Method for binding of off-flavour compounds in aquaculture systems

Abstract

According to an example aspect of the present invention, there is provided a method for binding of unpleasant off-flavour compounds in aquaculture systems by a cellulose-based material, which is preferably surface-modified with molecules having selective affinity to off-flavour compounds that are present in for example fish farming.

Description

METHOD FOR BINDING OF OFF-FLAVOUR COMPOUNDS IN AQUACULTURESYSTEMSFIELD

[0001] The present invention relates to a method for binding of off-flavour compounds in aquaculture systems by a cellulose-based material.BACKGROUND

[0002] Aquaculture is the fastest growing food-production sector and now farming of aquatic species accounts for 51% of the total world’s production (FAO, 2024). Furthermore, land-based intensive recirculating aquaculture system (RAS) enables reduction in water consumption and nutrient discharge in comparison to open aquaculture such as pond and cage farming. In recent decades, RASs have become increasingly important, although still forming only a fraction of the global fish farming, as they consume less water per kg of fish produced and are an environmentally sustainable means of meeting global food demand. However, certain unwanted flavour compounds (off- flavours) can be formed in RAS due to microbial activity in aquaculture water and biofilms, which easily accumulate in fish muscle tissue. Off-flavour compounds are typically produced as metabolic by-products of certain microbial species such as Cyanobacteria, Actinobacteria, Myxobacteria, and Sorangium.

[0003] The sensory properties of fish vary based on fish species, their physical and chemical properties, feed ingredients, storage conditions, and processing. Off-flavours in fish flesh have been widely documented for, for example in arctic charr Salvelinus alpinus (Houle et al., 2011), Atlantic salmon Salmo salar (Burr et al., 2012), barramundi Lates calcarifer (Percival et al., 2008), largemouth bass Micropterus salmoides. Nile tilapia Oreochromis nilolicus. and rainbow trout Oncorhynchus mykiss (Robertson et al., 2005). The presence of off-flavour in fish flesh is perceived as a quality defect and often disliked by consumers, which can lead to high financial losses in producers’ earnings.

[0004] Off-flavours perceived in fish are often described as musty and earthy flavours and odors that fish consumers find objectionable. These flavours are typicallyinduced by the terpene compounds geosmin (GSM, trans- l,10-dimethyl-trans-9-decalol) and 2-methylisoborneol (MIB, (l-R-exo)-l,2,7,7-tetramethyl-bicyclo [2.2.1] heptan-2-ol). Additionally, a wide variety of other compounds are also known to cause unwanted flavours in fish, such as alcohols, aldehydes, carboxylic acids, pyrazines, and terpenes (Lindholm-Lehto 2022; Mahmoud and Buettner 2017) and dozens of compounds have been identified (Mahmoud and Buettner 2016). Typically, flavour and off-flavour compounds are volatile or semi-volatile compounds with a wide range of solubility in water, ranging from readily soluble (e.g., 1000 g L'1acetoin) to more scarcely soluble (e.g., 11.8mg L'1TCA) (Mahmoud and Buettner 2017).

[0005] Off-flavours are absorbed into the fish via gills, skin, and gastrointestinal tract by lipid-rich tissues, gills being the main path of uptake (Howgate 2004). GSM and MIB are concentrated into the fish flesh until an equilibrium state is reached between the water phase and the fish. Their concentrations in water and the time of exposure are the main factors affecting those in fish flesh (Howgate 2004), but also for example fish species, water temperature, size, and age of fish are of importance (Percival et al., 2008). The exchange of chemicals is assumed to proceed through a passive process, affected by the lipophilic nature of the compounds and the concentration in the aqueous part of fish (Howgate 2004). Once formed, off-flavour compounds are relatively stable against chemical and biological degradation.

[0006] Accumulated off-flavours are typically removed from the fish flesh by depurating the fish in clean water (Burr et al., 2012; Davison et al., 2020). Unfortunately, this often takes from days to weeks, causing economic losses due to delays of harvest and high consumption of clean water (Burr et al., 2012). The required time depends on the initial off-flavour concentrations in fish, process arrangements in depuration, properties of depuration water, water temperature, and the rate of fish metabolism (Davidson et al., 2020; Howgate 2004; Lindholm-Lehto et al., 2019a). The depuration water must be clean and free of off-flavors and the system pre-disinfected (Houle et al., 2011; Lindholm-Lehto et al., 2019a). Depuration increases production costs in RAS due to investments in depuration facilities and equipment and may be difficult in conditions with limited access to high-quality water.

[0007] The fish are not fed during depuration, and the feeding is stopped hours beforehand (typically 48 h before; Podduturi et al., 2021) to ensure the best possible waterquality and depuration results. However, fish often lose weight, and their lipid content decreases (Burr et al., 2012; Lindholm-Lehto et al., 2019a) which can induce unwanted changes in the fatty acid profile of fish (Lindholm-Lehto et al., 2022). Feed cost is a large proportion of total production costs in intensive aquaculture (>50%, Rana et al., 2009; 63%, Arru et al., 2019). It is therefore important to understand feeding efficiency and aim for cost-effectiveness.

