Preparation method of half-dried freshwater fish

Abstract

The invention belongs to the technical field of aquatic product processing, and particularly relates to a preparation method of a semi-dry freshwater fish, which comprises the following steps: S1, carrying out low-temperature plasma treatment on the back muscle of the freshwater fish for 3-5 minutes, and then adding the back muscle into a soaking solution according to a material-liquid ratio of 0.5-1.5 / 5 (w / v) to obtain a pickled sample; s2, carrying out segmented wind-heat drying on the pickled sample; the sectional air-heat drying at least comprises three sections of air-heat drying, the temperature of the first section of air-heat drying is 21-26 DEG C, and the humidity is 60-70%; the temperature of the second-stage wind heat drying is 30-35 DEG C, and the humidity is 40-50%; the temperature of the third-section wind heat drying is 35-40 DEG C, and the humidity is 20-30%. According to the method disclosed by the invention, by combining flexible treatment of low-temperature plasma and variable-temperature drying, the finally obtained fish meat is more tender and smoother, and the problem of dry and hard meat quality caused by excessive drying is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of aquatic product processing, and particularly relates to a preparation method of semi-dried freshwater fish. Background Art

[0002] Freshwater fish has a certain earthy smell, so consumers need to go through a series of deodorization processes after purchase, and the process is cumbersome. At present, most traditional aquatic products are pickled with high salt, combined with a sun-drying process, which has high salt content and low moisture content. However, the low heat transfer coefficient and surface hardening of food hinder the removal of moisture, resulting in a longer drying time during the pickling process of traditional aquatic products, resulting in a decline in product quality, poor rehydration, hard texture, and excessive production energy consumption.

[0003] Prior art CN101254003B discloses a method for preparing semi-dried seasoned fish food, including pretreatment of raw fish, rinsing with clean water, drying and other process flows. Before rinsing with clean water, soak the fish body in a mixed aqueous solution of salt and EDTA; before drying, mix a certain amount of sodium isovitamin C into the seasoning for pickling treatment; and dry the fish body using a low-temperature drying technology of 10 to 20°C, so that the moisture content of the product fish body is between 40 and 65%. The ratio of the mixed aqueous solution of salt and EDTA is: 2 to 10 grams of salt and 0.2 to 0.5 grams of EDTA are contained by weight in every 100 milliliters of water, and the soaking time of the fish body is 10 to 60 minutes. The amount of sodium isovitamin C mixed in the seasoning is 0.2 to 0.5% of the weight of the pickled fish. However, the method uses salt penetration and soaking, which will cause local muscle hardness and affect the uniformity of texture.

[0004] Prior art CN201510819730.9 proposes a method for producing a deodorized, low-salt, semi-dried freshwater fish, which is pre-treated, rinsed with 0.5% salt water, drained, marinated, washed, air-dried at 15-20°C, shaped, vacuum sealed, inspected, and stored. The invention uses low-salt, low-temperature deodorization, marinating, and low-temperature semi-air-drying. While achieving deodorization and low salt, low-temperature conditions are used, and the degree of oxidation of the fish body is low, which better preserves the meat quality and nutrition of the freshwater fish. At the same time, a step-by-step, gradually heated, and slowly rehydrated air-drying method is used to speed up the air-drying speed and efficiency, and prevent the problem that the moisture in the meat is not easy to evaporate after the fish skin clumps during the constant temperature one-time air-drying process. In this scheme, low temperature is first used to evaporate the moisture on the surface of the fish body, and then the moisture in the meat is evaporated by heating after slow rehydration treatment, which increases the evaporation efficiency and does not affect air drying. However, this method may lead to protein dissolution and nutrient loss compared to longer rinsing, limited penetration depth of marinade, and low seasoning uniformity.

