Composite coating material for retaining freshness of fishes

Abstract

Raw materials of the composite coating material comprise a solvent and a film forming material, and the solvent is a component with the largest weight ratio in the raw materials; the film-forming material comprises micromolecular konjac glucomannan with the average molecular weight of 800000 or below, and is obtained by fermenting glucomannan through lactic acid bacteria; the content of the micromolecular konjac glucomannan in the solvent is more than 2.0 g / 100 mL. The fish food preservative has a good film forming effect on the surface of fish food, and can effectively limit the entry of external air, inhibit the number of microorganisms on the surface of fish, delay the oxidation of fat and realize the effects of corrosion prevention, fresh keeping and oxidation resistance; the micromolecular konjac glucomannan has biodegradability, and the composite coating material can take water as a solvent, and has the characteristics of no toxicity, safety and environmental protection.

Description

Technical Field

[0001] The present invention relates to a fresh-keeping coating material, and particularly to a composite coating material for fish. Background Art

[0002] The biological coating fresh-keeping technology stems from concerns about the potential hazards of traditional chemical preservatives and the demand for environmentally friendly and sustainable fresh-keeping solutions. Since the 1990s, with the increasing global awareness of food safety and environmental protection, biological coatings, as a natural and biodegradable fresh-keeping method, have gradually become the focus of attention in the food industry. Early research mainly focused on exploring the possibility of using different natural polymers as coating materials, such as chitosan, cellulose derivatives, proteins, and polysaccharides.

[0003] The biological coating fresh-keeping technology has been widely applied in many food fields such as fruits, vegetables, and meats. For example, on fruits and vegetables, chitosan coatings can effectively extend the shelf life and maintain color and taste. In meat preservation, biological coatings containing lysozyme can significantly inhibit microbial growth, reduce lipid oxidation, and maintain the freshness of meat products. However, there are still some challenges. First, it is difficult to control the uniformity and strength of the coating, especially on irregularly shaped foods. Second, cost issues limit its widespread application in some fields. Finally, how to ensure the biodegradability and safety of the coating while guaranteeing the fresh-keeping effect is still a problem to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art and provide a composite coating material for fish fresh-keeping with good fresh-keeping effect.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows: A composite coating material for fish fresh-keeping, the raw materials of which include a solvent and a film-forming material, and the solvent is the component with the largest weight percentage in the raw materials; the film-forming material includes small molecule konjac glucomannan with an average molecular weight of less than 800,000, which is obtained by fermenting glucomannan with lactic acid bacteria; the content of the small molecule konjac glucomannan in the solvent is 2.0 g / 100 mL or more.

[0006] Preferably, the average molecular weight of the small molecule konjac glucomannan is 1,000 to 500,000.

[0007] Preferably, the content of the small molecule konjac glucomannan in the solvent is 3.0 g / 100 mL to 8.0 g / 100 mL.

[0008] Preferably, the solvent is water.

[0009] Preferably, the preparation method of the small molecule konjac glucomannan is as follows: Lactobacillus plantarum is cultured to obtain a Lactobacillus plantarum fermentation broth; after the Lactobacillus plantarum fermentation broth is mixed with a glucomannan substrate, the pH value is adjusted to 4.5-6.5, and the mixture is incubated at 30-45 °C to obtain a decomposition solution; the decomposition solution is filtered and dried to obtain the small molecule konjac glucomannan.

[0010] More preferably, the temperature for culturing Lactobacillus plantarum is 30-35 °C.

[0011] More preferably, the time for culturing Lactobacillus plantarum is 24-72 h.

[0012] More preferably, the incubation time is 10 min-360 min.

[0013] More preferably, the filtration is performed using an ultrafiltration membrane.

[0014] Preferably, the raw material further includes an antibacterial agent; the content of the antibacterial agent in the solvent is 0.1 g / 100 mL or more.

[0015] More preferably, the content of the antibacterial agent in the solvent is 0.2 g / 100 mL-1 g / 100 mL.

[0016] More preferably, the antibacterial agent includes phenyl lactic acid.

[0017] Preferably, the raw material further includes an antioxidant; the content of the antioxidant in the solvent is 0.02 g / 100 mL or more.

[0018] More preferably, the content of the antioxidant in the solvent is 0.03 g / 100 mL-0.2 g / 100 mL.

