WO2008075396A1

WO2008075396A1 - Edible matrices and relevant applications and preparation method

Info

Publication number: WO2008075396A1
Application number: PCT/IT2007/000876
Authority: WO
Inventors: Stefano Farris; Luciano Piergiovanni; Giovanni Ronchi; Roberto Rocca
Original assignee: Mirante S.R.L.
Priority date: 2006-12-19
Filing date: 2007-12-17
Publication date: 2008-06-26
Also published as: ITMI20062443A1; WO2008075396B1

Abstract

The invention concerns edible matrices for the protection of the substrates (food or not). The water soluble matrix has a glycerol-lipid-protein content Y (by weight) defined by the expression Y = X1 + f1 (X1) + f2 (X1) wherein X1 is the quantity % of protein (pigskin gelatin) and f1 (X1) and f2 (X1) are respectively the amounts of glycerol and lipid (acetylated monoglycerides), strictly depending on the protein content. Said matrices contain also an emulsifier and an anti-foam agent, and provide, among other properties, sealability, transparency, gas and vapour barrier, etc..

Description

EDI BLE MATRICES AND RELEVANT APPLICATIONS AND PREPARATION METHOD.

The present invention relates to edible matrices, intended for the protection of foodstuffs and for coating different substrates (i.e. synthetic, artificial, natural materials) such as films and containers (even siliceous) for packaging applications.

BACKGROUND OF THE INVENTION

With the increased consumption of ready-to-eat foodstuffs and the higher demand of wasting and recycling packaging materials, the request for edible packaging has generated a big interest especially in the last decade.

Consequently, this technical area is now a patent crowded field in which even a minimal (at first glance unimportant) improvement can result in a smart commercial success.

PRIOR ART

PCT Publication WO2004/026035 gives a large technological background indicating approximately thirty patents and references to scientific publications.

US Patent n° 5,019,403 (May 1991) discloses a method to coat alimentary substrates and/or agricultural derivatives by means of lipid-protein matrices: by modifying in situ the pH of the starting solution, the properties of the final edible film/coating are improved (e.g. gas and water vapour barrier properties). Moreover, the inclusion of active compounds and large quantities of products belonging to the three principal classes of macromolecules (i.e. protein, lipids, and polysaccharides) are considered. At the present time, however, both the techniques of manufacture and the analyses concerning the film/coating properties are questionable. Essential data to evaluate the true efficiency of the film are also lacking in said document. Finally, the application of the proposed matrices is limited to agricultural substrates, without mention to any other type of surfaces. US Patent n° 5,543,164 (June 1966) describes a method to obtain edible films and coatings: formulations are proposed based on the chemical, enzymatic or thermal denaturation of the used protein matrix in order to promote bond formation by inter- and intra-molecular disulfide bridges. Indeed, several proteins such as whey protein isolate (WPI) show sulphur amino acids (SAAs) such as cysteine and cystine: cysteine is important to maintain the tertiary structure of proteins as the oxidation of the thiol groups (SH) of two not contiguous cysteine residues can form disulfide (SS) bridges between chains of similar or different nature. Also the good barrier properties to water vapour are emphasized. However, there is no mention about the possible utilization of pigskin gelatin, which is free of SAAs.

Sobral (Food hydrocolloyds 15:423 (2001) describes the main chemical-physical characteristics of said pigskin gelatin to form films, but does not consider the direct application on food or not-food matrices.

Guilbert [ LWT- Food Science and Technology, 29: 100-7 (1996) ] studies various edible films and coatings without considering the use of pigskin gelatin as a possible starting macromolecule, but focusing only on the application of said films directly on the surface of different foodstuffs.

On the contrary, Anker et al. worked on edible lipo-protein matrices in which the protein fraction is represented by WPI and the lipid matrix by an acetylated monoglyceride.

In addition, all the afore mentioned studies focused on the characterization of such edible films obtained in laboratory, without any reference to specific industrial application on matrices or support of different type.

Miller [Trends in Food Science and Technology, 8: 228-237 (1997)] mentions the possibility of obtaining edible films and coatings using molecules of different origin (e.g. proteins, lipids, and polysaccharides) as a starting raw material, but envisaging the exclusive direct application only on food matrices. There are books and chapters dedicated to the edible films and coatings development, which consider their application only to food [ Cuq. B et al. Edible films and coatings as active layers. In ROONEY, M. (Ed.) Active Food Packaging. Blackie Academic and Professional (1944) ].

Only Krochta and Seok-ln take into consideration the application of an edible coating on a plastic film, but only as a tool to improve its oxygen barrier and optical characteristics. Moreover, only hydrophilic matrices (protein or polysaccharide) blended to a plasticizer (glycerol, sorbitol, saccarose, PG and PEG) were considered, without any reference to the possible use of a lipid matrix in order to improve the water vapour barrier properties of the plastic film. In addition, gelatin (of any origin) is never prefigured as a starting bio- macromolecule. Finally, the deposition of the developed edible coating only concerned the corona-treated (the outer one) side of the plastic film. This implies that: - the adhesion of the edible layer on the treated surface is of course made easier, but it does not mean that the same edible layer will adhere properly also on the untreated side; - the deposition on the treated side precludes the huge potential and advantages that could arise from an edible matrix, as it will never be in direct contact with the foods [Seok - In H et al. Packaging Technology and Science, 17: 13-21 (2004); Seok- In, H. et al, Packaging Technology and Science, 18: 1-9 (2004) ].

