Process for the obtention of a cutin-enriched product

Abstract

The present invention discloses a process for obtaining a cutin-enriched product from the cutin-containing portion of a plant matter, wherein said process comprises treating said cutin-containing portion with water at high temperatures and pressures. The invention also discloses a cutin-enriched product and uses thereof.

Description

[0001]PROCESS FOR THE OBTENTION OF A CUTIN-ENRICHED PRODUCT FIELD OF THE INVENTIONThe present invention relates to a process for obtaining a cutin-enriched product from acutin-containing plant material. The invention also relates to a cutin-enriched product and to the uses thereof. BACKGROUND OF THE INVENTIONOne of the most important challenges for agriculture in the coming future is to feed thegrowing world population. Accordingly, post-harvesting residues, also called “agro-waste” are expected to increase. This “agro-waste” is composed by the non-edible plant waste from crops, roots, fruits and other vegetables. This type of plant-based matter is rich in useful substances, such as lipids, polysaccharides or aromatic compounds, with potentialapplications in the fabrication of polymeric materials (Heredia-Guerrero et al., Journal ofExperimental Botany, vol.68, no.19, pp 5401-5410, 2017). However, this residues need to be chemically treated or isolated to extract the specific macromolecules of interest with potential industrial applications. Examples of this type of macromolecules are, among others, cellulose, lignin, suberin or cutin. Cutin is a major structural component of the plant cuticle, the outer layer of aerial parts ofthe plant. It is a long-chain polyester made from hydroxyl or epoxy fatty acids linked by esterbonds. In nature, it appears as an amorphous polymeric network, mechanically and chemically stable and resistant (Fich et al.,Annu. Rev. Plant Biol.2016, 29:67:207-233; Zeisler-Diehl et al., J Plant Physiol 2018,227:66-74, doi: 10.1016 / j.jplph.2018.03.018).Further, the cutin matrix is accompanied by hydrophobic compounds collectively referred toas waxes. Additionally, the cutin matrix contains a modest number of phenolic compounds,mostly hydroxycinnamic acid derivatives, and flavonoids. Due to the characteristicsmentioned above, cutin is set apart from other polymers, such as polyhydroxyalkanoates (PHA) or other thermoplastic polyesters produced through chemical or enzymaticpolymerizations, that are currently attracting industrial and biotechnological interest(Benitez et al., Biochim. Biophys. Acta, 2004; 1674(1), 1-3, doi:10.1016 / j.bbagen.2004.06.012).Currently, the most common methods reported in the literature for cutin isolation follow longmulti-step procedures that involve a dewaxing step accompanied by the use of enzymes for the removal of polysaccharides or alkaline hydrolysis at elevated temperature. On top of that, reported processes require a long reaction time, additional separation steps, organic co-solvent(s), and neutralization of reactants required in alkaline hydrolysis. Furthermore, both processes generate quite a small amount of product, making them more suitable for laboratory-scale use and chemical analysis. Several examples of alkaline hydrolysis of cutin-containing plants have been reported, thus, despite a few variations, the protocols are well known.WO2023198943 A1 relates to a method that allows cutin from plant waste to be obtainedby milling the plant waste, adding an alkaline solution and performing a first ultrasonicextraction in an alkaline medium. The supernatant obtained is separated and mixed with an acid solution from which cutin will precipitate after the solution has been kept at least 4°C for at least four hours.EP 4116352 A1 teaches a process for the extraction of cutin from tomato waste comprisingsoaking the tomato waste in an alkaline solution subjecting this alkaline solution to heattreatment, isolating the liquid phase of the heat-treated alkaline mixture from the solidresidue, the liquid phase being an alkaline cutin solution. After acidifying the alkaline cutinsolution by adding an organic acid, cutin from the liquid phase was isolated by means ofcentrifugation. EP3039064A1 discloses a method for extraction of a polyester polymer composed of acomplex mixture of interesterified, long-chain ω-hydroxy acid with typically a 16- or 18-carbon skeleton from the waste of tomato peels. The method comprises a thermal treatmentof the tomatoes peels, in which tomato peels are immerged in an alkaline solution; a filtrationphase; a step of acidification, a centrifugation phase after which the supernatant isdiscarded or reintroduced in the process for another extraction, while the solid residue is kept and centrifuged. Despite cutin extraction being known in previous reports, the harsh process of alkaline hydrolysis leads to total hydrolysis of ester bonds after which a mixture of fatty hydroxyl acidmonomers is obtained. The monomers may then be re-polymerized also with other syntheticor naturally derived suitable monomers, however the depolymerization-repolymerizationprotocol is flawed from the energy- and step-efficiency viewpoint as it does not takeadvantage of the native polyester scaffold which is inevitably lost. On the other hand, besides alkaline hydrolysis, thermal processes are also known for aclean depolymerization of cutin-containing plant parts. For example, EP3386303A1 teachesmethods of preparing cutin-derived monomers, oligomers, or combinations thereof fromcutin-containing plant matter. The method comprises heating the cutin-derived plant matterin a solvent at elevated temperature and pressure, which, combined with long reactiontimes, enable a clean and quantitative depolymerization of cutin.Methods capable of affording native cutin (or a product enriched in native cutin) in a straightforward manner are desirable as such bio-polymeric products may be of great interest not only in a variety of fields (from cosmetics to materials science) but could also exploit all the advantageous properties of cutin without the need for further depolymerisation / re-polymerization steps.In summary, improved methods of native cutin enrichment without producing itsdepolymerisation are currently unavailable and would be highly desirable due to thepotential uses of the native cutin polymer structure. BRIEF DESCRIPTION OF THE INVENTION The inventors have surprisingly found that by treating cutin-containing plants or parts thereof with water at high temperatures (i.e. between 300 and 500 °C) and pressures (i.e. between 85 and 400 bar), and for a short reaction time (i.e. less than 50 seconds), a cutin-enriched product can be obtained wherein the native structure of the cutin is preserved.This process improves on the efficiency of removal of non-cutin species from the plantcuticles, such as waxes, essential oils, and other soluble species in the aqueous mediumsunder the specified conditions, without breaking up the native cutin structure which is mostof the times subjected to re-polymerization. The efficiency of the process of the invention iseven more evident in the supercritical range of temperatures and pressures, whereinextremely short reaction times (between fractions of a second and as low as 2 seconds) arerequired for enriching a plant matter containing cutin with cutin, however specific subcriticalconditions of temperature and pressure may also afford similar results still at very shortreactions times (only units of seconds). Advantageously, the addition of acid(s) may furtherimprove the efficiency of the process as the polysaccharide fraction of the cutin-containingplant is degraded and removed with the liquid fraction formed with the treatment whileleaving the cutin in the cutin-enriched product virtually untouched. Therefore, a first aspect of the invention relates a process for obtaining a cutin-enrichedproduct from the cutin-containing portion of a plant matter, said process comprising treatingsaid cutin-containing portion with water at a temperature between 300 and 500 °C and at apressure between 85 and 400 bar, during less than 50 seconds.Another aspect of the invention relates to a cutin-enriched product comprising, preferablyconsisting of: -between 40 and 75 wt.% cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin-enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.Alternatively, an aspect of the invention relates to a cutin-enriched product, obtainable bythe process of the first aspect, comprising, preferably consisting of: -between 40 and 75 wt.% cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin-enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS. Lastly, the present invention relates to the use of the cutin-enriched product as defined above in the manufacture of polymers, preferably bioplastics, more preferably polyesters; material coatings; cosmetic products; and food emulsifiers. More particular embodiments of the present invention are explained in more detail in the detailed description, drawing and examples. DESCRIPTION OF THE FIGURES Figure 1. Normal distribution of particles in the size of samples and feeds.Figure 2. Solid yield for experiments done on PhUN1 (A), on PhUN2 (B) and comparisonof solid yields for experiments without and with the addition of acetic acid - framed (C).Figure 3. Solid sample composition and feed composition over different reaction times at375 °C for experiments done on PhUN1 (A), on PhUN2 (B) and comparison of experimentswithout and with the addition of acetic acid - framed (C).Figure 4. The amount of cellulose and protein remaining in the solid part of the sample after the process for experiments done on PhUN1 (A), on PhUN2 (B) and comparison ofexperiments without and with the addition of acetic acid - framed (C).Figure 5. FTIR spectrum of raw tomato peel, sample 0.48 s and sample 1.51 s in the rangeof wavenumber 2800 – 3700 cm-1 (A); 900 – 1800 cm-1 (B).Figure 6. Microscope pictures of raw tomato peel before milling (A) and after milling (B) and ESEM picture of tomato peel after milling (C). Figure 7. ESEM picture of sample suspensions for different applied conditions: upper row 5000x magnification; bottom row 80000x magnification. DETAILED DESCRIPTION OF THE INVENTION A first aspect of the invention relates a process for obtaining a cutin-enriched product fromthe cutin-containing portion of a plant matter, said process comprising treating cutin-containing portion with water at a temperature between 300 and 500 °C and at a pressurebetween 85 and 400 bar, during less than 50 seconds. This first aspect will be also referredto as “process of the invention” throughout the text.Cutin may vary in composition and structure depending on the plant species, tissue type,and environmental conditions, however in general terms, in the context of the present invention refers to a waxy substance found in the cuticle of plants and composed mainly of fatty acids, which are cross-linked to form a polyester network. A “plant matter” refers to organic material derived from plants. This term encompasses various parts of plants such as leaves, stems, roots, flowers, fruits, and seeds, as well as the products derived from them. Plant matter is composed of complex organic compoundsincluding a cutin-containing portion, carbohydrates (such as cellulose, hemicellulose,starch, and sugars), lignin, proteins, fats, oils, vitamins, minerals, and other organic molecules. Based on the above, the cutin-containing portion of a plant matter refers to portions thatcontain cutin in high weight-percentage of cutin (e.g., fruit peels, leaves, shoots, stems,aerial plant organs, etc.), as well as other portions that have a low density of cutin (e.g., seeds), preferably the former. Preferably, the cutin-containing portion of a plant matter contains at least 25 wt.%, at least 30 wt.%, at least 35 wt.% of cutin. Any suitable amount of cutin-containing portion of a plant matter for the process of the invention could be chosen by a skilled person, preferably at least 1 gram, more preferably at least 1 Kg.The “cutin enriched product” as defined in the present invention is a product, preferably asolid product, where cutin wt.% increases after treating the cutin-containing portion of aplant matter in the conditions defined in the first aspect and cutin is the major component(cutin wt.% is more than 50 wt.% in the product). Any plant matter which comprises cutin is suitable to be used in the process of the invention leading to a cutin enriched product. As cutin is virtually present in every aerial part of plants,in a specific embodiment, the cutin-containing aerial portion of a plant matter is used in theprocess of the invention; more particularly, the aerial parts of the plant matter do not comprise the bark of said plant matter. In an embodiment, the cutin-containing portion of a plant matter is the cutin-containingportion of fruit-bearing plant matter, preferably the fruit, wherein the fruit-bearing plantmatter is selected from tomato, grape, apple, pear, papaya, peach, or a combination thereof.In an embodiment, the process of the invention comprises the steps of:a) optionally, pre-treating the cutin-containing portion of a plant matter;b) mixing said optionally pretreated cutin-containing portion of a plant matterwith water to obtain a suspension; c) treating said suspension with water at a temperature between 300 and 500°C and at a pressure between 85 and 400 bar to obtain the cutin-enriched product and a liquid fraction, wherein said treatment is carried out during less than 50 seconds; andd) optionally, separating the cutin-enriched product from the liquid fractionOptionally, the process of the invention comprises a pre-treatment step a). This pre- treatment aims to reduce the size of the raw material before the formation of the suspensionand / or to further separate the cutin-containing portion (e.g. fruit peels and / or seeds) fromthe remainder of the plant matter. Even more particularly, the pre-treatment may further separate the cutin-containing portion with higher cutin content (e.g. fruit peels) from thosewith lower cutin content (e.g. seeds). Any known pre-treatment known in the technical fieldof the present invention may be useful as a pre-treatment step. In an embodiment, the cutin-containing portion of a plant matter is pre-treated by pressing, grinding, drying,centrifugation, (ultra)sonication, milling (wet or dry milling), sCO2 extraction, CO2 explosion, ammonia explosion, steam explosion or a combination thereof. Different types of pre- treatments can also be sequentially carried out. For example, when fruit-bearing plants are used as cutin-containing portion, the sequence of pressing, separation of peel and juice and peel drying may be particularly carried out.In a particular embodiment, the cutin-containing portion of a plant matter is pre-treated bypressing said cutin-containing portion, preferably by pressing the fruit of a fruit-bearing plantmatter selected from tomato, grape, apple, pear, papaya, peach, or a combination thereof,in order to obtain a pomace. Said pomace may be, optionally, further pre-treated according to any of the pre-treatment methods already mentioned above (preferably, drying, grindingand / or milling) or directly suspended in water and subjected to step c).Thus, in a preferred embodiment, the pomace of tomato, grape, apple, pear, papaya, peach,or a combination thereof is used in step b of the step of the invention; more preferably thepeel of said fruits.In the context of the invention, the term “pomace” refers to the by-product remaining afterknown operations such as fruit or vegetable juice pressing processes, wine crush operations, puree and concentrate operations, canning processes, and other foodmanufacturing processes. Pomace may include, for example, skins, pulp, seeds, and ediblepart of stems of the fruit and / or vegetable. In some cases the pomace can derive from orcontain other parts of the fruit and vegetable such as pod, stalk, flower, root, leaves andtuber. In a juice extraction process, the pomace is typically in the form of a part of presscake.In a preferred embodiment, tomato pomace is used in the process of the invention (step b);even more preferably tomato peel is used. As tomato pomace is available from manysuppliers worldwide (for example, Morning Star Company, LaBudde Group, Aterimar, etc.), its efficient valorization can be achieved by employing the process of the invention.The optionally pre-treated cutin-containing portion of a plant matter is mixed with water toobtain a suspension (step b). In an embodiment the amount of said cutin-containing portionof a plant matter in the suspension is between 0.1 and 50%, preferably between 1 and 30%,even more preferably between 4 and 11% (as w / w = weight / weight).In another embodiment, the amount of said cutin-containing portion of a plant matter in thesuspension is at least 0.1%, at least 0.5%, at least, 1%, at least 2%, at least 3%, preferably at least 4% (w / w).In another embodiment, the amount of said cutin-containing portion of a plant matter in thesuspension is less than 50%, less than 40%, less than 30%, preferably less than 20% (w / w).In an embodiment, no additives are used in the process of the invention, meaning that onlywater and the cutin-containing portion of a plant matter are mixed.However, in order to improve the performance of the process, the inventors have found thatadditives may be further added to the suspension of step b). In an embodiment, an acid isfurther added to the suspension of step b).Acids promote the hydrolysis of polysaccharides (cellulose, hemicellulose) while the stabilityof the cutin ester bond is unaffected. The acid can be an organic or an inorganic acid. In anembodiment, the acid is an acid selected from the group consisting of acetic acid, formic acid, p-toluenesulfonic acid (PTSA), trifluoroacetic acid, camphorsulphonic acid, citric acid, oxalic acid HCl, H2SO4, HNO3, H3PO4, and mixtures thereof; preferably acetic acid and / or H2SO4; more preferably the acid is acetic acid. In another embodiment the acid is added in an amount comprised between 10% and 70% on a dry basis suspension, preferably between 15% and 60% on a dry basis suspension, more preferably between 20% and 50% on a dry basis suspension. The addition of acid causes the pH of the water to drop below a neutral pH. Thus,alternatively, the acid is added so as the pH of the water is below 7, preferably below 6.5,more preferably below 6. In another embodiment, the acid is added so as the pH of the water is comprised between 2 and 6.5, preferably between 2.5 and 6. In an