Method and device for desalinating a salted food product using an electrodialysis process

Abstract

The present invention relates to a method for desalinating a salted food product using electrodialysis, which comprises: - arranging in series multiple compartments (1, 2, 3, 4) that form a device for electrodialysis in such a way that the first compartment contains a positive electrode and the final compartment contains a negative electrode, the compartments being connected in series by connecting means, wherein the connecting means (5, 6, 7) comprise ion-separating means (10, 11, 12), - introducing a piece of food product (14) to be desalinated into a diluate (2), - applying an electric field between the two electrodes, such that an electrodialysis operation is carried out, by means of which a desalinated solution is obtained in the second compartment (2). The invention also relates to a device for carrying out the method.

Description

[0001] PROCEDURE AND DEVICE FOR DESALTING A SALTED FOOD PRODUCT BY AN ELECTRODIALYSIS PROCESS

[0002] DESCRIPTION

[0003] FIELD OF INVENTION

[0004] The present invention relates to a method for desalting a food product that comprises applying an electric field to a container, which will cause and allow the movement of the sodium ions contained in the product towards the cathode, and the movement of the chloride ions towards the anode, leaving the piece desalted, considerably shortening the desalting time, compared to other more common methods.

[0005] It also relates to a device for desalting a food product according to the method of the invention.

[0006] STATE OF THE PRIOR ART

[0007] Currently, several methods are used in the food industry for desalting salted food products. The most widely used is the immersion method, for example, involving salted cod pieces in vats containing refrigerated water at 5°C. This water is periodically replaced, every 6 to 8 hours, until the product reaches the desired salt content after 36 to 56 hours, depending on the type of cod and the desired salt content.In the patent registry we can also find ES2192459A - which discloses a method for desalting that uses a continuous supply of water, in conjunction with easy and quick to control stirring means, which treats the product in a homogeneous way, precisely reducing the salt content and practically maintaining the quality attributes, both in terms of the texture of the desalted cod and its gelatin content, and a reduction in desalting time by 18% compared to the conventional discontinuous desalting system (immersion method). Magnússon et al. (2006) describe a process to achieve a salt content of 1% in the final product, using a fillet:water ratio of 1:5, desalted under refrigeration (3°C to 5°C) for 72 hours, with water stirring two or three times a day and with water replacement at 7 and 24 hours.Another similar process talks about a fillet:water ratio of 1:4, under the same temperature conditions, without stirring, for 94 hours and with a total water change halfway through the process (Erikson et al., 2004). Andrés et al. (2005a) carried out desalting tests using a fillet:water ratio of 1:9, obtaining total mass variations of 26.6±0.3% in fillets with skin and 26.4±0.1% in skinless fillets, after 12 hours of desalting, establishing that under the same process conditions there were no statistically significant differences in the yield obtained in skinless fillets compared to fillets with skin.However, Barat et al. (2004b) in experiments carried out desalting cod with a 1:9 fish:water ratio at 5°C with and without water exchange for 24 hours, showed that the best results were obtained for desalting without water exchange, obtaining a "ready-to-use" product with a NaCl concentration over 3% in the muscle, acceptable for consumption. However, none of the aforementioned methods allows precise control of the variables in the desalting process to significantly shorten desalination times and minimize water consumption.

[0008] Electrodialysis is currently used in the food industry to treat liquids such as wines, to achieve a specific level of demineralization and to stabilize tartaric acid (Corti, SV, & Paladino, SC, 2016). Electrodialysis applications have also been described to reduce the acidity of tropical fruit juices, increasing their use as ingredients in the manufacture of products such as ice cream, beverages, jams, cakes, and cocktails (Sotomayor Grijalva, MC, 2010). It is also used in the food industry to demineralize, deacidify, and desalt excess whey from cheese and butter production, obtaining proteins and high-value by-products such as calcium, making them suitable for direct marketing or for producing dairy-based beverages (Ávila et al., 2000).