Even with many merits, edible films and coatings described in the literature are not exempt from some negative aspects, such as:

Tough manufacturing: in several cases, the efficient production of said coatings, is time and money-consuming; examples are given by the method proposed originally by Krochta in the first patent (pH control in situ) or by all Authors/Inventors that, to stabilize film/coatings, keep it in a climatic chamber at a specific temperature and for a time not lower than 16 hours; Lack of universality : all the solutions proposed up to the present show interesting properties, but none of them is present at the same time in the edible layer. Some edible films show good aesthetic (optical) properties, others or gas (oxygen and carbon dioxide) or water vapour barrier properties; other films, finally, are claimed as a good vehicle of active substances. However, neither films nor coatings are indicated as having these and other characteristics all together. Moreover, there is no indication of the usefulness and efficiency of films both on food and no-food matrices (e.g. plastic films, glass or cellulose);

High costs: in all the literature examples, films and coatings are cited as able to provide specific functions or specific good characteristics when deposited as thick layers (thickness above 50 microns).

It is worth noting that, in most cases, edible layers are obtained using (separately or blended) substances belonging to the three main groups of macro nutriments: proteins, polysaccharides, lipids. It is widely accepted that the proper way to obtain edible films, which are able to satisfy the different requests linked to the foods protection and preservation, consists in the contemporaneous use of a polysaccharide or a protein matrix mixed to a lipid matrix. Said films are an excellent means to guarantee an almost total protection to the food. In this way the advantages derived from these components are combined: the lipid matrix show good water vapour barrier, whereas proteins and polysaccharides (both hydrocolloids) act as a gas barrier, providing at the same time the necessary strength to the final film, thanks to the formation of a continuous network between the different molecules. A plasticizer is usually added in order to provide flexibility to the films. The impulse to use edible matrices directly on the foodstuffs is already strong; the impulse to use them to partially replace synthetic packaging films can be much stronger. Although excellent efforts and results have been obtained in the preparation of bio-based polymers (e.g. those obtained from the lactic acid, PLA), nothing exists to date concerning the use of edible matrices as packaging material. The reason is essentially linked to the nature of such bio- polymers, being too brittle and moisture sensitive to act as the plastic packaging. SUMMARY OF THE INVENTION AND BRIEF DESCRIPTION OF THE DRAWINGS. The first objective of the invention is to provide edible matrices which do not show the inconveniences of the Prior Art, in particular those mentioned above. Another objective is to provide specific methods, which are economical. A further scope is to provide substrates which support the edible matrices, in particular for the preparation of films and containers with enhance properties for the packaging. The most important features of the invention are recited in the claims which are considered herein incorporated.

Aspects and advantages of the invention will more clearly appear from the following description of the preferred embodiments which refer to figures 1-5, diagrams of the performances of the products and methods according to the invention. In particular, figure 1 shows the influence of the amount of each component on the oxygen transmission rate (OTR) for all the tested formulations.

Figure 2 shows the effect of the various components on another important characteristic of plastic films, namely water vapour transmission rate (WVTR).

Figure 3 represents the opacity variation of an oriented polypropylene film (OPP) coated with different edible layers obtained by varying the concentration of the different component. Figure 4 highlights the important anti-UV property of the different edible coatings over the control film (OPP without coating). The extent of the positive effect of each coating is obviously related to the different concentration of the three macro-nutriments. Finally, figure 5 shows the sharp improvement of the slipping property of the OPP film as a consequence of the application of a thin edible coating. In particular, both the static and the kinetic friction coefficients (COF) show values lower than those of the original film, both in the "film over film" and in "film over metal" test, as it can be seen also from table 4. DETAILED DESCRD?TION OF THE INVENTION

This invention provides methods to obtain edible matrices and their applications on substrates. According to a feature of the invention, an optimal adhesion to the substrates is reached thanks to the selection of specific macromolecules: proteins, lipids, polyalcohol, emulsifiers and, in certain cases, inorganic charges acting as anti-blocking agents. The addition of these inorganic fillers to the original formulation, however, makes the coating according to the invention no more 'edible'. This is because these components, from a legal point of view, can not be considered neither as ingredients nor additives, contrary to the other substances mentioned before.

The use of pigskin gelatin as a protein is more favourable. Preferably, acetylated mono- glycerides or bee waxes are used as hydrophobic components, whereas monostearate glyceric alcohol or soy lecithin are used as a emulsifier. Moreover, the formulations according to the invention comprise an anti-foam agent pertaining to the family of poly- dimethylsiloxanes. Finally, kaolin or aluminium silicates can be used as an inorganic filler. Among the many benefits arising from the new matrices, we only refer to those related to their characteristics and properties better than those of films without the invention (uncoated) and also existing synthetic coatings.

