A method for eliminating earthy smell and improving meat quality of euryhaline fish in situ based on a factory circulating water system

Abstract

This invention relates to the field of aquaculture, specifically a method for in-situ elimination of the muddy taste and improvement of meat quality in euryhaline fish based on a factory-scale recirculating aquaculture system (RAS). Addressing the problem of muddy taste accumulation in euryhaline fish (such as shad, bass, and rainbow trout) within RAS systems, this invention employs a micro-stepwise pulsed salinity enhancement model, simultaneously adjusting the maximum air intake of the protein separator and targeting the introduction of salt-tolerant geosmin-degrading bacteria. Without disrupting the nitrification function of the core biological filter in the RAS system, in-situ physical stripping and biodegradation of broken algae and muddy taste substances (GSM and 2-MIB) are achieved. Simultaneously, the brackish, high-osmotic environment forces the fish to accumulate free amino acids for osmotic pressure compensation, significantly removing the muddy taste and increasing the concentration of umami amino acids in the fish meat. This invention is highly automated, avoiding the high mortality rate associated with traditional pond transfer methods and significantly increasing the economic added value of aquatic products.

Description

Technical Field

[0001] This invention relates to the field of aquaculture and aquatic product quality control. Specifically, it is a method for in-situ elimination of earthy taste and improvement of meat quality in euryhaline fish based on a factory-style recirculating aquaculture system. For euryhaline fish such as shad, bass, and rainbow trout, the method achieves in-situ elimination of earthy taste substances and quality improvement by inducing the accumulation of fresh amino acids in the muscle through dynamic salinity model and microecological targeted regulation. Background Technology

[0002] Currently, due to their high-density aquaculture characteristics, recirculating aquaculture systems (RAS) have high organic loads in the water, making them highly susceptible to the growth of actinomycetes and cyanobacteria-producing algae. These microorganisms produce geosmin (GSM) and dimethylisoborneol (2-MIB), which are highly lipid-soluble and can rapidly penetrate the gill epithelial cells of fish and accumulate in adipose tissue. Existing methods for removing fish odor through "hanging water" have three major technical bottlenecks: First, transferring fish to different ponds for capture can cause severe stress-induced lactic acid buildup in sensitive fish such as shad, seriously damaging the flavor of the meat; second, the core of the RAS system's biological filtration—the nitrifying bacterial community—is extremely sensitive to salinity fluctuations. Once a drastic change in salinity causes cell osmotic pressure imbalance and death, the ammonia nitrogen in the system will reach lethal concentrations within hours; finally, traditional salting methods often overlook the "secondary pollution" caused by cell rupture, i.e., the concentration of free odor-causing substances released after the death of odor-producing bacteria increases instantaneously.

[0003] Therefore, developing a method that can both protect the system's micro-ecology and achieve in-situ, efficient removal of fishy odors and enhancement of freshness is a problem that the industry urgently needs to solve. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by using a refined environmental control system (RAS) to eliminate the earthy taste of euryhaline fish and reshape their meat flavor.

[0005] The primary technical problem this invention aims to solve is to provide an in-situ deodorization process that can balance the physiological health of fish with the homeostasis of the aquatic micro-ecosystem. Traditional deodorization methods often involve drastic environmental changes, causing severe stress reactions or even death in sensitive species such as shad and bass. This invention, by constructing a micro-step pulse salinity model, aims to provide a technical approach that induces a smooth transition of fish physiological metabolism to a hyperosmolar mode without interrupting the aquaculture process or damaging fish tissues.