[0009] The lack of desalination methods based on electrodialysis applied to solid foods, and the existence of desalination methods for a food product, such as cod, that use significant amounts of water and long desalination times, has generated the need for a procedure for the treatment of solid foods that contain significant amounts of salt and also have a notable porosity in their structure. A method of these characteristics, applied to a salted food product, such as salted cod, can allow for the use of smaller amounts of water and significantly reduce the time required for the processes mentioned in this section.

[0010] DESCRIPTION OF THE INVENTION

[0011] The present invention is based on the application of the electrodialysis technique to desalt a salted food product, especially a solid salted food product, and preferably pieces of salted cod.The present invention relates to a desalination process based on the electrodialysis technique, which is an electrochemical separation process that allows the salt dissolved in water to be moved to another solution, using electrical energy in the form of direct current (DC) applied between two electrodes, one called the cathode (negative electrode) (8) where the water reduction reaction to hydrogen mainly occurs, and another called the anode (positive electrode) (9) where the water oxidation process to oxygen mainly occurs, and where, through ion separation means, preferably selective ion exchange membranes (10,11,12), the anions and cations present in the salt dissolved in water (DILUTED) (2) are transported towards the CONCENTRATED compartment (3) and towards the CATHOLYTE (1), leaving an unaligned solution.

[0012] The present invention relates firstly to a process for desalting a salted food product by electrodialysis, comprising:

[0013] - having in a first compartment (1) a device suitable for electrodialysis, a first solution of at least one salt and / or an inorganic acid, compatible with food use, with a first electrode immersed in said solution,

[0014] - placing in a second compartment (2) of the device one or more pieces of salted food product (14) in water,

[0015] - place in a third compartment (3) a second sodium chloride solution,

[0016] - placing in a fourth compartment (4) of the device a third solution of an inorganic anion compatible with food use, preferably sulfate, and of hydroxide whose cation is compatible with food use, preferably sodium hydroxide, with a second electrode immersed in said second solution,

[0017] - the compartments being connected in series by connecting means, such that ion separation means (10,11,12) are arranged in the connecting means (5,6,7),

[0018] - introduce the piece of food product to be desalted (14) into the compartment called DILUTED (2),

[0019] - applying an electric field between the two electrodes of said device by means of a current source (13), such that an electrodialysis operation is carried out, by means of which oxidation of water to oxygen occurs at the anode (9), the anions and cations present in the salt dissolved in the water of the second compartment (2), which come from the piece of salted food product, travel through the separation means (10,11) towards the third compartment (3) and the compartment (1) leaving a misaligned solution in the second compartment (2).

[0020] The first compartment is also called CATHOLITE (1).

[0021] The second compartment is also called DILUTED (2).

[0022] The third compartment is also called CONCENTRATE (3). The fourth compartment is also called ANOLYTE (4).

[0023] The pieces of food product (14) that are arranged in a second compartment (2) of the device are placed in the DILUTE (2) with a controlled amount of water.

[0024] Desalting time varies depending on several factors, such as: the size of the food product, its thickness, and the percentage or degree of desalting required for a culinary application.

[0025] The food product may be any salted, solid food product, and in particular, may be selected from: salted bacon, seafood sausages, seaweed, anchovies, sardines, herring, oversalted olives, and cod, and preferably cod.

[0026] The electric field can be applied in two ways: by circulating a controlled current or by applying a constant potential difference between the electrodes.

[0027] The value of the current intensity that is circulated is between 0.1 and 200 mA / cm 2 , preferably between 1 and 50 mA / cm 2 .

[0028] The value of the potential difference between the electrodes can be between 5 and 50 volts.

