Ultralow-temperature epinephelus preservation method
By pretreating grouper with a compound preservative solution and using an ultra-low temperature preservation method with optimized cooling rate, the problems of short shelf life and quality decline of grouper have been solved, achieving efficient and safe long-term preservation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-04
- Publication Date
- 2026-04-07
AI Technical Summary
Existing methods for preserving grouper have problems such as short shelf life, quality decline, and severe juice loss. Furthermore, traditional ultra-low temperature preservation technology is prone to damaging cell structure and cannot meet the requirements for high-quality preservation.
Grouper was pretreated with a compound preservative solution (longan polysaccharide and chitosan), combined with optimized precooling and rapid cooling rates, and then frozen and stored at ultra-low temperatures to form a stable glassy structure that protects the cells and inhibits microbial growth and enzyme activity.
Extending the shelf life of grouper to 6-12 months significantly reduces juice loss, maintains its tender texture and original flavor, minimizes nutrient loss, meets food safety requirements, and is simple and cost-effective.
Abstract
Description
Technical Field
[0001] This invention relates to the field of grouper preservation technology, specifically to a method for ultra-low temperature preservation of grouper. Background Technology
[0002] Grouper is a high-quality saltwater fish, prized for its delicious flavor and rich nutritional value. However, its freshness deteriorates rapidly after being caught, leading to a decline in taste. Therefore, it requires thorough preservation treatment.
[0003] Currently, the main methods for preserving grouper include chemical preservation, modified atmosphere packaging (MAP), and cryogenic preservation. Chemical preservation involves adding preservatives and antioxidants (such as potassium sorbate and tea polyphenols) to inhibit microbial growth and slow down oxidation. While chemical preservation can extend the shelf life of grouper to some extent, it may alter its flavor and texture. MAP involves filling sealed bags with gases such as carbon dioxide or nitrogen to reduce oxygen levels, inhibiting microbial growth and enzyme activity, thus achieving preservation. However, MAP requires high-quality packaging materials and equipment, resulting in higher costs. Furthermore, the effectiveness of MAP is affected by various factors such as gas ratios and packaging seal; improper control can significantly reduce its effectiveness. Cryogenic preservation includes refrigerated preservation and ultra-low temperature preservation. Refrigerated preservation is a common method, where grouper is stored at -2 to 2°C. This method is simple to operate and low in cost, but its shelf life is usually only 7-10 days, which is short and cannot meet the needs of long-distance transportation and long-term storage. During refrigeration, the enzymes in the grouper's body still have a certain degree of activity and will continue to carry out biochemical reactions, causing the quality of the fish to gradually deteriorate. Ultra-low temperature preservation technology has been applied in some food preservation fields, but its application in grouper is relatively limited. Traditional ultra-low temperature preservation methods are prone to forming large ice crystals in the grouper cells during rapid cooling, causing cell rupture, damaging the tissue structure, and resulting in severe loss of juices after thawing, affecting the taste and quality of the grouper. In addition, existing ultra-low temperature preservation technologies often do not fully consider the characteristics of grouper itself, and lack targeted optimization in terms of cooling rate and pretreatment methods, making it difficult to meet the requirements for high-quality preservation of grouper.
[0004] In conclusion, developing an ultra-low temperature preservation method that can effectively maintain the quality of grouper, reduce nutrient loss, extend shelf life, and is simple to operate and cost-effective is of great practical significance. Summary of the Invention
[0005] In view of the shortcomings of existing technologies, this invention proposes a method for ultra-low temperature preservation of grouper. By optimizing key aspects such as pretreatment and cooling rate, this method solves the problems of short shelf life, quality decline, and severe juice loss in existing grouper preservation methods, thereby achieving high-quality preservation of grouper.
