Method for prolonging quality of frozen fillet by using chitosan / konjac glucomannan-based composite coating

Abstract

The invention discloses a method for prolonging the quality of frozen fillets by using a chitosan / konjac glucomannan-based composite coating film, and the preparation method comprises the following steps: fully mixing chitosan and konjac glucomannan powder with deionized water for swelling, preparing the composite coating film according to different substance weight ratios, and finally applying the coating film to the preservation of the frozen fillets. Wherein the composite coating material comprises chitosan and konjac glucomannan, and the auxiliary materials comprise acetic acid and glycerol. The chitosan and konjac glucomannan used in the invention are green, healthy and non-toxic, and the composite coating film prepared from the raw materials conforms to the food health concept; according to the present invention, the chitosan and the konjac glucomannan are blended to prepare the compact structure so as to effectively block the permeation of water, such that the fresh-keeping effect of the frozen fillet can be easily improved, the preparation process is simple, the raw materials are environmentally friendly and low in cost, and the method can be widely used in the field of food film coating.

Description

Technical Field

[0001] The present application belongs to the technical field of food preservation, and in particular relates to a method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating. Background Art

[0002] Fish, a general term for freshwater fish and marine fish, is rich in vitamins, tender and delicious, and has the characteristics of low fat and high protein, which is very popular among people. Especially for young children who are in the period of physical development, they should eat more fish. It can be seen that people's demand for fish and its products remains high. During the transportation of fish, it is usually stored at -18℃ for preservation; during transportation, nutrients such as protein and fat in fish are decomposed and even rotten due to oxidation reactions caused by long-term exposure to air.

[0003] At present, in the field of frozen fish storage, existing technologies usually adopt new freezing auxiliary technology or improve packaging methods combined with low-temperature freezing to extend the storage period of fish. However, the high price of new freezing auxiliary equipment, high production energy consumption, and low efficiency have greatly limited the promotion and use of new freezing auxiliary technology; and the new packaging technology will change the flavor of the fish itself by adding antioxidants and antibacterial agents, which is not the optimal solution for the preservation of frozen fish.

[0004] The main material of traditional frozen fish cling film is plastic products, which are limited to its wide application due to its low coverage, environmental pollution and biosafety. Chitosan, as a natural polysaccharide, is widely used in the field of food preservation due to its non-toxicity, antibacterial, degradation safety and film-forming properties. However, the high cost, poor barrier properties, poor mechanical properties and low light transmittance of chitosan limit its use alone. Konjac glucomannan is a natural high-molecular soluble dietary fiber with low price, high light transmittance and high biocompatibility. It can be prepared into an ideal coating material by fully mixing with chitosan.

[0005] Therefore, how to combine safe, healthy and low-cost konjac glucomannan material with chitosan to prepare a coating for improving the quality of frozen fish fillets during long-term storage, further reducing costs, and at the same time ensuring that the quality and nutrition of fish meat are not reduced while maximizing the storage period has become a hot trend in frozen fish research. Summary of the invention

[0006] The technical problem to be solved by this application is to overcome the deficiencies in the prior art that there are no effective preservation means for fish and its products, the existing preservation technical means cannot be promoted due to high prices, change the flavor of the fish itself, the traditional fresh-keeping film has low safety and poor mechanical properties, and the polysaccharide coating film lacks an effective preparation method and cannot be utilized. Therefore, a method for prolonging the quality of frozen fish fillets with a chitosan / konjac glucomannan-based composite coating film is provided. This application uses chitosan and konjac glucomannan as the base materials, and prepares the coating film material by uniformly mixing them according to a certain mass ratio, achieving high barrier properties to prevent the deterioration of the quality of fish, and the prepared coating film material has ideal gas barrier and water barrier properties, can effectively prevent water loss and the intrusion of external air, and thus delay the hardening and oxidation of frozen fish and achieve the preservation effect.

[0007] This application adopts the following technical solutions to solve the above technical problems:

[0008] First aspect:

[0009] This application provides a method for prolonging the quality of frozen fish fillets with a chitosan / konjac glucomannan-based composite coating film, which specifically includes the following steps:

[0010] (1) Dissolve chitosan in acetic acid solution for later use;

[0011] (2) Dissolve glucomannan in water to obtain a glucomannan solution for later use;

[0012] (3) Stir the chitosan solution and the glucomannan solution to obtain a coating solution, immerse the fish in the coating solution, and freeze it.

