Process of valorisation of AGRO-food wastes and / or by-products

Abstract

A process of valorisation of agro-food wastes and / or by-products is provided, wherein a solid raw material to be processed is submitted to a sequence of solid-liquid extraction steps arranged to produce solid extracts of nutraceutical substances. Such a sequence comprises three steps in a first of which extraction is carried out with cold water, in a second with a hydroalcoholic solution and in a third with hot water, and the extracted liquids are processed for obtaining: - a dry solid extract containing dietary fibres and water-soluble polyphenols; - a dry solid extract rich in water-insoluble polyphenols; and - a dry solid extract rich in vegan proteins, wherein the processing of the liquid extracts obtained in the first and second steps includes a filtration and concentration step, and the processing of the liquid extract obtained in the third step includes a precipitation step followed by a centrifugation step, and wherein the filtration step and the concentration step and the centrifugation step, respectively, are followed by a drying step.

Description

[0001] PROCESS OF VALORISATION OF AGRO-FOOD WASTES AND / OR BY¬

[0002] PRODUCTS

[0003] Technical Field

[0004] This invention relates to valorisation of agro-food wastes, residues and / or by-products in view of their reuse, and more particularly it concerns a process of nutraceutical valorisation of such materials.

[0005] Background Art

[0006] The Food and Agriculture Organization (FAO) estimates that every year approximately 1 / 3 of all food produced for human consumption in the world is lost or wasted, to a global amount of about 1.6 gigatons of "primary product equivalents" and about 1.3 gigatons of edible part of food. A large amount of those substances could instead be reused and this would enable considerably reducing both the cost for waste disposal and the potential negative impact on the environment. At the same time, also the volume of crop residues (nonedible plant parts that are left in the field after harvesting) is very important.

[0007] In view of this, recently much attention has been directed to the recovery of bioactive compounds from different agro-food residues and wastes, such as leaves, peels, barriers, seeds, wood, culls, pits, pulp, press cakes, grape pomace, malts, hops, husks, spent grain and so forth. Many of these substances could be valorised as animal feed or compost, or transformed into energy fuel based on the vegetal matrix or also could be used in a wide variety of industrial products, such as wood-based panels, biofertilisers, biofibres etc.

[0008] Research on these agro-food matrices has also revealed that valorisation can result in a wide range of natural bioactive compounds providing an excellent pool of molecules for the production of nutraceuticals, functional foods and food additives.

[0009] The invention just concerns this nutraceutical valorisation.

[0010] Processes and apparatuses for nutraceutical valorisation are known in the art, which are based on the extraction of reusable substances by means of turbulence and / or shear stress and / or hydrodynamic cavitation. Examples are disclosed in US 2021 / 002326 Al and CZ 2017488 A3.

[0011] WO 2018 / 146647 Al discloses an apparatus and a process using successive high turbulence and high shear stress and high cavitation mixing stages for intensifying the chemical kinetics of processes requiring separation of different phases, including a solidliquid separation. The document discloses examples of use for nutraceutical valorisation, yet the procedures disclosed in such examples are aimed at extracting individual products or product categories (more particularly carotenes and polyphenols) and provides no suggestion for obtaining an as far as possible complete extraction of the different categories of substances reusable for nutraceutical purpose present in the processed raw material.

[0012] Brewer’s Spent Grain (BSG), Spent Coffee Ground (SCG), Spent Tea Leaves (STL), typically waste tea leaves resulting from beverage production, Olive Leaves (OL) and Grape Pomace (GP), as well as Orange Peels (OP), are among the agro-food by-products most studied from the standpoint of nutraceutical valorisation, due to their worldwide available quantity as well as to their bioactive compound content.