[0006] The technical solution of this invention is as follows: A method for ultra-low temperature preservation of grouper includes the following steps: (1) Pretreatment: Remove the internal organs, scales and gills from freshly caught grouper, rinse thoroughly with clean water, drain, and then soak the grouper in a compound preservative solution for 15-30 minutes. The compound preservative solution consists of 0.5-1.5% longan polysaccharide, 1.0-3.0% chitosan, and the remainder water. Longan polysaccharide has good glass transition properties and can form a stable glassy state at low temperatures, protecting cell structure. At the same time, longan polysaccharide and chitosan have antibacterial and film-forming properties, which can form a protective film on the surface of the fish to inhibit microbial growth. The amount of longan polysaccharide and chitosan used is small and will not affect the flavor of the grouper itself.
[0007] (2) Pre-cooling: The pre-treated grouper is placed in a pre-cooling room at 0 ~ 4℃ to pre-cool, so that the temperature of the fish decreases evenly and the temperature gradient during rapid cooling is reduced to reduce the damage to the fish.
[0008] (3) Rapid cooling: The pre-cooled grouper is rapidly cooled down at a rate of 5 to 10°C / minute to reduce the body temperature to -18 to -20°C. A reasonable cooling rate can cause the water in the grouper cells to quickly form tiny ice crystals, reducing damage to the cell structure.
[0009] (4) Ultra-low temperature freezing: Frozen storage at -18~-20℃. The ultra-low temperature environment can greatly inhibit the growth of microorganisms and the activity of enzymes, effectively extending the shelf life of grouper.
[0010] Furthermore, the mass concentration of the compound preservative solution in the pretreatment step is 1.5% to 4.5%.
[0011] Furthermore, the precooling time in the precooling step is 30 to 60 minutes.
[0012] Furthermore, the longan polysaccharide is derived from longan pulp, specifically obtained through a water extraction and alcohol precipitation method. The preparation method of the longan polysaccharide includes the following steps: Longan pulp was collected, air-dried, and mixed with distilled water at a mass-to-volume ratio of 1g:4mL. Extraction was carried out at 90±2℃ for 6 hours, filtered, and the filtrate was concentrated by rotary evaporation at 68-72℃ until it reached a viscous state. While still hot, the filtrate was slowly poured into 4 times its volume of 95wt% ethanol, sealed, and allowed to stand to obtain an alcohol precipitate. The precipitate was prepared into a 5.0g / ml solution with water, and papain was added to make the final concentration of papain 1g / ml. The solution was incubated at 50±2℃ for 3 hours to inactivate the enzyme. The precipitate was centrifuged to obtain the supernatant, which was then concentrated to remove water, yielding longan polysaccharide.
[0013] Compared with the prior art, the beneficial results of the present invention are as follows: The ultra-low temperature preservation method of the present invention can extend the shelf life of grouper to 6-12 months, and the preservation effect is significantly improved compared with traditional preservation methods, which can meet the preservation needs of grouper during long-distance transportation and long-term storage. The pretreatment and cooling steps of this invention effectively reduce cell damage caused by ice crystals, significantly reducing the juice loss rate of the grouper after thawing, generally controlling it to below 5%. It also results in lower microbial content and a lower TVB-N value (TVB-N is related to the degree of protein denaturation and is an important indicator of freshness), preserving the tender texture and original flavor of the grouper. Simultaneously, the nutritional components of the grouper are well preserved, with minimal loss of nutrients such as protein and unsaturated fatty acids. The composite preservative solution used in this invention is made of natural ingredients, contains no harmful chemicals, meets food safety requirements, and avoids the chemical residue problems that may exist in chemical preservation methods, making it safer and more environmentally friendly. Furthermore, the effective components of this preservative solution are used in low quantities, are readily available, and have a simple preparation method, which helps to reduce preservation costs. The ultra-low temperature preservation method of the present invention has a clear and simple operation process, and the required equipment is a common freezing and refrigeration device, which is easy to promote and apply in actual production. Detailed Implementation
[0014] To better understand the technical content of this invention, the invention will be further described below with reference to specific embodiments.