[0029] For the device to start operating, an electric field is established between the electrodes (positive or anode (9) and negative or cathode (8)), which causes the cations (positive ions), present in the DILUTED (2), to be transported towards the cathode (8) and the anions (negative ions), present in the DILUTED (2), to be transported towards the anode (9). The configuration of the ion separation means (10,11,12), preferably ionic membranes, causes the ions to migrate from the DILUTE solution (2) causing the solution in the DILUTE (2) to lose salinity and the food product to also be desalinated by forcing the chloride and sodium ions out of the food product into the solution and the subsequent migration of the chloride ions to the CONCENTRATE compartment (3) through the ion separation means (11) and of the sodium ions to the CATHOLYTE compartment (1) through the ion separation means (10).In this process, the solution of the CONCENTRATE (3) simultaneously gains salinity. Furthermore, it should be noted that, on the surface of the electrodes, oxygen will form (at the anode or positive electrode) (9) and hydrogen will form (at the cathode or negative electrode) (8). Given the low value of the current density that is circulated, the amount of gases generated is very low and does not pose any significant risk in the handling of the device.

[0030] The fact of establishing a potential difference between the electrodes will cause the common salt, which covers and is inside the food product, especially cod (14), to accelerate its passage into the water, since the chloride ions (anions present in the salt) are directed towards the anode (9) through the ion separation medium, preferably an anion exchange membrane (11) and the sodium ions (cations present in the salt) are directed towards the cathode (8) through the ion separation medium, preferably a cation exchange membrane (10).The way of operating the device will involve setting a potential difference between the positive (9) and negative (8) electrodes, so that the current that will circulate can vary over time, or a certain current passage can be set between the positive (9) and negative (8) electrodes, so that the potential difference to be applied between the electrodes can vary in order to maintain that fixed current passage. In both cases, a current circulation will occur between the electrodes, forcing the migration of the ions present in the different solutions that are arranged between the positive and negative electrodes. The final result is that the piece of food product, especially cod, loses salt that also passes to another aqueous stream that is not in contact with the food product.Since the potential difference applied between the electrodes circulates a direct electric current, the circulation time and current intensity are related to the amount of salt removed from the part, thus allowing the desired degree of desalting to be established. The nature and low value of the circulating current do not alter the quality of the desalted product.

[0031] The present invention also relates to a device for carrying out the procedure defined above, by means of electrodialysis, comprising:

[0032] - at least 4 compartments (1,2,3,4) connected in series by means of a connecting means between each pair of compartments (5,6,7):

[0033] - a first compartment (1) for housing a solution of at least one salt and / or inorganic acid compatible with food use, with a first electrode (8) immersed in said solution, said first compartment (1) being connected by a first connecting means (5) to

[0034] - a second compartment (2) for housing one or more pieces of salted food product (14) suspended in water, connected by a second connecting means (6) to

[0035] - a third compartment (3) for housing a solution of at least one inorganic salt compatible with food use, connected by a third connecting means (7) to

[0036] - a fourth compartment (4) to house a solution of at least one inorganic salt compatible with food use (preferably sodium sulphate) and a hydroxide whose cation is compatible with food use (preferably sodium hydroxide),

[0037] - the first (8) and second electrode (9) being connected by an electrical connection,

[0038] - ion separation means (10,11,12) arranged inside each of the joining means (5,6,7),

[0039] - a connection to external means for generating electric current (13) between the two electrodes (8,9). In the device of the invention there may be more than one of any of the four types of compartments. The compartments may be named as indicated in the section relating to the method.

[0040] According to particular embodiments, in the device of the invention there may be a CATHOLYTE (1), an ANOLYTE (4), more than one CONCENTRATE (3) and more than one DILUTE (2).

[0041] The connecting means arranged between each pair of compartments may be a thread, a clamping joint or a clamp.

[0042] The salt and / or inorganic acid compatible with food use can be, for example, sodium chloride, hydrochloric acid, sulfuric acid, and are preferably sodium chloride and hydrochloric acid.

[0043] According to particular embodiments, the first solution of at least one salt and / or inorganic acid compatible with food use has a concentration between 0.05M and 1M, preferably between 0.050M and 0.1M, and more preferably 0.1M.

[0044] In the event that there is more than one salt, more than one acid, or combinations of them in the solution in compartment (1), each of the salts or acids may be at a different concentration.

[0045] According to particular embodiments, the solution in the hydrochloric acid compartment (1) has a concentration between 0.05M and 1M, preferably 0.1M.