[0013] Preferably, step (1) satisfies at least one of the following conditions:

[0014] The mass fraction of the acetic acid solution is 1-3%.

[0015] The mass-volume ratio of the chitosan to the acetic acid solution is 1:(100-200) g / mL;

[0016] The chitosan is animal-derived chitosan;

[0017] The dissolution of chitosan in acetic acid solution also includes the operation of stirring and mixing evenly.

[0018] Preferably, step (2) satisfies at least one of the following conditions:

[0019] The glucomannan includes konjac glucomannan;

[0020] The molecular weight of the glucomannan is 2 million - 2 million (konjac glucomannan itself is a polysaccharide polymer, and the specific molecular weight is uncertain)

[0021] The mass ratio of the glucomannan to the water is 1:(100 - 200), for example, 1:150;

[0022] Dissolving the glucomannan in water further includes an operation of stirring and swelling. Preferably, the stirring time is 90 - 120 min;

[0023] The water includes deionized water.

[0024] Preferably, step (3) satisfies at least one of the following conditions:

[0025] The mass ratio of the chitosan solution to the glucomannan solution is 1:(2:1);

[0026] Glycerol is further added during the stirring of the chitosan solution and the glucomannan solution;

[0027] The stirring time is 120 - 150 min;

[0028] After the stirring, an operation of centrifugation is further included.

[0029] In step (3), it satisfies at least one of the following conditions:

[0030] The centrifugation time is 2 - 5 min;

[0031] The centrifugation speed is 4000 rpm;

[0032] The centrifugation is carried out in a centrifuge.

[0033] Preferably, in step (3), the time for immersing in the coating solution is 5 - 30 s;

[0034] The freezing temperature is -20 - -15 °C, for example, -18 °C.

[0035] The second technical solution of the present application is a chitosan / phenolic acid composite coating film prepared by using the above preparation method.

[0036] The third technical solution of the present application is the application of the above chitosan / phenolic acid composite coating film in the field of preservation of other meat foods.

[0037] On the basis of conforming to common general knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present application.

[0038] The reagents and raw materials used in the present application are all commercially available.

[0039] (1) The positive and progressive effects of this application are as follows: The chitosan / konjac glucomannan-based composite coating prepared in this application has better barrier properties compared to single materials, can effectively resist the influence of external factors on frozen fish fillets, and the modified chitosan has a broad-spectrum antibacterial effect, can resist psychrophilic bacteria, and reduce microbial activity.

[0040] (2) The composite coating prepared in this application has a good effect on the storage and preservation of frozen fish fillets, and has a good improvement effect on the hardness and other indicators of the fish fillets. Brief Description of the Drawings

[0041] This application can be better understood by referring to the description given in the following text in combination with the attached drawings. The attached drawings are included in this specification together with the following detailed description and form a part of this specification, and are used to further illustrate the preferred embodiments of this application and explain the principles and advantages of this application.

[0042] Among them:

[0043] Figure 1 is the change of the total volatile basic nitrogen content of frozen fish fillets with the storage days after being preserved with the chitosan / konjac glucomannan-based composite coating.

[0044] Figure 2 is the change of the hardness of frozen fish fillets with the storage days after being preserved with the chitosan / konjac glucomannan-based composite coating.

[0045] Figure 3 is the surface microstructure of the chitosan / konjac glucomannan-based composite coating observed by scanning electron microscopy.

[0046] Figure 4 is the cross-sectional microstructure of the chitosan / konjac glucomannan-based composite coating observed by scanning electron microscopy.

[0047] Figure 5 is the Fourier transform infrared spectroscopy analysis diagram of the chitosan / konjac glucomannan-based composite coating. Detailed Embodiments

[0048] The following further illustrates this application by way of examples, but does not limit this application to the scope of the described examples. The experimental methods without specific conditions in the following examples are carried out according to conventional methods and conditions, or are selected according to the product specifications.

[0049] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0050] The raw materials in the following examples are all commercially available.

