ITMI20070457A1 - COMPOSITIONS BASED ON STARCH AND ITS USE AND ACHIEVEMENT - Google Patents

Description

The present invention relates to biodegradable compositions based on starch, a plasticizing agent, proteins and transglutaminase; the process for obtaining said compositions; their use for the production of biodegradable items, especially useful for the packaging of food products, and the biodegradable items thus obtained.

STATE OF THE ART

Various attempts are known in the art to obtain compositions capable of combining good biodegradability characteristics alongside the necessary characteristics of production and quality, in order to obtain products for packaging and disposable items, in particular for food, which can be eliminated while respecting the environment.

In particular, compositions of biodegradable polymers obtained by synthesis processes, such as for example polyylactic acid, obtained from natural polymers by microorganisms, such as for example polyhydroxybutyrate, or obtained starting from natural products as such, are known in the art. , including waste, with low environmental impact and low cost, such as polysaccharides. For this last category of natural polymers, it is possible to recover in the literature a considerable number of examples of biodegradable compositions, also for packaging, which differ from each other for the natural polymer used, for the additives used, for the production methods and for the different uses.

For example, the compositions for obtaining expanded products have been studied, as in the United States patent US7067651, which describes a mixture comprising starch and water, and possibly a plasticizer such as glycerol and its derivatives, a reinforcing agent such as limestone or diatomaceous earth , a binder which in particular may consist of egg white or soy protein, in a base or a salt. In European patent application EP1075188, compositions are described comprising starch, high percentages of proteins, cellulose fibers and hydrates of metal salts, with a density typical of expanded packaging.

Other foam compositions useful for obtaining biodegradable products are further described in the international patent application W09965977; in European patent applications EP950690, EP696611 and in patent application EP 1347008; in the European patent application EP1035163; in international application WO92I0539; in international patent application W00220238 and in Japanese application JP05278738.

Biodegradable compositions and their production processes, suitable for the production of disposable products, are described for example in the European patent application EP474095; in Chinese application CN 1362449; in the German patent application DE 19802718; in Chinese patent application CN 1339540 and in international patent application W02003046082.

The following documents relate to biodegradable compositions suitable for molding, obtained by injection molding, extrusion or die-forming processes: US patent US5288318; international patent application W09731979; European patent application EP 1258242; European patent applications EP542155 and EP8I9147; British patent application GB2050459; European applications EP 1241214 and EP 1241215; Japanese patent application JP3247707; European patent application EP863942; European patent application EP596437; French patent application FR269I467 and Italian patent application IT1060099.

In particular, the United States patent US6506824 describes thermoplastic compositions which, when molded by injection, provide homogeneous articles, comprising starch, a cellulose ester, a plasticizer and a compatibilizing agent for the starch and cellulosic phases, consisting of polymers grafted with ethylene vinyl alcohol copolymers. , ethylene acrylic acid, aliphatic polyesters or amides.

Biodegradable compositions suitable for packaging are described for example in the international patent application WO9950346; in Chinese application CN1368517; in the European patent application EP775173 and in the international patent application WO0151557; in international patent application WO2002088245; in international patent application WO200 1051556, where in particular in addition to starch there are fibers and proteins fixed to each other; in the German patent application DEI9841382; in the European patent application EP817804, where compositions characterized by starch covalently bound to proteins are exemplified, and in the German patent application DE3937168.

Compositions for packaging and for disposable products comprising modified starch and / or destructured starch and / or destructuring agents are exemplified in the international patent application WO2005047385; in European patent application EP1109858; in patent application WO200 1060898 and in patent application EP 1229075,

Mixtures for the production of packaging films, including edible ones, are for example described in the international patent application WO2003000060; in the European patent application EP506650; in international patent application W00049899. In particular, Italian patent application IT1322991 describes a process for obtaining biodegradable films, also edible, based on natural polymers optionally mixed with proteins, which may or may not be pre-crosslinked.

Compositions containing cross-linked polysaccharides and their related obtaining processes are described in the international patent application WO03035026; in international patent applications W00039214 and WO0039215; in the international patent application WO0130905, which crosslinks polysaccharides and proteins by means of a polyaldehyde; in US patent application US20030100739; in European patent application EP1047725, where polysaccharides and proteins are conjugated; and in the international patent applications WO9319125 and WO9413737, where the cross-linking takes place by means of aldehydes, anhydrides or epoxides.

