be in the range of about 30 v% to about 90 v%, about 55 v% to about 80 v% and about 60 v% to about 70 v%. The forming step may involve stirring at a temperature in the range of about 20 °C to about 90 °C, about 30 °C to about 80 °C and about 50 °C to about 70 °C for a duration of about 60 minutes to about 80 minutes and about 60 minutes to about 70 minutes. The final pH of the solution of plant protein polymeric matrix formed may be in a range of about 3.5 to 4.5. The concentration of the plant protein polymeric matrix in the solution may be in the range of about 1 wt% to about 20 wt%, about 2 wt% to about 15 wt%, about 3 wt% to about 8 wt%.

[0051] The method may further comprise homogenizing the mixture of the modifed clay and the plant protein polymeric matrix at a speed in the range of about 15,000 rpm to about 20,000 rpm, and about 17,000 rpm to about 20,000 rpm for a duration in the range of about 10 minutes to about 25 minutes and about 15 minutes to about 20 minutes and at a temperature in the range of about 50 °C to about 90 °C, about 75 °C to about 90 °C and about 80 °C to about 90 °C. The homogenizing step may be conducted in a homogenizer well known in the art. The homogenized mixture may be further stirred for a duration of about 1 hour to about 2 hours at a temperature in the range of about 50 °C to about 90 °C, about 75 °C to about 90 °C and about 80 °C to about 90 °C and cooled down to room temperature to produce the composition. Advantageously, the vigorous stirring and / or homogenization at high speed enables the composition to have uniform distribution of the polysaccharide / clay / plant protein polymeric matrix throughout the composition.The method may further comprise the step of removing organic solvent from the resulting composition. The removing step may be conducted by rotary evaporation, diafdtration and / or distillation methods well known in the art.

[0052] The weight percentage of the organic solvent remaining in the resulting composition may be in the range of about 0 wt% to about 10 wt% or 0 wt% to about 20 wt% based on the total weight of the composition. Advantageously, as the method of preparing the composition as described herein involves minimal use of organic solvent, it is environmentally friendly and provides a safer alternative to produce packaging (such as food packaging). The resulting composition without any organic solvent present is useful for preparing coatings on substrate which may otherwise be sensitive to organic solvent. The polysaccharide, clay and the plant protein polymeric matrix may be as defined above. Exemplary, non-limiting embodiments of a method of forming a coating comprising a composition as defined herein or a composition formed from the method as defined herein on a substrate will now be disclosed. The method of forming the coating comprising the composition as described herein or the composition formed from the method as defined herein on the substrate comprises the step of applying the composition as described herein on a substrate to form the coating thereon. The applying step may be selected from slot die coating, doctor blading, bar coating, rotogravure coating or combinations thereof. The applying step may include blade coating using a bird applicator at a speed of 50 mm / second to about 70 mm / second.

[0053] The coating comprising the composition as described herein has a thickness in the range of about 3 pm to about 15 pm, about 5 pm to about 15 pm, about 7 pm to about 15 °m, or about 9 pm to about 15 pm.

[0054] The method may further comprise the step of, before the applying step, providing the composition as described herein.

[0055] The method may comprise before the applying step, the step of coating an anchor coating agent on the substrate. Advantageously, the application of such anchor coating agent allows for the bonds between the substrate and the composition to be strengthened. The anchor coating agent may be polyacrylate based, polyurethane based, epoxy-based or combinations thereof.

[0056] The method may comprise after the applying step, the step of drying the substrate coated with the composition as described herein. The drying step may be conducted at roomtemperature and may be further subjected to vacuum drying at a temperature in the range of about 60 °C to about 70 °C.

[0057] Exemplary, non-limiting embodiments of a substrate coated with the composition as defined herein or the composition formed from the method as defined herein will now be disclosed. There is provided a substrate coated with the composition as defined herein or the composition formed from the method as defined herein.

[0058] The substrate may be selected from food (such as eggs), plastic, polyamide, cellulosic, multilayer composite or combinations thereof. The plastic may be selected from the group consisting of polyethylene terephthalate, polypropylene, polyethylene, polystyrene and combinations thereof. The polyamide may be selected from the group consisting of nylon 6,6, nylon 11, nylon 12, nylon 6,12, nylon 4,6, nylon 6 Kevlar, wool, silk and combinations thereof. The cellulosic may be selected from the group consisting of cellulosic films, paper, cotton, modal, lyocell, rayon and combinations thereof. The multilayer composite may be selected from metalized polyolefin film, metalized paper, Alox coated polyolefin film or Silox coated polyolefin film and combinations thereof.