[0019] More preferably, the antioxidant includes tea polyphenols.

[0020] The present invention has the following beneficial effects:

[0021] (1) The composite coating material of the present invention has a good film-forming effect on the surface of fish food, can effectively limit the entry of external air, inhibit the number of microorganisms on the surface of fish, delay the oxidation of fat, and achieve the effects of anti-corrosion, freshness preservation and antioxidant;

[0022] (2) The small molecule konjac glucomannan has biodegradability, and the composite coating material can use water as a solvent, and has the characteristics of non-toxic, safe and environmentally friendly.

[0023] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0024] The accompanying drawings, which form a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0025] Figure 1 is a physical diagram of the composite coating material in Embodiment 2 of the present invention;

[0026] Figure 2 is a physical diagram of the fish blocks treated with the composite coating material in Embodiment 2 of the present invention;

[0027] Figure 3 is a graph showing the change in pH value of the fish blocks treated with the composite coating materials in Embodiments 1 to 3 of the present invention over the storage time;

[0028] Figure 4 is a physical diagram of the composite coating material in Comparative Example 1;

[0029] Figure 5 is a physical diagram of the composite coating material in Comparative Example 2;

[0030] Figure 6 is a graph showing the change in pH value of the fish blocks treated with the composite coating materials in Embodiment 2 of the present invention and Comparative Examples 1 to 2 over the storage time;

[0031] Figure 7 is a graph showing the change in the number of colonies of the fish blocks over the storage time after being soaked in aqueous solutions of phenyl lactic acid bacteriostatic agents with different concentrations;

[0032] Figure 8 is a graph showing the change in absorbance of the fish blocks over the storage time after being soaked in aqueous solutions of tea polyphenol antioxidants with different concentrations;

[0033] Figure 9 is a graph showing the change in water loss rate of the fish blocks treated with the composite coating materials in Comparative Example 3 and Embodiments 4 to 12 over the storage time;

[0034] Figure 10 is a graph showing the change in cooking loss rate of the fish blocks treated with the composite coating materials in Comparative Example 3 and Embodiments 4 to 12 over the storage time;

[0035] Figure 11 is a graph showing the change in pH value of the fish blocks treated with the composite coating materials in Comparative Example 3 and Embodiments 4 to 12 over the storage time. Detailed implementation manners

[0036] To make the objectives, solutions, and beneficial technologies of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and drawings. It should be noted that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention.

[0037] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recited.

[0038] In the description herein, it should be noted that unless otherwise specified, "above" and "below" include the recited number, the meaning of "multiple" in "one or more" is two or more, and the meaning of "multiple" in "one or more" is two or more.

[0039] An embodiment of the present invention provides a composite coating material for fish freshness preservation, the raw materials of which include a solvent and a film-forming material, the solvent being the component with the largest weight percentage in the raw materials; the film-forming material includes a small molecule konjac glucomannan with an average molecular weight of 800,000 or less, obtained by fermenting glucomannan with lactic acid bacteria; the content of the small molecule konjac glucomannan in the solvent is 2.0 g / 100 mL or more.

[0040] Konjac Glucomannan (KGM for short) is a water-soluble polysaccharide, mainly extracted from konjac tubers, and is a natural renewable resource with sufficient reserves. KGM is inexpensive and has unique gel properties. The konjac glucomannan polysaccharide is a high-molecular heteropolysaccharide formed by the polymerization of glucose and mannose residues with a molecular ratio of 1:1.6 - 1.7 through β-1,4 glycosidic bonds. Konjac glucomannan is a water-soluble non-ionic polysaccharide. The main chain is composed of D-mannose and D-glucose linked by B-1,4 glycosidic bonds. There is a branched-chain structure loop linked by B-1,3 bonds at the C position of mannose in the main chain. There are about 3 branched chains for every 32 sugar residues, and some sugar residues have acetyl groups. Natural konjac glucomannan is composed of radially arranged micelles, and its structure has two types: d-type (amorphous) and p-type (crystalline). However, natural konjac glucomannan has low solubility in water, poor processability, insufficient stability, and its gelling properties do not meet the requirements of coating materials. In the present invention, by fermenting glucomannan with lactic acid bacteria, a small-molecule konjac glucomannan with good film-forming effect on fish food is obtained, which has excellent solubility, gelling properties and thickening properties, and can form a uniform, water-resistant, acid-resistant and alkali-resistant film together with water on the food surface.