[0006] This invention presents a combined physical-biological elimination mechanism for "secondary pollution" caused by fishy-smelling substances, utilizing environmental osmotic pressure differences to induce the enrichment of umami amino acids in fish meat. This invention provides the application of the above-mentioned in-situ deodorization and flavor-enhancing control method in the pretreatment of high-value euryhaline fish such as shad, sea bass, and rainbow trout. It is a control strategy that is highly compatible with existing factory aquaculture equipment, low-cost, and easily scalable.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale recirculating aquaculture system includes the following steps:

[0009] 1) Step-by-step salinity and biofilter acclimatization steps: 25-30 days before harvest, concentrated artificial seawater or sea salt is added to the RAS system via an automated dosing system. The replenishment process follows a "micro-step pulsed increase," controlling the daily salinity rise rate of the system water at 1.0‰-1.5‰, with a target salinity range of 10‰-15‰. Specifically, the replenishment amount is based on the ammonia nitrogen (NH3) levels fed back by the online water quality monitor. 4+ -N) and nitrite (NO) 2- Real-time adjustment of N-N concentration ensures stable succession of the nitrification system under salinity fluctuations.

[0010] 2) Physical stripping and targeted micro-ecological reconstruction steps: When the water salinity rises to the critical range of 5‰~7‰, the enhanced purification process is initiated:

[0011] Physical stripping: Adjust the air intake of the protein separator in the RAS system to achieve an air-to-water ratio of 1:15 to 1:25, and use the high surface tension of the brackish water to strip the dead bacteria and the organic debris they release out of the system.

[0012] Biodegradation: Salt-tolerant geosmin-degrading bacteria, including Bacillus subtilis acclimated to brackish water, are targeted into the system to maintain the total effective viable bacteria concentration in the water at 10. 5 ~10 7 CFU / mL.

[0013] 3) Physiological regulation and flesh remodeling under hyperosmolar stress: Once the water salinity reaches the target range of 10‰–15‰, maintain a constant level for 10–15 days. During this period:

[0014] Ambient temperature control: The water temperature is kept constant at 18~22°C through a heat pump system.

[0015] Precision feeding: Feed with anti-stress formulated feed, which contains 0.1% betaine and 0.05% high-stability vitamin C by mass.

[0016] Metabolic compensation: The semi-brackish, hypertonic environment induces fish to activate an osmotic pressure compensation mechanism, which promotes the enrichment of free amino acids (including glycine, glutamic acid, and alanine) in muscle cells.

[0017] Based on the above technical solution, in a first aspect of the present invention, a method for in-situ elimination of the earthy taste and improvement of the meat quality of euryhaline fish based on a factory-scale circulating water system is provided, comprising the following steps:

[0018] A) Stepped salinity and biofilter synergistic acclimatization: 30 days before the aquaculture harvest, in the initial freshwater environment, concentrated artificial seawater or sea salt is added to the factory-style recirculating aquaculture system (RAS) through the dosing system to control the salinity of the system to rise in a micro-step pulse manner, raising the salinity to the target salinity of brackish water.

[0019] B) Protein separation enhancement and targeted microecological reconstruction: As salinity increases, the gas-water ratio of the protein separator in the RAS system is adjusted to 1:15~1:25, and salt-tolerant geosmin-degrading bacteria are introduced into the system at the same time.

[0020] C) Amino acid remodeling of meat under hyperosmolar stress: Maintain the salinity of the RAS system at a constant level within the target brackish water range and feed the animal with stress-resistant functional compound feed until harvest.

[0021] Furthermore, the euryhaline fish mentioned are shad, perch, or rainbow trout.

[0022] Furthermore, in step A), the rate of increase in system salinity is strictly controlled at 1.0‰~1.5‰ / day, with a target salinity range of 10‰~15‰. The micro-step pulsed increase refers to dividing the daily salinity increase of 1.0‰~1.5‰ into 3-5 dripping cycles, which are then pulsed into the return water section of the RAS system via an automatic dosing pump within 24 hours, avoiding localized hyperosmolar shocks caused by a single large-dose salt addition.

[0023] Furthermore, the dosing system in step A) is linked with the online water quality monitor of the RAS system to form a closed-loop feedback control: the online water quality monitor monitors the water quality, and when ammonia nitrogen (NH3) is detected... 4+ -N) concentration ≥0.5 mg / L or nitrite (NO) 2- When the concentration of -N) is ≥0.1mg / L, the dosing and salinity enhancement operation will be automatically suspended until the water quality index drops back below the safe threshold before the dosing will resume.