Indeed, when applied as a coating, the matrix of the invention:

1) perfectly adheres to the no treated side of the film, i.e. the "no corona-treated" one; accordingly, said matrix can be deposited without problems on the inner side of the packaging, which directly comes into direct contact to the food; thus, there is no need of adhesion promoters (the so-called primers), which are extremely toxic; 2) makes sealable plastic films (like PET) which are per sέ not sealable. Furthermore, it lowers the seal temperature of other films (like PP). For this reason, the new edible coating itself acts as an excellent substitute of the well known cold-sealants which are toxic, expensive and require a difficult process to be applied ("register" application);

3) is a smooth coating as it does not produce foaming phenomena which normally occur in the industrial scale when working with the most of the conventional matrices; indeed foams create problems to the production management and to the final product as the presence of micro-bubbles influences negatively the film performances.

4) provides an excellent barrier to gas and aromas: consequently its application on a plastic film highly permeable to gas and aromas (e.g. PP) provides an additional property which is normally achieved by the deposition of synthetic substances;

5) similarly, such a coating imparts an optimal barrier to water vapour when it is applied on films which originally do not have such a characteristic (e.g. PET);

6) improves the slipping properties of the film both on itself and on metallic surfaces, reducing both the static and the kinetic coefficients;

7) increases the transparency of the films on which it is applied; this is a very important feature, especially from an aesthetic point of view.

8) shows optimal barrier to UV rays, in particular UVc, which are extremely health hazardous;

9) makes "active" a packaging which initially is not. This is because it is possible to incorporate active substances such antimicrobials, antioxidants, aromas, pigments, fragrances;

10) from a legal point of view, all components according to the invention are allowed as food contact materials [European Directive 2002/72/EC, 2007/19EC; 21 CFR (Code of Federal Regulations, USA) § 182.2727]; for that reason, the matrix does not represent a health hazardous substrate when in direct contact with foodstuffs;

11) in the native status and after deposition it is odourless and colourless. Hence, it will not affect neither the final characteristic of the packaging nor the food sensorial properties;

12) it can be coloured by adding edible pigments; as such, the matrix according to the invention can act as a true ink.

According to a first feature of the invention, said matrices comprise: as a protein, the pigskin gelatin characterized by a Bloom value between 120 and 300; as a lipid, acetylated monoglycerides from palm oil, the acetylating degree being between 50% and 90%, or bee wax; as a plasticizer, vegetal glycerol; as an emulsifier, glycerol alcohol mono stearate of vegetal origin or soy lecithin; as anti-blocking agents, kaolin (0 < 2 μm) and aluminium-silicates (0 < 3.5 μm); as anti-foam agent, a polydymethylsiloxane.

According to an other feature of the invention, the protein content will be in the range 2 - 25% (^w/ _w), depending on the properties to be enhanced. The percentage of the lipid component and of the plasticizer are defined as a function of said protein content (Xi) whereby X₂ = glycerol = U (Xi) and X₃ = lipid =f₂ (Xi)- Characteristically, the percentage sum of the three components is expressed by the following formula:

Y = X, + f,(Xi) + f₂(Xi) (1)

In one preferred embodiment U and f₂ are:

f_i (X_ι ) = _Λ[-^X_ι and Z₂ (JT₁ )= -^Lx₁, whereby (1) can be written as:

Both the glycerol and the lipid content can slightly differ from the values of formula (2) by values comprised in the range of ± 2.0%.

Moreover, part of the lipid component can be substituted by a solvent to enhance some specific characteristics of the matrix.

The other components are used in the following amounts: emulsifier: from 0.5 to 3%,preferably 1 % (^w/ _w) of the solution; anti-blocking agents: kaolin, from 1% to 10%, preferably 4.5% (^w/ _w) on the solution; aluminium-silicates, from 1% to 10%, preferably 4% (^w/ _w) on the solution; anti-foaming agent: from 1 to 10 ppm, preferably 8 ppm; The complement to 100% will be given by the solvent (H_∑O).

The method according to the invention to obtain the starting matrix (in form of a slurry) is as follows:

1) The starting aqueous glycerol-protein solution is submitted to stirring (500 r.p.m.) at 77⁰C for 60 minutes;

2) pH is taken to a value of 9 ± 0.5 by adding 1 M Na OH;

3) the above mentioned specific amounts of lipid and emulsifier are dissolved at 135°C for 15 minutes and added to the main solution;

4) the anti-foaming agent is added in its above-mentioned quantity;

5) the anti-blocking agent is added in its above-indicated amount;

6) the whole solution is kept under stirring (1000 rpm) at 6O⁰C for 15 minutes. The thermal treatment sub 1) assures the complete denaturation of the protein (pigskin gelatin) which looses its ternary structure, moving from the folded to the unfolded conformation. Therefore, new interactions between said protein and the other molecules can take place in correspondence of bond sites previously not available. The pH adjustment of said protein to its isoelectric point (in correspondence of which positive and negative charges of this amphoteric molecule are equivalent) is necessary in order to speed up its solubilization and its interaction with molecules of opposite charge.