[0046] According to particular embodiments, the solution in the compartment (1) of sodium chloride and hydrochloric acid has a concentration between 0.05M and 1M, preferably 0.1M. The concentration of both substances may be the same or different.

[0047] According to particular embodiments, the first electrode (8) is an electrode connected to the negative pole of the current source (13). Said electrode can be made of various materials, such as graphite, platinized titanium and any solid metal (aluminum, copper, nickel, iron, zinc, titanium, among others) or alloys (stainless steel, carbon steel, bronze, aluminum alloys, bismuth / tin, among others),

[0048] According to particular embodiments, the second electrode (9) is an electrode connected to the positive pole of the current source (13). Said electrode can be made of various materials such that said materials are not susceptible to corrosion or this occurs to a very low extent, such as carbon, graphite, platinized titanium, boron-doped diamond (BDD), oxygen dimensionally stable anode (oxygen DSA), among others.

[0049] The means of ion separation are ionic membranes (10,11,12).

[0050] According to particular embodiments, the membranes are ion exchange membranes, such that two of them are cationic membranes and one of them is anionic.

[0051] The cationic and anionic membranes are always arranged alternately. In particular, the first cationic membrane (10) is arranged in the junction means (5) arranged between the first compartment (1) and the second compartment (2), and the second cationic membrane (12) is arranged in the junction means (7) arranged between the third compartment (3) and the fourth compartment (4).

[0052] According to a particular embodiment, the device comprises, as illustrated in Figure 1, from left to right:

[0053] - 4 compartments in series (1,2,3,4), joined by 3 connecting threads (5,6,7) between each two compartments:

[0054] - a compartment (CATHOLITE) (1) containing a solution containing 0.1 M sodium chloride and / or 0.1 M hydrochloric acid and in which a graphite electrode (8) is immersed, which is the negative electrode,

[0055] - a second compartment (DILUTED (2)) to hold inside one or more pieces of food product (14), especially salted cod together with a quantity of distilled water,

[0056] - a third compartment (CONCENTRATE (3)) to hold 0.1M sodium chloride, which has sufficient electrical conductivity to prevent the current intensity from being too low at the start of the process, and

[0057] - a fourth compartment (ANOLYTE (4)) for housing a graphite electrode (9) which is the positive electrode immersed in a solution containing 0.1 M sodium sulphate and / or 0.1 M sodium hydroxide,

[0058] - a set of ion exchange membranes, arranged between the two electrodes, such that two membranes are cationic (10 and 12) and one membrane is anionic (11)), and are arranged within the threaded unions (5,6,7), which separate the different compartments (1,2,3,4), so that they are alternated, with the anionic membrane between the two cationic membranes.

[0059] BRIEF DESCRIPTION OF THE FIGURES

[0060] To complement the description being made and in order to help better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which the following has been represented for illustrative and non-limiting purposes:

[0061] Figure 1. - Diagram of a front view of the device of the invention with its numbered components.

[0062] Figure 2.- Schematic of a detailed view of the system's operation. DETAILED EXPOSURE OF IMPLEMENTATION MODES

[0063] The example shown below refers to cod (14), but can be applied to any other salted food product. The introduction of a piece of salted cod (14) into the DILUTE compartment (2) allows a salted food product to be desalted using a quantity of water that is normally lower than that used in conventional processes and in a much shorter time. Furthermore, the method of the invention allows the desalination time to be selected, which is directly related to the percentage or degree of desalination that is to be achieved for the desired culinary application.