[0024] Furthermore, in step A), calcium chloride and magnesium sulfate are added to the concentrated artificial seawater or sea salt to maintain the calcium ion concentration at 150-200 mg / L and the magnesium ion concentration at 300-400 mg / L during the salinization process, thereby enhancing the calcium balance regulation of the fish's chlorine-secreting cells and reducing the scale loss rate.

[0025] Furthermore, in step B), when the salinity of the water body reaches the critical point of 5‰ due to the micro-step pulse increase, the air intake of the protein separator in the industrial circulating water (RAS) system is adjusted so that the air-to-water ratio in the system reaches 1:15 to 1:25, so as to take advantage of the physical property of increased surface tension of brackish water to accelerate the stripping of cyanobacterial and actinomycete cell debris that have been broken due to salinity stress.

[0026] Furthermore, in step B), when the salinity of the water reaches 5‰, salt-tolerant geosmin-degrading bacteria are introduced into the water at the front end of the biological filter. The salt-tolerant geosmin-degrading bacteria are Bacillus subtilis that have been acclimatized to brackish water and use geosmin (GSM) and dimethyl isoborneol (2-MIB) as the sole carbon source.

[0027] Furthermore, the salt-tolerant geosmin-degrading bacteria are applied daily for 3-5 consecutive days, with each application ensuring an effective viable bacteria concentration of 10 in the total RAS water. 5 ~10 7 CFU / mL.

[0028] Furthermore, in step C), the system salinity remains constant at 10‰~15‰ for 10~15 days, during which the water temperature is precisely controlled at 18~22℃ by a temperature control device to reduce the oxygen consumption of fish through hyperosmolar metabolism.

[0029] Furthermore, the anti-stress functional compound feed in step C) is based on conventional commercial feed, with the addition of 0.1% betaine and 0.05% high-stability vitamin C by mass, for the purpose of protecting the liver and gallbladder and assisting in osmotic pressure regulation.

[0030] In a second aspect, the present invention provides the application of the above-described method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale recirculating aquaculture system in the intensive farming and pre-market quality improvement pretreatment of shad, bass, rainbow trout or other economically important fish species with euryhaline characteristics.

[0031] A third aspect of the present invention provides a pretreatment method for improving the quality of euryhaline fish before they are marketed, which includes the method described above for in-situ elimination of the earthy taste and improvement of the meat quality of euryhaline fish based on a factory-style circulating water system.

[0032] The advantages of this invention are:

[0033] 1. This invention provides a method for refined water quality control based on a factory-scale recirculating aquaculture system (RAS). Targeting euryhaline fish such as shad, bass, and rainbow trout, this method utilizes a dynamic salinity model and targeted microecological regulation to achieve in-situ elimination of earthy odor substances and induced accumulation of fresh amino acids in muscle tissue, thus improving quality. Addressing the issue of earthy odor accumulation in euryhaline fish (such as shad, bass, and rainbow trout) within RAS systems, this invention employs a micro-stepwise pulsed salinity enhancement model, raising water salinity at a very slow rate of 1.0‰~1.5‰ daily to 10‰~15‰. Simultaneously, the air intake of the protein skimmer is adjusted, and salt-tolerant geosmin-degrading bacteria are targeted. This method achieves in-situ physical stripping and biodegradation of broken algae and earthy odor substances (GSM and 2-MIB) without disrupting the core nitrification function of the RAS system's biological filter. Meanwhile, the semi-brackish, high-osmotic environment forces the fish to accumulate free amino acids for osmotic pressure compensation, significantly removing the muddy taste and increasing the concentration of flavorful amino acids in the fish meat.