[0051] Example 1

[0052] A preparation method of a chitosan / konjac glucomannan-based coating film, comprising the following steps:

[0053] (1) Prepare an acetic acid solution with a mass fraction of 1%;

[0054] (2) Weigh 2 g of chitosan, add it to 100 g of acetic acid solution and stir for 75 min to obtain coating solution 1 for standby;

[0055] (3) Weigh 2 g of konjac glucomannan, add it to 100 g of deionized water, and stir at room temperature for 105 min;

[0056] (4) According to the mass ratio of 2:1, weigh 66.7 g of chitosan solution (step two) and 33.3 g of konjac glucomannan solution (step three), mix them evenly, and add 1 g of glycerol and stir at room temperature for 135 min to obtain coating solution 2 for standby;

[0057] (5) Centrifuge coating solutions 1 and 2 in steps two and four for 3 min to remove impurities such as air bubbles;

[0058] (6) Immerse the fish fillets in coating solutions 1 and 2 for 20 s respectively, and place them in the freezer at -18 °C. The surfaces of the fish fillets are covered with a chitosan / konjac glucomannan-based composite coating film.

[0059] Example 2

[0060] A preparation method of a chitosan / konjac glucomannan-based coating film, comprising the following steps:

[0061] (1) Prepare an acetic acid solution with a mass fraction of 1%;

[0062] (2) Weigh 2 g of chitosan, add it to 100 g of acetic acid solution and stir at room temperature for 75 min to obtain coating solution 1 for standby;

[0063] (3) Weigh 2 g of konjac glucomannan, add it to 100 g of deionized water, and stir at room temperature for 105 min;

[0064] (4) According to the mass ratio of 2:1, weigh 66.7 g of chitosan solution (step two) and 33.3 g of konjac glucomannan solution (step three), mix them evenly, and add 1 g of glycerol and stir at room temperature for 135 min to obtain coating solution 2 for standby;

[0065] (5) Centrifuge coating solutions 1 and 2 in steps two and four for 3 min to remove impurities such as air bubbles;

[0066] (6) Immerse the fish fillets in coating solutions 1 and 2 for 20 s respectively, and place them in the freezer at -18 °C. The surfaces of the fish fillets are covered with a chitosan / konjac glucomannan-based composite coating film.

[0067] Example 3

[0068] A preparation method of a chitosan / konjac glucomannan-based coating film, comprising the following steps:

[0069] (1) Prepare an acetic acid solution with a mass fraction of 1%;

[0070] (2) Weigh 2 g of chitosan, add it to 100 g of acetic acid solution, and stir at room temperature for 75 min to obtain coating solution 1 for standby;

[0071] (3) Weigh 2 g of konjac glucomannan, add it to 100 g of deionized water, and stir at room temperature for 105 min;

[0072] (4) According to a mass ratio of 1:1, weigh 33.3 g of chitosan solution (step two) and 33.3 g of konjac glucomannan solution (step three), mix them evenly, and add 1 g of glycerol and stir at room temperature for 135 min to obtain coating solution 2 for standby;

[0073] (5) Centrifuge coating solutions 1 and 2 in steps two and four for 3 min to remove impurities such as air bubbles;

[0074] (6) In step six, immerse the fish fillets in coating solutions 1 and 2 for 20 s respectively, and place them in a freezer at -18 °C. The surfaces of the fish fillets are covered with a chitosan / konjac glucomannan-based composite coating film.

[0075] Example 4

[0076] A preparation method of a chitosan / konjac glucomannan-based coating film, comprising the following steps:

[0077] (1) Prepare an acetic acid solution with a mass fraction of 1%;

[0078] (2) Weigh 2 g of chitosan, add it to 100 g of acetic acid solution and stir at room temperature for 75 min to obtain coating solution 1 for standby;

[0079] (3) Weigh 2 g of konjac glucomannan, add it to 100 g of deionized water, and stir at room temperature for 105 min;

[0080] (4) According to a mass ratio of 1:2, weigh 33.3 g of chitosan solution (step two) and 66.7 g of konjac glucomannan solution (step three), mix them evenly, and add 1 g of glycerol and stir at room temperature for 135 min to obtain coating solution 2 for standby;

[0081] (5) Centrifuge coating solutions 1 and 2 in steps two and four for 3 min to remove impurities such as air bubbles;

[0082] (6) In step six, immerse the fish fillets in coating solutions 1 and 2 for 20 s respectively, and place them in a freezer at -18 °C. The surfaces of the fish fillets are covered with a chitosan / konjac glucomannan-based composite coating film.