Compositions containing cross-linked and / or complexed polymers are also used in other fields, as can be seen, for example, in the international patent application WO2004105485, which uses them as release vehicles in the pharmaceutical or nutraceutical field; in the European patent application EP 1466630, which uses them as absorbent means in sanitary material and in the patent application EP 140596 which uses them as constituents of bandages and sutures.

The starch-based compositions can also be used in the field of animal nutrition. For this purpose, see patent application EP 1241946, which describes objects suitable for consumption by pets including starch, proteins, edible fibers and salts of hydrated metals and patent application US20060188632.

In the food, pharmaceutical and cosmetic fields, the binding capacity of transglutaminases, ubiquitous enzymes widespread in the animal kingdom, has been extensively studied. These enzymes have the ability to catalyze the formation of covalent bonds between the peptide bond of glutamine residues with the amino group of lysine residues of the protein side chains.

Protein or polysaccharide gels, obtained by means of transglutaminases are described for example in US patent 4917904; in Japanese patent application JP58 149645; in US patent 5968568, in Japanese patent JP2629886; in international patent application WO2006056700; in Japanese patent application JP2005229907, where in particular the controlled gelatinization behavior of starch covered with a protein component that has undergone cross-linking by transglutaminase is studied

In patent application EP982038 transglutaminase is used as a cross-linking agent in a protein / polysaccharide covering agent containing an active principle.

Transglutaminases have also been used to modify, through the conjugation of aminopolysaccharides, the immunogenic properties of proteins, their absorption or their possibilities of application in the medical field; see for example the international patent application WO0022103; European patent application EP809110 and international patent application WO2001079474.

DESCRIPTION OF THE INVENTION

The Applicant has found that a composition comprising natural polysaccharides, such as starch, plasticizers, proteins, transglutaminases and water, has optimal workability characteristics for the production of rigid, semi-rigid and rubbery biodegradable articles, preferably useful for packaging, and in particularly suitable for contact with food.

For the purposes of the present invention, the expression "composition" or "composition of the present invention", unless otherwise specified, means the composition net of the aqueous component.

The component present in greater quantities is starch, which is present in the composition in a variable percentage between 40% and 70%, with an optimal range between 45% and 50% calculated as a percentage net of the aqueous component. The starch used can be Standard starch (characterized by a percentage by weight of amylose between 18-30%), Waxy starch (characterized by a percentage by weight of low amylose, less than 5%) or starch with a high amylose content. (amylose by weight between 35% and 70%); the relative percentage between these three types of starch can vary in the composition between 0% and 100%. Starch can be native starch derived from corn, potato, wheat, rice, tapioca, sorghum, rye, oat or a combination of these. This mixture of starches will hereinafter be referred to as "starch".

To improve the characteristics of the starch, that is to make the starch a thermoplastic product, in order to improve its workability and its final characteristics, a plasticizing agent is used, such as polyalcohol such as ethylene glycol, propylene glycol or glycerol. In particular, the optimal weight ratio between starch and plasticizer varies in the range from 5: 1 to 2: 1, so that the percentage quantity of preferred plasticizer, with reference to the total weight of the composition, varies between 8% and 40%. A further constituent of the composition of the invention is the protein component. Said protein component, which should preferably not have characteristics of adhesiveness in contact with water, and therefore not cause problems of surface stickiness, can have a randomized structure, but must contain specific amino acids: in particular, it must contain glutamine (gln) and glieina (gly), or glutamine and lysine (lys), in quantities respectively equal to or greater than 3% and 7% assumed to be one hundred the number of total amino acids.

The protein component must also have a molecular weight sufficient to give rise, in the presence of a protein cross-linking agent, to a sensory sensible cross-linking without the aid of specific instruments, in particular it must have a molecular weight greater than 10 kDalton, with a value optimal greater than 30 kDalton and less than 180 kDalton.