[0034] 2. The operation of this invention is highly automated, which not only avoids the high mortality rate caused by the traditional "water-lifting" method in the transfer pool, but also greatly improves the economic added value of aquatic products. Attached Figure Description

[0035] Figure 1 A kinetic model of the effects of stepwise salinization and microecological reconstruction on the elimination of fishy-smelling bacteria and earthy-smelling substances in the muscle of shad in the RAS system;

[0036] Figure 2 A kinetic model of the effects of stepwise salinity increase and microecological reconstruction on the elimination of fishy-tasting bacteria and earthy-tasting substances in sea bass muscle in the RAS system;

[0037] Figure 3 A kinetic model of the effects of stepwise salinization and microecological reconstruction on the elimination of odorous bacteria and earthy substances in rainbow trout muscle from RAS system. Detailed Implementation

[0038] The specific implementation methods provided by the present invention will be described in detail below with reference to the embodiments.

[0039] Example 1: In-situ deodorization and flavor enhancement treatment of shad

[0040] This embodiment uses a factory-style recirculating aquaculture system (RAS) shad farming pond 30 days before market launch as the operating subject (average fish size 600g / fish, density 40kg / m³). 3The initial water salinity was approximately 0.3‰. During the salinity acclimatization phase, the automatic dosing system and the online water quality monitor were linked in a closed loop (with ammonia nitrogen ≥ 0.5 mg / L or nitrite ≥ 0.1 mg / L set as the feedback pause threshold). The artificial seawater was added at a rate of 1.0‰ per day, divided into three dripping cycles. The automatic dosing pump pulsed the seawater into the return water section of the RAS system within 24 hours to avoid local hyperosmolar shocks caused by a single large dose of salt. Calcium chloride and magnesium sulfate were also added to maintain the calcium ion concentration at 150 mg / L and the magnesium ion concentration at 300 mg / L, thereby reducing physiological stress and preventing scale loss. When the system water salinity reaches 5‰, adjust the air intake of the protein separator to achieve an air-to-water ratio of 1:25. Utilize the high surface tension of brackish water to remove cell debris. For 3-5 consecutive days, add salt-tolerant geosmin-degrading bacteria (Bacillus subtilis acclimated to brackish water and using GSM and 2-MIB as the sole carbon source), ensuring an effective viable bacteria concentration of 10⁻⁶ in the water each time. 5 ~10 7 CFU / mL; through the above combined treatment, the abundance of actinomycetes in the water was controlled at 10. 2 CFU / mL or lower, cyanobacterial cell density controlled at 10 3 The concentration of GSM in the fish was below 10‰ (cells / mL). Subsequently, the system salinity was maintained at a constant level within the target range of 10‰ for 10-15 days. During this period, the water temperature was precisely controlled at 22℃ using a temperature control device to reduce the oxygen consumption of the fish's hyperosmolar metabolism. Throughout this time, the fish were fed an anti-stress formulated feed supplemented with 0.1% betaine and 0.05% high-stability vitamin C to induce the accumulation of fresh free amino acids in the muscle and subcutaneous tissue. Sampling tests showed that the GSM concentration in the shad decreased to 0.25 μg / kg or below, and the 2-MIB concentration decreased to 0.7 μg / kg or below, completing the in-situ deodorization and freshness enhancement treatment.

[0041] Example 2: In-situ deodorization and flavor enhancement treatment of sea bass