The presence of anti-blocking agent (whether kaolin or aluminium-silicate) is of fundamental importance to avoid that the coated films adhere strongly to themselves when winded as rolls, due to the interaction between the coated side of the film and the opposite one, which is "corona-treated". Indeed, as the inorganic micro-charges protrude partially from the coated side of the plastic film, they form an obstacle to the interaction between said side and its corona-treated opposite side thereby limiting the blocking phenomenon. The anti-foaming agent addition is also of great importance as otherwise the protein matrix would naturally produce undesired foam during the agitation phase.

The second step of the method according to the invention is the deposition of the edible slurry. Several methods can be utilized according to the desired characteristics of the final product. For example, the coating deposition technique will be used when very thin, even and perfectly dry layers have to be applied on plastic films , as we will see in detail in the next examples.

If the edible film is intended as a wrapping for food matrices or surfaces of different nature (for example for decoration purposes), nebulization (by means of specific aerographs) will be the suitable technique, which enable the obtainment of special effects (e.g. "like-orange peel" surfaces). The matrix deposition can also take place by casting or pouring the surfaces to be coated (e.g. in the case of concave bodies). In other cases (e.g. to make coloured decorations on glass or paper) specific instruments (e.g. brushes, drifts) will be used. The matrix according to the inventions finds several uses. For instance, it has. been tested as edible coating on many plastic films in substitution of the synthetic coatings used until now, with surprising and excellent results. Indeed the deposited edible coating provided new characteristics to the plastic films, enhancing their specific properties: gas and water vapour barrier; optical properties (in terms of transparency and opacity); UV barrier; sealability even at temperature below the conventional temperatures for plastic films; slipping properties with sharp reduction of both the static and the kinetic friction coefficient (CoF); possibility of releasing active substances like antimicrobials, antioxidants, fragrances and aromas within the packaging; direct contact with the food without representing a health hazardous substrate. The same edible matrix has also been employed to wrap several food surfaces to limit specific negative reactions and thus to prolong the shelf-life. It has been successfully tested on surfaces of different origin like glass containers, in order to protect them against the solar radiation thanks to the presence of specific anti-UV pigments previously incorporated in said matrix. It has been also used to cover and decorate cellulose-based products like paper and paperboard intended for packaging purposes. Inks fall also in the invention scope. Examples Following materials have been used:

^■ pigskin gelatin 133 Bloom (6,67° at 10⁰C) (Prodottigianni S.P.A., Italy)

^■ vegetable glycerol 99,5% (Gioma Varo S.r.l., Italy)

■ acetylated monoglycerides VERACET 70 (Prodottigianni S.p.a., Italy)

^■ emulsifying agent VEROL N-40 (Prodottigianni S.p.a., Italy)

■ bee wax (Gasid, Italy) ^■ anti-blocking agent: kaolin (KAOFLO 230 D, Thiele Kaolin Company, U.S.A.), aluminium- silicate (SIPERNAT 44 MS, Degussa, Germany)

^■ sodium hydrate NaOH 1N (Sigma-Aldrich, Italy)

^■ anti-foam: dimetylpolysiloxane KF-96-200CS (Prodottigianni S.p.a., Italy) Methods

Preparation of the Film-forming Solution. Various protein-based solutions in water were prepared by varying the protein concentration between 2% and 25%. The glycerol amount varies between 4% and 5%, and the lipid content between 0.01% and 6.5%. The amount of emulsifier is always equal to 1%, and the anti-blocking between 1% and 10% (^w/_w) on the total weight of the solution, both for the kaolin and the aluminium silicate. Lastly the anti-foam agent is added in the amount of δ ppm. To obtain the edible matrix, the glycol-protein-based water solution is stirred at 500 r.p.m. at 77⁰C for 60 minutes, to obtain the protein denat u ration and the possibility of interactions between macromolecules. The pH is adjusted to 9.0 using 1M NaOH; in this way the positive and negative charges of the protein become equivalent, promoting the interaction between substances differently charged. Specific amount of the lipid and the emulsifier components (previously dissolved at a temperature of 135° for 15 minutes) are added to the original solution, followed by the addition of the antiblocking agent (kaolin or aluminium silicate) when the gelatine content is equal or higher than 10%. At the end, the anti-foam agent (poly-dimethyl siloxane) is added in the above specific quantity to avoid foam formation. Heat stirring is continued (1000 r.p.m.) for 15 minutes, in order to allow bonds formation and interactions between the molecules in the solution. Finally, an even and smooth solution is obtained, which is free of bubbles and foams and transparent, colourless and odourless.

Deposition of the Edible Matrix. As anticipated, the methods of depositing and coating depend on the substrate to coat and on the desired characteristics of the final product. In particular, the main methods of deposition are:

Coating. It is used for the deposition of very thin layers on plastic films. The edible matrix obtained as before is kept under continuous stirring in metallic tanks (1000 litres) at a controlled temperature (77°C). The anti-foam agent avoids the foam formation and hence the liquid matrix exits the container. Through ad-hoc pump systems the matrix is continuously transferred into another smaller container (200 litres), where it is continuously stirred and from where it reaches an open-sky rectangular basin of about 20 litres. An engraved chrome- plated copper roll is wetted with the coating, excess is removed by a doctor knife, and the coating remaining in the engraved cells below the roll surface is transferred to the web at the gravure roll/backup roll nip. in order to remove the liquid solvent (i.e. water) the coated web is firstly passed through a narrow gap limited by infrared rays lamps. Their action raises quickly the surface temperatures in order to increase the efficiency of the solvent removal for the next step, in which the web moves through a narrow tunnel superiorly limited by heating plates emitting forced air at 90⁰C. In this way sticking phenomena of the film during rewinding are avoided.