The proteins suitable for use in the present invention are preferably of vegetable origin since they have higher glutamine contents than animal proteins; these can derive from cereals or legumes such as soy, pea, wheat, bean and broad bean. The preferred percentage of the protein component is in the range between 0.5% and 5%, with an optimal range between Γ1% and 2% calculated as a percentage of the weight of the composition. The characteristics described above for the protein component make it suitable for the reaction with a cross-linking enzymatic component, such as transglutaminase. The preferred transglutaminase in the present invention derives from microorganisms, in particular of the genus Streptoverticillium sp., Preferably of the S-8112 strain. This transglutaminase, which consists of a single polypeptide chain of 331 amino acids, with a molecular weight of 38 kDalton, allows a reaction between the lysine and glutamine residues of the different polypeptide chains of the protein component described above, thus forming isopeptide bonds that they give life to protein aggregates stabilized by covalent bonds. To obtain an optimal cross-linking of the protein component, transglutaminase, which is used in a mixture with maltodextrin in a ratio of 1: 100 preferably (hereinafter always referred to as transglutaminase), must be used in a percentage greater than or equal to 1% by weight with respect to the protein component (i.e. between 0.005% and 0.05% of the composition, considering a protein content between 0.5% and 5% of the same), with optimal percentage values in the range between 2% and 3%.

In order to achieve optimal crosslinking, a suitable degree of hydration of the mixture is also important; this hydration is obtained by adding water during the mixing step, as reported below.

Cellulose is also added to the described composition, preferably with fibers having a length in the range between 20 and 1000 μm, even more preferably between 200 and 400 µm. The preferred diameter of the fibers ranges from 20 to 35 µm, preferably from 28 to 32 µm. These preferred dimensions are obtained by means of a preventive treatment of whitening and pulverization of the raw cellulose. Cellulose is present in the composition in quantities ranging from 5% to 30%, preferably between 10% and 25%. Possibly a part of the cellulose in powder, varying between 4% and 15% of the composition, is a modified cellulose, for example partly esterified with stearic acid, carboxymethylated or hydroxypropyl carboxymethylated. In particular, the presence of stearic acid allows a reduction in the viscosity of the material being processed and the different functional groups of the cellulose allow a greater interaction of the same with the protein-saccharide matrix.

If you want to change the mechanical properties such as Young's modulus and tensile strength, part of the starch present is modified starch.

This modified starch is cationized starch, which is used in a percentage equal to about 1% of any cellulose present, to further favor the interaction and therefore the formation of bonds between the cellulose with negative charges, and the polysaccharide component. cationized. The formation of these bonds confers better homogeneity and better mechanical properties to the final articles obtained with said composition. Furthermore, as a processing agent, the composition may contain a lubricating agent, such as a stearate (preferably of an alkaline or alkaline earth metal), in a percentage greater than 0.1% and less than or equal to 2%, an emulsifying agent in a percentage between 0.5% and 5%, with a preferred range between 0.8% and N.5%.

The emulsifying agent, which is preferably lecithin, even more preferably of soy or sunflower, usually in powder, allows a greater interaction between the components of the composition and a better workability of the product in the subsequent thermal and mechanical processing of the mixture and in the final phase of forming the biodegradable product.

Finally, the composition can optionally contain an inorganic component, for example inorganic fillers such as silica, zeolite, bentonite, kaolin, talc. These inert fillers can be used in the form of nanofillers which, thanks to their nanometric dimensions and their hydrophilicity, are able to fit into the macro-molecular structure of the starch-based matrix and form bonds with it. These inorganic fillers, present in a percentage between 0.1% and 10%, allow to modify both the humidity of the composition, subtracting part of the free water, and the mechanical properties such as flexibility, rigidity and plasticity of the final product. .

Said mixture obtained can include the addition of non-toxic dyes, in particular food dyes. Preferably, antioxidants, preferably natural, and in any case suitable for contact with food, are added to the mixture to extend the shelf-life of the final product.

Preferably, said composition is formulated in the form of granules or in the form of thermoformable plates with apparent density varying between 0.7 and 1 g / cm <3>

The object of the present invention is therefore a biodegradable composition comprising natural polysaccharides, such as starch, plasticizers, proteins, transglutaminases and water, in particular formulated in the form of granules.

In particular, the present invention relates to a biodegradable composition comprising from 40% to 70% of starch, from 8% to 40% of plasticizer, from 5% to 30% of cellulose, from 0.5% to 5% of proteins. , from 0.005% to 0.05% of a cross-linking enzyme, preferably transglutaminase, where the percentage values are all expressed with reference to the total weight of the composition (i.e. where the sum of the individual components represents 100% of the composition).