[0042] This embodiment selects a rearing pond 30 days before market launch, with an average fish size of 500g / fish and a stocking density of 35kg / m³. The initial environmental salinity is 0.3‰. During the system's steady-state acclimatization period (days 1-12), concentrated artificial seawater or sea salt is first replenished to the RAS system using an automated dosing pump. A micro-step pulse model is used to control the salinity increase at a rate of 1.0‰ per day, divided into 5 dripping cycles. The automated dosing pump pulses the salt into the return water section of the RAS system over 24 hours to avoid localized hyperosmolar shocks caused by single large-dose salt additions. Calcium chloride and magnesium sulfate are additionally added to maintain calcium ion concentrations at 200 mg / L and magnesium ion concentrations at 400 mg / L, thereby strengthening the function of chlorine-secreting cells in the fish and reducing scale loss. When the water salinity reaches the critical point of 5‰, the air intake of the protein skimmer is adjusted to achieve an air-to-water ratio of 1:15, utilizing the high surface tension of the brackish water to remove dead fish-producing bacteria and organic debris. Simultaneously, salt-tolerant geosmin-degrading bacteria (Bacillus subtilis acclimated to brackish water and using GSM and 2-MIB as the sole carbon source) were introduced into the system daily for 3-5 consecutive days (days 13-17), with each injection ensuring an effective viable bacteria concentration of 10. 5 ~10 7 The concentration of CFU / mL was used to achieve targeted degradation of GSM and 2-MIB. Through the dual effects of microecological competition and physical stripping, the abundance of flocculating actinomycetes in aquaculture water was suppressed to 10. 2 CFU / mL or below, while simultaneously reducing and maintaining cyanobacterial cell density at 10. 3 The concentration of GSM and 2-MIB in the fish muscle was kept below 15‰ for 10-15 days. The system salinity was maintained at a constant level within the target range of 15‰. The water temperature was precisely controlled at 18℃ to reduce the oxygen consumption due to hyperosmolar metabolism in the fish. Throughout the entire conditioning process and before harvest (days 28-30), the fish were fed a stress-resistant formulated feed supplemented with 0.1% betaine and 0.05% high-stability vitamin C to protect the liver and gallbladder and assist in osmotic pressure regulation. Once the concentrations of GSM and 2-MIB in the fish muscle were reduced to below 0.05 μg / kg, the fish underwent deodorization and freshness enhancement pretreatment and were ready for market.

[0043] Example 3: In-situ deodorization and flavor enhancement treatment of rainbow trout

[0044] This embodiment selects a recirculating aquaculture system (RAS) rainbow trout farming pond 30 days before market launch as the subject of the operation (average fish size 800g / fish, density 40kg / m³). 3(The initial freshwater salinity is approximately 0.3‰), and a parameter closed-loop control mechanism is used for quality improvement. During the salinity acclimatization phase, the automatic dosing system is linked with the water quality monitor (set to ammonia nitrogen ≥0.5 mg / L or nitrite ≥0.1 mg / L as the trigger threshold), increasing the dosage at a rate of 1.5‰ per day, divided into 5 dosing cycles. The automatic dosing pump pulses the solution into the return water section of the RAS system within 24 hours, avoiding localized hyperosmolar shocks caused by single large-dose salt additions. Calcium chloride and magnesium sulfate are also added to maintain calcium ion concentrations at 200 mg / L and magnesium ion concentrations at 300 mg / L, precisely strengthening the fish's chlorine-secreting cells and preventing scale loss. When the water salinity exceeds the 5‰ critical point, the system simultaneously triggers a dual physical and biological deodorization mechanism. This not only adjusts the air intake of the protein separator to achieve an air-to-water ratio of 1:25 to accelerate the removal of cell debris, but also continuously injects brackish water-acclimatized geosmin-degrading bacteria (Bacillus subtilis acclimatized in brackish water, using GSM and 2-MIB as the sole carbon source) into the system daily for 5 consecutive days. Subtilis), each application ensures an effective live bacteria concentration of 10 in the water. 5 ~10 7 CFU / mL; Due to the combined effects of physical stripping and microecological competition, the lower limit of actinomycete abundance in water bodies needs to be controlled at 10. 1 ~5×10 1 Within the CFU / mL range, the cyanobacterial cell density needs to be maintained at 10. 2 ~5×10 2 At the cell / mL level, highly efficient lipid enrichment is used to cut off odor substances at the source. As salinity rises and stabilizes at the target brackish water range of 10‰ (for 10-15 days), the temperature control system strictly controls the water temperature at 18℃, which is suitable for the hypertonic metabolism of cold-water fish. Throughout the process, the fish are fed an anti-stress feed containing 0.1% betaine and 0.05% high-stability vitamin C. The high-osmotic stress of the environment and nutritional compensation promote the accumulation of a large amount of fresh free amino acids in the muscle cells of rainbow trout. Sampling and testing confirmed that the GSM in the fish muscle reached the extremely low limit of 0.25 μg / kg, and 2-MIB dropped to below 0.7 μg / kg, thus completing the in-situ deodorization and freshness enhancement and meeting the high-quality market standards.