[0008] Several methods have been studied and tested to remove off-flavours or decrease their formation in RAS, but so far without a conclusive result. These include oxidizing chemical addition (Lindholm-Lehto et al., 2019a, 2019b), ozonation (Powell and Scolding 2018), advanced oxidation processes (AOPs) (Rurangwa and Verdegem 2015), bacterial degradation (Azaria et al., 2017), ultrasound treatment (Nam-Koong et al., 2016), and adsorption, for example, with activated carbon (Burr et al., 2012). Significant effort has been made to overcome the off-flavour induced challenges and improve the profitability of RAS farming. Despite extensive studies, removal of off-flavors is so far based primarily on purging in fresh water.

[0009] CN107983318B discloses binding of off-flavour compounds by using a ceramic material and polyurethane filler as a solid support. This patent publication does not, however, disclose cellulose-based materials as the solid support.

[0010] CN1 17923592A on the other hand discloses a method for circulating water treatment of a shrimp culture. Chitosan is loaded onto a non-woven fabric to produce the water treatment material. This patent publication does not, however, relate to fish farming nor discloses removal of off-flavour compounds and the use of cyclodextrin in modifying the non-woven fiber.

[0011] Off-flavors are also a challenge in cell-cultured fish manufacturing (Carneiro et al., 2022). Changing environmental conditions in the different stages of cell-cultured fish manufacturing could cause formation of unwanted off-flavor compounds. Unwanted fish-flavors can be attributed to microbial growth, enzymatic action, and environmental conditions. The taste of cell-cultured fish products is sensitive to the non-desired flavor compounds. Thus, there is a need to manage certain off-flavor compounds that are similar to those present in aquaculture applications.

[0012] There is thus a need for a technology establishing a method for minimizing off-flavours, which is suitable in commercial for example RAS farms at a reasonable cost.SUMMARY OF THE INVENTION

[0013] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0014] According to an aspect of the present invention, there is provided a method for binding of off-flavour compounds in aquaculture systems by a cellulose-based material.

[0015] According to a further aspect of the present invention, the cellulose-based material is surface modified with molecules that have selective affinity to certain, in particular lipophilic off-flavour compounds.

[0016] These and other aspects, together with the advantages thereof over known solutions are achieved by the present invention, as hereinafter described and claimed.

[0017] The method of the present invention is mainly characterized by what is stated in the characterizing part of claim 1.

[0018] Considerable advantages are obtained by means of the present invention. The cellulose-based material used in the invention selectively binds off-flavour compounds from circulating water. Off-flavour compounds are formed in the circulating water environment as a result of microbial activity. The compounds accumulate easily to the flesh of the fish and give the fish a muddy or earthy taste and smell, which consumers generally find unpleasant. The purpose is to remove taste defects from the fish, which is currently done by depurating it in clean water before putting the batch of fish on sale. Depuration typically takes from days to weeks, which consumes a lot of water, slows down the sale of the batch and increases production costs. With the help of the present invention, part of the off-flavor compounds formed in the system can be bound as efficiently as possible. This aims to shorten and minimize the depuration time and lower the production costs.

[0019] Next, the present technology will be described more closely with reference to certain embodiments.EMBODIMENTS

[0020] The present technology provides means for binding of off-flavour compounds in aquaculture systems with cellulose-based materials, which have been surface-modified with molecules having selective affinity to certain, in particular lipophilic off-flavour compounds, which are especially present in fish farming.

[0021] FIGURE l is a chart showing the concentration (ng / L) of GSM in tank water during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. In particular, the modified samples Al and A9 are modified by treatment in a solution having a chitosan concentration of 5 g / L, while the modified samples A2 and A8 are first treated in a solution having a chitosan concentration of 5 g / L, and thereafter activated and modified with a solution of cyclodextrin at a concentration of 2.5 mM.

[0022] FIGURE 2 is a chart showing the concentration (ng / L) of MIB in tank water during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material.

[0023] FIGURE 3 is a chart showing the concentration (mg / L) of GSM in water before / after filters during time (measurement days) with A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Before A3,A7”, “After A3,A7”, “Before A2,A8”, “After A2,A8”, “Before A1,A9”, “After A1,A9”

[0024] FIGURE 4 is a chart showing the concentration (mg / L) of MIB in water before / after filters during time (measurement days) with A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Before A3,A7”, “After A3,A7”, “Before A2,A8”, “After A2,A8”, “Before A1,A9”, “After A1,A9”

[0025] FIGURE 5 is a chart showing the concentration (ng / kg) of GSM in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscosematerial, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The sensory threshold of 250 ng / kg (Grimm et al.,2004) has been depicted with a dark line. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0026] FIGURE 6 is a chart showing the concentration (ng / kg) of MIB in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The sensory threshold of 700 ng / kg (Robertson et al.,2005) has been depicted with a dark line. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0027] FIGURE 7 is a chart showing the concentration (ng / kg) of IPMP (2 -isopropyl 3-methoxypyrazine) in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0028] FIGURE 8 is a chart showing the concentration (ng / kg) of methional in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0029] FIGURE 9 is a chart showing the concentration (ng / kg) of hexanal in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0030] FIGURE 10 is a chart showing the concentration (ng / kg) of hexenoic acid in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”.