[0064] The operation of this device is based on applying a potential difference between the two electrodes (positive (9) and negative (8)). When we apply an electric field, the sodium ions found in the salted cod compartment (DILUTED) represented as (2) in a generic way in figure 2, migrate through the cationic membrane (MIC) represented as (10) in a generic way in figure 2 and enter the CATHOLYTE represented as (1) in a generic way in figure 2, replacing each proton that is lost in the process of reduction of water to hydrogen, thus maintaining ionic electroneutrality within the CATHOLYTE (1), since the chlorides remain stable by not being able to escape through the cationic membrane, MIC, (10).Likewise, we also force the chloride ions (-) from compartment (2) containing the salted cod (14) to exit through the anionic membrane, MIA, represented generically as (11) in Figure 2, towards the CONCENTRATE represented generically as (3) in Figure 2, where we initially had sodium chloride, thus increasing its content. In the ANOLYTE represented generically as (4) in Figure 2, where the oxidation reaction of water to oxygen takes place, the migration of sodium ions also occurs, crossing the cationic membrane, MIC, represented generically as (12) in Figure 2, towards the CONCENTRATE compartment (3). Therefore, the NaCl content in (3) increases. In this way we manage to desalinate the cod and move part of its salt to other compartments of the system (1 and 3).

[0065] EXAMPLE 1:

[0066] In this example we fill the compartments from left to right illustrated in figure 2 as (1,2,3,4), with 150 mL of 0.1 M hydrochloric acid in the CATHOLYTE (1), in the DILUTE (2) we place the cod sample (14) of 2 to 2.5 g with 50 mL of distilled water, in the CONCENTRATE (3) with 50 mL of 0.1 M NaCI and in the ANOLYTE (4) with 150 mL of 0.1 M NaOH. A controlled current intensity of 100 mA is imposed for a time of 120 minutes to achieve a degree of desalination of 96% on the initial salt content of the cod piece.

[0067] RESULTS: Starting initially with a total sodium chloride content in the salted cod sample of 0.508 grams, and imposing a controlled current intensity of 100 mA for 120 minutes, we obtain the following results:

[0068] In the CATHOLYTE (1) a content of 0.890 grams of sodium chloride is determined, in the DILUTED (2) 0.152 grams of sodium chloride are determined, in the CONCENTRATE (3) 0.716 g of sodium chloride and in the ANOLYTE (4) 0.004 g of sodium chloride. And in the sample of cod that has been subjected to the electrodialysis process, a total content in the piece of 0.022 grams of sodium chloride is detected. These data imply that a percentage of desalination has been achieved, in the piece of salted cod, after subjecting it to the process described of 96% on the initial salt content of the piece of cod.

[0069] EXAMPLE 2:

[0070] In this example we fill the compartments from left to right illustrated in figure 2 as (1,2,3,4), with 30 mL of 0.1 M hydrochloric acid + 120 mL of 0.1 M NaCl in the CATHOLYTE (1), in the DILUTE (2) the cod sample (14) of 2 to 2.5 g in 50 mL of distilled water is introduced, in the CONCENTRATE (3) 50 mL of 0.1 M NaCl are introduced and in the ANOLYTE (4) 120 mL of 0.1 M Na2 SO4 + 30 mL of 0.1 M NaOH. A controlled potential difference of 15 V is imposed for a time of 60 minutes to achieve a degree of desalination of 66 on the initial salt content of the cod piece.

[0071] RESULTS: Starting initially with a total sodium chloride content in the salted cod sample of 0.446 grams, and imposing a controlled potential difference of 15V, for a period of 60 minutes, we obtain the following results:

[0072] In the CATHOLITE (1) a content of 0.841 grams of sodium chloride is determined, in the DILUTE (2) 0.239 grams of sodium chloride, in the CONCENTRATE (3) 0.332 grams of sodium chloride and in the ANOLYTE (4) 0.03 grams of sodium chloride. And in the cod sample after subjecting it to the electrodialysis process, 0.150 grams of sodium chloride are detected. These data imply that a percentage of desalination has been achieved in the salted cod piece after subjecting it to the process described of 66% on the initial salt content of the cod piece.