[0041] The composite coating material for fish freshness preservation provided by the embodiments of the present invention has the following advantages:

[0042] (1) The composite coating material of the embodiments of the present invention has a good film-forming effect on the surface of fish food, can effectively limit the entry of external air, inhibit the number of microorganisms on the fish surface, delay the oxidation of fat, and achieve the effects of anti-corrosion, freshness preservation and antioxidant;

[0043] (2) The small-molecule konjac glucomannan has biodegradability, and the composite coating material can use water as a solvent, and has the characteristics of non-toxic, safe and environmentally friendly.

[0044] The composite coating material for fish freshness preservation can be obtained by uniformly mixing each raw material.

[0045] In the embodiments of the present invention, the average molecular weight of the small-molecule konjac glucomannan is 1000 - 500000.

[0046] The molecular weight of the small-molecule konjac glucomannan can be controlled by filtration after fermentation. For example, by using an ultrafiltration membrane (Koch ultrafiltration membrane) with a pore size between 0.002 - 0.1 μm, a self-made konjac glucomannan solution with an average molecular weight of 1000 - 500000 can be obtained.

[0047] In the embodiments of the present invention, the content of the small-molecule konjac glucomannan in the solvent is 3.0 g / 100 mL - 8.0 g / 100 mL.

[0048] In some embodiments of the present invention, the content of the small molecule konjac glucomannan in the solvent is 3.0 g / 100 mL to 6.0 g / 100 mL.

[0049] In an embodiment of the present invention, the solvent is water.

[0050] In an embodiment of the present invention, the preparation method of the small molecule konjac glucomannan is as follows: Lactobacillus plantarum is cultured to obtain a Lactobacillus plantarum fermentation broth; after the Lactobacillus plantarum fermentation broth is mixed with a glucomannan substrate, the pH value is adjusted to 4.5 to 6.5, and the mixture is incubated at 30 to 45 °C to obtain a decomposition solution; the decomposition solution is filtered and dried to obtain the small molecule konjac glucomannan. Generally, Lactobacillus plantarum cannot directly ferment and decompose glucomannan. Therefore, Lactobacillus plantarum is first cultured to produce related enzymes, and after a large number of Lactobacillus plantarum have propagated, better fermentation results can be obtained through fermentation.

[0051] The Lactobacillus plantarum can be various commercially available Lactobacillus plantarum, such as Lactobacillus plantarum Lp90 produced by Zhenjiang Tianyi Biotechnology Co., Ltd.

[0052] In some embodiments of the present invention, the temperature for culturing Lactobacillus plantarum is 30 to 35 °C.

[0053] In some embodiments of the present invention, the time for culturing Lactobacillus plantarum is 24 to 72 h.

[0054] When culturing Lactobacillus plantarum, a medium suitable for the large-scale propagation of Lactobacillus plantarum can be used, such as MRS medium.

[0055] In some embodiments of the present invention, the incubation time is 10 min to 360 min.

[0056] In some embodiments of the present invention, the filtration is performed using an ultrafiltration membrane.

[0057] In an embodiment of the present invention, the raw material further includes an antibacterial agent; the content of the antibacterial agent in the solvent is more than 0.1 g / 100 mL.

[0058] In some embodiments of the present invention, the content of the antibacterial agent in the solvent is 0.2 g / 100 mL to 1 g / 100 mL.

[0059] In some embodiments of the present invention, the content of the antibacterial agent in the solvent is 0.2 g / 100 mL to 0.6 g / 100 mL.

[0060] In some embodiments of the present invention, the bacteriostatic agent includes phenyllactic acid. Phenyllactic Acid (PLA for short) is a new type of natural biological preservative with broad-spectrum bacteriostatic effect, having the advantages of non-toxic, pollution-free, good stability, wide applicability, etc., and can inhibit the growth of spoilage bacteria and pathogenic bacteria on the surface of aquatic products.

[0061] In the embodiments of the present invention, the raw material further includes an antioxidant; the content of the antioxidant in the solvent is 0.02 g / 100 mL or more.