[0031] FIGURE 11 is a chart showing the concentration (ng / kg) of octanal in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0032] FIGURE 12 is a chart showing the concentration (ng / kg) of octanoic acid in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2,5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”.

[0033] FIGURE 13 is a chart showing the concentration (ng / kg) of acetoin in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0034] FIGURE 14 is a chart showing the concentration (ng / kg) of phenylacetaldehyde in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0035] FIGURE 15 is a chart showing the concentration (ng / kg) of a-terpineol in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”.

[0036] FIGURE 16 is a chart showing the concentration (ng / kg) of TCA (2,4,6- trichloroanisole) in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in thechart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0037] FIGURE 17 is a chart showing the concentration (ng / kg) of vanillin in fish flesh during time (measurement days) with control sample, A3 and A7 reference viscose material, A2 and A8 modified chitosan 5 g / L; cyclodextrin 2.5 mM material, and Al and A9 modified chitosan 5 g / L material. The order of the bars in the chart is the following, when viewed from left to right: “Control”, “A3,A7”, “A2,A8”, “A1,A9”

[0038] FIGURE 18 is a chart showing the concentration (ng / kg) of GSM, MIB, octanoic acid and phenylacetaldehyde in different fiber materials.

[0039] FIGURE 19 is a chart showing the weight (g) of sampled fish during the experiment with different fiber materials, and in the controls without treatment.

[0040] FIGURE 20 is a chart showing the concentrations of geosmin (GSM) in recirculating water (ng / L) and in fabric (ng / kg) comprising citric acid conjugated cyclodextrin (“Citric acid”) and in fabric (ng / kg) comprising chitosan conjugated cyclodextrin (“Cyclodextr”), respectively.

[0041] FIGURE 21 is a chart showing the concentrations of 2-methylisoborneol (MIB) in recirculating water (ng / L) and in fabric (ng / kg) comprising citric acid conjugated cyclodextrin (“Citric acid”) and in fabric (ng / kg) comprising chitosan conjugated cyclodextrin (“Cyclodextr”), respectively.

[0042] The present invention is based on applying a cellulose-based material, which is surface modified with molecules having ability to bind off-flavour compounds, to an aquaculture system.

[0043] More precisely, one aspect of the present invention is a method for binding of off-flavour compounds in aquaculture systems by a cellulose-based material, wherein the method comprises introducing a native plant-based cellulose material or a regenerated cellulose material to an aquaculture system, wherein the cellulose material is surface modified with molecules having both hydrophilic and hydrophobic moiety, and thereby selectively binding off-flavour compounds from the aquaculture system.

[0044] By modifying the cellulose by inclusion of amphiphilic molecules, that is, molecules having both a hydrophilic and a hydrophobic moiety, the capability of thecellulose material to capture off-flavour compounds is improved. Unlike untreated cellulose which mainly has a hydrophilic structure, the modified cellulose surface provides for hydrophilic sites that are capable of interacting with impurities having a hydrophobic structure, which is the case for several off-flavour compounds that can be present in aquaculture systems.

[0045] According to one embodiment of the present invention, the off-flavour compounds are lipophilic, in particular terpene-based, such as geosmin (GSM) and 2- methylisoborneol (MIB).

[0046] Terpene compounds, such as GSM and MIB, can induce off-flavours in fish that often described as musty and earthy flavours and odours that fish consumers find objectionable. By binding such lipophilic off-flavours to the hydrophobic moi eties of the molecules on the surface modified cellulose, the water quality of aquaculture systems can be improved.

[0047] According to one embodiment of the present invention, the cellulose material is surface modified with cyclic oligosaccharide, such as cyclodextrin.

[0048] Cyclic oligosaccharides can provide for both hydrophilic and hydrophilic characteristics. In particular, cyclic oligosaccharides, such as cyclodextrins, have a hydrophilic exterior and a hydrophobic interior. The hydrophobic interior of the cyclic oligosaccharide provides for retention sites capable of capturing lipophilic compounds. Surface modification by introduction of cyclic oligosaccharides onto a cellulose based material can thereby provide a cellulose material with hydrophobic cavities that are capable of selectively or semi -selectively interacting with off-flavour compounds based on their size and lipophilic properties.