Claims

CLAIMS 1. A method for desalting a salted food product by electrodialysis, comprising: - having in a first compartment (1) of a device for electrodialysis, a first solution of at least one salt and / or an inorganic acid, compatible with food use, with a first electrode immersed in said solution, - placing in a second compartment (2) of the device one or more pieces of salted food product (14) in water, - place in a third compartment (3) a second sodium chloride solution, - placing in a fourth compartment (4) of the device a third solution of an inorganic anion compatible with food use and a hydroxide whose cation is compatible with food use, preferably sodium hydroxide, with a second electrode immersed in said second solution, - the compartments being connected in series by connecting means, such that ion separation means (10,11,12) are arranged in the connecting means (5,6,7), - introduce the piece of food product to be desalted (14) into the compartment called DILUTED (2), - applying an electric field between the two electrodes of said device by means of a current source (13), such that an electrodialysis operation is carried out, by means of which oxidation of water to oxygen occurs at the anode (9), the anions and cations present in the salt dissolved in the water of the second compartment (2), which come from the piece of salted food product (14), travel through the separation means (10,11) towards the third compartment (3) and the compartment (1) leaving a misaligned solution in the second compartment (2).

2. The method according to claim 1, wherein the food product is selected from: salted bacon, seafood sausages, seaweed, anchovies, sardines, herring, oversalted olives and cod, and is preferably cod.

3. The method according to claim 1, wherein the application of the electric field is carried out: by circulating a controlled current or by applying a constant potential difference between the electrodes.

4. The method according to claim 1, wherein a current with an intensity between 0.1 and 200 mA / cm is passed between the electrodes. 2 , preferably between 1 and 50 mA / cm 2 .

5. The method according to claim 1, wherein a potential difference between the electrodes of between 5 and 50 volts is applied.

6. The method according to claim 1, wherein the ion separation means (10,11,12) are ionic membranes.

7. A device for carrying out the method defined in one of claims 1 to 6, by electrodialysis, comprising: - at least 4 compartments (1,2,3,4) connected in series by means of a connecting means between each pair of compartments (5,6,7): - a first compartment (1) for housing a solution of at least one salt and / or an inorganic acid compatible with food use, with a first electrode (8) immersed in said solution, said first compartment (1) being connected by a first connecting means (5) to - a second compartment (2) for housing one or more pieces of salted food product (14) suspended in water, connected by a second connecting means (6) to - a third compartment (3) for housing a solution of at least one inorganic salt compatible with food use, connected by a third connecting means (7) to - a fourth compartment (4) for housing a solution of at least one inorganic salt compatible with food use, and a hydroxide whose cation is compatible with food use, - the first (8) and second electrode (9) being connected by an electrical connection, - ion separation means (10,11,12) arranged inside each of the joining means (5,6,7), - a connection to external means for generating electric current (13) between the two electrodes (8,9).

8. The device according to claim 7, wherein the connecting means arranged between each pair of compartments is selected from a thread, a clamping joint and a clamp.

9. The device according to claim 7, comprising more than one third compartment and more than one second compartment.

10. The device according to claim 7, wherein the salt and / or inorganic acid compatible with food use are selected from sodium chloride, hydrochloric acid, sulfuric acid.

11. The device according to claim 7, wherein the first solution has a concentration between 0.05M and 1M, preferably between 0.051M and 0.1M, and more preferably 0.1M.

12. The device according to claim 7, wherein the compartment (1) comprises more than one salt, more than one acid, or combinations thereof and each of the salts or acids is present in a different concentration.

13. The device according to claim 7, wherein the compartment (1) comprises sodium chloride and hydrochloric acid in a concentration between 0.05M and 1M, preferably 0.1M, selected from the same concentration for both or different.

14. The device according to claim 7, wherein the first electrode (8) is made of a material selected from graphite, platinized titanium, a solid metal and alloys.

15. The device according to claim 14, wherein the first electrode is made of a material selected from aluminum, copper, nickel, iron, zinc, titanium, stainless steel, carbon steel, bronze, aluminum alloys, bismuth / tin alloys.

16. The device according to claim 7, wherein the second electrode is made of a material selected from carbon, graphite, platinized titanium, boron-doped diamond, and oxygen dimensionally stable anode.

17. The device according to claim 7, wherein the ion separation means are ionic membranes (10,11,12), alternating between anionic and cationic membranes.

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