[0062] In some embodiments of the present invention, the content of the antioxidant in the solvent is 0.03 g / 100 mL to 0.2 g / 100 mL.

[0063] In some embodiments of the present invention, the content of the antioxidant in the solvent is 0.03 g / 100 mL to 0.08 g / 100 mL.

[0064] In some embodiments of the present invention, the antioxidant includes tea polyphenols. Tea Polyphenols (TP for short) can delay fat oxidation, reduce the destruction of amino acids, maintain the freshness of aquatic products, and thus improve the quality of aquatic products.

[0065] When in use, the composite coating material for fish freshness preservation is coated on the surface of preliminarily processed fish products such as raw fish pieces and raw fish meat to form a film layer, or the preliminarily processed fish products such as raw fish pieces and raw fish meat are soaked in the composite coating material for fish freshness preservation, and a film layer will be formed on the surface after taking out. When it is necessary to remove the obtained film layer, it can be washed off or wiped off with water.

[0066] Example

[0067] The following examples more specifically describe the content disclosed in the present invention. These examples are only for illustrative purposes, because various modifications and changes within the scope of the disclosure of the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples can be obtained through conventional commercial channels or synthesized according to conventional methods, and can be used directly without further treatment. Unless otherwise stated, the instruments used in the examples can be obtained through conventional commercial channels.

[0068] The composite coating materials of the following examples and comparative examples are obtained by mixing their raw materials evenly.

[0069] When the raw material dosage is expressed in "g / 100mL" below, it refers to the amount of the raw material relative to every 100 mL of the solvent. For example, "the dosage of small molecule konjac glucomannan is 2.0 g / 100mL" means "2.0 g of small molecule konjac glucomannan is used per 100 mL of the solvent".

[0070] In the following cases, the microbial count uses the plate count agar (PCA) medium (g / L), and the components are: tryptone 5 g / L, yeast extract 2.5 g / L, glucose 1.0 g / L, agar 15.0 g / L; sterilized at 115 °C for 20 min.

[0071] Example 1

[0072] The raw materials of the composite coating material in this example are distilled water (solvent) and self-made small molecule konjac glucomannan (film-forming material); the dosage of small molecule konjac glucomannan is 2.0 g / 100mL.

[0073] The preparation method of small molecule konjac glucomannan in this example is: Lactobacillus plantarum is cultured in MRS medium at 30 °C for 24 h to obtain the Lactobacillus plantarum fermentation broth; after the Lactobacillus plantarum fermentation broth is mixed with the glucomannan substrate, the pH value is adjusted to 6.5 and incubated at 30 °C for 20 min to obtain the decomposition solution; the decomposition solution is filtered through an ultrafiltration membrane, and the small molecule konjac glucomannan with a molecular weight range of 1000 - 500,000 daltons is retained.

[0074] Example 2

[0075] The composite coating material in this example is as Figure 1 shown.

[0076] The raw materials of the composite coating material in this example are distilled water (solvent) and self-made small molecule konjac glucomannan (film-forming material); the dosage of small molecule konjac glucomannan is 4.0 g / 100mL.

[0077] The small molecule konjac glucomannan in this example is the same as that in Example 1.

[0078] Example 3

[0079] The raw materials of the composite coating material in this example are distilled water (solvent) and self-made small molecule konjac glucomannan (film-forming material); the dosage of small molecule konjac glucomannan is 6.0 g / 100mL.

[0080] The small molecule konjac glucomannan in this example is the same as that in Example 1.

[0081] The fresh-keeping effect of the composite coating materials prepared in Examples 1 to 3 was tested: Multiple fish blocks obtained in the same batch were immersed in the composite coating materials of each example, and then taken out and stored refrigerated - five 5-g fish blocks were processed for each example, and distilled water was used as the control group, with a total of (3 + 1)×5 = 20 fish blocks processed; The shape of the fish blocks treated with the composite coating material of Example 2 was as shown in Figure 2 , and a uniform film layer was formed on the surface of the fish blocks by the composite coating material. The batter was relatively thin and there were no dead corners.

[0082] On the day after coating, the 3rd day after coating, the 6th day after coating, the 9th day after coating, and the 12th day after coating, one fish block was taken from each group to test the pH value; The specific method for measuring the pH value was as follows: 45 mL of distilled water was added to one fish block, homogenized with a high-speed discrete homogenizer, and left to stand for 30 min, then measured with a pH meter. The pH test results are shown in Figure 3 .