[0005] Prior art CN113491322B discloses a method for preparing semi-dried abalone, comprising the following steps: using fresh abalone as raw material, after shelling and viscera removal, using a sodium alginate aqueous solution containing papain to rinse off dirt on the surface of the abalone gastropod muscle, using an aqueous solution containing sodium chloride, sucrose and Agaricus bisporus extract to soak for 4-8 days, then using a 65°C-75°C-85°C hot water bath gradient heating, draining, placing at a temperature of 40-60°C, humidity of 50%-70% for 3-5 months, and regularly using microwaves to promote Maillard reaction inside the abalone gastropod muscle, to prepare a semi-dried abalone product with a "soft-core" mouthfeel. However, the 65°C-75°C-85°C hot water bath gradient heating precooking and subsequent constant temperature drying of the invention can cause tissue shrinkage and oxidation problems, affecting taste, texture and nutrition. In addition, the process is complex and the time cycle is long, which is not suitable for large-scale industrial production.

[0006] Prior art CN 117064042 A relates to a method for processing low-salt air-dried golden pomfret. The method comprises: removing the internal organs of the golden pomfret, making incisions on both sides of the fish body, and washing; using a low-temperature plasma jet device to treat deionized water below the liquid surface for 5 to 300 seconds, sealing the treated water and refrigerating it at 0 to 4°C for 10 to 40 minutes to obtain low-temperature plasma activated water; preparing a saline solution with a concentration of 0.2 to 4%, and mixing the low-temperature plasma activated water with the saline solution at a volume ratio of 1:1 to 10 to obtain a pickling solution; immersing the golden pomfret in the pickling solution, pickling at 0 to 4°C, and turning the fish body over once every 5 to 8 hours; taking out after pickling, draining the water, and air-drying under temperature and humidity control. The advantages are: significantly reducing the salt content and lipid oxidation degree of the air-dried golden pomfret; increasing the elasticity, adhesiveness and chewiness of the golden pomfret, with lower hardness and brighter color. However, the invention uses low-temperature plasma activated water for treatment, which takes a long time and is a more complicated process. Moreover, the active ingredients in the activated water (such as active oxygen, active nitrogen, etc.) may gradually disappear over time and storage conditions, resulting in a decrease in the effect (such as reduced bactericidal effect; reduced protein oxidation and fat oxidation effects, and reduced production of favorable flavor and taste components). In addition, when low-temperature plasma activated water is used to treat fish meat, oxidative substances cannot completely penetrate into deep tissues, and their effects are mainly concentrated on the surface of the fish meat.

[0007] Prior art CN 112931802 A uses dielectric barrier discharge plasma as a low-temperature plasma treatment system, and uses an air pump to introduce air into the DBD reactor through the air inlet as a plasma working gas. The semi-dried cured fish product to be treated is placed in a container, which is connected to the gas outlet of the DBD reactor by an air guide tube. During the treatment process, nitrogen, oxygen, etc. in the air will be ionized in the plasma treatment system to generate various particles containing nitrogen and oxygen, and further react to generate various substances such as NO2, O3, NO, etc., which enter the container containing semi-dried cured fish through the air guide tube, and the oxidation characteristics of these substances are used to promote the moderate oxidation of the cured fish lipids, generating a variety of lipid oxidation products with special aromatic odors, thereby improving the flavor of the cured fish. However, the invention uses hot air constant temperature drying, which has a slow drying speed and low efficiency, and the energy required for the entire drying process is relatively large, resulting in high energy consumption. Secondly, constant temperature drying easily aggravates the hardening of the fish surface, affecting the texture and taste of the product. In addition, constant temperature drying will cause a greater loss of nutrients in the fish. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing semi-dried freshwater fish with high rehydration rate and stable storage property.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A method for preparing semi-dried freshwater fish comprises the following steps:

[0011] S1, taking freshwater fish back muscle and subjecting it to low-temperature plasma treatment for 3-5 minutes, and then adding it to the soaking solution according to a material-liquid ratio of 0.5-1.5 / 5 (w / v) to obtain a pickled sample;

[0012] S2. The pickled sample is subjected to segmented air-heat drying; the segmented air-heat drying includes at least three segments of air-heat drying, wherein the temperature of the first segment of air-heat drying is 21-26°C and the humidity is 60-70%; the temperature of the second segment of air-heat drying is 30-35°C and the humidity is 40-50%; the temperature of the third segment of air-heat drying is 35-40°C and the humidity is 20-30%.