embodiment, the temperature for treating the cutin-containing portion of a plant matter is comprised between 310 ºC and 500 ºC, preferably between 310 ºC and 450 ºC, more preferably between 310 ºC and 400 ºC.In an embodiment, the temperature is comprised between 374 ºC and 450 ºC, even morepreferably the temperature is between 380 ºC and 400 ºC. In an alternative embodiment, the temperature comprised between 300 ºC and 370 ºC, more preferably between 300 ºC and 350 ºC, even more preferably between 305 ºC and 325 ºC.In an embodiment, the pressure for treating the cutin-containing portion of a plant matter iscomprised between 150 and 350 bar, preferably between 175 and 300 bar, more preferablybetween 200 and 260 bar.In an embodiment, the pressure for treating the cutin-containing portion of a plant matter iscomprised between 221 and 350 bar, preferably between 230 and 300 bar, more preferably between 240 and 260 bar.In an alternative embodiment, the pressure for treating the cutin-containing portion of a plantmatter is comprised between 100 bar and 220 bar, preferably between 150 bar and 220 bar, more preferably between 180 bar and 210 bar.In an embodiment, in step c), the temperature is comprised between 310 ºC and 500 ºC,preferably between 310 ºC and 450 ºC, more preferably between 310 ºC and 400 ºC, andthe pressure is comprised between 150 and 350 bar, preferably between 175 and 300 bar, more preferably between 200 and 260 bar.In a particular embodiment of the invention, the water suspension of the cutin-containingportion of a plant matter is treated with water in supercritical conditions. One skilled in theart would know that the supercritical conditions for water are reached at 374 ºC and 221bar. Thus, in a preferred embodiment, the process comprises treating the cutin-containingportion of a plant matter with water at a temperature between 374 °C and 500 °C and at apressure between 221 and 400 bar, more preferably at a temperature between 374 and 450°C and at a pressure between 221 and 260 bar.In an alternative particular embodiment, the process comprises treating the cutin-containingportion of a plant matter with water at a temperature between 300 °C and 370 °C and at apressure between 100 bar and 220 bar, more preferably at a temperature between 300 ºC and 350 °C and at a pressure between 150 bar and 220 bar, even more preferably at a temperature between 305 ºC and 325 ºC and at a pressure between 180 bar and 210 bar.Due to the high temperatures and pressures reached in the treatment of the cutin-containingportion of a plant matter for obtaining a cutin-enriched product, advantageously shortreaction times could be used, surprisingly without any negative consequence on the cutinnative structure in the cutin-enriched product. Maintaining the reaction time under 50seconds is necessary for obtaining the a cutin-enriched product wherein cutin preserves its native structure and depolymerisation of the cutin ester linkages is avoided, even at the hightemperatures / pressures as those defined in the process of the invention.In preferred embodiments of the first aspect, the treatment of the cutin-containing portion ofa plant matter is performed during less than 30 seconds, or even less than 10 seconds.In particular embodiments, the treatment time is less than 3 seconds, less than 2 seconds,even more preferably less than 1.5 seconds, particularly when supercritical conditions are adopted. In an alternative embodiment of the invention, the treatment of the one or more plants isperformed between 0.01 to 50 seconds, preferably between 0.02 to 30 seconds, between0.03 to 10 seconds, between 0.04 to 3 seconds, even more preferably between 0.05 to 1.5 seconds.Thus in a particular embodiment, the process comprises treating the water suspension ofthe cutin-containing portion of a plant matter with water at a temperature between 374 °Cand 500 °C and at a pressure between 221 and 400 bar during a time comprised between0.04 to 3 seconds, more preferably at a temperature between 374 and 450 °C and at apressure between 221 and 260 bar during a time comprised between 0.05 to 1.5 seconds.In an alternative particular embodiment, the process comprises treating the watersuspension of the cutin-containing portion of a plant matter with water at a temperaturebetween 300 °C and 370 °C and at a pressure between 100 bar and 220 bar during a timecomprised between 1 and 30 seconds, more preferably at a temperature between 300 ºCand 350 °C and at a pressure between 150 bar and 220 bar during a time comprisedbetween 2 and 20 seconds, even more preferably at a temperature between 305 ºC and325 ºC and at a pressure between 180 bar and 210 bar during a time comprised between3 and 10 seconds.From treating the cutin-containing portion of a plant matter with water under the conditionsdescribe above, and subsequent cooling a cutin-enriched product and a liquid fraction areobtained. The cooling is preferably performed to room temperature. The liquid fractionmainly comprises extractives, proteins and cellulose / hemicellulose and / or the corresponding monomers thereof.Optionally, a step of separating the cutin-enriched product from the liquid fraction can beperformed. This separation step can be performed by any means commonly known by the person skilled in the art. In an embodiment, the separation is performed by centrifugationand / or filtration, preferably by filtration.Optionally, the separated cutin-enriched product may be further mixed with other components, preferably with gums and / or vegetable oils. This mixing may achieve a cutin- enriched product where the properties of the cutin-containing portion in the plant cuticles are mimicked. Non-limiting examples of suitable gums are guar gum, locust bean gum, gellan gum, Arabic gum, carrageenan. Non-limiting examples of vegetable oil are olive oil, rapeseed oil, soybean oil, corn oil, peanut oil, avocado oil. The process of the invention can be carried out in any reactor capable of holding the temperatures and pressures defined in the first aspect, typically a stainless steel reactor,preferably a tubular stainless-steel reactor. Such reactor comprises a vessel where thewater suspension of the cutin-containing portion of a plant matter and the water areintroduced, either from the same inlet or from different inlets. In order to withstand the hightemperatures and pressures required, the reactor is typically made of corrosion-resistantmaterials such as stainless steel or alloys. The reactor system includes a heat source, such as electric heaters or combustionchambers, to raise the temperature of the mixture of the one or more plants and water tothe targeted temperature. In a preferred embodiment of the first aspect, supercritical conditions within the defined ranges of pressure and temperature are used, thus heat is applied to the reactor vessel toachieve desired temperature and pressure.The reactor includes a feeding system by which the suspension of cutin-containing portionof a plant matter and water are introduced into the reactor vessel either continuously orbatch-wise. Preferably, the reactor is a continuous reactor. Water is injected into the reactorvessel at high pressure and temperature, preferably to reach supercritical water conditions.However, also subcritical water conditions may be used according to the ranges of pressureand temperature defined above.In particular, the reactor vessel is preceded by a T mixer where the preheated SCW streamand suspension with the cutin-containing material stream are mixed. After instantaneousmixing, a stream comprising the water medium and the cutin-containing portion runsthrough the above-mentioned reactor under the pressure, temperature and reaction timeconditions defined in the first aspect. The residence time of the one or more plants in thereactor vessel, as already stated, is carefully controlled (under 50 seconds) to optimize theconversion process, maximize the yield of desired products and avoid cutindegradation / depolymerisation.The reactor comprises also an outlet, where the output stream comes out. At the reactoroutlet, a decompression valve is placed. The output stream is then instantaneously cooleddown. This cooling prevents further side-reactions.Optional agitation or mixing mechanisms within the reactor vessel may ensure thoroughmixing of the cutin-containing portion of a plant matter and water, particularly in a batchreactor. The optional agitation or mixing mechanisms promote efficient heat and masstransfer and enhance the extraction process.Next, as already stated, the reaction mixture is optionally subjected to separation processessuch as filtration and / or centrifugation.Apparatuses for carrying out the process of the invention are already known, such as in C.M. Martinez et al., The Journal of Supercritical Fluids, Vol. 143, 2019, 242-250, DOI:10.1016 / j.supflu.2018.08.017).The cutin enriched product comprises more than 50 wt.% cutin. The cutin enrichement inthe product (compared to cutin content in the initial cutin-containing portion of a plant matter) is at least 10 wt.%, at least 20 wt.%, at least 30 wt.%, preferably the cutin enrichment is comprised between 10 and 50 wt.