[0083] Effect Example 1

[0084] Performance Test of Chitosan / Konjac Glucomannan-Based Coating Film Preparation

[0085] (1) Thickness Measurement

[0086] The thickness of the composite coating film was measured using a digital micrometer (Shenzhen Yuan Hengtong Technology Co., Ltd., Guangdong, China). Ten points were randomly selected on the film (8.5 cm × 8.5 cm), and the thickness of the film was measured. The final result was calculated as the average value.

[0087] (2) Mechanical Properties

[0088] The composite film was cut into 1 cm × 5 cm strips. The thickness (mm) was measured using a micrometer, and the average value was taken. Anti-slip tapes 1 cm wide were fixed on both sides to prevent falling off. The 1 cm × 5 cm film was fixed on the stretching arm of the texture analyzer. The initial distance was set to 3 cm, and the speed was 1 mm / s. The tensile strength and elongation at break of the film were measured. The calculation formulas are as follows:

[0089]

[0090] Tensile Strength:

[0091] Elongation at Break:

[0092] In the formula, F is the maximum tensile strength (N), X is the thickness of the film (mm), Y is the width of the film (mm), ΔL and L0 are the tensile length and the original length of the film (mm), respectively.

[0093] (3) Water Vapor Transmission Rate

[0094] The water vapor permeability of the indicator film was measured at 25°C. The indicator film (2 cm × 2 cm) was covered on the mouth of a glass bottle with a depth of 8 cm and a diameter of 1 cm, and the bottle was filled with dry silica gel particles. Subsequently, the glass bottle was placed in a desiccator (containing saturated potassium sulfate solution), and the weight of the glass bottle was accurately weighed every day.

[0095] The calculation formula is as follows:

[0096] Water Vapor Transmission Rate

[0097] In the formula, W is the increased weight of the glass bottle (g), x is the initial thickness of the indicator film (m), T is

[0098] the storage time (s), A is the permeation area of the indicator film (m2), and ΔP is the saturated vapor pressure of water at 25°C (Pa).

[0099] (4) Analysis of the performance results of chitosan / kombucha glucan-based coatings

[0100] The chitosan solution prepared in Step 2 of Example 1 and the kombucha glucan solution prepared in Step 3 were uniformly mixed in different ratios (1:0, 1:1, 1:2, 1:3, 2:1, 2:3, 3:1, and 3:2). After drying treatment, the thickness, tensile strength, elongation at break, and water vapor transmission rate of the film were measured. Three samples were set for all treatment groups, and the final results were averaged for analysis.

[0101] Table 1 Effects of different ratios of chitosan / kombucha glucan composite coatings on performance

[0102]

[0103] As shown in Table 1, the single chitosan film had a lower thickness due to its ordered structure. With the addition of kombucha glucan, the ordered structure of chitosan was disrupted, and the thickness of the composite coating increased (P<0.05). As the content of kombucha glucan gradually increased and the coating ratio increased from 1:0 to 1:3, the elongation at break of the composite coating increased significantly, and the tensile strength decreased significantly (P<0.05). This structure indicates that the addition of kombucha glucan effectively regulates the ductility of the chitosan film, and then realizes the improvement of the ductility of the film with appropriate tensile strength. Under the condition of 2:1, the coating had a tensile strength of 19.05 Mpa and the elongation at break also increased to 26.37%, and the comprehensive performance of the coating was the best at this time. The water vapor transmission rate is an important index to judge the barrier performance of the composite coating. A lower water vapor transmission rate can effectively prevent fish from being affected by the external environment. As the ratio of chitosan / kombucha glucan in the coating gradually increased, the water vapor transmission rate decreased significantly (P<0.05). Under the condition of a ratio of 2:1, the minimum value of the water vapor transmission rate was 8.24 (10-10 g / (m2·s·Pa)), which proved that the cross-linking of the hydroxyl group of chitosan and the carboxyl group of kombucha glucan formed a tight structure, thereby enhancing the barrier property of the composite film.