[0013] The raw materials are uniformly selected from the back muscles of fresh freshwater fish. Firstly, the back muscles are relatively high in nutritional value, more tender, with fine muscle fibers and good taste; secondly, the back muscles have less fat content and are less affected by oil oxidation during the process of making dried fish; and the higher protein content can ensure that the dried fish has a crispier taste after production.

[0014] Compared with constant temperature drying, segmented air-heat drying has the following main advantages: First, segmented air-heat drying can increase the drying speed. By drying at different temperatures, the evaporation rate of water can be accelerated, thereby shortening the drying time. In comparison, constant temperature drying requires a longer time to achieve the same drying effect; secondly, during the segmented air-heat drying process, lower temperatures can help maintain the color and taste of the fish meat, and avoid over-drying that causes the texture of the fish meat to become hard or the color to become darker; finally, compared with constant temperature drying, segmented air-heat drying can better retain the nutrients in the fish meat. Drying at a lower temperature can slow down the loss of nutrients, allowing the fish meat to remain more nutritious.

[0015] The temperature setting of the segmented air-heat drying is obtained after multiple optimizations of the present invention. Too high a temperature will have an adverse effect on the quality of fish products: it will cause the fish to be over-dried, lose too much water, become too hard or too brittle, and affect the taste. At too high a temperature, the protein in the fish may undergo thermal denaturation, affecting the taste and texture, and leading to the loss of nutrients. High temperature will accelerate the oxidative decomposition of fat, affecting the flavor of the fish, and may produce unpleasant odors. If the temperature is too low, the residual moisture in the fish will evaporate slowly, and the drying may not be thorough, resulting in a high moisture content. When air-drying, if the moisture content needs to meet the requirements of semi-dry products, the drying time needs to be extended, but too long a time will easily breed corrupt microorganisms. It is more difficult to remove residual moisture at low temperatures, and the drying time will be significantly extended, affecting production efficiency.

[0016] The initial temperature is set at 21-26℃. The initial drying stage is the stage of evaporation of surface moisture of the fish meat. This temperature range is set to ensure the slow evaporation of surface moisture. The humidity is controlled at 60-70%. At this stage, the moisture content of the fish meat is high, and a higher humidity is required to avoid rapid water loss on the surface to prevent the surface from hardening.

[0017] The temperature in the middle stage is set at 30-35℃. This temperature can speed up the migration and evaporation rate of the water inside the fish meat. It should not be too high, otherwise it will cause texture changes or nutritional loss. This stage is the most important stage in the entire drying process. The temperature cannot be too low, otherwise it will prolong the drying time; it cannot be too high, otherwise it will affect the flavor and taste. The humidity is controlled at 40-50%. At this time, the water inside the fish meat gradually migrates outwards. Properly reducing the humidity can speed up the evaporation rate of the water.

[0018] The temperature is set at 35-40℃ in the later stage to reduce residual moisture and complete drying. The high temperature setting at this stage helps to remove residual moisture in the fish meat and ensure the final quality and preservation of the dried product. However, the temperature should not be too high to avoid destroying the flavor and texture of the fish meat. The humidity should be controlled at 20-30%. Low humidity helps to further remove residual moisture and achieve the desired semi-drying effect.

[0019] The invention obtains semi-dried freshwater fish with softer texture, higher rehydration rate and longer shelf life by controlling appropriate temperature and humidity, while also not affecting the taste.

[0020] In one preferred embodiment, the process of low-temperature plasma treatment is as follows: the low-temperature plasma power is 200-380W and the voltage is 55-75kV.