Nebulization. This technique of deposition is very good for surfaces to be protected and/or decorate. The matrix is put within a metallic container mounted on an aerograph, connected on its turn to a compressor to deliver a compressed air flow at a pressure between 2 and 3.5 bar. By controlling the aerograph nozzle cleft it is possible to obtain various effects, like perfectly smooth surfaces or a typical "like-orange peel" aspect of the coating used to protect different foods (e.g. bakery products, dry fruit) or to coat glass containers, paperboard surfaces etc.

Casting / Pouring. This technique of deposition fits for concave surfaces on which the edible matrix is to be directly poured up to their complete covering. A typical example concerns cellulose dishes or the plastic vase-containers. Dipping. It is particularly useful to coat pieces of fresh fruit. The fruit parts are directly immersed within the edible matrix for a short time (< 2 sec.) to avoid imbibitions of the fruit matrix.

Decoration. Useful to make writings and/or drawings on specific surfaces. In this case, matrices purposely added with edible pigments, in order to get a coloured edible water solution, can be used. For its application, accessories like brushes and punches can be used. The edible matrix has been successfully tested on paper and paperboard surfaces to decorate tin, plats, vases through writings or drawings.

Thickness of the edible film/coating. The thickness of the uncoated plastic films was measured with a micrometer (Dialmatic DDI030M, Bowers Metrology, Bradford, UK) to the nearest 0.001 mm at 10 different random locations. For the determination of the thickness of the edible layers (Table 1) coated on the plastic films, a 10 x 10 cm sample was cut and weighed (M₁). The edible coating was mechanically removed by hot water (80⁰C) and the resulting base film weighed (M₂). The thickness of the coating was obtained using the following equation: ι₌ M, - M_{2 χ m (1 )}

P where:

M₁ = unit total mass (plastic film + coating) (g dm^"2) M₂ = unit mass of the plastic film (g dm^"2) p = density (g cm^"3) / = thickness (μm)

being M₁ - M₂ and p known. The thickness of the edible coating was also measured using an optical microscope (OM) (Micro Nikon Eclipse ME600 Laboratory Imaging, Nikon Instruments, Sesto Fiorentino, Italy) at 10Ox magnification. In this case, films after storage were fixed on a rectangular steel holder and a sharp razor blade was then used in a specific way to cut them, in order to permit the right observation of the cross section of the composite films. Finally, the thickness of the edible layers was quantified using the software NIS- Element (Nikon Instruments, Sesto Fiorentino, Italy).

Water Vapour Transmission Rate (WVTR). WVTR was determined by water vapour transmission rate instrument Lyssy L-80 (PBI Dansensor A/S, Ringsted, Denmark). The testing methods as described by ASTM E 398-03 Standard Method were used. Film samples were double masked by manufacturer supplied aluminium foil masks with effective film test area 42 cm² to prevent the film being damaged during the test. Each sample was mounted onto instrumental cylinders, followed by analysis. Testing was performed at 23 ± 0.5⁰C and 65% RH. The average value of five independent samples was used to establish WVTR values (expressed in g m^'224h^"1).

Oxygen Transmission Rate (OTR). For the oxygen transmission rate measurement, an OPT-5000 (PBI Dansensor A/S, Ringsted, Denmark) equipped with a zirconia oxygen sensor was used, on the basis of the nearly-isostatic standard method. Samples were put in a paperboard mask with a testing area of 42 cm² and then inserted in the instrument. Measurements were performed at constant temperature (23 ± 0.5⁰C) and relative humidity (0%) conditions. The final OTR values (mL m^"2 24h^"1) arose from the average of five independent samples.

Seal Strength Determination. The sealability properties of the coated films were evaluated according to the Standard ASTM F88-85 using a dynamometer (mod. Z005, Zwick Roell, UIm, Germany). Film strips were placed on top of one another, and an area of 2.54 3 1.5 cm (at the edge of the film) was heat-sealed from 50⁰C to 90⁰C for 1 sec. of dwell time at 4 atm pressure, using a thermal heat-sealer Model- 12ASL (Sencorp System Inc., Hyannis.Mass., U.S.A.). The final seal strength values (N) arose from the average of ten independent samples.

Opacity (Haze). Haze was measured in accordance with ASTM D 1003-00, using an UV- Vis spectrophotometer (Lambda 650, PerkinElmer, Waltham, USA) fitted to a 150 mm integrating sphere (PerkinElmer, Waltham, USA) in order to trap also the diffuse transmitted light. Measurements were performed in the wavelength range 380 - 780 nm. The final haze values (as % of the total incident radiation) arose from the average of five independent samples. Anti-UV properties. Anti-UV properties were evaluated by collecting transmittance spectra of coated and non-coated plastic films in the UV region 340-200 nm, and then calculating the area under each curve by an integration process. The smaller the area value, the greater will be the anti-UV properties for the specific film taken into account. The anti-UV property too was estimated using a 150 mm integrating sphere.