% Further extraction of the cutin enriched product, preferably in solid form, with an organic solvent may selectively remove additional impurities or undesired components, such as residual extractives and proteins. By performing this additional extraction with an organic solvent, the content of cutin in the solid is then further increased up to 80%, 90%, 95% or even up to 99%. In a preferred embodiment, the invention refers to a process for obtaining a cutin-enrichedproduct from the pomace of a fruit selected from tomato, grape, apple, pear, papaya, peach,or a combination thereof, preferably from tomato pomace, said process comprising the steps of: a) optionally, mechanically grinding and / or milling the pomace, preferablytomato pomace, and, optionally, separating tomato peel from tomato seedsin the pomace; b) mixing said optionally mechanically pre-treated pomace, preferably tomatopomace, with water to obtain a suspension;c) treating said suspension with water at a temperature comprised between 310ºC and 450 ºC, preferably between 310 ºC and 400 ºC, and at a pressurecomprised between 175 and 300 bar, preferably between 200 and 260 bar, to obtain the cutin-enriched product and a liquid fraction, wherein said treatment is performed during a time between 0.03 and 10 seconds; andd) optionally, separating the cutin-enriched product from the liquid fraction bycentrifugation and / or filtration.In a more preferred embodiment of the first aspect of the invention, the invention refers toa process for obtaining a cutin-enriched product from tomato pomace, said processcomprising the steps of:a) mechanically grinding and / or milling the tomato pomace;b) mixing said mechanically pre-treated tomato pomace with water to obtain asuspension; c) treating said suspension with supercritical water at a temperature comprisedbetween 374 ºC and 450 ºC and at a pressure comprised between 221 barand 260 bar to obtain the cutin-enriched product and a liquid fraction,wherein said treatment is performed during a time between 0.05 and 1.5 seconds; d) separating the cutin-enriched product from the liquid fraction bycentrifugation and / or filtration;e) optionally, subjecting the cutin-enriched product to washing with an organicsolvent and drying. In a particular embodiment of the first aspect of the invention, the invention refers to aprocess for obtaining a cutin-enriched product from tomato pomace, said processcomprising the steps of: a) mechanically grinding and / or milling the tomato pomace;b) mixing said mechanically pre-treated tomato pomace with water to obtain asuspension; c) treating said suspension with supercritical water at a temperature between300 °C and 370 °C and at a pressure between 100 bar and 220 bar during atime comprised between 1 and 30 seconds, more preferably at a temperature between 300 ºC and 350 °C and at a pressure between 150 bar and 220 bar during a time comprised between 2 and 20 seconds, even morepreferably at a temperature between 305 ºC and 325 ºC and at a pressurebetween 180 bar and 210 bar during a time comprised between 3 and 10seconds so as to obtain the cutin-enriched product and a liquid fraction; d) separating the cutin enriched product from the liquid fraction bycentrifugation and / or filtration;e) optionally, subjecting the cutin enriched product to washing with an organicsolvent and drying. Cutin-enriched product As a result of the method of the invention a cutin-enriched product, preferably in a solidform, is obtained. Therefore, another aspect of the invention relates to a cutin enrichedproduct obtainable by means of the process defined in the first aspect of the invention. In a particular embodiment, the cutin-enriched product obtainable by means of the processdefined in first aspect, comprises, preferably consists of:- between 40 and 75 wt.% cutin;- between 25 and 60 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS. In a particular embodiment, the cutin-enriched product obtainable by means of the processdefined in first aspect, comprises, preferably consists of:- between more than 50 wt.% and 75 wt.% or less of cutin;- between 25 and 60 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS. In a particular embodiment, the cutin-enriched product obtainable by means of the processdefined in first aspect, comprises, preferably consists of:- between more than 50 wt.% and 75 wt.% or less of cutin;- between 25 and 50 wt.% or less consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.The invention also refers to a cutin-enriched product, wherein said cutin-enriched productcomprises, preferably consists of: -between 40 and 75 wt.% cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.The invention also refers to a cutin-enriched product, wherein said cutin-enriched productcomprises, preferably consists of: -between more than 50 wt.% and 75 wt.% or less of cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.The invention also refers to a cutin-enriched product, wherein said cutin-enriched productcomprises, preferably consists of: -between more than 50 wt.% and 75 wt.% or less of cutin;- between 25 wt.% and 50 wt.% or less consisting of extractives, cellulose andproteins; and wherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.In particular, the cutin-enriched product obtainable by means of the process defined in thefirst aspect of the invention comprises:- between 40 and 75 wt.% cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins; and wherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). In particular, the cutin-enriched product obtainable by means of the process defined in the first aspect of the invention comprises:- between more than 50 wt.% and 75 wt.% or less of cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins;and wherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). In the context of the invention the term “extractives” refers to fats, resin, wax, phenoliccompounds, pigments, oils, and other organic compounds unbounded together which arepresents in the cutin enriched product. These can be further removed by appropriate organicsolvents such as ethanol, sCO2, methanol, supercritical methanol, acetone, hexane, chloroform, dichloromethane, diethyl ether, ethyl acetate, tetrahydrofuran and isopropanol. The specific composition of the cutin enriched product will depend on the specific conditions (temperature, pressure and reaction time). Generally, under identical conditions of pressure and temperature, the shorter the reaction time the lower the wt.% of cutin enrichment, whereas by prolonging the reaction time the higher is the enrichment (at the same time some minor cutin depolymerisation might occur). In an embodiment of the invention the cutin enriched product obtainable by means of the process of the invention comprises between 45 and 75 wt.% cutin, preferably between 50and 75 wt.% cutin, even more preferably between 55 and 75 wt.% cutin.In an embodiment of the invention the cutin enriched product obtainable by means of theprocess of the invention comprises between 12 and 25 wt.% extractives, preferably between15 and 25 wt.% extractives.In an embodiment of the invention the cutin enriched product obtainable by means of the process of the invention comprises between 5 and 20 wt.% cellulose, preferably between10 and 20 wt.% cellulose. In an embodiment of the invention the cutin enriched product obtainable by means of theprocess of the invention comprises between 3 and 7 wt.% proteins, preferably between 3and 6 wt.% cellulose.In an embodiment, the cutin enriched product obtainable by means of the process of the invention does not comprise hemicellulose. A cutin-enriched product obtainable by means of the process of the first aspect, whereinthe process is characterized by a reaction time comprised between 3 and 10 seconds, atemperature comprised between 300 ºC and 320 ºC and a pressure comprised between200 bar and 220 bar; andwherein the cutin enriched product comprises: -between 55 and 68 wt.% cutin;- between 9 and 11 wt.% extractives;- between 15 and 17 wt.% cellulose; and- between 3 and 5 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). A cutin enriched product obtainable by means of the process of the first aspect, whereinthe process is characterized by a reaction time comprised between 1 and 1.5 seconds, atemperature comprised between 380 ºC and 400 ºC and a pressure comprised between 250 bar and 260 bar; and wherein the cutin enriched product comprises: -between 70 and 75 wt.% cutin;- between 13 and 15 wt.% extractives;- between 5 and 8 wt.% cellulose; and- between 2 and 4 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm,preferably below 150 µm, even more preferably below 120 µm as measured by DLS(Dynamic Light Scattering). A cutin enriched product obtainable by means of the process of the first aspect, whereinthe process is characterized by a reaction time of less than 1 second and more than orequal to 0.6 seconds, a temperature comprised between 380 ºC and 400 ºC and a pressure comprised between 240 bar and 260 bar; and wherein the cutin enriched product comprises: -between 60 and 65 wt.% cutin;- between 24 and 26 wt.% extractives;- between 2 and 4 wt.% cellulose; and- between 5 and 7 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). A cutin enriched product obtainable by means of the process of the first aspect, whereinthe process is characterized by a reaction time of less than 0.6 seconds, a temperaturecomprised between 380 ºC and 400 ºC and a pressure comprised between 240 bar and 260 bar; and wherein the cutin enriched product comprises:- between 54 and 66 wt.