[0021] The use of low-temperature plasma for pre-treatment has the following advantages: first, it can effectively kill bacteria, parasites and other microorganisms on the fish, thereby ensuring the hygiene and safety of the dried fish; second, it has little impact on the quality of the fish meat and can maintain the nutritional content, taste and color of the fish meat; in addition, it can effectively remove the odor in the fish meat, making the dried fish purer and odor-free during the production process; finally, it can improve production efficiency and will not cause excessive processing of the fish meat.

[0022] Too high power and voltage or too long a time will lead to excessive oxidation of protein and fat in the fish, causing loss of nutrients and easy spoilage; too low a power and voltage or too short a time will have no effect and will not significantly enhance the flavor and taste of the fish.

[0023] In one of the preferred embodiments, the soaking solution comprises, by weight: 5-7 parts of salt, 2-4 parts of glycerol, 3-5 parts of phosphate, and 80-92 parts of water.

[0024] Glycerol and phosphates work together to improve the water retention and tenderness of food. Glycerol prevents excessive water loss during the drying process by maintaining hydration, while phosphates help maintain the hydration structure of the food, especially during the low-temperature drying stage. The synergistic effect of the two can improve the water retention of fish meat and make it taste more tender. And combined with the effect of low-temperature plasma on protein structure, it is more conducive to water retention.

[0025] Low-temperature plasma treatment can generate a large number of free radicals and active oxygen species, which can react with oxidative substances in food to reduce the oxidation of fatty acids. Glycerol itself has a certain antioxidant effect and can help reduce the rate of fat oxidation. The effect of low-temperature plasma and glycerol work synergistically, making food more stable during storage and reducing the oxidative degradation of fatty acids and other nutrients.

[0026] Excessive addition of food additives may lead to negative effects, destroying the natural taste, flavor and nutritional value of fish.

[0027] In one preferred embodiment, the back muscles of freshwater fish are cut into rectangular fish blocks and then subjected to low-temperature plasma treatment.

[0028] In one preferred embodiment, the length, width and thickness of the rectangular fish block are 3-5 cm, 2-4 cm and 1-3 cm respectively.

[0029] In a preferred embodiment, the freshwater fish is at least one of mandarin fish, seabass, carp, bream, snakehead carp, grass carp, tilapia, silver carp and bighead carp.

[0030] In one preferred embodiment, the moisture content of the semi-dried freshwater fish is 35%-40%.

[0031] In a preferred embodiment, the rehydration rate of the semi-dried freshwater fish is 20%-31%.

[0032] The beneficial effects of the present invention are:

[0033] Low-temperature plasma acts on the surface of freshwater fish through plasma generated by high voltage, which can reduce the production of fishy smell through the action of active substances such as oxygen free radicals and nitrogen free radicals. Secondly, low-temperature plasma can destroy cell membranes, enhance the hydration of fish meat, and help improve the permeability of solutions (glycerol, phosphate, etc.) in the subsequent pickling process. Thereby inhibiting the growth of microorganisms, reducing the damage of microorganisms to fish meat, and extending the shelf life. More importantly, low-temperature plasma can also change its molecular structure by interacting with proteins, etc. The oxidative denaturation of proteins helps to improve the flavor and improve the tenderness and moisture retention capacity of the meat, preventing excessive water loss during the drying process. Further combined with the flexible treatment of variable temperature drying, the final fish meat is more tender and smooth, avoiding the problem of dry and hard meat caused by excessive drying. Moreover, the moisture distribution of the fish meat treated with plasma is more uniform during the variable temperature drying process, which helps to maintain the moisture balance of the fish meat and obtain a semi-dried freshwater fish with a better taste. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Lipid oxidation analysis of the semi-dried fish products processed in Example 1, Comparative Example 2 and Comparative Example 6;

[0035] Figure 2 The results of melanoidin changes in the semi-dried fish products processed in Example 1, Comparative Example 2 and Comparative Example 6 are shown. DETAILED DESCRIPTION

[0036] The present invention is not limited to the following specific embodiments. A person skilled in the art can implement the present invention in various other specific embodiments according to the contents disclosed in the present invention, or any simple changes or modifications made to the design structure and ideas of the present invention fall within the protection scope of the present invention. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0037] Example 1

[0038] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 65kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were placed in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked for 3 hours at 4°C to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), respectively, and semi-dried fish products were obtained after drying for 24 hours.