[0104] Effect Example 2

[0105] Effect of chitosan / kombucha glucan-based coating on total volatile basic nitrogen in frozen fish fillets

[0106] (1) Determination method of total volatile basic nitrogen in frozen fish fillets

[0107] The determination was carried out in accordance with the method of GB5009.228-2016. The fish meat and distilled water were placed in a digestion tube for 30 minutes, 1.0 g of magnesium oxide was added, and automatic distillation was carried out for 3 minutes using the Kjeldahl titration method. It contained 30 ml of boric acid solution and a mixed indicator, and finally titrated with 0.1 mol / L hydrochloric acid. The calculation formula is as follows:

[0108] Total volatile basic nitrogen = (V3 - V4) × C2 × 14 / M3 × 100

[0109] Wherein, V3 is the volume of hydrochloric acid consumed by the fish meat (mL); V4 is the volume of hydrochloric acid consumed by the blank (mL); C2 is the concentration of the standard hydrochloric acid titration solution (mol / L); M3 is the mass of the fish meat (g).

[0110] (2) Result analysis of total volatile basic nitrogen in frozen fish fillets After the fresh fish meat is sliced, fish fillets with uniform shape and size and no obvious differences are selected. They are randomly and evenly divided into three groups. After draining the water, they are respectively immersed in water, coating solution 1 and coating solution 2 for 20 s to make the liquid adhere to the surface of the fish meat. After taking out and draining, the coating 1 treatment group and the coating 2 treatment group are obtained, and the water immersion treatment group is used as the blank control.

[0111] Appendix Figure 1 It is the total volatile basic nitrogen of frozen fish fillets during the 3 - month storage of three different treatment groups. Obviously, with the increase of storage days, the total volatile basic nitrogen of all treatment groups shows a significant increasing trend (P < 0.05). This is because the degradation of protein in the fish meat during storage causes the value to increase. Different from the blank control group, the coating 1 treatment and the coating 2 treatment show a significant inhibitory effect on the increase of total volatile basic nitrogen (P < 0.05). Under the condition of 3 - month storage, the total volatile basic nitrogen of the fish meat treated with coating 1 is 14.28 mg / 100 g, and the total volatile basic nitrogen of the fish meat treated with coating 2 is 12.26 mg / 100 g, both of which are lower than the upper limit of 20 mg / 100 g of total volatile basic nitrogen in fish stipulated in the GB2733 - 2015 detailed rules. It shows that the coating treatment plays a certain protective role on frozen fish fillets, and the composite coating shows a more ideal effect.

[0112] Effect Example 3

[0113] Effect of chitosan / konjac glucomannan - based coating on the hardness of frozen fish fillets

[0114] (1) Determination method of the hardness of frozen fish fillets

[0115] Use a TX.XT Plus C texture analyzer to measure the texture of the fish meat. Select the P50 probe, set the total strain to 50%, the force arm to 30 kg, two cycles, with an interval of 5 seconds each time.

[0116] (2) Result analysis of the hardness of frozen fish fillets

[0117] After slicing fresh fish, select fish slices with uniform shape, size and no obvious differences. Randomly and evenly divide them into three groups. After draining the water, immerse them in water, coating solution 1 and coating solution 2 for 20 s respectively, so that the liquid adheres to the surface of the fish. After taking them out and draining, the coating 1 treatment group and the coating 2 treatment group are obtained, with the water immersion treatment group as the blank control.

[0118] Attached Figure 2 is the change curve of the hardness of frozen fish slices during 3 months of storage for three different treatment groups. Obviously, with the increase of storage days, the hardness of all treatment groups shows a significant decreasing trend (P<0.05). This is because under the condition of long-term frozen storage, the ice crystals formed by the water in the fish continuously aggregate and increase, resulting in the destruction of muscle tissue, and then showing a decreasing trend in hardness. Within 1 month of storage, the hardness of the fish slices decreased significantly (P<0.05). The hardness of the blank control was 752.33 g, the hardness of coating 1 was 802.33 g, and the hardness of coating 2 was 847.00 g. This data indicates that the treatments of coating 1 and coating 2 have a protective effect on the hardness of frozen fish slices. Under the conditions of storage for 2-3 months, the hardness of the coating 2 treatment group is higher than that of the coating 1 treatment group and the blank control. This is because the intervention of the composite coating effectively blocks the invasion of external water, thereby delaying the phenomenon of ice crystal recombination inside the fish, and further extending the storage period of the fish. This result is confirmed by the water vapor transmission rate. It is further illustrated that the coating treatment plays a protective role on frozen fish slices, and the composite coating plays a more positive role in extending the storage period of frozen fish slices.