% cutin;- between 10 and 14 wt.% extractives;- between 8 and 20 wt.% cellulose; and- between 3 and 4 wt.% proteins; andand wherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). A cutin-enriched product obtainable by means of the process of the first aspect, wherein the process is characterized by a reaction time at 375 ºC (as defined in the examples)comprised between 1 and 3 seconds, a temperature comprised between 380 ºC and 400ºC and a pressure comprised between 240 bar and 260 bar; andwherein the cutin enriched product comprises:- between 62 and 72 wt.% cutin;- between 14 and 25 wt.% extractives;- between 2 and 7 wt.% cellulose; and- between 3 and 6 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). A cutin enriched product obtainable by means of the process of the first aspect, wherein the process is characterized by a reaction time at 375 ºC (as defined in the examples) comprised between less than 1 second and more than 0.5 seconds, a temperaturecomprised between 380 ºC and 400 ºC and a pressure comprised between 240 bar and260 bar; and wherein the cutin enriched product comprises: -between 55 and 60 wt.% cutin;- between 12 and 20 wt.% extractives;- between 8 and 18 wt.% cellulose; and- between 2 and 6 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). A cutin enriched product obtainable by means of the process of the first aspect, wherein theprocess is characterized by a reaction time at 375 ºC (as defined in the examples) of 0.5seconds or less and more than 0.01 seconds, a temperature comprised between 300 ºCand 400 ºC and a pressure comprised between 200 bar and 260 bar; andwherein the cutin enriched product comprises: -between 65 and 67 wt.% cutin;- between 10 and 14 wt.% extractives;- between 13 and 16 wt.% cellulose; and- between 3 and 4 wt.% proteins; andwherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). In an embodiment, the cutin enriched product obtainable by means of the process defined in the first aspect of the invention consists of:- between 55 and 72 wt.% cutin;- between 10 and 25 wt.% extractives;- between 3 and 16 wt.% cellulose; and- between 3 and 6 wt.% proteins.In the context of the invention, a D10 distribution means that the 10% of the particles has asize comprised between 3 and 20 µm, a D50 distribution means that the 50% of the particleshas a size comprised between 20 and 30 µm and a D90 distribution means that the 90% ofthe particles has a size comprised between 30 and 130 µm, the particle size beingmeasured by DLS.In an embodiment, the cutin enriched product obtained by means of the method of theinvention shows a size distribution of D10 comprised between 3 and 20 µm, D50 comprised20-30 µm and D90 comprised between 30 and 130 µm, measured by DLS.The cutin of the enriched solid obtained by means of the method of the invention shows astructure very similar to the native structure, since the ester bonds in the initial cutin remainnon-hydrolized during the process, as shown by the comparison of the FTIR spectra of rawtomato peel and the cutin enriched product obtained after performing the process of theinvention, as can be seen in Figure 5.Another aspect of the invention relates to a cutin enriched product, wherein the cutinenriched product comprises:- between 40 and 75 wt.% cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins; and wherein said cutin enriched product is characterized by a size particle below 180 µm,preferably below 150 µm, even more preferably below 120 µm as measured by DLS(Dynamic Light Scattering).Another aspect of the invention relates to a cutin enriched product, wherein the cutinenriched product comprises:- between more than 50 wt.% and 75 wt.% or less of cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins;and wherein said cutin enriched product is characterized by a size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS (Dynamic Light Scattering). The cutin-enriched product may be in combination with other components, preferably with gums and / or vegetable oils. This combination may mimic the properties of the cutin- containing portion in the plant cuticles. Non-limiting examples of suitable gums are guar gum, locust bean gum, gellan gum, Arabic gum, carrageenan. Non-limiting examples of vegetable oil are olive oil, rapeseed oil, soybean oil, corn oil, peanut oil, avocado oil.All the embodiments mentioned above in relation to the cutin-enriched product obtainableby means of the process of the first aspect apply to the cutin-enriched product defined in the previous paragraph.Uses of the cutin enriched productAnother aspect of the invention relates to the use of the cutin enriched product in the manufacture of polymers, preferably bioplastics, more preferably polyesters; material coating; cosmetic products; and food emulsifiers. Further embodiments 1. Process for obtaining a cutin-enriched product from the cutin-containing portion of aplant matter, said process comprising treating said cutin-containing portion with water at a temperature between 300 and 500 °C and at a pressure between 85 and 400 bar, during less than 50 seconds.2. Process according to embodiment 1, comprising the steps of:a) optionally, pre-treating the cutin-containing portion of a plant matter;b) mixing said optionally pre-treated cutin-containing portion with water toobtain a suspension; c) treating said suspension with water at a temperature between 300 and 500°C and at a pressure between 85 and 400 bar, wherein said treatment is carried out during less than 50 seconds, to obtain the cutin-enriched product and a liquid fraction; and d) optionally, separating the cutin-enriched product from the liquid fraction.3. Process according to embodiment 1 or 2, wherein the cutin-containing portion of aplant matter is the fruit of a fruit-bearing plant matter, preferably a fruit selected fromtomato, grape, apple, pear, papaya, peach, or a combination thereof; morepreferably is the pomace of said fruit; even more preferably is tomato pomace.4. Process according to any one of embodiments 1 to 3, wherein the cutin-containingportion of a plant matter is pre-treated by grinding, drying, wet or dry milling, sCO2extraction, CO2 explosion, centrifugation, sonication, ammonia explosion, steam explosion or a combination thereof.5. Process according to any one of embodiments 2 to 4, wherein the amount of thecutin-containing portion of a plant matter in the suspension of step b) is between 0.1and 50 wt.%, preferably between 1 and 30 wt.%, even more preferably between 4 and 11 wt.%.6. Process according to any one of embodiments 2 to 5, further comprising the additionto the suspension of step b) of an acid.7. Process according to embodiment 6, wherein the acid is selected from the groupconsisting of acetic acid, formic acid, p-toluenesulfonic acid (PTSA), trifluoroaceticacid, camphorsulphonic acid, citric acid, oxalic acid HCl, H2SO4, HNO3, H3PO4, and mixtures thereof; preferably acetic acid and / or H2SO4; more preferably acetic acid.8. Process according to embodiment 7, wherein the acid is added in an amountcomprised between 10% and 70% on a dry basis, preferably between 15% and 60% on a dry basis, more preferably between 20% and 50% on a dry basis. Process according to any one of the preceding embodiments, wherein thetemperature for treating the cutin-containing portion of a plant matter is comprisedbetween 374 ºC and 500 ºC, preferably between 374 ºC and 450 ºC, and the pressure is comprised between 221 and 400 bar, preferably between 221 and 260 bar.Process according to any one of the preceding embodiments, wherein the treatmentis performed during less than 30 seconds, preferably less than 10 seconds; more preferably the treatment is performed between 0.05 to 10 seconds.Process according to any one of embodiments 1 to 8, wherein the cutin-containingportion of a plant matter is the pomace of a fruit selected from tomato, grape, apple,pear, papaya, peach, or a combination thereof, preferably tomato pomace, said process comprising the steps of: a) optionally, mechanically pre-treating the pomace, preferably tomato pomace,by grinding and / or milling; b) mixing said optionally mechanically pre-treated pomace, preferably tomatopomace, with water to obtain a suspension;c) treating said suspension with water at a temperature comprised between 310ºC and 450 ºC, preferably between 310 ºC and 400 ºC, and at a pressurecomprised between 175 and 300 bar, preferably between 200 and 260 bar, to obtain the cutin-enriched product and a liquid fraction, wherein said treatment is performed during a time between 0.03 and 10 seconds; andd) separating the cutin-enriched product from the liquid fraction bycentrifugation and / or filtration.A cutin-enriched product obtainable by means of the process defined inembodiments 1 to 11, wherein the cutin-enriched product comprises, preferably consists of: -between 40 and 75 wt.% cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins;and wherein said cutin-enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS.13. A cutin-enriched product obtainable according to embodiment 12, wherein the cutinenriched product comprises: -between 40 and 75 wt.% cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins;and wherein said cutin-enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS. 14. A cutin-enriched product, wherein the cutin-enriched product comprises:- between 40 and 75 wt.% cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by DLS. 15. Use of the-cutin enriched product according to any one of embodiments 12 to 14 inthe manufacture of polymers, preferably bioplastics, more preferably polyesters; material coatings; cosmetic products; and food emulsifiers. EXAMPLESMaterials and methodsTomato pomace was provided by Pronat Company (Don Benito, Badajoz, Spain). Acetic acid used in some experiments was purchased from Panreac. Chloroform 99% andmethanol for UV, IR, HPLC, and ACS, used for Soxhlet extraction were purchased fromAcros Organics and Panreac respectively. For acidic hydrolysis, sulfuric acid 72 % wasused. The 72 % was prepared in-house using 96% sulfuric acid purchased from Panreac. Calcium carbonate used for the neutralization of samples was purchased from Sigma Aldrich. Water used for Soxhlet extraction, experiments, and other analysis, when it wasnecessary, was Milli-Q and type III grade, produced in the laboratory of University ofValladolid, on equipment from company Millipore (Milan, Italy). Tomato pomace separation To separate peel and seeds fractions, around 1kg of pomace was placed in approximately5 liters of type III water in a square-shaped container, well mixed, and left for approximately10 min during which the fractions were separated. Seeds remain at the bottom of the container while the peel floats on the surface. Afterward, the peel was collected from the surface, yet some seeds remained in the peel fraction. The absorbed water was first drained by squeezing and finally, the tomato peel fraction was placed in a well-ventilated room for approximately two weeks or in the oven with ventilation at 60 ºC for a few days for drying. Dry tomato peel contained approximately 5 % of moisture. Dry tomato peel was first ground in a kitchen blender and finally, ball milled using Retsch equipment, for 4 h. Even though peel and seed fractions were separated as representative example of one embodiment of the process of the invention, this is not required as both peel and seeds contain substantial amounts of cutin, nevertheless seeds may contain higher amount of proteins. Experimental setup The experiments were done at two plants for continuous Supercritical Water Hydrolysis(SCWH) named PHUn1 and PHUn2. In both cases, a tubular reactor was used, whichconsisted of a stainless steel pipe with a wall thickness enough to sustain very high pressure. While the inner diameter of the pipe is constant, the length is changeable which allows us to change reaction time with already fixed SCW and biomass suspension stream flows. The tubular reactor is preceded by a T mixer where the preheated SCW stream and suspension with the cutin-containing material stream are met. Inside of the T mixer, instantaneous mixing happens (microseconds) and a homogenous reaction stream runsthrough the above-mentioned tubular reactor. At the reactor exit, a decompression valve isplaced. Due to the sudden decrease in pressure and based on the Joule-Thomson effect,the output stream is instantaneously cooled down when the reactions are stopped.The main difference between the two plants is that PHUn2 has an automatically controlleddecompression valve while this valve is manual in PHUn2; PHUn2 is equipped with a flashseparator where the product, which comes from the reactor, is separated in two streams:downstream (product concentrated stream) and upstream (product free stream). Testedconditions are shown in Table 1. The raw material for these experiments was prepared by mixing milled tomato peel with water in a way that the final concentration of suspension was between 4 and 11 %. Additionally, experiments 6 and 8 (Table 1 below) were done with the addition of acetic acid (50 % on a dry basis suspension) in biomass suspension. Table 1. Conditions tested in experimentsEquipment No.Reaction Reaction time Reaction Reaction pressure time at 375 °C temperature 10.25 s 0.48 s 390 ± 6.46 °C 258 ± 7.50 barPHUn12 1.05 s 1.84 s 388 ± 2.23°C 254 ± 7.45 bar3 6.33 s 0.40 s 312 ± 9.83 °C 206 ± 8.50 bar4 0.06 s 0.16 s 398 ± 21.33 °C 251 ± 1.32 bar5 0.37 s 0.86 s 394 ± 4.09 °C 251 ± 3.90 bar6* 0.49 s 0.79 s 386 ± 9.56 °C 251 ± 3.51 barPHUn27 0.51 s 0.80 s 385 ± 11.89 °C 251 ± 1.55 bar8* 0.52 s 0.70 s 382 ± 6.18 °C 241 ± 1.43 bar9 0.53 s 0.70 s 381 ± 7.95 °C 241 ± 1.05 bar10 0.89 s 1.51 s 387 ± 6.14 °C 251 ± 1.57 bar*In those conditions acetic acid was added to the tomato peel suspension.In hydrothermal processes, the Severity factor (R0) is often used to describe experimentalconditions by combining the impact of reaction time and temperature. The severity factor provides a measurement of how much reaction has occurred in time ti at temperature Ti relative to a reference temperature Tb has taken place. Similar values of R0 would lead tosimilar effects on the reactions than the studied conditions (Posmanik et al., 2017, DOI:10.1016 / j.supflu.2016.09.004). This work calculated reaction time at 375 °C from theformula for a severity factor (R0) (Equation 1): R0= tix exp ((Ti-Tb) / ω) (Eq 1)where ti is the reaction time (s), Ti is the reaction temperature (K), and Tb is the base orreference temperature (K). In most studies, the reference temperature is assigned to 100°C. Further, ω is a fitted parameter (Equation 2) where Tf represents the middle of the range for experimental conditions (floor temperature) (K), R is the universal gas constant (J / (molK))and Ea is the activation energy of the biomass (kJ / mol). In literature, the commonly usedvalue for this factor is 14.75 K, corresponding to the activation energy (Ea) of hemicellulosehydrolysis (111 kJ / mol). However, all experiments, except experiment number 3, were runaround the critical point of water when the reaction medium has considerably different properties when compared to 100 °C. For that reason, the reference temperature in this application was 375 °C. Additionally, tomato peel is a complex biomass structure, therefore, the calculation of the fitting parameter based only on the activation energy of hemicellulosemay be an oversimplification. The activation energy of biomass was calculated as the sumof the share of activation energies of the following tomato peel compounds (Equation 3): cellulose (164 kJ / mol), hemicellulose (111 kJ / mol), and part of tomato peel which is calculated as pectin (111 kJ / mol). Additionally, the activation energy of protein (157 kJ / mol) is also taken into account although proteins are not originally part of the peel but seeds that remain in the peel fraction after the above-explained separation process. These compounds of the tomato peel were chosen due to the expectation that they would be primarily hydrolyzed in the process. For the Tf, the middle of experimental conditions was used at 350 °C. Taking this into account, the final number obtained for the activation energy was 141.11 kJ / mol and the fitting parameter was 22.88 K. ^ω = ^^ ^^^ (Eq 2) Ea (tomato peel) = Σ (yi x Eai) (Eq 3)Feed and sample characterization For all performed experiments (see Table 1) sampling was done from two sources: prepared tomato peel suspension (hereafter called feed) and the sample obtained after the process (hereafter called sample). Both samples appeared as suspensions partially dissolved inwater. The liquid and solid phases are separated by centrifugation. The solid phase, afterseparation, was washed several times with water and left to dry.Microscopy and environmental scanning electron microscopy analysis The conventional microscopy method was used to study the surface morphology of raw tomato peel before and after the milling process (tomato peel in powder). The microscope- type Leica DM1000 LED from Leica Microsystems, Spain was used. Micrographs were obtained at 40x magnification. An environmental scanning electron microscopy (ESEM) (FEI QUANTA 200 FEG ESEM, FEI Company Czech Republic) was used to study tomato peel powder and the sample’s surface characteristics. The sample suspensions were analyzed, as obtained during the process, under low-vacuum conditions (0.6 mbar). Micrographs were obtained at 4000x, 5000x, and 80000x magnification. Energy Dispersive Spectroscopy (EDS) data were collected with an EDAX Genesis module coupled to the ESEM. The surface morphology of raw tomato peel before milling showed the characteristic shape of the epidermal cells (Figure 5A). The cells’ size was varied from 30 µm and more. This kind of structure had already been noted in the literature (Moreira, Bento, Pais, Petit, Escórcio, Correia, Pinheiro, Haliński, et al., 2020). After the milling process, when particle size was reduced to less than 250 µm the epidermal cell structure was destroyed as can beseen in Figure 5B. The same conclusion was confirmed by the ESEM picture of thepowdered tomato peel (Figure 5C).ESEM pictures of samples (Figure 6) were done from sample suspensions as it wasobtained in the process in order to prevent coagulation or any other influence on surface morphology during drying. However, there was no significant difference in surfacemorphology regardless of applied