A further aspect of the present invention concerns the process for obtaining the composition described above and its formulation in granules.

Initially, the starch and the plasticizer are mixed, preferably in a turbomixer equipped with two types of speeds: one main and one peripheral.

This starch-plasticizer mixture is subjected to a dehydration process, preferably in a ventilation oven, at a temperature ranging from 80 ° C to 170 ° C, for a time between 15 and 60 minutes, decreasing as the temperature increases. temperature. The starch-plasticizer mixture thus obtained must undergo a cooling process until it reaches a temperature equal to or lower than 55 ° C, before adding water, the protein component and the enzyme, to avoid the phenomenon of gelation of the starch which would lead to a morphological and structural change of the mixture, and a denaturation of the protein components (proteins and enzyme).

Once the required temperature is reached, water is added, which is normally used in quantities between 20% and 50% of the total weight of the mixture, preferably between 25% and 35%.

The temperature of the mixture, after the addition of the aqueous component, must preferably be kept between 5 ° C and 54 ° C, with an optimal range between 35 ° C and 40 ° C, to favor the rapid reaction, i.e. with a shorter time. 30 minutes, between the enzyme and the proteins, without deactivating the enzymatic activity.

The mixture is kept under stirring for a time comprised between 10 and 30 minutes, preferably 15 minutes, under a constant speed and between 2 and 8 m / s.

Once the crosslinking of the proteins is complete, the inert components, such as cellulose, possibly modified, and any modified starch described above can be added to the mixture. The inert components (ie cellulose) must be added after the formation of the cross-linking of the matrix; otherwise the water would bind to the inert hydrophilic component and would no longer be available for hydration of the protein and saccharide components; therefore the transglutamination reaction would not occur. This mixture is subjected to a mixing process (normally in a turbomixer) at a speed greater than 16 m / s, with an optimal speed between 25 m / s and 32 m / s, for a time of 1-2 minutes, maintaining a temperature below 50 ° C,

The process agents are then added to the mixture, i.e. the lubricant and the emulsifier as described above, and there is a further mixing step in the turbomixer with the same process conditions used after the aggregate has been reached, which thus allows to obtain the composition object of the invention.

The mixture thus obtained is subjected to a processing procedure in an extruder with the possibility of obtaining plates or granules at the end of the process to obtain granules (pellets): the mixture is inserted, by means of a gravimetric dosing device, in a co-rotating intermeshing twin-screw extruder with head holes about 1-5mm in size.

The screw revolutions of the extruder are set in the range between 70 and 150 r.p.m., and the pressure inside the extruder must be kept at values below 6 MPa and in any case such as to allow a constant flow rate of the material through the extruder. .

The extruder must be equipped with a degassing system to eliminate excess water, useful in the previous stages for the hydration of starch and crosslinking of proteins. The degree of depression must be less than 0.1 MPa, with preferred values between 0.02 and 0.06 MPa. Part of the water, in fact, must be kept in the mixture for the processing process to take place correctly; the mixture coming out of the extruder must not have an absolute humidity lower than 10%.

The material flows inside the extruder through a series of passages each characterized by a specific temperature and screw profile. The temperature in the different areas of the extruder can vary in the range between 75 ° C and 105 ° C, with the need to reach values around 90 ° C-95 ° C; at these temperatures and in conditions of sufficient humidity (greater than 20% on the mixture) in fact the starch granules break with continuous diffusion, outside of it, of its polymers (amylose and amylopecty). There is the maximum destructuring of the polysaccharide component and a rapid decrease in its density.

In the intermesching co-rotating twin-screw extruder, thermal destructuring is accompanied by mechanics due to high pressures and shear stresses; for this reason the chemical-physical properties of the mixture are the result of the composition of several variables; raw materials, geometry of the extruder components, flow rate, temperature, humidity, screw speed, torque the most important.

Subsequently, the material comes out of the extruder and undergoes a cooling and drying process by blowing in air and passing through calenders with cooling rollers, with a set temperature ranging between 5 ° C and 15 ° C. The rollers of the calenders are preferably Teflon-coated to allow a regular sliding of the extruded product on the rollers and, consequently, a homogeneous drying. The low temperature and the air flow thus allow a fast cooling. The amylose and amphiopectin polymers of the starch granule show a tendency to re-associate into an ordered structure during the cooling phase, the starch then retrograde until reaching a crystalline order and this allows the stiffening of the extrudate itself.