[0013] Examples of valorisation processes for some of the above raw materials, using the apparats disclosed in WO 2018 / 146647 AL are described in the degree theses "Experimental characterization of a novel, multistage, countercurrent, cavitation solidliquid extractor and its applicability to agro-food industrial waste valorization", A. Mannala, Turin 2020, https: / / webthesis.biblio.polito.it / 15610 / ; "Development of a novel green process for spent tea leaves valorization", L. Mellino, Turin 2021, https: / / webthesis.biblio.polito.it / 18764; and "Experimental development of an integrated BSG valorisation process and design of a 2000 tpy demo-unit." R. Chighine, Turin 2022, https: / / webthesis.biblio.polito.it / 21943.

[0014] KODDAMI ALI ET AL: “Techniques for Analysis of Plant Phenolic Compounds” Molecules 2013, Vol.18, pages.2328-2357 discloses the application of different methods used in the analysis of phenol compounds in vegetable-based products.

[0015] RABETAFIKA HOLY NADIA ET AL: “Fractionation of apple by-products as source of new ingredients: Current situation and perspectives” TREND IN FOOD SCIENCE & TECHNOLOGY, ELSEVIER SCIENCE PUBLISHERS, GB, vol.40, no. l pages 99-114, contains a review of uses of apple by-products as sources of fibres and phytochemical compounds, with particular emphasis on fractionation processes.

[0016] US 2015 / 327572 discloses a method including a concentration step for obtaining proteins from mixtures of vegetal materials,

[0017] CRAVOTTO GIANCARLO ET AL: “Pilot Scale Cavitational Reactors and Other Enabling Technologies to Design the Industrial Recovery of Polyphenols from Agro-Food By-Products, a Technical and Economical Overview” FOODS, vol.7, no.9, 21 August 2018, pages 1-14, discloses how cavitational reactors can promote processing of food products for production of nutraceuticals.

[0018] Yet, all these documents only disclose extraction of some categories of molecules and do not suggest a process allowing a complete valorisation of the starting by-products. Summary of Invention

[0019] It is an object of the present invention to provide a process of nutraceutical valorisation of agro-food wastes and / or by-products obviating the drawbacks of the prior art.

[0020] It is another object of the present invention to provide a process of nutraceutical valorisation of agro-food wastes and / or by-products that is environment-friendly and that, thanks to the exploitation of techniques of phase contact intensification for the extraction, has very reduced reaction times making it industrially applicable.

[0021] In a process according to the invention a solid agro-food waste and / or by-product is submitted to a sequence of three solid-liquid extraction steps, in a first of which extraction is carried out with cold water, in a second with a hydroalcoholic solution and in a third with hot water, and the liquid extract obtained in each step is processed for respectively obtaining:

[0022] - a dry solid extract containing dietary fibres and water-soluble polyphenols;

[0023] - a dry solid extract rich in water-insoluble polyphenols; and

[0024] - a dry solid extract rich in vegan proteins.

[0025] Advantageously, the three extraction steps are carried out in systems with phase contact intensification arranged to ensure turbulence and / or shear stress and / or cavitation levels exceeding given limit values.

[0026] According to the invention, the processing of the liquid extracts obtained in the first and second steps includes a filtration and concentration step, and the processing of the liquid extract obtained in the third step includes a precipitation step followed by a centrifugation step.

[0027] According to a preferred feature of the invention, the processing of the liquid extract obtained in the third step includes a precipitation step with pH shift down to the isoelectric point followed by the centrifugation step.

[0028] According to a further preferred feature of the invention, the filtration and concentration step and the centrifugation step are followed by a respective drying step

[0029] Preferably, according to the invention, the drying step is performed in order to obtain a dry solid extract with a final moisture content < 5% by weight.

[0030] Advantageously, the solid residues coming out from the first and second extraction steps are squeezed to recover extracted microcomponents with high nutraceutical value present in a liquid phase soaking the solid residue.

[0031] According to an advantageous feature of the invention, before the extraction steps, a soaking step is carried out in which the solid material to be submitted to the extraction is soaked with a liquid with such a liquid / solid mass ratio that a completely wet material is obtained where the liquid phase is present in the whole porosity of the solid phase, such a soaking being carried out with either fresh water or an aqueous liquid extract coming out from the first extraction step in the case of the raw material, and with liquid extracts coming out from the second and third extraction steps, respectively, in the case of the solid residues to be submitted to such extraction steps.