conditions. Thus, although particle size was drasticallyreduced in the process it did not influence the main structure with cutin as the dominant component. Characterization of the solid phaseFor the calculation of the yield of the solid part of the sample, the following procedures andequations were used. Firstly, determination of the total amount of solid in water in prepared feeds suspensions and obtained samples suspensions (TS), part of the feeds and samples that was dissolved in water (DS), and part of feeds and samples suspended but not dissolved in water (SS) was performed. Furthermore, the TS value can also be related to feed and sample concentration. For determination, TS, approximately 2 g of well-mixed, homogeneous suspension was placed in the previous temperate and measured aluminium pan and put in the oven at 105 °C overnight to dry. In the same way, DS was determined by filtering approximately 2 g of well-mixed, homogeneous suspension through a 22 µm filter in the previous temperate and measured Al pan and putting it in the oven at 105 °C overnight to dry. Further, the SS value is obtained as the difference between TS and DS. Finally, the yield of the solid was calculated by utilization of equation 4 and the results are shown in Table 2. Solid yield Table 2. Solid yield of the experiments Experiment Solid yield (%)1 92.072 83.803 92.134 94.275 77.286* 83.277 82.028* 77.319 84.7210 70.08The solid phase of feed and sample was characterized by following the same procedure explained previously for the preliminary characterization of tomato peel fraction. Liquid phase analysis The liquid part of the samples was analyzed to determine the yield of products of hydrolysis of polysaccharides after carrying out the process of the invention, primarily C5 and C6 sugars as well as sugar degradation products. To transform the residual oligomers in the liquid phase into monomeric sugars that can be examined and measured by HPLC, the liquid phase of the samples was subjected to one-step acid hydrolysis. The procedure involved adding 72% sulfuric acid in a way that the final acid concentration was 4%. Hydrolysis was run for 1h at 120 °C. Finally, the sample was cooled at room temperature and neutralized with CaCO3 up to pH 6 to prepare it for HPLC analysis. Thereafter, HPLC analysis was done as described above. Tomato peel elementary analysis and characterizationIn Table 3 presents the elementary composition of tomato peel fraction, which wasdetermined at the Sciences and Technology Park, University of Burgos using EA Flash 2000Elemental Analyzer (Thermo Fisher Scientific), TCD Detector, and Mettler Toledo XP6Microbalance. The technique used for analysis was elemental analysis by combustion, where both organic and inorganic substances are converted into elemental gases which, after subsequent reduction, are separated in a chromatographic column and transferred to a thermal conductivity detector.As expected, carbon was the dominant element. A small amount of nitrogen detected withelementary analysis refers very likely to proteins from tomato seeds remaining in the peel fraction after separation.Table 3 Elementary compositionElement N C H SAmount, % 1.49 ± 0.04 58.85 ± 0.05 8.33 ± 0.06 0.00The initial composition of tomato peel used in the experiment is determined as follows: Determination of Extractives. Extractives were extracted by Soxhlet extraction with chloroform and methanol for 5 hours separately and finally water extraction for 24h. First, a rotary evaporator was used to evaporate solvents for chloroform and methanol extractives. Finally, extractives were placed in the oven at 50 °C overnight to dry completely. Water extractives were first frozen and afterward placed in a laboratory freeze dryer for a few days to dry completely. The total amount of extractives was calculated as the sum of individual fractions. Determination of total phenolic content.Besides total extractive content, phenolic compounds, as one group of extractives wereseparately additionally determined (Table 4 below). Firstly, raw tomato peel powder and thesolid part of the samples were subjected to extraction with methanol in the ratio of 1:10(g:ml) at room temperature for one hour with constant stirring. Therefore, the mixture was filtered by vacuum filtration to obtain a liquid extract. Finally, the concentration of phenoliccompounds was determined by utilization of the Folin-C1ocalteu method. Additionally, asimilar extraction was done with water. Tabla 4. Total phenolic content (reaction time at 375 ºC is shown)Sample Total phenolic content Raw tomato peel 0.14 % 0.15 %Sample 1 (0.48 s) 2.22 0.04 Sample 2 (1.84 s) 2.85 % 0.12 %Determination of the amount of carbohydrates. Samples free of extractives were placed in pressure tubes and first treated with 72 % sulfuric acid at 30 °C. Upon completion of 60- minute hydrolysis, the mixture was diluted so the acid reached a 4 % concentration by adding deionized water, and tubes were then placed for 1 h at 120 °C. Afterward, the hydrolysis solution was cooled at room temperature and filtered through previously measured ashless filter paper. The solid phase on filter paper was washed several times with deionized water and placed in the oven at 40 °C overnight for drying while the liquid phase was neutralized with calcium carbonate up to pH 6 to prepare samples for HPLCsugar analysis. Oven-dried solids on filter paper were measured and afterward placed in crucibles at 550 °C to determine ash. Oven-dry solids were considered native cutin, which can be confirmed by FTIR analysis of this solid.For said HPLC analysis, a Shodex SH-1011 column at 50 ºC was used. Sulfuric acid (0.01N) was used as the mobile phase with a 0.8 mL / min flow rate. A Waters IR detector 2414 was used to identify the sugars and their derivatives. Quantification was carried out using standard calibration curves.Determination of the protein content. Total Kjeldahl nitrogen was determined according toAPHA Standards Methods and then total proteins were calculated as Kjeldahl N × 6.25.Determination of moisture and ash content. The amount of moisture was determinedfollowing the NREL procedure for the Determination of Total Solids in Biomass and Total Dissolved Solids in Liquid Process Samples while ash content was determined following the NREL (National Renewable Energy Laboratory) procedure for the Determination of Ash in Biomass (Sluiter et al., 2008a) (Sluiter et al., 2008b). The moisture amount was used for the calculation of oven dry weight (ODW). This value was later used for all calculations where ODW was required.The composition analysis of the tomato peel fraction before the experiment is given in Table5. Table 5. Compositional analysis for a tomato peel sample before the process of theinvention (dry basis)Fraction Amount, % w / w A comparison between the content of cutin in the product before and after the experimentsdescribed in Table 1 is shown in Table 6. For a better characterization of mass balancevariation, the quantitative determination of cutin content and other components in thetomato peel was carried out before and after each experiment. Table 6. Amount of cutin and other components (wt.% on a dry basis) in the product before and after the process of the invention Hemicellulose *In those conditions acetic acid was added to the tomato peel suspension. Particle size analysis The particle size of the feed (“before” in Table 7 below) and obtained cutin-enriched sample(“after” in table 7 below) was analyzed before centrifugation. The measurement was carriedout by a Dynamic Light Scattering (DLS) Mastersizer 2000. The particle size distributionwas calculated based on volume distribution. Table 7. Standard percentile readings from the analysis d (0.1), d (0.5) and d (0.9) Experiment Before / After d (0.1), µm d (0.5), µm d (0.9), µmBefore 13.838 63.327 196.3621 After 3.018 17.026 39.732Before 14.816 70.582 221.4922 After 7.227 29.836 61.932Before 8.767 46.730 177.316After 4.500 19.995 61.356Before 13.880 82.554 226.601 After 3.356 17.127 47.214Before 12.373 75.159 206.867 After 4.107 22.242 60.951Before 13.880 82.554 226.6017 After 3.765 21.683 63.902Before 11.016 76.513 219.1058* After 4.566 21.031 53.417Before 11.612 81.564 242.2009 After 5.575 24.759 114.322Before 14.563 84.021 245.38510 After 20.084 61.712 111.822*In those conditions acetic acid was added to the tomato peel suspensionCharacterization of cutin by FTIR analysis. FTIR analysis was conducted with a BrukerTensor 27 spectrometer. All spectra were recorded in the range from 4000 to 400 cm-1 with4 cm-1resolution. The recorded spectra were baseline-subtracted and normalized to themaximum peak intensity. Table 8 shows a comparison of the main FTIR peaks of the cutinenriched products (corresponding to experiments 1 and 10 of tables 1 and 2) with the raw tomato peel (before running said experiments). Table 8. Main FTIR peaks and their assignments (cm-1) Assignment Sample 1 Sample 10 Raw tomato peelTomato peel ν(C-C) aromatic (conjugated1518 1516 Phenolic compounds ν(C-C) aromatic (conjugated1438 Phenolic compounds ν(C-O) Cutin, polysaccharides Phenolic compounds δ(CH2) rocking722 724 720 Cutin, waxesFrom table 8, it appears that most of the native cutin FTIR peaks are preserved after usingthe method of the invention.