Transparency. Transparency was determined according to ASTM D 1746-88. In particular, the transparency of both uncoated and coated films was measured in terms of specular transmittance, i.e. the transmittance value obtained when the transmitted radiant flux includes only that transmitted in the same direction as that of the incident flux in the range 540-560 nm. Then, the correspondent transparency value was obtained by the following equation:

(T₃) = 100 l_s /I₀ (2) where:

T_s = specular transmittance at 550 nm l_s = light intensity with the specimen in the beam I₀ = light intensity with no specimen in the beam The examples described below emphasize the surprising characteristics and properties of the edible matrix according to the invention. In all the examples, reference is made to five different formulations, shown in Table 1.

Table 1. Percentage composition of the five different formulations as reported in the examples.

Formulation

Bio-molecule 1 2 3 4 5

Protein 10.30% 10.30% 2.30% 2.30% 6.30%

Plasticizerr 5.0% 4.0% 4.50% 4.50% 8.40%

Lipid 2.65% 0.80% 3.0% 1.0% 1.60%

Emulsifier 1.0% 1.0% 1.0% 1.0% 1.0%

Anti-blocking 2.0% 4.0% 6.0% 8% 10%

Anti-foam 1.0%) 1.0%o 1.0%o 1.0%o 1.0%o

Solvent 79.0% 79.9% 83.2% 83.2 72.7%

Total 100% 100% 100% 100% 100%

Example 1. Herein, the effect of the coating deposition (1 μm thick) on the water vapour transmission rate of a coextruded oriented polypropylene film (30 μm thick) is described. In particular, the influence of the concentration of the different components in the matrix (especially the lipid one) is emphasized. To gain a better understanding of the influence of the different formulations, Figure 1 shows as the lowest WVTR values, and therefore the highest barrier properties, belong to formulation 3. This is due both to the highest lipid concentration (which is directly responsible of the hydrophobicity of the coating) and to the lowest protein concentration (which affects the water vapour barrier of the coating being highly hydrophilic) of this formulation. This is demonstrated by the fact that in the formulation

1 , even rf the lipid quantity is a little lower than formulation 3, WVTR increases more than proportionally because of the high protein concentration. On the contrary, in the formulation

2, even if the protein concentration is the same, the WVTR value still increases as the lipid concentration reaches its lowest value. In the formulation 4, even if the lipid percentage is slightly higher than in formulation 2, the WVTR value is much more lower because the protein concentration is set at its lowest value. Finally, by considering formulation 5, a particularly high WVTR value is reached even if the protein and lipid concentrations are at intermediate values. In this case it has to be considered the important role played by the plasticizer, whose concentration is almost twofold that used for the other formulations. In conclusion, both the protein and the lipid component strongly affect the water vapour barrier, even in opposite ways. In any cases, all the tested formulations showed WVTR values lower than that of the uncoated film, to point out the efficacy of the edible coating in the improvement of such important characteristic of the plastic films.

Example 2. Herein, the effect of the coating deposition (1 μm thick) on the oxygen transmission rate of a coextruded oriented polypropylene film (30 μm thick) is described. In particular, the influence of the concentration of the different components in the matrix (especially the protein one) is emphasized. Figure 2 shows that the lowest OTR value is related to the formulations 1 and 2, having the highest protein content. This emphasizes the important role of the gelatin used to obtain the edible coating of the invention. The difference between these two formulations is due to the different lipid amount, which affects negatively the OTR values because it acts as apparent plasticizer, interrupting the continuity of the protein lattice. This is confirmed by the fact that the highest OTR value among the tested formulations is for the formulation 3, in which the lipid and the protein components reach, respectively, their highest and lowest level. On the contrary formulation 4 shows an OTR value half than that of the formulation 3, as the lipid concentration is three times lower. OTR value for formulation 5 is higher than that of formulations 1 and 2, but lower than formulations 3 and 4. This is because its protein content is nearly intermediate to that of the other four formulations. In conclusion, the amount of the protein used in the edible coating formulation influences proportionally the oxygen barrier property, whereas the lipid content acts in opposite way. In any cases, the positive effect of the edible layer according to the invention on a plastic film is demonstrated. A very thin layer (1μ) is indeed able to provide surprising enhanced effects on one of the fundamental properties of the plastic film for food packaging applications: as shown, the application of the edible coating on the plastic film (coextruded OPP 30μ thick) leads to a oxygen barrier increase of around 200%.

Example 3. Herein, the effect of the coating deposition (1 μm thick) on the sealability of a coextruded oriented polypropylene film (30 μm thick) is described. In particular, the influence of the concentration of the different components in the matrix (especially the protein one) is emphasized (Table 2). In particular, the formulations with the lowest amount of gelatin associated to the highest percentages of the lipid component showed inferior sealing properties.