[0059] Advantageously, having the composition coated on the substrate allows for production of packaging (such as food packaging) with high gas barrier, enhanced mechanical property and / or antimicrobial property which increases the shelf-life of the products (such as food). Further aadvantageously, the enhanced mechanical property of the composition (comprising clay) reduces the breakage rate of the substrate being coated (such as chicken egg).

[0060] In the present disclosure, a green method is disclosed to modify the clay with a polysaccharide in an aqueous condition and mixing a solution of plant protein polymeric matrix in an organic solution into the modified clay to produce the composition (such as aqueous zein / clay / chitosan dispersion or aqueous organic zein / clay / chitosan dispersion) with low organic solvent content. The method does not comprise the addition of a plasticizer and / or a silane coupling agent to form the composition. The composition of the present disclosure may be applied in one example, but not limited to, to prolong the shelf life of food (such as chicken eggs).BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The disclosure will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0062] Figure la shows Scanning Electron Microscope (SEM) images of PET film uniformly coated with an example of the composition of the present invention (zein / clay / chitosan (12 / 48 / 40)) at scale bar of 100pm.

[0063] Figure lb shows SEM images of PET film uniformly coated with an example of the composition of the present invention (zein / clay / chitosan (12 / 48 / 40)) at scale bar of 1pm.

[0064] Figure 2 shows a bar chart comparing the Haugh Unit of unwashed chicken eggs, oil coated chicken eggs and zein / clay / chitosan coating eggs [ZG0.5C: zein / clay / chitosan(16 / 60 / 250); ZG1.5C: zein / clay / chitosan( 10 / 40 / 50); ZG2.5C: zein / clay / chitosan(7.5 / 30 / 62.5)].

[0065] EXAMPLES

[0066] Non-limiting examples of the invention will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention

[0067] Example 1: Preparation of the composition [zein / clay / chitosan (12 / 48 / 40) dispersion (4.5wt%)|

[0068] Preparation of clay dispersion in water (2.4 wt%)

[0069] 10 g of Polymer grade montmorillonites (PGW) clay (supplied by Nanocor, Inc., United States) was mixed into 400 g of deionized (DI) water under stirring and continuously stirred for 3 hours. 0.6 ml of acetic acid (supplied by Merck Pte Ltd, Singapore) was then added to the dispersion and heated up to 60 °C under stirring. After stirring for 3 hours at 60 °C, the resulting dispersion was homogenized at 15,000 rpm for 5 minutes using a T18 homogenizer (manufactured by IKA, Germany). The pH value of the obtained suspension was finally adjusted to approximately 4 using acetic acid.

[0070] Preparation of zein solution (2,9 wt%)

[0071] 3 g of zein (supplied by Sigma Aldrich, Missouri, United States) was dissolved in 75 g of ethanol (supplied by Fisher Scientific, New Hampshire, United States) and 25 g of water mixture (75 v% ethanol) at 70 °C under stirring for 1 hour. After cooling down to room temperature, the pH value of the resulting solution was adjusted to approximately 4. Preparation of chitosan solution (3.8 wt%)2% acetic acid (6 g acetic acid in 294 g water) under stirring at 75 °C. After cooling down to room temperature, acetic acid was added in to adjust the pH to approximately 4 to get clear chitosan stock solution (3.8 wt%).

[0072] Preparation of zein / clay / chitosan (12 / 48 / 40) dispersion (4.5wt%)

[0073] 25 g of chitosan solution (4 wt%) was mixed into 50 g of clay dispersion (2.4 wt%) under stirring at 75 °C. At 75 °C, the obtained dispersion was homogenized at 15,000 rpm for 15 minutes using a T18 homogenizer followed by stirring overnight. 10 g of zein solution (2.9 wt%) was injected into the above dispersion under homogenization at 15,000 rpm followed by further homogenization for 15 minutes (using a T18 homogenizer) at 75 °C The dispersion was kept stirring for 1.5 hours at 75 °C followed by cooling down to room temperature under stirring The weight percentage of ethanol in the obtained aqueous organic zein / clay / chitosan dispersion was 8.8 wt%.