Claims

CLAIMS1. Process for obtaining a cutin-enriched product from the cutin-containing portion of aplant matter, said process comprising treating said cutin-containing portion withwater at a temperature between 300 and 500 °C and at a pressure between 85 and 400 bar, during less than 50 seconds, wherein the cutin-enriched product has more than 50 wt.% of cutin.

2. Process according to claim 1, comprising the steps of:a) optionally, pre-treating the cutin-containing portion of a plant matter;b) mixing said optionally pre-treated cutin-containing portion with water toobtain a suspension; c) treating said suspension with water at a temperature between 300 and 500°C and at a pressure between 85 and 400 bar, wherein said treatment is carried out during less than 50 seconds, to obtain the cutin-enriched product and a liquid fraction; and d) optionally, separating the cutin-enriched product from the liquid fraction.

3. Process according to claim 1 or 2, wherein the cutin-containing portion of a plantmatter is the fruit of a fruit-bearing plant matter, preferably a fruit selected fromtomato, grape, apple, pear, papaya, peach, or a combination thereof; more preferably is the pomace of said fruit; even more preferably is tomato pomace.

4. Process according to any one of claims 1 to 3, wherein the cutin-containing portionof a plant matter is pre-treated by grinding, drying, wet or dry milling, sCO2extraction, CO2explosion, centrifugation, sonication, ammonia explosion, steam explosion or a combination thereof.

5. Process according to any one of claims 2 to 4, wherein the amount of the cutin-containing portion of a plant matter in the suspension of step b) is between 0.1 and50 wt.%, preferably between 1 and 30 wt.%, even more preferably between 4 and 11 wt.%.

6. Process according to any one of claims 2 to 5, further comprising the addition to thesuspension of step b) of an acid.

7. Process according to claim 6, wherein the acid is selected from the group consistingof acetic acid, formic acid, p-toluenesulfonic acid (PTSA), trifluoroacetic acid,camphorsulphonic acid, citric acid, oxalic acid HCl, H2SO4, HNO3, H3PO4, and mixtures thereof; preferably acetic acid and / or H2SO4; more preferably acetic acid.

8. Process according to claim 7, wherein the acid is added in an amount comprisedbetween 10% and 70% on a dry basis, preferably between 15% and 60% on a dry basis, more preferably between 20% and 50% on a dry basis.

9. Process according to any one of the preceding claims, wherein the temperature fortreating the cutin-containing portion of a plant matter is comprised between 374 ºCand 500 ºC, preferably between 374 ºC and 450 ºC, and the pressure is comprised between 221 and 400 bar, preferably between 221 and 260 bar.

10. Process according to any one of the preceding claims, wherein the treatment isperformed during less than 30 seconds, preferably less than 10 seconds; more preferably the treatment is performed between 0.05 to 10 seconds.

11. Process according to any one of claims 1 to 8, wherein the cutin-containing portionof a plant matter is the pomace of a fruit selected from tomato, grape, apple, pear,papaya, peach, or a combination thereof, preferably tomato pomace, said process comprising the steps of: a) optionally, mechanically pre-treating the pomace, preferably tomato pomace,by grinding and / or milling; b) mixing said optionally mechanically pre-treated pomace, preferably tomatopomace, with water to obtain a suspension;c) treating said suspension with water at a temperature comprised between 310ºC and 450 ºC, preferably between 310 ºC and 400 ºC, and at a pressurecomprised between 175 and 300 bar, preferably between 200 and 260 bar, to obtain the cutin-enriched product and a liquid fraction, wherein said treatment is performed during a time between 0.03 and 10 seconds; andd) separating the cutin-enriched product from the liquid fraction bycentrifugation and / or filtration.

12. A cutin-enriched product obtainable by means of the process defined in claims 1 to11, wherein the cutin-enriched product comprises, preferably consists of: -between more than 50 wt.% and 75 wt.% or less cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin-enriched product is characterized by a D90 size particle below180 µm, preferably below 150 µm, even more preferably below 120 µm as measured byDynamic Light Scattering.

13. A cutin-enriched product obtainable according to claim 12, wherein the cutinenriched product comprises: -between more than 50 wt.% and 75 wt.% or less of cutin;- between 10 and 25 wt.% extractives;- between 2.5 and 20 wt.% cellulose; and- between 2.5 and 7.5 wt.% proteins;and wherein said cutin-enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by Dynamic Light Scattering.

14. A cutin-enriched product, wherein the cutin-enriched product comprises:- between more than 50 wt.% and 75 wt.% or less of cutin;- between 60 and 25 wt.% consisting of extractives, cellulose and proteins; andwherein said cutin enriched product is characterized by a D90 size particle below 180 µm, preferably below 150 µm, even more preferably below 120 µm as measured by Dynamic Light Scattering.

15. Use of the-cutin enriched product according to any one of claims 12 to 14 in themanufacture of polymers, preferably bioplastics, more preferably polyesters; material coatings; cosmetic products; and food emulsifiers.

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