[0049] According to one embodiment of the present invention, the molecules having both hydrophilic and hydrophobic moiety are cyclic oligosaccharide molecules that are attached to the cellulose material, or to linker molecules present on the cellulose material, preferably the cyclic oligosaccharide molecules are cyclodextrin molecules. The molecules having both a hydrophilic and a hydrophobic moiety are preferably cyclic polysaccharide molecules. In some preferred embodiments, the molecules having both a hydrophilic and a hydrophobic moiety are cyclodextrin molecules. Cyclic polysaccharides, and in particular cyclodextrins, provide for selective retention sites for many off-flavour compounds, suchas terpene-based off-flavours. The cyclodextrin can be attached to the cellulose material by different mechanisms, such as by forming covalent bonds to the cellulose material, or in particular to linker molecules introduced onto the cellulose material, or by forming crosslinking bonds. These are examples of stable modification mechanisms, by which the functionality of the modified cellulose surface can be maintained for a prolonged period of time, such as several days, when submerged in water.

[0050] According to one embodiment of the present invention, the surface modification comprises providing a cationic charge to a surface of the cellulose material by chitosan adsorption, followed by covalent conjugation of cyclic oligosaccharides, such as cyclodextrins.

[0051] One mechanism for cellulose surface modification includes introduction of chitosan onto the cellulose surface, wherein the chitosan act as linker molecules between the cellulose and the cyclic oligosaccharide. The chitosan modification mechanism can be achieved in a two-step process, wherein the cellulose material is first treated in a chitosan solution to adsorb chitosan on the surface of the cellulose material. The chitosan solution can be provided as an acidic solution, such as in acetic acid buffer solution. Preferably, the pH is below 6, such as 4.5-5.5, without being limited thereto. Such a chitosan treatment introduces cationic charges to the surface of the cellulose material, and enables linkage of a cyclic oligosaccharide compound to the cellulose material. The contact time of the chitosan adsorption step can be, for example, 0.5-2 hours, without being limited thereto. The thus treated cellulose material is preferably washed to remove excess chitosan prior to contacting the cellulose material with the cyclic oligosaccharide.

[0052] In the second step of the above-discussed embodiment, the obtained chitosan treated fabric is contacted with a cyclic oligosaccharide compound, to thereby achieve covalent conjugation of the cyclic oligosaccharide to the cellulose material. In some embodiments, the cyclic oligosaccharide is a cyclodextrin compound, such as carboxylated cyclodextrin. The cyclic oligosaccharide compound can be added in acidic solution, such as acetic acid or MES (2-(N-morpholino)ethanesulfonic acid) buffer solution. The pH can at this stage be maintained at a pH below 6, such as around 4.5-5.5. In addition to the cyclic oligosaccharide compound, the treatment solution preferably contains activation agents, such as l-ethyl-3 -(3 -dimethylaminopropyl) carbodiimide hydrochloride (EDC), and / or N-hydroxysuccinimide (NHS) or sulfo-NHS (N-hydroxysulfosuccinimide). Thecellulose material can be added into the solution containing the cyclic oligosaccharide and the activation agents, and the contacting time can be, for example 1-20 hours, such as 2-4 hours, without being limited thereto.

[0053] According to another embodiment of the present invention, the surface modification comprises polycarboxylic acid assisted crosslinking of cyclic oligosaccharide to the cellulose material, preferably the surface modification comprises citric acid assisted crosslinking of cyclodextrin to the cellulose material.

[0054] Thus, in some embodiments, the mechanism for providing the modified cellulose material is through a crosslinking reaction. In such embodiments, a cyclic oligosaccharide is crosslinked to the cellulose material in the presence of polycarboxylic acid, i.e., a carboxylic acid having more than one carboxyl groups, and through heat treatment. Preferably, the polycarboxylic acid has three or more carboxyl groups. Polycarboxylic acids, such as citric acid, are capable of forming a cross-linking structure between the cellulose material and a cyclic oligosaccharide. In some embodiments, the crosslinking of the cellulose material is carried out with citric acid and cyclodextrin. Citric acid is a non-toxic polycarboxylic acid with three carboxyl groups capable of forming ester bonds with the hydroxyl groups of cellulose and the cyclic oligosaccharide. The crosslinking reaction can be carried out in the presence of a catalyst, such as sodium phosphate (NaTfcPC ). The polycarboxylic acid assisted crosslinking reaction is heat activated, whereby said embodiment can include a step of heat treating a cellulose material that has been contacted with the polycarboxylic acid and the cyclic oligosaccharide.