[0045] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system, characterized in that, Includes the following steps: A) Stepped salinity and biofilter acclimatization: 30 days before the aquaculture harvest, in the initial freshwater environment, concentrated artificial seawater or sea salt is added to the factory-style recirculating water system through a dosing system to control the salinity of the system to rise in a micro-step pulse manner, raising the salinity to the target brackish water salinity; the rate of increase of the system salinity is strictly controlled at 1.0‰~1.5‰ / day, and the target salinity range is 10‰~15‰; B) Protein Separation Enhancement and Targeted Microecological Reconstruction: When the salinity of the water body rises to 5‰, the air-to-water ratio of the protein separator in the industrialized circulating water system is adjusted to 1:15~1:25, and salt-tolerant geosmin-degrading bacteria are introduced into the system. These bacteria are Bacillus subtilis, acclimated to brackish water and using geosmin and dimethyl isoborneol as the sole carbon source. The salt-tolerant geosmin-degrading bacteria are introduced daily for 3~5 consecutive days, with each introduction ensuring an effective viable bacteria concentration of 10 in the total industrialized circulating water body. 5 ~10 7 CFU / mL; C) Amino acid remodeling of meat under hyperosmolar stress: The salinity of the factory-scale circulating water system is maintained at a constant level within the target brackish water range, and the plant is fed an anti-stress functional compound feed until harvest; the anti-stress functional compound feed is made by adding 0.1% betaine and 0.05% high-stability vitamin C by mass to conventional commercial feed.

2. The method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system according to claim 1, characterized in that, The euryhaline fish mentioned are shad, perch, or rainbow trout.

3. The method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system according to claim 1, characterized in that, The micro-step pulsed rise mentioned in step A) refers to dividing the daily salinity increase of 1.0‰~1.5‰ into 3-5 dripping cycles and injecting it into the return water section of the RAS system in a pulsed manner over 24 hours via an automatic dosing pump.

4. The method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system according to claim 1, characterized in that, In step A), the dosing system is linked with the online water quality monitoring instrument of the factory-scale circulating water system to form a closed-loop feedback control: the online water quality monitoring instrument monitors the water quality, and when ammonia nitrogen (NH3) is detected... 4+ -N) concentration ≥0.5 mg / L or nitrite (NO) 2- When the concentration of -N) is ≥0.1mg / L, the dosing and salinity enhancement operation will be automatically suspended until the water quality index drops back below the safe threshold before the dosing will resume.

5. The method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system according to claim 1, characterized in that, In step A), the concentrated artificial seawater or sea salt replenished contains additional calcium chloride and magnesium sulfate, so that the calcium ion concentration in the water is maintained at 150-200 mg / L and the magnesium ion concentration is maintained at 300-400 mg / L during the salinization process.

6. The method for in-situ elimination of earthy odor and improvement of meat quality in euryhaline fish based on a factory-scale circulating water system according to claim 1, characterized in that, In step C), the system salinity remains constant at 10‰~15‰ for 10~15 days, during which the water temperature is precisely controlled at 18~22℃ using a temperature control device.

7. The method for in-situ elimination of earthy odor and improvement of meat quality of euryhaline fish based on a factory-style recirculating aquaculture system as described in any one of claims 1-6, in the intensive farming and pre-market quality improvement pretreatment of economic fish with euryhaline characteristics.

8. A pretreatment method for improving the quality of euryhaline fish before they are marketed, comprising the method for in-situ elimination of earthy odor and improvement of meat quality of euryhaline fish based on a factory-scale circulating water system as described in any one of claims 1-6.

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