[0083] The pH test results showed that the self-made small-molecule konjac glucomannan solutions with concentrations of 2.0 g / 100 mL, 4.0 g / 100 mL, and 6.0 g / 100 mL could all slow down the change of pH. During the test time, the pH value of the grass carp fish blocks gradually increased with the increase of time because the grass carp meat was rich in protein and had short peptide chains, which were easy to decompose. With the extension of the storage period, under the action of external microorganisms and endogenous enzymes, ammonia and amine substances were decomposed, resulting in the generation of volatile odors and the increase of pH value. It was concluded from the data that the concentrations of 4.0 g / 100 mL and 6.0 g / 100 mL of small-molecule konjac glucomannan solution had a good inhibitory effect on the continuous increase of the pH value of grass carp fish blocks, and the effects were basically equivalent.

[0084] Comparative Example 1

[0085] The composite coating material of this comparative example was as shown in Figure 4 .

[0086] The raw materials of the composite coating material in this comparative example were distilled water (solvent) and konjac glucomannan (film-forming material); The dosage of konjac glucomannan was 4.0 g / 100 mL.

[0087] The konjac glucomannan in this comparative example was a commercially available product, purchased from the purified konjac powder (grade I / 3A) of Yichang Weite Konjac Glue Co., Ltd.

[0088] Comparative Example 2

[0089] The composite coating material of this comparative example was as shown in Figure 5 .

[0090] The raw materials of the composite coating material in this comparative example are distilled water (solvent) and konjac glucomannan (film-forming material); the dosage of konjac glucomannan is 4.0 g / 100 mL.

[0091] The konjac glucomannan in this comparative example is commercially available low-polymer konjac glucomannan, purchased from Hefei Bomei Biotechnology Co., Ltd., PK2989-100g / CAS No: 37220-17-0

[0092] From Figure 1 、 Figure 4 、 Figure 5 it can be seen that in terms of dissolution form, the fluidity of self-made small-molecule konjac glucomannan is significantly better than that of commercially available konjac glucomannan; commercially available konjac glucomannan adheres severely to the wall, and it is easy to have problems such as too thick coating on fish blocks, dead corners, and poor sealing when processing fish blocks. There is little difference in the dissolution form between self-made and commercially available low-polymer glucomannan, and the wall-adhering effects are also relatively similar.

[0093] The preservation effect of the composite coating materials prepared in Comparative Examples 1 and 2 was tested: Multiple fish blocks obtained from the same batch were immersed in the composite coating materials of each example, and then taken out and stored refrigerated - five 5-g fish blocks were processed for each comparative example, and a total of 2×5 = 10 fish blocks were processed; on the day after coating, the 3rd day after coating, the 6th day after coating, the 9th day after coating, and the 12th day after coating, one fish block was taken from each group to test the pH value; the specific method for measuring the pH value was: 45 mL of distilled water was added to one fish block, homogenized with a high-speed discrete homogenizer, and left to stand for 30 min, and then measured with a pH meter. The obtained test results were compared with the results of Example 2 and summarized in Figure 6 From Figure 6 it can be seen that the increase in the pH value of the commercially available konjac glucomannan in Comparative Example 1 is more obvious. Compared with Comparative Examples 1 and 2, Example 2 of the present invention has a better inhibitory effect on the increase in the pH value of fish meat blocks.

[0094] Ordinary commercially available low-polymer konjac glucomannan products have a higher purity; when the glucomannan in the present invention is treated with lactic acid bacteria, in addition to small-molecule konjac glucomannan, the product also contains some other fermentation products of lactic acid bacteria. It is speculated that these components play an auxiliary role in fish preservation. In addition, it may also be related to the configuration tendency of the small-molecule konjac glucomannan produced by lactic acid bacteria fermentation.