[0015] Preparation method of longan polysaccharide: Longan pulp was collected, air-dried, and mixed with distilled water at a mass-to-volume ratio of 1g:4mL. Extraction was carried out at 90±2℃ for 6 hours, filtered, and the filtrate was concentrated by rotary evaporation at 68-72℃ until it reached a viscous state. While still hot, the filtrate was slowly poured into 4 times its volume of 95wt% ethanol, sealed, and allowed to stand to obtain an alcohol precipitate. The precipitate was prepared into a 5.0g / ml solution with water, and papain was added to make the final concentration of papain 1g / ml. The solution was incubated at 50±2℃ for 3 hours to inactivate the enzyme. The precipitate was centrifuged to obtain the supernatant, which was then concentrated to remove water, yielding longan polysaccharide.
[0016] The initial mass before preservation is recorded as m1. After preservation, the thawed grouper is gently wiped of its surface juice with clean filter paper and weighed, and the mass after preservation is recorded as m2. Juice loss rate = (m1-m2) / m1×100%.
[0017] The volatile basic nitrogen (TVB-N) value of fish meat was determined using a Kjeldahl nitrogen analyzer, in accordance with GB 5009.228-2016. The total bacterial count was determined according to GB 4789.2-2016, the method for microbiological testing of food.
[0018] Example 1: Ultra-low temperature preservation method for grouper (1) Pretreatment: Take freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1.5% compound preservation solution (of which the mass fraction of longan polysaccharide is 0.5%, the mass fraction of chitosan is 1.0%, and the remainder is water) for 15 minutes.
[0019] (2) Pre-cooling: Place the pre-treated grouper in a pre-cooling room at 0~4℃ for 30 minutes.
[0020] (3) Rapid cooling: The temperature of the fish is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 10℃ / minute.
[0021] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0022] Preservation effect test: Before preservation, the initial TVB-N value was 8.31±0.28 mg N / 100g, and the total bacterial count was 3.02 lg (CFU / g)~3.25 lg (CFU / g).
[0023] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing showed that the thawed fish meat had a normal color, clear, tight, and intact fibers, and elastic tissue with minimal nutrient loss. The juice loss rate of the grouper was 4.5±0.2%, the TVB-N value was 10.32±0.24 mg N / 100g, and the bacterial count was 4.54 lg (CFU / g)~4.67 lg (CFU / g).
[0024] After 12 months of preservation, the fish meat has a normal color, clear, relatively tight and intact fibers, elastic tissue, and minimal loss of nutrients. The juice loss rate of the grouper is 5.7±0.3%, the TVB-N value is 13.59±0.21 mg N / 100g, and the colony count is 5.34 lg (CFU / g)~5.78 lg (CFU / g).
[0025] Example 2: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 4.5% compound preservation solution (1.5% longan polysaccharide, 3.0% chitosan, and the remainder is water) for 15 minutes.
[0026] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0027] (3) Rapid cooling: Use liquid nitrogen spraying at a cooling rate of 10℃ / minute to reduce the fish body temperature to -18~-20℃.
[0028] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0029] Preservation effect test: Before preservation, the initial TVB-N value was 8.49±0.25 mg N / 100g, and the total bacterial count was 3.34 lg (CFU / g) to 3.58 lg (CFU / g).
[0030] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing showed that the thawed fish meat had a normal color, clear, tight, and intact fibers, and elastic tissue with minimal nutrient loss. The juice loss rate was 4.0±0.1%, the TVB-N value was 9.89±0.25 mg N / 100g, and the bacterial count was 4.26 lg (CFU / g)~4.37 lg (CFU / g).
[0031] Example 3: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 4.5% compound preservation solution (1.5% longan polysaccharide, 3.0% chitosan, and the remainder is water) for 15 minutes.
[0032] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0033] (3) Rapid cooling: The temperature is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 5℃ / minute.
[0034] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0035] Preservation effect test: Before preservation, the initial TVB-N value was 8.56±0.29 mg N / 100g, and the total bacterial count was 3.67 lg (CFU / g)~3.86 lg (CFU / g).