[0032] In a variant embodiment, the soaking carried out before the extraction in the third step is carried out with an aqueous solution of an alkaline compound, with such a liquid / solid mass ratio that a completely wet solid material is obtained where the liquid phase is present in the whole porosity of the solid phase. In this variant embodiment, a supernatant liquid phase resulting from the centrifugation of the liquid extract coming out from the third extraction step is processed with a hydroalcoholic solution to cause insolubilisation and precipitation of carbohydrates, oligosaccharides and dietary fibres, and the thus obtained precipitate is submitted to a centrifugation step followed by a drying step in order to obtain a dry solid extract rich in dietary fibres preferably with a moisture content < 5%.

[0033] Brief Description of Drawings

[0034] The above and other features and advantages of the present invention will become apparent from the following description of preferred embodiments made by way of nonlimiting example with reference to the accompanying drawings, in which:

[0035] - Fig. 1 shows a block diagram of a first embodiment of the process according to the invention;

[0036] - Fig. 2 shows a block diagram of a second embodiment of the process according to the invention;

[0037] - Fig. 3 is a block diagram similar to Figs. 1 and 2 showing the application of the invention to an agro-food by-product;

[0038] - Fig. 4 is a further block diagram similar to Figs. 1 and 2 showing the application of the invention to an agro-food by-product;

[0039] - Fig. 5 is a further block diagram similar to Figs. 1 and 2 showing the application of the invention to an agro-food by-product;

[0040] - Fig. 6 is a further block diagram similar to Figs. 1 and 2 showing the application of the invention to an agro-food by-product;

[0041] - Fig. 7 is a further block diagram similar to Figs. 1 and 2 showing the application of the invention to an agro-food by-product.

[0042] Description of Embodiments The invention provides a process based on sequential solid-liquid extraction steps, more particularly three steps, in which the raw material to be valorised, namely a vegetal matrix and / or an agro-food by-product and / or waste is respectively extracted with:

[0043] - cold water, to obtain a powdered dry solid extract containing dietary fibres and water- soluble polyphenols;

[0044] - hydroalcoholic solutions, to obtain a powdered dry solid extract rich in water insoluble polyphenols;

[0045] - hot water, to obtain a powdered dry solid extract rich in vegan proteins.

[0046] Hereinafter and in the drawings, the raw material will be referred to as "vegetal matrix".

[0047] Such steps are performed with an intensified, single-stage or multi-stage solid-liquid contactors, of rotor-stator type, operating in co-current or countercurrent, which generate high turbulence and / or high shear stress and / or high hydrodynamic cavitation, or combinations thereof,

[0048] A first embodiment of the invention will now be described with reference to Fig. 1. In the block diagram, corresponding elements in the different steps are denoted by corresponding reference numerals, differing in the initial digit.

[0049] In the first extraction step, the vegetal matrix is dried in order to reduce its moisture content (e.g. at a level < 14%) so as to prevent the starting of the fermentation process during the stockage and moving phase, and then it is ground to obtain a final size distribution falling within a range convenient for the contactor operation (0.05 to 5.00 mm, preferably 0.1 to 1.0 mm). The ground vegetal matrix is then soaked at ambient temperature with either fresh water or an aqueous liquid extract coming out from the same first extraction step, with a liquid / solid mass ratio in the range 2 to 10, depending on the moisture adsorption characteristics of the specific vegetal matrix. This soaking step is aimed at obtaining a completely wet vegetal matrix, where the liquid phase is present in the whole porosity of the solid phase. Soaking is essential when countercurrent intensified extractors are used, in order to avoid the loss of the countercurrent flow regime and the worsening of the global ratio (mass of liquid extractant / mass of solid matrix), whereas carrying out soaking with liquid extract is much less important for co-current intensified extractors. For the sake of simplicity of the drawing, such preparatory operations have not been explicitly shown.