[0055] In some embodiments of the method relying on a crosslinking reaction, a solution comprising polycarboxylic acid and cyclic oligosaccharide is prepared. The poly carboxylic acid can be added, for example, in an amount of up to 15 wt.%, such as from 0.1, 0.2, 0.5, 1, or 5 wt.% up to 5, 7, 10, or 15 wt.%, when calculated based on the total weight of the solution. The cyclic polysaccharide can be added in an amount of, for example, up to 15 wt.%, such as from 0.5, 1, 1.5, 3, or 5 wt.% up to 5, 7, 10 or 15 wt.%, when calculated based on the total weight of the solution. The said solution is then applied to the cellulose material. Preferably, the cellulose material is impregnated with the solution, for example, for a time period of 10-45 minutes, without being limited thereto. Water contained in the cellulose material is preferably removed prior to heat treatment at temperatures initiating the crosslinking reaction, such as temperatures of 140°C or more.The temperature can be, for example, from 140°C, 150°C, or 160°C up to 180°C, 190°C, or 200°C.

[0056] According to one embodiment of the present invention, the off-flavour compounds are at least partly trapped inside the hydrophobic cavities of the cyclodextrins.

[0057] The internal structure of cyclodextrins provide for a hydrophobic cavity that enables retention of lipophilic compounds. In some embodiments, the cyclodextrin is a cyclic oligosaccharide comprising 6-8 glucose monomers. In particular, the cyclodextrin can be independently selected from the group consisting of a-cyclodextrin, P-cyclodextrin, and y-cyclodextrin, or any combination thereof. These represent the three main types of cyclodextrins, which are capable of at least partly trapping, or capturing, typical off- flavours, such as terpene-based compounds, in their interior structure, forming cavities.

[0058] According to one embodiment of the present invention, the chitosancyclodextrin modified cellulose material binds more GSM and MIB than a cellulose material without such modification.

[0059] According to another embodiment of the present disclosure, the polycarboxylic acid crosslinked cellulose material binds more GSM and MIB than a cellulose material without such modification.

[0060] The herein described surface modification provides a cellulose material with amphiphilic properties, in particular by inclusion of cyclic oligosaccharides. Unmodified cellulose materials lack such hydrophilic interaction sites, whereby more GSM and MIB are bound to cellulose materials modified by the method of the present disclosure when compared to unmodified cellulose materials.

[0061] According to one embodiment of the present invention, the method comprises introducing the surface-modified cellulose material into an aquaculture system for farming aquatic organisms, such as into a fish farming tank and / or pond.

[0062] In the context of the present disclosure, it has been observed that cellulose materials that are surface-modified by introduction of molecules having both hydrophilic and hydrophobic moieties, in particular cyclic oligosaccharides, are capable of capturing off-flavours in aquaculture systems. Furthermore, it has been shown that such surface- modified cellulose remains active for several days. Thereby, the method of the presentinvention can reduce the need for a separate depuration treatment, or reduce the duration of a depuration treatment. This in turn provides considerable water and time savings in an aquaculture system. It can also have a positive effect on the well-being of the cultured aquatic life.

[0063] According to one embodiment of the present invention, the aquaculture system is a recirculating aquaculture system (RAS).

[0064] RAS systems are closed or semi-closed systems, that are especially prone to accumulation of impurities, including off-flavour compounds. Therefore, the method of the present disclosure is especially well-suited for such aquaculture systems.

[0065] According to one embodiment of the present invention, the cellulose material is selected from cellulose non-wovens, cellulose fabrics, viscose fabric, lyocell fabrics, modal fabrics, cotton, hemp fabrics, aerogels and particles trapped within an inert permeable material.

[0066] In some embodiments, the cellulose material is provided in the form of a nonwoven or woven fabric, such as one or more fabric in the aforementioned list. A fabric can be arranged within an aquaculture system as a filtering arrangement, providing a large contact area and controllable flow through the cellulose material.

[0067] The cellulose material can be surface-modified by contacting the cellulose material with a solution wherein the concentration of the molecules having both hydrophilic and hydrophobic moiety is up to 15 wt.%, such as up to 3, 5, or 10 wt.%, when calculated based on the total weight of the solution. The concentration of the molecules having both hydrophilic and hydrophobic moiety can be, for example, at least 0.1, 0.5, 1, 1.5, 3, or 5 wt.%, when calculated based on the total weight of the solution.

[0068] According to one embodiment of the present invention, the cellulose material contains chitosan, attached by spontaneous adsorption from chitosan solution with concentration up to 5 g / 1. In particular, the method comprises treating the cellulose material with a chitosan solution having a concentration within a herein disclosed range.

[0069] According to one embodiment of the present invention, the cellulose material contains chitosan-cyclodextrin complex manufactured by first adsorbing chitosan from a solution with a chitosan concentration up to 5 g / L and then immobilizing cyclodextrinfrom a solution with a cyclodextrin concentration up to 2.5 mM. In particular, the method comprises treating the cellulose material with a chitosan solution, and subsequently a cyclodextrin solution, having a concentration within a herein disclosed range.