[0036] After being stored for 6 months, the thawed fish meat had a normal color, clear, tight and intact fibers, and elastic tissue. The loss of nutrients was minimal. The juice loss rate of the grouper was 4.6±0.1%, the TVB-N value was 10.35±0.29mg N / 100g, and the colony count was 4.51 lg (CFU / g)~4.74 lg (CFU / g).
[0037] Example 4: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1% compound preservative solution (0.2% longan polysaccharide, 0.8% chitosan, and the remainder is water) for 15 minutes.
[0038] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0039] (3) Rapid cooling: Use liquid nitrogen spraying at a cooling rate of 10℃ / minute to reduce the fish body temperature to -18~-20℃.
[0040] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0041] Preservation effect test: Before preservation, the initial TVB-N value was 9.02±0.23 mg N / 100g, and the total bacterial count was 3.25 lg (CFU / g)~3.49 lg (CFU / g).
[0042] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing showed that the thawed fish meat had a relatively normal color, clear, tight, and intact fibers, elastic tissue, and minimal loss of nutrients. The juice loss rate of the grouper was 6.2±0.1%, the TVB-N value was 15.98±0.33 mg N / 100g, and the bacterial count was 5.54 lg (CFU / g)~5.89 lg (CFU / g).
[0043] Compared to Example 1, the concentration of preservative ingredients is reduced, and the preservation effect is reduced, but its overall preservation effect is still better than the comparative example.
[0044] Comparative Example 1: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1.5% compound preservative solution (trehalose 0.5% by mass, chitosan 1.0% by mass, and the remainder is water) for 15 minutes.
[0045] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0046] (3) Rapid cooling: The temperature of the fish is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 10℃ / minute.
[0047] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0048] Preservation effect test: Before preservation, the initial TVB-N value was 8.93±0.21 mg N / 100g, and the total bacterial count was 3.35 lg (CFU / g)~3.66 lg (CFU / g).
[0049] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing revealed that the thawed fish meat was slightly darker in color, with clearly defined and relatively tight fibers, and the meat tissue retained some elasticity. The grouper's juice loss rate was 10.4±0.1%, the TVB-N value was 27.64±0.37 mg N / 100g, and the bacterial count was 6.36 lg (CFU / g) to 6.75 lg (CFU / g).
[0050] Compared to the previous example, the preservation effect was poor.
[0051] Comparative Example 2: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1.5% preservation solution (chitosan mass fraction is 1.5%, the remainder is water) for 15 minutes.
[0052] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0053] (3) Rapid cooling: The temperature of the fish is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 10℃ / minute.
[0054] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0055] Preservation effect test: Before preservation, the initial TVB-N value was 9.61±0.24 mg N / 100g, and the total bacterial count was 3.19 lg (CFU / g)~3.34 lg (CFU / g).
[0056] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing revealed that the thawed fish meat was dark in color, with indistinct fibers, and the meat tissue retained slight elasticity. The grouper's juice loss rate was 12.5±0.3%, the TVB-N value was 34.44±0.59 mg N / 100g, and the bacterial count was 6.79 lg (CFU / g) to 7.02 lg (CFU / g).
[0057] Compared to the previous example, the preservation effect was poor.
[0058] Comparative Example 3: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1.5% compound preservative solution (0.5% longan polysaccharide, 1.0% chitosan, and the remainder water) for 15 minutes.
[0059] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0060] (3) Rapid cooling: The temperature of the fish is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 15℃ / minute.
[0061] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0062] Preservation effect test: Before preservation, the initial TVB-N value was 9.40±0.19 mg N / 100g, and the total bacterial count was 3.74lg (CFU / g)~3.87lg (CFU / g).
[0063] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0-4℃. Testing revealed that the thawed fish meat was dark in color, with indistinct fibers, and the meat tissue retained slight elasticity. The grouper's juice loss rate was 8.3±0.2%, the TVB-N value was 20.36±0.59 mg N / 100g, and the bacterial count was 6.02 lg (CFU / g) to 6.35 lg (CFU / g).