Table 2. Influence of the edible coating on the film sealability^*.

Seal-temperature (⁰C)

Formulation 50 55 60 65 70

1 seal seal seal seal seal

2 seal seal seal seal seal

3 seal seal seal seal seal

4 no seal no seal no seal no seal seal

5 no seal no seal no seal no seal seal

OPP no seal no seal no seal no seal no seal

Sealability strength values varied from 0.5 to 4.0 N depending on the specific formulation.

It can be noted the surprising sealing effect of the edible coating applied on a PP film typically used for food packaging. The thin edible layer makes possible the sealing of the film at temperatures much more lower than those usually required to seal two sides of the uncoated plastic film (around 115°-120°C). These results demonstrate the huge practical importance of the present invention. The industrial costs are strongly reduced and not- sealant films, like polyethylene-terephthalate (PET), can become sealant after the deposition of the edible coating according to the invention. Moreover, increasing the thickness of the coating, it is possible sealing at lower temperatures; also for this reason, the lacquer of the invention appears as an excellent substitute of the cold sealant, compared to which results in a lower toxicity, and in a simpler and faster application on the plastic web (no "register" deposit is required). Finally, costs are strongly inferior.

Example 4. Herein, the effect of the coating deposition (1 μm thick) on the opacity (haze) of a coextruded oriented polypropylene film (30 μm thick) is described. In particular, the influence of the concentration of the different components in the matrix (especially the protein one) is emphasized. Figure 3 shows opacity values lower than that of the uncoated polypropylene film for all tested formulations of the invention. Even if the differences are not significant, it is worth noting that the opacity of the neutral film does not decrease notwithstanding the presence of the additional edible layer. This aspect is very important from a practical point of view, because the transparency property is linked to the capacity to see through the film (and thus to see the food included). Accordingly, a further meaningful and surprising property of the edible coating of the invention appears evident: when applied on a plastic film, it does not worsen its opacity but seems even to improve it. Example 5. Herein, the effect of the coating deposition (1 μm thick) on the absorption of the UV radiation of a coextruded oriented polypropylene film (30 μm thick) is described. In particular, the influence of the concentration of the different components in the matrix (especially the protein one) is emphasized (Figure 4 and Table 3).

Table 3. Anti-UV properties of the different formulations according to the invention.

Formulation Area

1 8249

2 8184

3 9043

4 8911

5 8554 OPP 8841 From Figure 4 it can be observed that the curves have a similar trend up to 240 nm; from this point on, important and surprising differences appear, which make the edible coating according to the invention unique and original. Between 240 and 229 nm three of the five tested formulations (3, 4, and 5) show transmittance values (%T) higher than that of uncoated polypropylene; the other two formulations (1 and 2) show a curve slightly downshifted, due to the smaller amount of radiation able to move through these coated films than that normally able to pass through the uncoated PP film. From 220 nm, all the tested formulations show greater anti-UV properties than that of the uncoated PP film. In particular, formulations 1 and 2 show the highest capability to absorb UV radiations. This is undoubtedly due to the highest protein concentration. Indeed from 235 nm, curves related to the above mentioned formulations drop sharply, as a result of the reduced amount of transmitted radiation. The maximum difference between these two formulation and the uncoated PP film is at around 212 nm. Here, PP coated films according to formulations 1 and 2 transmit only 6.5% of the incident radiation, whereas the uncoated PP film transmits approximately 47%. These results are confirmed by the values of the areas under each curve obtained from each formulation, as reported in Table 3. This example shows another excellent characteristic of the edible coating according to the invention and the relevant methods. The capacity to absorb UV radiation is very important to prevent undesired deterioration of the packaged foodstuffs. This is particularly true considering that the maximum absorption of this radiation by the edible coating occurs in correspondence to the most dangerous UV region, i.e. the UVc one.

Example 6. It shows the important effect deriving from the presence of the edible coating on the slipping properties of plastic films both on themselves and on metallic surfaces (Table 4). In particular, the enhanced "slipping properties" arise from the lipid component, which acts as the most common slipping agents used for the polyolefines (eurucamide and oleamide). From a practical point of view the improvement of such properties is of great importance, especially at industrial scale. Using such coatings including a lipid component able to behave like a true slip agent allows a layer of film to slide easily over another layer of film (e.g. on a roll), or over machine surfaces during film manufacture and packing, reducing the coefficient of friction (CoF). Therefore, the final result will be the increased line speed in the manufacturing process and the enhancement of the packaging machine operations, finally resulting in an increased output.

Table 4. Coefficient of Friction (CoF) of three different plastic films in the presence and absence of the edible coating obtained according to the formulation 3.