[0095] Reference Example 1: Influence of phenyl lactic acid (bacteriostatic agent) on fish meat products

[0096] Prepare soaking solutions (aqueous solutions) with phenyllactic acid concentrations of 0.0 g / 100 mL, 0.1 g / 100 mL, 0.2 g / 100 mL, 0.3 g / 100 mL, 0.4 g / 100 mL, and 0.5 g / 100 mL respectively. Take 5 g of fresh fish pieces and soak them in each soaking solution for 5 minutes. After taking them out and storing them refrigerated for a certain number of days, use tweezers to pick up the fish meat and put it into centrifuge tubes respectively, add 10 mL of normal saline and homogenize, then dilute to obtain dilutions of 10 -2 、10 -3 、10 -4 respectively.

[0097] Pour the culture medium into plates. After the plates solidify, use a pipette to aspirate 100 μL of the dilution and spray it on the surface of the plates, then use a spreader to spread the dilution evenly. Make 3 plates for each dilution concentration. Transfer the spread plates to a constant temperature incubator and incubate at 37 °C for 2 days. Observe and count the number of colonies in the petri dishes, and summarize the total number of colonies. The specific results are shown in Figure 7 .

[0098] It can be seen from the figure that when the phenyllactic acid concentration is 0.1 g / 100 mL, it has an antibacterial effect on fish products. When the concentration reaches 0.2 g / 100 mL, it already has a good antibacterial effect.

[0099] Reference Example 2: Effect of Tea Polyphenols (Antioxidants) on Fish Meat Products

[0100] Prepare soaking solutions (aqueous solutions) with tea polyphenol concentrations of 0 g / 100 mL, 0.01 g / 100 mL, 0.03 g / 100 mL, 0.05 g / 100 mL, and 0.07 g / 100 mL respectively. Take 5 g of fresh fish pieces and soak them in each soaking solution for 5 minutes. After taking them out and storing them refrigerated for a certain number of days, use tweezers to pick up the fish meat, add 25 mL of 20% TCA (trichloroacetic acid) solution and homogenize at high speed. Centrifuge at 4 °C and 8000 rpm for 10 minutes, and dilute the supernatant to 50 mL. Take 5 mL of the dilution and add 5 mL of 0.02 mol / L TBA solution, react in a boiling water bath for 20 minutes, take it out and cool it to room temperature with running water, and measure the absorbance at 532 nm. The blank sample is obtained by diluting 25 mL of 20% TCA to 50 mL and taking 5 mL of the solution and adding 5 mL of TBA solution. Fish meat lipid peroxides will have a color reaction with thiobarbituric acid and have a characteristic absorption at 532 nm. The absorption intensity and the concentration of malondialdehyde are linearly related within a certain range. The lower the absorbance, the better the antioxidant effect. The effects of different concentrations of tea polyphenols on the lipid oxidation of fish meat are shown in Figure 8 as follows.

[0101] Under the action of tea polyphenols at different concentrations, the increase in the OD value of fish meat was slower than that of the control group, indicating that tea polyphenols can effectively inhibit lipid oxidation. After 6 days of storage, due to the long storage time, the degree of fish meat spoilage was relatively high, and the OD values of all fish meat samples decreased. It can be seen that under the action of the control group and low-concentration tea polyphenols (0.01 g / 100 mL), the fluctuations in the OD value were relatively large. After the tea polyphenol concentration reached a certain level, the antioxidant effect tended to be stable. The antioxidant effect of tea polyphenols on fish products may be due to the combination of the phenolic hydroxyl groups of tea polyphenols with free radicals, truncating the lipid oxidation reaction chain, thereby inhibiting the lipid oxidation process and reducing the generation of oxidation products.

[0102] Comparative Example 3, Examples 4 to 12: Formulation and preparation method

[0103] The raw materials of the composite coating materials in the following cases are two or more of distilled water (solvent), self-made small molecule konjac glucomannan (film-forming material), phenyl lactic acid (bacteriostatic agent), and tea polyphenols (antioxidant); the dosages of small molecule konjac glucomannan, phenyl lactic acid, and tea polyphenols in each case are listed in Table 1;

[0104] In Examples 4 to 12, the preparation method of small molecule konjac glucomannan was as follows: Lactobacillus plantarum was cultured in MRS medium at 35 °C for 72 h to obtain a Lactobacillus plantarum fermentation broth; after mixing the Lactobacillus plantarum fermentation broth with the glucomannan substrate, the pH value was adjusted to 4.5, and the mixture was incubated at 45 °C for 100 min to obtain a decomposition solution; the decomposition solution was filtered through an ultrafiltration membrane, and small molecule konjac glucomannan with a molecular weight range of 1000 - 500,000 daltons was retained.