The material thus obtained is shaped into granules (pelletizing) with dimensions between 1 mm and 5 mm, preferably between 2 mm and 4 mm, and is conditioned under standard conditions, i.e. at 23 ° C and 55% of ambient humidity, up to upon reaching a condition of dynamic equilibrium with the environment.

A further object of the present invention therefore forms a process for obtaining a biodegradable composition based on starch, plasticizer, proteins and transglutaminase, and the granular formulation thereof.

A further aspect of the present invention relates to the use of the biodegradable composition based on starch, plasticizer, proteins, transglutaminase and water described above, for the preparation of biodegradable articles.

These articles are preferably useful for packaging, and in particular they are suitable for contact with preferably dry foods, and therefore for primary food packaging (for example trays, bowls, trays, plates, vases, cutlery, glasses or bottles) or for secondary food packaging. Always respecting the suitability for contact with food, it is possible to use this composition for the creation of dishes of all shapes, and all those objects suitable for contact / containment of food that can be used for catering or fast food services.

The present invention also relates to biodegradable articles obtained using the composition resulting from! process described above.

Finally, the present invention also relates to the production process of said biodegradable articles, starting from the composition of the present invention in granular form. For this purpose, the granules of the present invention are subjected to a thermoplastic forming process in an injection press, advantageously equipped with a cold runner mold. The screw turns of the extruder that precedes the nozzle of the material outlet in the injection molding machine must be set in an interval between 40 and 120 r.p.m. and the pressure inside the extruder must be kept constant in the different areas of the extruder except in the part near the material outlet nozzle where it must undergo a reduction of about three times.

The movable mold and the counter-mold, which is fixed, have different temperatures: the temperature of the movable mold varies in a range between 75 ° C and 90 ° C, while the counter-mold has a temperature between 4 ° C and 10 ° C. The product is left in the mold for about 20 seconds, so that a rapid cooling can take place, capable of giving rigidity to the matrix.

The following examples are illustrative and not limitative.

Example n ° 1

Preparation of a biodegradable composition comprising of starch, plasticizer, proteins, transglutaminase and water

A powder composition is prepared containing:

200 g of water

441.9 g Corn starch (30% Standard and 70% Waxy)

133 g pure vegetable glycerin 99.5 USP

l00 g cellulose powder C220

50 g sodium carboxymethylcellulose

50 g cellulose powder C1000

10 g soy protein extract (6.2 g lysine, 19.1 g glutamic acid, 4.2 g glycine, all referring to 100 g of protein) 0.1 g Activia WM transglutaminase enzyme

10 g calcium stearate

5 g soy lecithin powder

The mixing protocol that was used is the following:

mixing of starch and glycerol for 5 minutes at 16 m / s; passage in a ventilated oven at a temperature of 150 ° C for 15 minutes;

cooling of the mixture until it reaches room temperature (23-27 ° C);

addition of soy protein, enzyme and water and mixing at a speed of 8 m / s for 15 minutes, at an average temperature of 30 ° C and in any case not higher than 50 ° C;

addition of cellulose, lecithin and calcium stearate and mixing at 16 m / s for 5 minutes;

fast mixing (preferably at 32 m / s for 2 minutes or as needed) to obtain a correct interaction between the components, paying attention that the heat developed during the mixing process does not lead to an increase in temperature above 50 ° C.

extraction of the mixture from the mixer and cooling down to room temperature;

closing of the mixture in moisture barrier bags until it is used for the pelletizing phase.

Example n ° 2

Granulation of the biodegradable composition comprising of starch.

plasticizer, proteins, transglutaminase and water

The composition obtained in example 1 is subjected to an extrusion and granulation process, to obtain granules (pellets) with dimensions between 2 mm and 4 mm.

The composition of example 1 is inserted in a co-rotating intermesching twin-screw extruder with a circular head with 3 mm holes and equipped with a gravimetric dispenser.