Friction Coefficient (CoF)

'Film-to-film' test 'Film-to-metaP test

Base-film Treatment μk μ_s Mk μ_s

Uncoated 0.75 1.27 0.37 0.48

(± 0.05) (± 0.22) (± 0.04) (± 0.04)^*

OPP

Coated 0.17 0.52 0.21 0.47

(± 0.02) (± 0.07) (± 0.03) (± 0.03)^*

Uncoated 0.64 0.18 0.86 0.46

T T)PF (± 0.06) (± 0.03) (± 0.07) (± 0.08)^*

Coated 0.29 0.20 0.51 0.46

(± 0.04) (± 0.04) (± 0.08) (± 0.06)^*

Uncoated 0.42 0.54 0.27 0.34

PFT (± 0.03) (± 0.06)^* (± 0.02) (± 0.02)

Coated 0.22 0.58 0.20 0.42

(± 0.03) (± 0.10)^* (± 0.02) (± 0.03)

These data are obtained by utilizing the formulation 3 as shown in Table 1.

U₁₁= dynamic friction coefficient; μ, = _static friction coefficient

* Denotes a statistically not-significant difference between the two treatments (with and without coating) within each group (base-film type) forp < 0.05 (or 95% of the confidence interval).

Table 5 resumes the obtained results as described in the previous examples. Table S Properties and characteristics of the five formulations of the preceding examples

Properties/Characteristics

, _t. WVTR^* OTR" Wettability Opacity % Antⁱ-UV

Formulation , -2 -,,. -K , _τ -2 ~_^. -κ _{< tnm nΛ} , (Area

(g m 24h ) (mL m ' 24h ') (a 50⁰C) (Haze) _subtented)

1 1,4 135 0,3 3,35 8249

2 2,2 123 0,3 2,90 8184

3 1,1 878 0,1 2,58 9043

4 1,6 441 no weld 2,93 8911

5 2 202 no weld 3,16 8554

OPP 2,5 2200 no weld 3,95 8841

*23 ^βC; 65% RH ** 23*C; 0% RH

Claims

1) Edible matrix to protect food or not-food substances, consisting of a water solution at least comprising substantially: protein, lipid and glycerol and characterized in that the glyco-lipo-protein content (Y) expressed in % (^w/_w) is a function of its components according to the formula:

Y = X₁ + f₁(X₁) + f₂(X₁) (1) wherein:

- X₁ = protein amount (% ^w/_w);

- fi(Xi) = glycerol % amount (% ^w/_w), protein amount-dependent;

- f₂(X0 = lipid amount (% ^w/_w), protein amount - dependent,

said water matrix containing additionally minor quantities of an emulsifying agent and of an anti-foam agent, both substantially independent from that of the protein (X₁).

2) Thermo sealable edible matrix according to claim 1 , wherein formula (1) is expressed as:

Y = X₁ + K₁X₁ + K₂X₂ (2)

3) Matrix according to claim 2, wherein

K₁ = Mx₁)= ^Lx_x

is comprised between 2.25% and 2.80% of X₁, whereas:

is comprised between 0.01% and 0.25% of X₁

4) Matrix according to claim 1 , wherein the protein is selected from the group of gelatines, preferable pigskin gelatin having a Bloom value between 120 and 300, better of 250.

5) Matrix according to claim 1 , wherein the lipid is selected from the group of the vegetable oils and of the bee waxes, the preferred vegetable oils being acetyl monoglycerides from palm oils, with acetylation degree between 50% and 90%.

6) Matrix according to claim 1 , containing an emulsifying agent of vegetal origin selected between glyceric acid monostearate and soya lecithin, in amount between 0.5% and 3%, better 1%.

7) Matrix according to claim 1 , containing an inorganic anti-blocking agent selected between kaolin and aluminium-silicate in amount between 1% and 10%.

8) Matrix according to claim 1 , wherein the anti-foam agent is a poly-dimetylsiloxane in a quantity between 1 and 10 ppm (parts per million).

9) Method to prepare a matrix according to the preceding claims, wherein: glycerol-proteic water solution prepared at room temperature is heated to 70-90⁰C, preferably at 77°C for 40-80 minutes preferably for 60 minutes., under stirring at

400-600 r.p.m. 500 r.p.m; the phi is adjusted to the isoelectric point of the matrix by adding 1 N NaOH; lipid and emulsifying agent are added in the above mentioned quantities at 120-

150⁰C, preferably 135°C for 10-30 minutes, preferably 15-20 minutes; if necessary, the anti-blocking agent is added in the above mentioned quantities; the above indicated anti-foam is added; the whole solution is hence heat-stirred (100 r.p.m., 60⁰C) with the possible addition of edible pigments.

10) Thermoplastic films of olefinic, vynilic, amidic, imides, terephthalates polymers (with or without metalization) and bio-polymers like poly-lactic acid (PLA), poly- hydroxyalkanoates like poly-hydroxybutyrate (PHB)₁ coated with the matrix according to the above claims, and provided with high sealabilrty at temperatures form 40 to 130⁰C; adhesion on the external and even internal sides in the absence of primers; barrier to UV- ray s, gas, water vapour, organic vapours, fragrances and aromas, enhanced transparency and slipping properties; absence of odours and colours; anti-fungus and antioxidant activities and release of active substances, such as aromas and fragrances.

11) Film in particular on the basis of polypropylene and polyethylene terephthalates, showing a "maximum maximorum" of enhanced properties: barrier to O₂, CO2, H2O, vapours; sealability at temperatures even lower than 6O⁰C, UV absorption, in particular UVc; high transparency; high slipping characteristics; active substance release.