[0064] Comparative Example 4: Ultra-low temperature preservation method for grouper (1) Pretreatment: Select freshly caught grouper, remove the internal organs, scales and gills, wash with clean water and drain. Soak the grouper in a 1.5% compound preservative solution (0.5% longan polysaccharide, 1.0% chitosan, and the remainder water) for 15 minutes.
[0065] (2) Pre-cooling: Pre-cool in a pre-cooling room at 0~4℃ for 30 minutes.
[0066] (3) Rapid cooling: The temperature of the fish is reduced to -18~-20℃ by liquid nitrogen spraying at a cooling rate of 2℃ / minute.
[0067] (4) Ultra-low temperature freezing: frozen storage in an ultra-low temperature cold storage at -18~-20℃.
[0068] Preservation effect test: Before preservation, the initial TVB-N value was 9.25±0.20 mg N / 100g, and the total bacterial count was 3.71 lg (CFU / g)~3.33 lg (CFU / g).
[0069] After 6 months of preservation, the frozen grouper was removed and slowly thawed in an environment of 0~4℃. Testing revealed that the thawed fish meat was dark in color, with indistinct fibers, and the meat tissue had slight elasticity. The grouper's juice loss rate was 9.6±0.3%, the TVB-N value was 23.65±0.47 mg N / 100g, and the bacterial count was 6.34 lg (CFU / g)~6.67 lg (CFU / g).
[0070] Compared to the examples, Comparative Examples 3 and 4 showed poorer preservation effects. This indicates that the cooling rate has a significant impact on the preservation effect, and controlling a reasonable cooling rate is a key parameter to ensure the preservation of grouper.
[0071] The above description is only a part of the embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall fall within the protection scope of the present invention.
Claims
1. A method for ultra-low temperature preservation of grouper, characterized in that, Includes the following steps: (1) Pretreatment: Remove the internal organs, scales and gills from the freshly caught grouper, wash it, drain the water and soak it in a compound preservation solution, which is composed of longan polysaccharide, chitosan and water. (2) Pre-cooling: Pre-cool the pre-treated grouper at a temperature of 0~4℃; (3) Rapid cooling: Rapidly cool the pre-cooled grouper to -18 ~ -20℃; (4) Ultra-low temperature freezing: freeze and store at a temperature of -18 ~ -20℃.
2. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The composite preservative solution consists of 0.5%–1.5% longan polysaccharide, 1.0%–3.0% chitosan, and the remainder water by mass.
3. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The composite preservative solution consists of 1.5% longan polysaccharide, 3% chitosan, and the remainder water by mass.
4. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, In step (1), the mass concentration of the compound preservative solution is 1.5% to 4.5%.
5. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, In step (1), the grouper is soaked in the compound preservative solution for 15 to 30 minutes.
6. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The precooling time in step (2) is 30 to 60 minutes.
7. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, In step (3), the cooling rate is 5~10℃ / minute.
8. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The longan polysaccharide is longan pulp polysaccharide.
9. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The longan polysaccharide was obtained by water extraction and alcohol precipitation.
10. The method for ultra-low temperature preservation of grouper according to claim 1, characterized in that, The preparation method of the longan polysaccharide is as follows: Longan pulp was taken, dried in the shade, and mixed with water at a mass-to-volume ratio of 1g:4mL. The mixture was extracted at 90±2℃ for 6 hours, filtered, and the filtrate was concentrated by rotary evaporation at 68~72℃ until it became viscous. While still hot, the filtrate was slowly poured into 4 times its volume of 95wt% ethanol, sealed, and allowed to stand to obtain an alcohol precipitate. The alcohol precipitate was prepared into a solution with water, and papain was added to make the final concentration of papain 1g / ml. The solution was kept at 50±2℃ for 3 hours to inactivate the enzyme. The solution was centrifuged to obtain the supernatant, which was then concentrated to remove water to obtain longan polysaccharide.