[0070] In some embodiments of the present disclosure, the method includes replacing the surface-modified cellulose material after 5-12 days of use, preferably after 6-10 days of use. In test carried out in the context of the present disclosure, the maximum concentration of off-flavours in the modified cellulose material was identified around 8-10 days after submersion in the aquaculture system, depending on compounds measured.

[0071] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0072] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0073] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0074] The present technology is applicable in aquaculture systems, such as in fish farming systems, for binding of unpleasant off-flavour compounds.EXAMPLESof cyclodextrin to a cellulose materialExperimental set-up:• 8 individual RASs, each with 500 L tanks, replacement water of 500 L / kg feed (total volume of 1000 L)• Fixed-bed biofilters, readily matured• RAS-units: side-loop in 4 x 2, fiber in lateral flow 3x2 0,2 L / s, controls without fiber• Water quality monitoring to maintain good water quality• Rainbow trout Oncorhynchus mykiss. average weight in the beginning 1327g, 10 fish / tank and after the experiment 3800g, 3-4 fish / tank• Regenerated cellulose (viscose) non-woven was modified by using a two-step process. First chitosan was dissolved into 0.1 M acetic acid buffer at pH 5. Then it was freely allowed to adsorb on the surface of viscose fabric for a period of 1 hour. After the adsorption, the fabric was rinsed with pure buffer solution for 1 hour to achieve (“Chitosan-treated reference”). The chitosan-treated fabric was immersed into a solution of EDC (l-ethyl-3 -(-3 -dimethylaminopropyl) carbodiimide hydrochloride), NHS (N-hydroxysuccinimide), and carboxylated cyclodextrin dissolved in 0.1 M acetic acid buffer at pH 5 for 3 hours, resulting in covalent attachment of carboxylated cyclodextrin on the chitosan-treated fabric. The cyclodextrin-treated fabric was finally washed with the 0.1 M acetic acid buffer at pH 5 and then with pure water.Off-flavor analyses were carried out in laboratory according to Lindholm-Lehto (2022):Table 1.Results are presented in Figures 1-19.Example 2 - Citric acid conjugation of cyclodextrin to a cellulosic materialWoven cotton fabric (140 g / m2) was used as a substrate for cyclodextrin surface treatment. The cyclodextrin treatment was carried out at two activation levels, both of which were heat-activated and washed similarly.A) high activation level: P-cyclodextrin was dissolved in Milli-Q water with a concentration of 100 g / 1, followed by adding 100 g / 1 citric acid crosslinker and 3 g / 1 sodium phosphate catalyst (NaEEPC ).B) medium activation level: P-cyclodextrin was dissolved in Milli-Q water with a concentration of 12.5 g / 1, followed by adding 5 g / 1 citric acid crosslinker and 1.5 g / 1 sodium phosphate catalyst (NaEbPOQ.The attachment of cyclodextrin to cotton fabric was carried out as follows. The fabric was impregnated in the solution for 30 minutes and then dried at 80 °C for 60 minutes. The crosslinking was carried out by using a heat activation at 180 °C (high activation level) or 160 °C (medium activation level) for 15 minutes. The cyclodextrin-treated fabrics were washed with Milli-Q water and ethanol to remove unreacted cyclodextrin. Then, the cyclodextrin-treated fabrics were dried at 105 °C until they were completely dry. The manufactured fabrics were stored in room conditions.Example 3 - Durability of chitosan conjugated cyclodextrin and citric acid conjugated cyclodextrin in RAS conditionsSheets (297mm x 420mm) of cyclodextrin on cellulose fabric prepared A) by citric acid route, as presented in Example 2, and B) by chitosan-cyclodextrin route (5 g / L chitosan and 2.5 mM cyclodextrin), as presented in Example 1, were studied in a pilot-scale RAS.Rainbow trout Oncorhynchus mykiss was reared in a RAS with a biomass on 660 kg, on average 100g per individual (at 14°C, pH 7.5; O2 130%). Water replacement rate was adjusted to 600 L / kg feed. During the experiment, the fish biomass was increased from 573 kg to 664 kg and feeding was adjusted from 1.3% to 1.1%. The fish and the rearing conditions were actively monitored to ensure the well-being of fish. Samples of water and the cellulose fabric was taken once a day to monitor the selected off-flavor compounds of Table 1 in water and in fabric. The samples were stored in clean plastic (high density polyethene, HDPE) containers of 250 mL and stored in a freezer at -22°C until thawed for the analysis. The off-flavors were detected and quantified by a method based on SPME- GC-QQQ as reported in Lindholm-Lehto (2022).The results showed moderate fluctuation in concentrations in water (Fig. 20, Fig. 21). GSM was captured by the fabric modified by the chitosan route up to 80 000 ng kg'1. The concentrations began to decrease after 8 days, suggesting that the material's highest ability to capture was reached on day 8. The fabric modified by the citric acid route captured up to 30 000 ng kg'1, showing the highest concentrations also on day 8. MIB was captured up to 3600 ng kg-1 by the fabric A and up to 3000 ng kg-1 by fabric B. The highest concentrations were observed after 9 and 10 days. The fabric was designed to capture GSM, which explains the lower capturing ability of other compounds.CITATION LISTPatent literatureCN107983318BCN117923592ANon-patent literature:Arru, B., R. Furesi, L. Gasco, F. Madau, P. Pulina. 