[0039] Example 2

[0040] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 390W and a voltage of 65kV, and low-temperature plasma treatment was performed for 3 minutes. The samples were placed in a soaking solution (salt: 6g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked for 3 hours at 4°C to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours each at 25°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), and semi-dried fish products were obtained after drying for 24 hours.

[0041] Example 3

[0042] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 55kV for 3 minutes. The samples were soaked in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) at 4°C for 3 hours to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 22°C (humidity controlled at 60%), 35°C (humidity controlled at 45%) and 35°C (humidity controlled at 25%), respectively, and semi-dried fish products were obtained after drying for 24 hours.

[0043] Comparative Example 1

[0044] Constant temperature drying 1

[0045] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device. The power of the low-temperature plasma was 380W and the voltage was 65kV. The low-temperature plasma treatment was performed for 5 minutes. The samples were placed in an immersion solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked at 4°C for 3 hours to obtain a pickled sample. After pickling, the moisture on the surface of the fish block was wiped dry, and then placed in a heat pump dryer and dried at a constant temperature of 40°C (humidity controlled at 25%) for 24 hours.

[0046] Comparative Example 2

[0047] Constant temperature drying 2

[0048] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device. The power of the low-temperature plasma was 380W and the voltage was 65kV. The low-temperature plasma treatment was performed for 5 minutes. The samples were placed in an immersion solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked at 4°C for 3 hours to obtain a pickled sample. After pickling, the moisture on the surface of the fish block was wiped dry, and then placed in a heat pump dryer and dried at a constant temperature of 30°C (humidity controlled at 45%) for 24 hours.

[0049] Comparative Example 3

[0050] Constant temperature drying 3

[0051] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device. The power of the low-temperature plasma was 380W and the voltage was 65kV. The low-temperature plasma treatment was performed for 5 minutes. The samples were placed in an immersion solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked at 4°C for 3 hours to obtain a pickled sample. After pickling, the moisture on the surface of the fish block was wiped dry, and then placed in a heat pump dryer and dried at a constant temperature of 21°C (humidity controlled at 65%) for 24 hours.

[0052] Comparative Example 4

[0053] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 65kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were placed in a soaking liquid (salt: 7g / 100g) and soaked at 4°C for 3h to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8h at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%), and 40°C (humidity controlled at 25%).

[0054] Comparative Example 5

[0055] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 65kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were placed in a soaking solution (salt: 7g / 100g, glycerol: 3g / 100g) and soaked at 4°C for 3h to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8h at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%), and 40°C (humidity controlled at 25%).

[0056] Comparative Example 6

[0057] Low temperature plasma activated water treatment

[0058] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). Deionized water was excited for 5 minutes using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 65kV to obtain low-temperature plasma activated water. The sample was placed in a mixture of low-temperature plasma activated water and soaking liquid (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) with a volume ratio of 1:1, and soaked at 4℃ for 3h to obtain a pickled sample. After pickling, the moisture on the surface of the fish block was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8h at 21℃ (humidity controlled at 65%), 30℃ (humidity controlled at 45%) and 40℃ (humidity controlled at 25%).

[0059] Comparative Example 7

[0060] No plasma treatment

[0061] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The samples were soaked in soaking liquid (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) at 4°C for 3h to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8h at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), and semi-dried fish products were obtained after drying for 24h.

[0062] Comparative Example 8

[0063] Low temperature plasma power is too high

[0064] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 500W and a voltage of 65kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were soaked in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) at 4°C for 3 hours to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), respectively, and semi-dried fish products were obtained after drying for 24 hours.