[0119] Effect Example 4

[0120] Scanning electron microscope image of chitosan / kGM-based coating

[0121] Use a scanning electron microscope to scan and observe the dried sample of coating 2, and observe the surface microstructure and cross-sectional microstructure of coating 2 under the condition of a magnification of 1000 times. From Figure 3 it can be seen that the surface of the composite coating prepared by mixing chitosan and konjac glucomannan presents an ordered structure, which provides a basis for this effective barrier system, and the surface is relatively flat without unevenness.

[0122] From Figure 4 the cross-section, it can be seen that the morphology of coating 2 is relatively flat as a whole. Although there are some protrusions, the cross-section is relatively neat as a whole.

[0123] Therefore, combining Figure 3 and Figure 4It can be seen from the scanning microscopic image that the composite coating film has excellent morphological characteristics. The orderly and neat structure is corroborated with the low water vapor transmission rate, high tensile strength and high elongation at break, indicating that the chitosan / kombucha glucomannan-based coating film is an excellent composite coating material.

[0124] Effect Example 5

[0125] Fourier transform infrared spectroscopy of chitosan / kombucha glucomannan-based coating film

[0126] The coating films 1 and 2 were ground into powders, and the samples were scanned by a Fourier transform infrared spectrometer in the wavenumber range of 4000 - 400 cm -1 to analyze the coating film composition and the intermolecular interactions. It can be seen from Figure 5 that the broad peak of chitosan in coating film 1 at 3457 cm -1 is caused by the combination of internal N-H stretching vibration and O-H stretching vibration, and the absorption peak at 1020 cm -1 is related to the stretching vibrations of C-O-C band and -C-OH band in the chitosan glycosidic bond. The positions of the corresponding absorption peaks in coating film 2 changed, with the broad peak shifting to 3378 cm -1 , and the narrow peak shifting to 1046 cm -1 . The changes in the positions and intensities of the absorption peaks indicate an effective cross-linking effect between chitosan and kombucha glucomannan. The Fourier transform infrared spectroscopy results, together with the mechanical strength and scanning electron microscope images, indicate that with the addition of kombucha glucomannan, the performance of the composite coating film prepared in this application has been effectively improved.

[0127] Finally, it should also be noted that in this application, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0128] Although the present application has been disclosed above through the description of specific embodiments of the present application, it should be understood that those skilled in the art can design various modifications, improvements or equivalents to the present application within the spirit and scope of the appended claims. These modifications, improvements or equivalents should also be considered to be included within the scope claimed by the present application.

Claims

1. A method for extending the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating, characterized in that: The specific steps include: (1) dissolving chitosan in acetic acid solution for standby use; (2) dissolving glucomannan in water to obtain a glucomannan solution for later use; (3) The chitosan solution and the glucomannan solution are stirred to obtain a coating solution, the fish meat is immersed in the coating solution, and then frozen.

2. The method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating as claimed in claim 1, characterized in that: Step (1) satisfies at least one of the following conditions: The mass fraction of the acetic acid solution is 1-3%. The mass volume ratio of the chitosan to the acetic acid solution is 1: (100-150) g / mL; The chitosan is animal-derived chitosan; the animal-derived chitosan includes chitosan extracted from arthropods such as shrimps and crabs.

3. The method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating as claimed in claim 1, characterized in that: Step (2) satisfies at least one of the following conditions: The glucomannan includes konjac glucomannan; The molecular weight of the glucomannan is 200,000 to 2,000,000; The mass ratio of the glucomannan to the water is 1:(100-200), for example 1:150; The dissolving of glucomannan in water also includes stirring and swelling, preferably, the stirring time is 90 to 120 minutes; The water includes deionized water.

4. The method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating as claimed in claim 1, characterized in that: Step (3) satisfies at least one of the following conditions: The mass ratio of the chitosan solution to the glucomannan solution is 1:(1-3); Glycerol is further added during the stirring of the chitosan solution and the glucomannan solution; The stirring time is 120 to 150 minutes; The stirring step further includes a centrifugal operation.

5. The method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating as claimed in claim 1, characterized in that: In step (3), at least one of the following conditions is met: The centrifugation time is 2 to 5 minutes; The centrifugal speed is 4000 rpm; The centrifugation is performed in a centrifuge.

6. The method for prolonging the quality of frozen fish fillets by using a chitosan / konjac glucomannan-based composite coating as claimed in claim 1, characterized in that: In step (3), The time for the meat to be immersed in the coating liquid is 5 to 30 seconds; The freezing temperature is -20 to -15°C, for example -18°C.

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