2019. The introduction of insect meal into fish diet: The first economic analysis on European sea bass farming. Sustainability 11 : 1697. https: / / doi.org / 10.3390 / sul l061697Azaria, S., Nir, S., Van Rijn, J., 2017. Combined adsorption and degradation of the off- flavor compound2-methylisobomeol in sludge derived from a recirculating aquaculture system. Chemosphere 169:69-77. https: / / doi.Org / 10.1016 / j.chemosphere.2016.l l.051Burr, G. S., W. R. Wolters, K. K. Schrader, and S. T. Summerfelt. 2012. Impact of depuration of earthy-musty off-flavors on fillet quality of Altantic salmon, Salmo salar, cultured in a recirculating aquaculture system. Aquacultural Engineering 50:2836. https: / / doi.Org / 10.1016 / j.aquaeng.2012.03.002Carneiro, R., James, C., Aung, T., O’Keefe, S. 2022. Challenges for flavoring fish products from cellular agriculture. Current Opinion in Food Science 47: 100902. https: / / doi.Org / 10.1016 / j.cofs.2022.100902Davidson, J., Grimm, C., Summerfelt, S. Fischer, G., Good, C. 2020. Depuration system flushing rate affects geosmin removal from market-size Atlantic salmon Salmo salar. Aquacultural Engineering 90: 102104. https: / / doi.Org / 10.1016 / j.aquaeng.2020.102104FAO, 2024. Food and Agriculture Organization of the United Nations (FAO). The state of World Fisheries and Aquaculture. Blue transformation in action. FAO, Rome, Italy.Grimm, C. C., Lloyd, S. W., Zimba, P. V. 2004. Instrumental versus sensory detection of off-flavors in farm-raised channel catfish. Aquaculture 236:309-319. doi : 10.1016 / j . aquaculture.2004.02.020Houle, S., Schrader, K., Lefrancois, N. R., et al. 2011. Geosmin causes off-flavor in Arctic charr in recirculating aquaculture systems. Aquaculture Research 42:360365. https: / / doi.org / 10.111 l / j,1365-2109.2010.02630.xHowgate, P. 2004. Tainting of farmed fish by geosmin and 2-methylisoborneol: A review of sensory aspects and of uptake / depuration. Aquaculture 234: 155-181. https: / / doi.Org / 10.1016 / j.aquaculture.2003.09.032Lindholm-Lehto, P. C., Vielma, J., Pakkanen, H., Alen, R., 2019a. Depuration of geosmin and 2-methylisobomeol-induced off-flavors in recirculating aquaculture system (RAS) farmed European whitefish Coregonus lavaretus. J. Food Sci. Technol. 56:4585-4594. https: / / doi.org / 10.1007 / sl3197-019-03910-7Lindholm-Lehto, P. C., Suurnakki, S., Pulkkinen, J. T., Aalto, S. L., Tiirola, M., Vielma, J., 2019b. Effect of peracetic acid on levels of geosmin, 2-methylisoborneol, and theirpotential producers in a recirculating aquaculture system for rearing rainbow trout (Oncorhynchus mykiss). Aquae. Eng. 85:56-64. https: / / doi.Org / 10.1016 / j.aquaeng.2019.02.002Lindholm- Lehto, P. C. 2022. Developing a robust and sensitive analytical method to detect off- flavor compounds in fish. Environmental Science and Pollution Research 29:55866-55876. https: / / doi.org / 10.1007 / sl l356-022-19738-2Lindholm-Lehto, P. C., Koskela, J., Leskinen, H., Vielma, J., Kause, A. 2022. Off-flavors and lipid components in rainbow trout (Oncorhynchus mykiss) reared in RAS: Differences in families of low and high lipid contents. Aquaculture 559:738418. http s : / / doi . org / 10.1016 / j . aquaculture .2022.738418Mahmoud, M. A. A., Buettner, A. 2016. Characterisation of aroma-active and off-odor compounds in German rainbow trout (Oncorhynchus mykiss). Part I: Case of aquaculture water from earthen-ponds farming, Food Chemistry 210:623-630. https: / / doi.Org / 10.1016 / j.foodchem.2016.05.030Mahmoud, M. A. A., Buettner, A. 2017. Characterisation of aroma-active and off-odour compounds in German rainbow trout (Oncorhynchus mykiss). Part II: case of fish meat and skin from earthen ponds farming. Food Chem 232:841-849. https: / / doi.org / 10.1016 / j. foodc hem. 2016. 09. 172Nam-Koong, H., Schroeder, J. P., Petrick, G., Schulz, C. 2016. Removal of the off-flavor compounds geosmin and 2-methylisobomeol from recirculating aquaculture system water by ultrasonically induced cavitation. Aquae. Eng. 70:73-80. https: / / doi.Org / 10.1016 / j.aquaeng.2015.10.005Percival, S., Drabsch, P., Glencross, B. 2008. Determining factors affecting muddy-flavour taint in farmed barramundi (Lates calcarifer). Aquaculture 284: 136-143. http s: / / doi. org / 10.1016 / j. aquaculture.2008.07.056Podduturi, R., Petersen, M. A., Vestergaard, M., Hyldig, G., Jorgensen, N. O. G. 2021.Case study on depuration of RAS-produced pikeperch Sander lucioperca) for removal of geosmin and other volatile organic compounds (VOCs) and its impact on sensory quality. Aquaculture 530:735754. https: / / doi.Org / 10.1016 / j.aquaculture.2020.735754Powell, A., Scolding, J. W. S. 2018. Direct application of ozone in aquaculture systems. Reviews in Aquaculture, 10, 424-438. https: / / doi.org / 10. l l l l / raq.12169Rana, K. J., Siriwardena, S., Hasan, M. R. 2009. Impact of rising feed ingredient prices on aquafeeds and aquaculture production (FAO Fisheries and Aquaculture Technical Paper No. 541). Stirling, UK: Institute of Aquaculture, University of Stirling.Robertson, R. F., Jauncey, K., Beveridge, M. C. M., Lawton, L. A. 2005. Depuration rates and the sensory threshold concentration of geosmin responsible for earthy-musty taint in rainbow trout, Onchorhynchus mykiss. Aquaculture 245:89-99. http s : / / doi . org / 10.1016 / j . aquaculture .2004.11.045 Rurangwa, E., Verdegem, M. C. J. 2015. Microorganisms in recirculating aquaculture systems and their management. Reviews in Aquaculture 7: 117-130. https: / / doi.org / 10. I l l 1 / raq.12057