[0065] Comparative Example 9

[0066] Low temperature plasma power is too low

[0067] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 200W and a voltage of 65kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were placed in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked for 3 hours at 4°C to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), respectively, and semi-dried fish products were obtained after drying for 24 hours.

[0068] Comparative Example 10

[0069] Low temperature plasma voltage is too high

[0070] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 100kV, and low-temperature plasma treatment was performed for 5 minutes. The samples were placed in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) and soaked for 3 hours at 4°C to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), respectively, and semi-dried fish products were obtained after drying for 24 hours.

[0071] Comparative Example 11

[0072] Low temperature plasma voltage is too low

[0073] Fresh and clean silver carp were stored in crushed ice and processed immediately within 20 minutes after slaughter. The back muscles were cut into rectangular blocks of about 4cm×3cm×2cm (about 20g). The fish blocks were pre-treated using a low-temperature plasma device, with a low-temperature plasma power of 380W and a voltage of 25kV for 5 minutes. The samples were soaked in a soaking solution (salt: 7g / 100g; glycerol: 3g / 100g; phosphate: 5g / 100g) at 4°C for 3 hours to obtain pickled samples. After pickling, the moisture on the surface of the fish blocks was wiped dry, and then placed in a heat pump dryer for variable temperature drying, and dried for 8 hours at 21°C (humidity controlled at 65%), 30°C (humidity controlled at 45%) and 40°C (humidity controlled at 25%), and semi-dried fish products were obtained after drying for 24 hours.

[0074] The moisture content of the fish products obtained in Examples 1-3 and Comparative Examples 1-11, as well as the rehydration rate after rehydration for 60 minutes, were tested. The results are shown in Table 1.

[0075] Table 1 Moisture content of semi-dried fish products and rehydration rate after 60 minutes of rehydration

[0076]

[0077]

[0078] The data in Table 1 show that the rehydration rate of fish products obtained by variable temperature drying is higher than that of fish products dried at constant temperatures of 40°C, 30°C and 21°C, indicating that the fish products obtained by variable temperature drying have higher water reabsorption and more uniform texture. At the same time, the rehydration rate of fish products obtained by adding glycerol and phosphate to the soaking solution is higher, indicating that the addition of glycerol and phosphate increases the water retention of fish tissue and the texture of the obtained fish products is better. The rehydration rate of fish products obtained by adding low-temperature plasma water is lower than that of fish products directly treated with low-temperature plasma, indicating that the effect of fish meat directly treated with low-temperature plasma is better.

[0079] The appearance color and puncture hardness of the fish products obtained in Examples 1-3 and Comparative Examples 1-10 were tested, and the results are shown in Table 2.

[0080] Table 2 Color difference parameters and puncture hardness of semi-dried fish products

[0081]

[0082]

[0083] The data in Table 2 show that low-temperature plasma treatment has no adverse effect on the color of dried silver carp products, and the light reflection ability of the fish surface juice after low-temperature plasma treatment is enhanced, resulting in an increase in the brightness of the fish. Low-temperature plasma treatment increases the gloss of dried silver carp products, making the appearance color appear golden. At the same time, the results of Comparative Examples 4 and 5 show that the appearance color and gloss of the fish products obtained by drying after pickling in the soaking liquid without adding phosphate are reduced, indicating that phosphate can prevent the fish from changing color during the pickling process.

[0084] Secondly, the results of puncture hardness show that the puncture hardness of the fish products obtained by constant temperature drying is higher. The hardness of the fish products obtained under variable temperature drying and after low-temperature plasma treatment is lower. Moreover, with the increase of low-temperature plasma treatment time, the puncture hardness of the fish products gradually decreases. This is because low-temperature plasma combined with variable temperature drying has a positive effect on maintaining the texture of fish meat and can reduce the formation of a hard shell. Moreover, the soaking solution of Comparative Example 4 does not have the water-retaining effect of glycerol and phosphate on fish meat, which leads to an increase in the puncture hardness of the fish products. The semi-dried fish product obtained after 5 minutes of low-temperature plasma treatment in Example 1 has the lowest puncture hardness. Compared with Comparative Example 7 without low-temperature plasma treatment, the semi-dried fish products obtained in Examples 1-2 have a more uniform moisture distribution, a softer structure, and are more conducive to people's consumption and digestion.