[0074] The aqueous zein / clay / chitosan dispersion without ethanol was prepared through rotary evaporating off the ethanol.

[0075] Example 2: Method of coating a substrate with the composition (zein / clay / chitosan dispersion and characterization of the composition / coating on substrate Application of zein / clay / chitosan dispersion onto substrate

[0076] The zein / clay / chitosan dispersion obtained from Example 1 was blade coated onto substrates by using a bird applicator at a coating speed of 50 mm / second followed by air drying at room temperature and vacuum drying at 60 °C.

[0077] Application of zein / clay / chitosan dispersion onto chicken eggs

[0078] Washed chicken eggs were dipped into the zein / clay / chitosan dispersion obtained from Example 1 for 2 minutes and air dried in fume hood for 2 hours

[0079] Oxygen / Water Vapour Transmission Rate (OTR) / (WVTR) measurement

[0080] Oxygen and water vapour permeability of nanocomposites coated film was measured by using Mocon OX-TRAN Model 2 / 21 and Mocon Permatran W 3 / 33 respectively. Oxygen permeability measurements were conducted at 23 °C and 0% relative humidity. Water vapour permeability was conducted at 37.8 °C and 90% relative humidity.

[0081] SEM imaging

[0082] The surface of the clay / zein / chitosan coated on PET film was studied by Field Emission SEM (FE-SEM, JEOL JSM-7600).

[0083] Haugh Unit measurementChicken eggs were weighed and cracked on a flat surface. Vernier calliper was used to measure the height of the thick albumen. The Haugh Unit was then calculated as below, Haugh Unit = 100 * Log(h - 1.7*w + 7.6)

[0084] h: height of thick albumen; w: weight of egg

[0085] Egg grade is defined as AA: HU > 72; A: 60 < HU < 71; B: HU < 60

[0086] Discussion

[0087] The uniform coating of zein / clay / chitosan on PET film is demonstrated by SEM images as shown in Figures la and lb. The OTR and WVTR of PET film with and without zein / clay / chitosan(l 2 / 48 / 40) coating is listed in Table 1.

[0088] Table 1. OTR and WVTR of PET film with and without zein / clay / chitosan(l 2 / 48 / 40) coating

[0089]

[0090] With the improvement of the living standard and the enhancement of health consciousness of people, the requirements on the quality of chicken eggs are increased. At present, when commercial chicken eggs are washed, the bloom (water-soluble film) of the chicken eggs is damaged in the step of washing. This results in increased degradation of the quality of washed chicken eggs. Zein or prolamin derivative has the characteristics of no toxicity, good biocompatibility and biodegradability, and is widely applied to the coating preservation of fruits, vegetables, meats and eggs due to the excellent gas and water barrier property.

[0091] The zein / clay / chitosan dispersion of Example 1 was applied onto chicken eggs through dip coating. Other methods such as brushing, spray coating or roll coating can also be applied on an industry scale. The coated chicken eggs were air dried before shelf-life test. The coated chicken eggs were stored at air-conditioned environment with temperature of 22 °C and RH of 75%. The quality of chicken eggs was then studied by measuring their Haugh Unit. As shown in Figure 2, the Haugh Unit of zein / clay / chitosan (7.5 / 30 / 62.5) coated eggs is higher than 60 after 37 days storage. Haugh Unit of 60 or higher is defined as Grade A.In contrast, the Haugh Unit of oil coated eggs is 60 after 30 days storage and much lower than 60 after 37 days storage. As such, it can be seen that the shelflife of zein / clay / chitosan coated eggs is increased for more 20 % in comparison to that of oil coated eggs.

[0092] Compared with traditional chicken egg coating agent such as vegetable oil, mineral oil, paraffin and the like, the coating matrix zein / clay / chitosan developed as described herein has the advantages of natural sources, no toxicity, edibility, good biocompatibility and biodegradability, and has excellent gas / oil-water barrier property and tough texture. In addition, the introduction of chitosan into the coating provides antimicrobial properties to prevent the growth of microbiome on the chicken egg-shell and microbial transmission, which further prolongs its shelf-life. The enhanced mechanical property of zein / clay / chitosan with introduction of clay reduces the breakage rate of chicken egg.