[0050] The ground and soaked vegetal matrix is then fed to intensified solid-liquid extraction system 11, where cold water (1°C - 20°C, preferably 1°C - 10°C) is used as liquid extractant, with a liquid / solid mass ratio in the range 1 to 30, preferably 1 to 10. The permanence time of the vegetal matrix in the extraction system, or contact time between the liquid extractant phase and the vegetal matrix to be processed, in case of intensified extraction systems such as the ones used herein, is usually in the range 10 seconds to 10 minutes, preferably in the range 30 seconds to 2 minutes. Increasing the contact time would not result in a yield increase, because extraction is completed in that time interval given the intensities of the turbulence, the shear stress and the cavitation. On the contrary, such an increase would entail the risk of degradation: cracking of the extracted molecules and oxidation of the antioxidant fraction extracted due to the action of the OH+radicals that are generated in an aqueous environment in systems where a controlled cavitation is generated,

[0051] It is to be appreciated that, in case of initial soaking with the aqueous liquid extract, a first extraction (in case of batch operation) or a first extraction period (in case of continuous operation) is devoted to the obtention of the amount of liquid extract to be used for the initial soaking. After soaking, the process goes on by using the portion of liquid extract to be devoted to the soaking in closed cycle (extraction - soaking, extraction - soaking. . .).

[0052] Of course, such a portion is not lost, since it enters again the extractor together with the soaked solid phase.

[0053] The aqueous liquid extract coming out from extraction system 11 is fed to a filtration and concentration system 12 (a multiple effect vacuum evaporator or a membrane concentration system) in order to remove part of the liquid and is then fed to a drying system 13 (a plate or drum or spray drier or an equivalent drier), giving a product consisting of a powdered extract with a final moisture content < 5% by weight and containing dietary fibres and water-soluble polyphenols (antioxidants). In case drier 13 is a spray drier, the addition of maltodextrins may be necessary to prevent problems of flowability on the concentrate liquid extract fed by concentration system 12 to drier 13.

[0054] Before being fed to the second extraction step, the solid residue coming out from extraction system 11 is mechanically squeezed. Squeezing is an essential operation since such a residue is impregnated with liquid extract, namely liquid extractant plus microcomponents with high nutraceutical value that otherwise would be lost. Depending on the kind of extraction system 11, the step of squeezing the solid residue can be carried out by a press that ss part of the same system and recirculates the liquid phase coming out from the squeezing section to extractor 11. The liquid resulting from squeezing will be added to the liquid extract resulting from the extraction in case of a co-current extraction system, whereas in case of a countercurrent extraction system it will be added to the flow of liquid extractant to prevent deteriorating the countercurrent process configuration and reducing yields.

[0055] In the second extraction step, the squeezed solid residue is soaked at ambient temperature with the liquid extract coming out from this second extraction step, with the same modalities and for the same aim as disclosed in connection with the first step. For the second step too, the soaking of the solid phase has not been explicitly shown for the sake of simplicity of the drawing.

[0056] In intensified extraction system 21 of the second extraction step a hydroalcoholic ethanol solution (with EtOH / FFO mass ratio ranging from 4 / 96 up to 96 / 4, preferably from 20 / 80 up to 80 / 20) at ambient temperature (in the range 10°C to 35°C, preferably in the range 10°C to 25°C), with a liquid / solid mass ratio in the range 1 to 30, preferably in the range 1 to 10, is used as liquid extractant. Like the aqueous liquid extract coming out from the first extraction step, the hydroalcoholic liquid extract coming out from extraction system 21 is sent to a filtration and concentration system 22 and thereafter to a drying system 23 supplying a powdered extract with final moisture content < 5% by weight, containing the polyphenol fraction non soluble in water. In this case, addition of maltodextrin to the concentrate liquid extract provided by concentration system 22 is not necessary.