[0085] The thiobarbituric acid values ​​(TBARs) and melanoidin contents of the semi-dried fish products obtained in Example 1, Comparative Example 6 and Comparative Example 7 were tested. The results are as follows: Figure 1 , 2As shown. The TBARs value of the semi-dried fish product obtained in Example 1 is 1.96 mg / kg, while the TBARs value of Comparative Example 6 is 1.41 mg / kg, and the TBARs value of Comparative Example 7 is 1.21 mg / kg. Compared with the low-temperature plasma activated water used in Comparative Example 6, the TBARs value of the semi-dried fish product obtained in Example 1 is significantly increased, indicating that the direct low-temperature plasma operation on the fish meat is more effective in promoting fat oxidation than the low-temperature plasma activated water. Generally, for fish products, a TBARs value of less than about 7 mg / kg is within the acceptable range for consumers. Therefore, the lipid oxidation caused by the low-temperature plasma treatment in the embodiment will not produce obvious negative effects, but the oxidation products can enrich the flavor components of the dried fish products. Melanoidin is a type of black-brown substance with an aromatic odor produced by the Maillard reaction of reducing sugars and amino acid compounds. It is a type of water-soluble mixture with a complex structure and a high degree of polymerization. Compared with Comparative Examples 6 and 7, the fish product treated with low-temperature plasma in Example 1 has the highest content of melanoidin. Therefore, low-temperature plasma treatment can improve the color and flavor of dried silver carp products by appropriately accelerating the Maillard reaction process.

[0086] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing semi-dried freshwater fish, characterized in that: The following steps are involved: S1, taking freshwater fish back muscle and subjecting it to low-temperature plasma treatment for 3-5 minutes, and then adding it to the soaking solution according to a material-liquid ratio of 0.5-1.5 / 5 (w / v) to obtain a pickled sample; S2. The pickled sample is subjected to segmented air-heat drying; the segmented air-heat drying includes at least three segments of air-heat drying, wherein the temperature of the first segment of air-heat drying is 21-26°C and the humidity is 60-70%; the temperature of the second segment of air-heat drying is 30-35°C and the humidity is 40-50%; the temperature of the third segment of air-heat drying is 35-40°C and the humidity is 20-30%.

2. The method for preparing semi-dried freshwater fish according to claim 1, characterized in that: The process of low-temperature plasma treatment is as follows: the power of low-temperature plasma is 200-380W, and the voltage is 55-75kV.

3. The method for preparing semi-dried freshwater fish according to claim 1, characterized in that: The soaking solution comprises, by weight, 5-7 parts of salt, 2-4 parts of glycerol, 3-5 parts of phosphate, and 80-92 parts of water.

4. The method for preparing semi-dried freshwater fish according to claim 1, characterized in that: The back muscles of freshwater fish are cut into rectangular fish blocks and then treated with low-temperature plasma.

5. The method for preparing semi-dried freshwater fish according to claim 1, characterized in that: The length, width and thickness of the rectangular fish pieces are 3-5cm, 2-4cm and 1-3cm respectively.

6. The method for preparing semi-dried freshwater fish according to claim 1, characterized in that: The freshwater fish is at least one of mandarin fish, seabass, carp, bream, black carp, grass carp, tilapia, silver carp and bighead carp.

7. The method for preparing the semi-dried freshwater fish according to any one of claims 1 to 6, characterized in that: The moisture content of the semi-dried freshwater fish is 35%-40%.

8. The method for preparing the semi-dried freshwater fish according to any one of claims 1 to 6, characterized in that: The rehydration rate of the semi-dried freshwater fish is 20%-31%.

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