[0105] Table 1 Formulation of composite coating materials in Examples 4 to 13

[0106]

[0107] Comparative Example 3, Examples 4 to 12: Detection and analysis

[0108] Multiple fish blocks of the same batch were respectively immersed in the composite coating materials of Comparative Example 3, Examples 4 to 12, and then taken out and stored in the refrigerator for a certain number of days before various tests were carried out.

[0109] (1) Use of the film and sensory evaluation

[0110] ① Use of the film: The composite coating materials in Examples 4 to 12 could all cover the surface of the fish blocks, with good film-forming effects, which could protect the fish from contact with the outside world, were easy to clean, and achieved the effect of preserving the fish; the composite coating material in Comparative Example 3 had a poor film-forming effect and could not form a continuous film layer on the surface of the fish blocks;

[0111] ② Sensory evaluation: Take out the fish blocks stored in the refrigerator, remove the surface film layer, and conduct a sensory evaluation on the fish meat. The sensory evaluation criteria are shown in Table 2.

[0112] Table 2 Sensory scoring criteria for fish meat

[0113]

[0114] Through daily observation, it was found that by the 4th day, after the fish meat coated with the composite coating materials of Examples 4 - 12 was stored at low temperature, there was no obvious odor, the meat color was shiny, firm and elastic, and the sensory score reached over 90; while for Comparative Example 3, the meat color was slightly shiny, there was a fishy smell, it was moderately soft and had poor elasticity, and the sensory score was 75. By the 7th day, the sensory scores of the fish meat coated with the composite coating materials of Examples 4 - 5, 7 - 12 could still reach over 75.

[0115] (2) Water loss rate

[0116] The test method is as follows: Take out the fish blocks stored in the refrigerator, remove the surface film layer. Refer to the method of Thiansilakul. Accurately weigh 5 g of fish meat (W 1 ). After drying the water on the surface of the fish meat, place it in a dry centrifuge tube and centrifuge at 4°C and 6000 r / min for 10 min, then accurately weigh again (W 2 ). Calculate the water loss rate according to the formula:

[0117] WHC = (W 1 - W 2 ) / W 1 ×100%

[0118] The test results of the water loss rate are shown in Figure 9 . Through the test data, it can be found that the water loss rate of the first group of fish meat coated with the composite coating material of Comparative Example 3 is relatively large, and the effect of the fourth group is better than that of the first group; the effects of the second, third, seventh, and ninth groups are relatively close; the effects of the fifth, sixth, eighth, and tenth groups are the best. It can be seen that the effect of treating fish blocks with the composite coating materials of Examples 4 - 12 in terms of freshness preservation is significantly better than that of Comparative Example 3.

[0119] (3) Cooking loss rate

[0120] The test method is as follows: Take out the fish blocks stored in the refrigerator, remove the surface film layer. Place the fish blocks in a beaker filled with boiling water and heat for 5 min, cool to room temperature, and accurately weigh after draining water on a wire mesh for 20 min. The cooking loss rate is calculated according to the following formula:

[0121] Cooking loss rate = (F 0 - F 1 ) / F 0 ×100%

[0122] In the formula: F 0is the mass of the fish pieces before steaming; F 1 is the mass of the fish pieces after steaming. The test results are shown in Figure 10 .

[0123] The results show that with the passage of time, the steaming loss rate of the fish pieces is also gradually increasing. However, there are differences in the steaming loss of the fish pieces treated with different composite coating materials. The steaming loss rate of the first group of fish meat coated with the composite coating material of Comparative Example 3 is the largest, and the effects of the 5th, 8th, and 10th groups are the best, and the effects of the other groups are in the middle. It can be seen that the composite coating materials of Examples 4 to 12 have obvious effects in preventing spoilage of fish pieces.

[0124] (4) Juice loss rate

[0125] The juice loss rate refers to the percentage of the mass lost due to mechanical damage, etc. during the storage of fish in the initial mass of the fish fillets. The fish pieces to be tested are placed in plastic cups in advance and stored in the refrigerator. After a certain number of days, they are taken out and weighed. The juice loss rate is calculated according to the following formula:

[0126] Juice loss rate = (m 2 - m 0 ) / m 1 - m 0 ×100%

[0127] In the formula: m 0 is the mass of the plastic cup / g; m 1 is the total mass of the fish, juice and plastic cup / g; m 2 is the total mass of the plastic cup and juice / g.