[0057] In the third extraction step, similarly to what has been described in connection with the first and the second extraction steps, the squeezed solid residue coming out from the second step is soaked at ambient temperature with liquid extract coming out from the same third extraction step. In this case too, this soaking of the solid phase has not been explicitly shown in the figure for the sake of simplicity of the drawing. Thereafter, the soaked solid phase is fed to intensified solid-liquid extraction system 31 that uses as liquid extractant hot water at a temperature in the range 45°C to 75°C, preferably in the range 50°C to 65°C, with a liquid / solid mass ratio in the range 1 to 30, preferably in the range 1 to 10.

[0058] The aqueous liquid extract coming out from extraction system 31 is sent to a pH shift vessel 34 (e.g. an agitated cylindrical drum with vertical axis), where aqueous acid solutions are fed in order to reduce pH down to the isoelectric point (e.g. pH in the range 2,5 to 3,5), so as to obtain the precipitation of the protein fraction. The obtained suspension undergoes a centrifugation step and then it is fed to a drying system 33 that provides a powdered extract with final moisture content < 5% by weight, containing vegan proteins. Drying may require addition of maltodextrins for the same reasons stated for the aqueous liquid extract coming out from extraction system 11.

[0059] Intensified solid-liquid extraction systems 11, 21, 31 can be three separate apparatuses or they can be made by a single apparatus performing the three extraction is successive times and equipped with separate tanks for collecting the liquid extract and the dry solid extract produced in each extraction.

[0060] For implementing the process according to the invention, the apparatus(es) implementing extraction systems 11, 21, 31 must ensure turbulence and / or shear stress and / or hydrodynamic cavitation levels exceeding certain minimum levels, more particularly:

[0061] - turbulence: rotational Reynolds number Re > 300,000, preferably > 500,000;

[0062] - shear stress: shear rate y > 5,000 s'1, preferably > 7,500 s'1;

[0063] - hydrodynamic cavitation: cavitation number Ca < 0.95, preferably < 0.85; where Re, y and Ca are given by relations

[0064] - Re = (p N D2) / p, (#);

[0065] - y = (N-7TD) / T, (S'1);

[0066] - Ca = (P-Pv) / (0,5 p v2), (s'1); respectively, in which p = fluid density, N = rotation speed of the rotor in case of a rotorstator extraction system, D = rotor diameter, r = rotor-stator gap, P = fluid pressure, Pv= fluid vapour pressure, v = velocity of the fluid in the rotor-stator gap.

[0067] Examples of systems meeting those requirements are:

[0068] - TURBEX, commercialised by company Adritz AG, Graz (Austria);

[0069] - APV Cavitator, commercialised by company SPX FLOW Inc, Charlotte (North Carolina, USA);

[0070] - CAVSYS CAVITATOR, commercialised by company CAVITATOR SYSTEMS GmbH, Dresden (Federal Republic of Germany)

[0071] - ROTOCAV, commercialised by company E-PIC S.r.l., Mongrando (BI, Italy).

[0072] Among such systems, only TURBEX system, which is the subject matter of patent application WO 2018 / 146647 Al mentioned above, is a countercurrent multistage intensified extractor operating in, whereas the other ones are co-current systems.