[0093] INDUSTRIAL APPLICABILITY

[0094] The disclosed composition may be used as a coating for packaging. This is applicable to industries such as pharmaceuticals, food and beverages, where the composition can be used as a coating for packaging, such as, but not limited to, food packaging or food raw materials. It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

Claims1. A composition comprising: a) clay modified with a polysaccharide and b) a plant protein polymeric matrix, wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

2. The composition according to claim 1, wherein the composition does not comprise a silane coupling agent and / or a plasticizer.

3. The composition according to claim 1 or 2, wherein the clay has an aspect ratio in the range of about 5 to 1000.

4. The composition according to any one of claims 1 to 3, wherein the clay is a platelike structured clay.

5. The composition according to claim 4, wherein the plate-like structured clay is a pristine clay silicate selected from the group consisting of montmorillonite, halloysite, bentonite, laponite, kaolinite, saponite, vermiculite and combinations thereof.

6. The composition according to any one of the preceding claims, wherein the weight percentage of the clay is in the range of about 20 wt% to about 80 wt% based on the total weight of the composition.

7. The composition according to any one of the preceding claims, wherein the polysaccharide is an amino polysaccharide selected from the group consisting of chitosan, chitosan derivatives, and combinations thereof.

8. The composition according to any one of the preceding claims, wherein the weight percentage of the polysaccharide is in the range of about 20 wt% to about 80 wt% based on the total weight of the composition.

9. The composition according to any one of the preceding claims, wherein the plant protein polymeric matrix is a plant storage protein (prolamin) selected from the group consisting of corn (zein), wheat (gliadin), rye (secalin), barley (hordein), rice (glutelin), sorghum (kafirin), oats (avenin), derivatives and combinations thereof.

10. The composition according to any one of the preceding claims, wherein the weight percentage of the plant protein polymeric matrix is in the range of about 10 wt% to about 60 t% based on the total weight of the composition.

11. A method of preparing a composition according to any one of claims 1 to 10, the method comprising the step of mixing a solution of plant protein polymeric matrix and modified clay to form the composition, wherein the modified clay comprises clay modifiedwith a polysaccharide, and wherein the polysaccharide couples the modified clay to the plant protein polymeric matrix.

12. The method according to claim 11, wherein the method does not comprise the step of adding a plasticizer and / or a silane coupling agent to form the composition.

13. The method according to claim 11 or 12, wherein the method further comprises before the mixing step, the steps of:1) modifying clay with a polysaccharide by mixing a dispersion of clay with a solution of the polysaccharide under aqueous condition to form the modified clay; and 2) forming the solution of plant protein polymeric matrix by dissolving a plant protein polymeric matrix in an organic solution14. The method according to claim 13, wherein the modifying step further comprises the steps of:a) forming the solution of polysaccharide by dissolving the polysaccharide in an aqueous acid solution; andb) forming the clay dispersion by dispersing the clay in an aqueous solution.

15. The method according to claim 14, wherein the concentration of the aqueous acid solution is in the range of about 2% to about 5%.

16. The method according to any one of claims 13 to 15, wherein the organic solution is a mixture of an organic solvent with water.

17. The method according to claim 16, further comprising the step of removing organic solvent from the composition.

18. A method of forming a coating comprising a composition according to any one of claims 1 to 10 or a composition formed from the method of any one of claims 11 to 17 on a substrate, comprising the step of applying the composition on a substrate to form the coating thereon.

19. The method according to claim 18, wherein the applying step is selected from slot die coating, doctor blading, bar coating, rotogravure coating or combinations thereof.

20. The method according to claim 18 or 19, wherein the coating has a thickness in the range of about 3 pm to about 15 pm21. The method according to any one of claims 18 to 20, further comprising before the applying step, a step of coating an anchor coating agent on the substrate, wherein the anchor coating agent is polyacrylate based, polyurethane based, epoxy-based or combinations thereof.

22. A substrate coated with the composition according to any one of claims 1 to 10 or a composition formed from the method of any one of claims 11 to 17.

23. The substrate according to claim 22, wherein the substrate is selected from food, plastic, polyamides, cellulosic, multilayer composites or combinations thereof.

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