The process characteristics are as follows:

speed of the doser: 10 r.p.m .;

screw turns: 120 r.p.m .;

melting temperature: 95 ° C

head pressure: 9 bar;

screw profile (diameter of the screws): variable in the different areas and increasing from 4 mm to over 40 mm;

degree of degassing: 0.06 MPa;

compressed air cooling and Teflon-coated calendered rollers - pelletizing with a rotating blade mill

Example n ° 3

Molding of the granules obtained from a biodegradable composition comprising starch, plasticizer, proteins, transglutaminase and water The granules obtained in example 2 are subjected to a thermoplastic forming process in an injection press equipped with a cold runner mold, to obtain biodegradable articles .

The molding protocol is as follows:

single screw extruder with screw diameter 55 mm

zone temperatures: Z1: 90 / Z290 / Z3: 85 / 3⁄4: 80 / Z575

mobile mold temperature: 85 ° C;

counter-mold temperature: 10 ° C;

injection pressure: 16 MPa;

back pressure: 0.3 MPa;

cooling time: 20 seconds;

The composition obtained has the properties listed below:

• Bulk grain density: 0.698 g / cm <3>

• MFI granule: 100 ° C / 21kg: 3.26 g / 600 s

• Absolute granule humidity: 13.25%

• EMod (N / mm <2>) specimen: 508.63 ± 11.17

• Fmax (N) specimen: 787.79 ± 4.15

• εRupture% (A1 long to failure) specimen: 15.51 ± 4.36

The mechanical properties of the specimens obtained were evaluated with a Zwick Roell Z005 dynamometer (Germany) according to the ASTM D 882 standard. The specimens were made according to the standard with a parallel section length of 80 mm and a thickness of 4.5 ± 0.3 mm .

Claims (20)

CLAIMS 1. A composition comprising from 40% to 70% by weight of starch, from 8% to 40% by weight of a plasticizing agent, from 5% to 30% by weight of cellulose, from 0.5% to 5% in weight of proteins and from 0.005% to 0.05% by weight of a transglutaminase, with respect to the weight of the composition. 2. A composition according to claim 1, where starch is present in an amount between 45% and 50% with respect to the weight of the composition, 3. A composition according to claim 1, where the weight ratio between starch and plasticizing agent is comprised between 5: 1 and 2: 1. 4. A composition according to claim 1, where the proteins are present in an amount comprised between Γ1% and 2% with respect to the weight of the composition, 5. A composition according to claim 1, where the cellulose is present in an amount comprised between 10% and 25% with respect to the weight of the composition. 6. A composition according to claim 1, where the transglutaminase is present in an amount comprised between 2% and 3% with respect to the weight of the proteins. 7. A composition according to claim 1, where the plasticizing agent is a polyalcohol. 8. A composition according to claim 7, wherein said polyalcohol is selected from ethylene glycol, propylene glycol and glycerol. A composition according to claim 1, wherein the cellulose fibers have a length between 20 and 1000 μm and / or a diameter between 20 and 35 μm. 10. A composition according to claim 1, wherein the proteins have a glutamine and glyein or glutamine and lysine content equal to or greater than 3% and 7% respectively of the total amino acids. 11. A composition according to claim 1, wherein the proteins have a molecular weight higher than 10 kDa, preferably between 30 and 180 kDa. A composition according to claim 1, where the proteins are of vegetable origin 13. A composition according to claim 1, where the transglutamase is from microorganisms, preferably of the genus Streptovertìllium sp. 14. A composition according to claim 1, comprising a lubricant, an emulsifier and / or mineral fillers. 15. A composition according to claims 1-14 characterized in that it is in the form of granules. 16. Articles for packaging and / or containment and / or for food use, essentially consisting of a composition according to claims 1-15. 17. Articles according to claim 16 characterized by being in the form of trays, bowls, trays, plates, vases, cutlery, glasses or bottles. 18. Use of a composition according to claims 1-15 for the preparation of articles for packaging, contact and / or containment of foods, fluids and / or liquids. Use according to claim 18 characterized in that said articles are in the form of trays, bowls, trays, plates, vases, cutlery, glasses or bottles. 20. Process for the production of a composition according to claims 1-15, comprising the following steps: a) mixing of starch and plasticizer; b) dehydration and subsequent cooling of the mixture to a temperature below 55 ° C; c) addition of water, proteins and transglutaminase and subsequent mixing at a temperature below 55 ° C; d) addition of cellulose and subsequent mixing; e) optional addition of lubricant and / or emulsifier and subsequent mixing; f) optional granulation,