[0073] In a second embodiment of the invention, depicted in Fig. 2, an alkaline soaking step (block 35) is provided between the second and the third extraction steps. For this operation the squeezed solid residue coming out from the second extraction step is soaked at ambient temperature with an aqueous solution 0,005 to 0,5 M, preferably 0,05 to 0,1 M, of NaOH or an aqueous solution 0,005 to 0,5 M, preferably 0,05 to 0,1 M, of KOH or another equivalent alkaline aqueous solution. By way of example, KOH has been indicated as soaking liquid in the Figure. Similarly to the soaking with liquid extract, alkaline soaking uses a liquid / solid mass ratio in the range 2 to 10, depending on the moisture adsorption characteristics of the specific vegetal matrix. This soaking step is aimed at causing cleavage of lignin-carbohydrates / oligosaccharides / dietary fibres and lignin / proteins complexes by alkaline hydrolysis. Moreover, like the soaking steps disclosed in connection with the first embodiment, it allows obtaining a completely wet solid phase, where the liquid phase is present in the whole porosity of the solid phase. Thereafter, the soaked solid phase is fed to extraction system 31 for the third extraction step, which operates in the manner disclosed with reference to the first embodiment. The supernatant liquid phase of the protein centrifugation carried out in block 34 is fed to a precipitation vessel 44 (an agitated cylindrical drum with vertical axis), into which a FhO-ethanol mixture (with mass ratio ranging from 20 / 80 to 0 / 100, preferably from 5 / 95 to 0 / 100) is fed to cause insolubilisation and precipitation of carbohydrates / oligosaccharides / dietary fibres. The slurry resulting from the precipitation is submitted to a centrifugation step and then to a final drying step in a drier 43 so as to obtain a powdered extract with a final moisture content < 5% by weight, containing the dietary fibres that have not been extracted in the first step.

[0074] This second embodiment, thanks to the use of alkaline soaking and to the hydrolysis of the lignin-carbohydrates / oligosaccharides / dietary fibres bonds and the lignin / proteins bonds it causes, allows a practically complete extraction of the protein fraction as well as of the dietary fibre fraction that has not been extracted in the first step.

[0075] Figs. 3 to 5 show the application of the first embodiment of the invention to the valorisation of spent tea leaves, olive leaves and grape pomace, and Figs. 6 and 7 show the application of the second embodiment of the invention to the valorisation of brewer’s spent grain and spent coffee ground. The vegetal matrix processed is denoted by the respective acronym (STL, OL, GP, BSG and SCG). In these figures, the operative parameters (ratio between the constituents of the hydroalcoholic solution, alkaline solution concentration, liquid / solid mass ratios L / S, temperatures T, processing times t, pH) used in the different cases are indicated and, moreover, the filtration and concentration type and the drying type have been more precisely indicated. The numerical values indicated in blocks 11, 21, 31 refer to an extraction carried out by means of a system TURBEX EX30. The dry solid extracts produced with the different extraction steps and with the alkaline soaking, the composition of which depends on the processed matrix, are indicated as main categories, like in Figs. 1 and 2. On the other hand, the compounds of the different categories, for the vegetal matrices considered in the examples, are well known to the skilled in the art.

[0076] The figures are self-explanatory in view of the preceding description and they do not need further explanations. The above description makes clearly apparent that the invention solves the problems of the prior art, since it allows reusing all substances present in wastes and by-products and reusable for nutraceutical purposes. Moreover, for the processing, the process uses substances (ethanol and possibly alkaline hydroxides) well compatible with a green chemistry.

[0077] It is clear that the above description has been given only by way of non-limiting example and that changes and modifications are possible without departing from the scope of the invention as disclosed in the appended claims.

Claims

Claims1. Process of valorisation of agro-food wastes and / or by-products, wherein a solid raw material to be processed is submitted to a sequence of solid-liquid extraction steps arranged to produce solid extracts of nutraceutical substances, wherein said sequence of extraction steps includes three solid-liquid extraction steps in a first of which extraction is carried out with cold water, in a second with a hydroalcoholic solution and in a third with hot water, and the liquid extract obtained in each step is processed for obtaining:- a dry solid extract containing dietary fibres and water-soluble polyphenols;- a dry solid extract rich in water-insoluble polyphenols; and- a dry solid extract rich in vegan proteins; wherein the processing of the liquid extracts obtained in the first and second steps includes a filtration and concentration step, and the processing of the liquid extract obtained in the third step includes a precipitation step followed by a centrifugation step, and wherein the filtration step and the concentration step and the centrifugation step, respectively, are followed by a drying step.