Claims

CLAIMS:

1. A method for binding of off-flavour compounds in aquaculture systems by a cellulose- based material, characterized by introducing a native plant-based cellulose material or a regenerated cellulose material to an aquaculture system, wherein the cellulose material is surface modified with molecules having both hydrophilic and hydrophobic moiety, and thereby selectively binding off-flavour compounds from the aquaculture system.

2. The method according to claim 1, characterized in that the off-flavour compounds are lipophilic, in particular terpene-based, such as geosmin (GSM) and 2-methylisoborneol (MIB).

3. The method according to claim 1 or 2, characterized in that the cellulose material is surface modified with cyclic oligosaccharide, such as cyclodextrin.

4. The method according to any one of the preceding claims, characterized in that the molecules having both hydrophilic and hydrophobic moiety are cyclic oligosaccharide molecules that are attached to the cellulose material, or to linker molecules present on the cellulose material, preferably the cyclic oligosaccharide molecules are cyclodextrin molecules.

5. The method according to any one of the preceding claims, characterized in that the surface modification comprises providing a cationic charge to a surface of the cellulose material by chitosan adsorption, followed by covalent conjugation of cyclic oligosaccharides, such as cyclodextrins.

6. The method according to any one of claims 1-4, characterized in that the surface modification comprises polycarboxylic acid assisted crosslinking of cyclic oligosaccharide to the cellulose material, preferably the surface modification comprises citric acid assisted crosslinking of cyclodextrin to the cellulose material.

7. The method according to any one of claims 3-6, characterized in that the off-flavour compounds are at least partly trapped inside the hydrophobic cavities of the cyclodextrins.

8. The method according to claim 5 or 7, characterized in that the chitosan-cyclodextrin modified cellulose material binds more GSM and MIB than a cellulose material without such modification.

9. The method according to any of the preceding claims, characterized by introducing the surface modified cellulose material into an aquaculture system for farming aquatic organisms, such as into a fish farming tank and / or pond.

10. The method according to any of the preceding claims, characterized in that the aquaculture system is a recirculating aquaculture system (RAS).

11. The method according to any of the preceding claims, characterized by selecting the cellulose material from cellulose non-wovens, cellulose fabrics, viscose fabric, lyocell fabrics, modal fabrics, cotton, hemp fabrics, aerogels and particles trapped within an inert permeable material.

12. The method according to claim 5, characterized in that the cellulose material contains chitosan, attached by spontaneous adsorption from chitosan solution with concentration up to 5 g / 1.

13. The method according to claim 5, characterized in that the cellulose material contains chitosan-cyclodextrin complex manufactured by first adsorbing chitosan from a solution with a chitosan concentration up to 5 g / L and then immobilizing cyclodextrin from a solution with a cyclodextrin concentration up to 2.5 mM.

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