[0128] The obtained test results are opposite to the results of the water loss rate. Among them, the 5th, 6th, 8th, and 10th groups have the lowest loss rate and the best effect.

[0129] (5) pH value measurement

[0130] On the day after coating, the 3rd day after coating, the 6th day after coating, the 9th day after coating, and the 12th day after coating, one fish piece was taken from each group to measure the pH value; the specific measurement method of the pH value was: 45 mL of distilled water was added to one fish piece, homogenized with a high-speed discrete homogenizer, and left to stand for 30 min, and then measured with a pH meter. The results are shown in Figure 11 .

[0131] It can be seen from the figure that the pH value of the first group of fish meat coated with the composite coating material of Comparative Example 3 changes most significantly, indicating that the preservation effects of Examples 4 to 12 are better; the pH values of the fish meat treated with each example change differently. Among them, when stored for a relatively short period (3 days), the 5th, 6th, and 8th groups have the best preservation effects, and when stored for a longer period (12 days), the 5th, 8th, and 10th groups have the best preservation effects.

[0132] The test results of Comparative Example 3 and Examples 4 to 12 show that the composite coating material made of small molecule konjac glucomannan combined with bacteriostatic agents and antioxidants can further improve the fresh-keeping effect of the material; from the results of Comparative Example 3, Example 6, and Example 7, it can be seen that small molecule konjac glucomannan plays a key role in the fresh-keeping effect of the material.

Claims

1. A composite coating material for locking in the freshness of fish, characterized in that: Its raw materials include solvent and film-forming material, wherein the solvent is the component with the largest weight proportion in the raw materials; the film-forming material includes small molecule konjac glucomannan with an average molecular weight of less than 800,000, which is obtained by fermenting glucomannan with lactic acid bacteria; the content of the small molecule konjac glucomannan in the solvent is more than 2.0 g / 100 mL.

2. The composite coating material for locking freshness of fish according to claim 1, characterized in that: The average molecular weight of the small molecule konjac glucomannan is 1000-500000; the content of the small molecule konjac glucomannan in the solvent is 3.0 g / 100 mL-8.0 g / 100 mL; and the solvent is water.

3. The composite coating material for locking freshness of fish according to claim 1 or 2, characterized in that: The preparation method of the small molecule konjac glucomannan comprises the following steps: culturing Lactobacillus plantarum to obtain Lactobacillus plantarum fermentation liquid; mixing the Lactobacillus plantarum fermentation liquid with a glucomannan substrate, adjusting the pH value to 4.5-6.5, and keeping the mixture at 30-45° C. to obtain a decomposition liquid; filtering and drying the decomposition liquid to obtain the small molecule konjac glucomannan.

4. The composite coating material for locking freshness of fish according to claim 3, characterized in that: The temperature for culturing plant lactobacillus is 30-35°C; the time for culturing plant lactobacillus is 24-72 hours; the insulation time is 10 minutes-360 minutes; and the filtration adopts an ultrafiltration membrane.

5. The composite coating material for retaining freshness of fish according to any one of claims 1 to 4, characterized in that: The raw materials also include an antibacterial agent; the content of the antibacterial agent in the solvent is above 0.1 g / 100 mL.

6. The composite coating material for locking freshness of fish according to claim 5, characterized in that: The content of the antibacterial agent in the solvent is 0.2 g / 100 mL to 1 g / 100 mL.

7. The composite coating material for retaining freshness of fish according to claim 5, characterized in that: The antibacterial agent includes phenyllactic acid.

8. The composite coating material for retaining freshness of fish according to any one of claims 1 to 4, characterized in that: The raw material also includes an antioxidant; the content of the antioxidant in the solvent is above 0.02 g / 100 mL.

9. The composite coating material for retaining freshness of fish according to claim 8, characterized in that: The content of the antioxidant in the solvent is 0.03 g / 100 mL to 0.2 g / 100 mL.

10. The composite coating material for retaining freshness of fish according to claim 8, characterized in that: The antioxidant includes tea polyphenols.

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