2. Process according to claim 1, wherein the extraction steps are carried out in systems with phase contact intensification arranged to ensure turbulence and / or shear stress and / or cavitation levels exceeding:- rotational Reynolds number Re > 300,000, preferably > 500,000;- shear rate y > 5,000 s'1, preferably > 7,500 s'1:- cavitation number Ca < 0.95, preferably < 0.85.

3. Process according to claim 1 or 2, wherein the processing of the liquid extract obtained in the third step includes a precipitation step with pH shift down to the isoelectric point followed by the centrifugation step.

4. Process according to claim 1 or 2 or 3, wherein the filtration and concentration step and the centrifugation step are followed by a respective drying step in order to obtain a dry solid extract with a final moisture content < 5% by weight.

5. Process according to any preceding claim, wherein the solid residues coming out from the first and second extraction steps are squeezed to recover extracted microcomponents with high nutraceutical value present in a liquid phase soaking the solid residue.

6. Process according to any preceding claim, wherein- cold water used as liquid extractant in the first extraction step is at a temperature in therange 1°C to 20°C, preferably in the range 1°C to 10°C, and the liquid / solid mass ratio is in the range 1 to 30, preferably in the range 1 to 10;- the hydroalcoholic solution used as liquid extractant in the second extraction step is an hydroalcoholic solution of ethanol with EtOH / JLO mass ratio in the range 4 / 96 to 96 / 4, preferably in the range 20 / 80 to 80 / 20, and is at ambient temperature, preferably in the range 10°C to 35°C and more preferably in the range 10°C to 25°C;- hot water used as liquid extractant in the third extraction step is at a temperature in the range 45°C to 75°C, preferably in the range 50°C to 65°C.

7. Process according to any preceding claim, wherein the mass ratio between liquid extractant and processed solid in the three extraction steps is in the range 1 to 30, preferably in the range 1 to 10, and the contact time between liquid extractant and processed solid is in the range 10 s to 10 min, preferably in the range 30 s to 2 min.

8. Process according to any preceding claim, including, before extraction, a soaking step in which the solid material to be submitted to the extraction is soaked with a liquid with such a liquid / solid mass ratio that a completely wet material is obtained where the liquid phase is present in the whole porosity of the solid phase, such a soaking being carried out with either fresh water or an aqueous liquid extract coming out from the first extraction step in the case of the raw material, and with liquid extracts coming out from the second and third extraction steps, respectively, in the case of the solid residues to be submitted to such extraction steps.

9. Process according to any of claims 1 to 7, including:- before the extraction in the first and second steps, a soaking step in which the solid material to be submitted to the extraction is soaked with a liquid with such a liquid / solid mass ratio that a completely wet material is obtained where the liquid phase is present in the whole porosity of the solid phase, such a soaking being carried out with either fresh water or an aqueous liquid extract coming out from the first extraction step in the case of the raw material, and with a liquid extract coming out from the second extraction step in the case of the solid residue generated by the first extraction step; and- before the extraction in the third step, a soaking step in which the solid residue generated by the second extraction step is soaked with an aqueous solution of an alkaline compound, with such a liquid / solid mass ratio that a completely wet solid material is obtained where the liquid phase is present in the whole porosity of the solid phase.

10. Process according to claim 9, wherein a supernatant liquid phase resulting from the centrifugation of the liquid extract coming out from the third extraction step is processedwith a hydroalcoholic solution to cause insolubilisation and precipitation of carbohydrates, oligosaccharides and dietary fibres, and the thus obtained precipitate is submitted to a centrifugation step followed by a drying step in order to obtain a dry solid extract rich in dietary fibres.

11. Process according to claim 10, wherein the drying following the centrifugation of the precipitate results in obtaining a dry solid extract rich in dietary fibres with a moisture content < 5% by weight.

12. Process according to claim 9 or 10, wherein the hydroalcoholic solution is an FhO / ethanol solution with EtOH / lhO mass ratio in the range 20 / 80 to 0 / 100, preferably in the range 5 / 95 to 0 / 100, and a concentration in the range 0.005 to 0.5 M, preferably in the range 0.05 to 0.1 M.

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