An edible composite film and a method for preparing high-quality fish blocks by combining a pre-frying process

Abstract

The application belongs to the technical field of deep processing of aquatic products, and discloses an edible composite film and a method for preparing high-quality fish blocks by combining the edible composite film with a pre-frying process. The application is aimed at the problem that existing pre-fried fish blocks are prone to oxidation and have a short shelf life. Chitosan, sodium alginate and perilla extract are used as raw materials, and an edible composite coating film is obtained by mixing the raw materials in a certain proportion. The composite film can significantly inhibit the fat oxidation of fish blocks, and the pre-fried fish blocks prepared by using the composite film have better quality.

Description

Technical Field

[0001] This invention relates to the field of aquatic product deep processing technology, specifically to a method for preparing high-quality pre-fried fish chunks, and more specifically, to a method for preparing high-quality fish chunks using an edible composite film combined with a pre-frying process. Background Technology

[0002] China is the world's largest aquaculture nation and also the largest processor and trader of aquatic products. Grass carp (Ctenopharyngodon idella), one of my country's traditional "four major freshwater fish," has long held the top position in freshwater aquaculture production due to its rapid growth, wide availability of feed, and high yield. According to the "2025 China Fisheries Statistical Yearbook," my country's grass carp production reached 6.165 million tons in 2024, accounting for approximately 18% of freshwater fish production, making a significant contribution to ensuring national food security and the supply of high-quality protein for the population. However, for a long time, the processing and consumption of grass carp has primarily focused on live sales and basic processing, with insufficient deep processing and low added value. With the accelerating pace of life and changing consumption habits, the market demand for convenient, quick, and nutritious pre-cooked dishes has surged, providing unprecedented development opportunities for the deep processing and comprehensive utilization of grass carp. Processing grass carp into pre-cooked dishes can not only effectively alleviate the problems of limited sales radius and large price fluctuations associated with live fish, but also meet consumers' demand for convenient and delicious aquatic products, possessing broad market prospects and significant economic value.

[0003] Deep-frying is a long-standing and popular cooking method that imparts a unique golden color, crispy texture, and rich aroma to food. For fish, the high-temperature processing during deep-frying not only sterilizes and cooks it but also significantly improves its flavor and texture, effectively masking the muddy taste that some freshwater fish may have, thus increasing consumer acceptance. However, fish pieces pre-treated with deep-frying (i.e., pre-fried fish pieces) face the following significant quality deterioration issues during refrigeration, freezing, or distribution: (1) Deep frying accelerates fat oxidation. During pre-frying, the surface and interior of the fish pieces absorb a large amount of frying oil, while some of the fish's own fat dissolves due to heat. Although high-temperature frying can sterilize for a short time, it also triggers fat hydrolysis and oxidation reactions. During the cooling and storage stages after frying, due to its large surface area, ample contact with air, and lack of an effective protective layer, residual oxygen and its own free radicals continuously trigger a chain reaction of fat oxidation, leading to a rapid increase in peroxide value (POV) and thiobarbituric acid value (TBARS). The product quickly develops a rancid taste and loses its commercial value.

[0004] (2) Severe deterioration of texture seriously affects the taste of the product and consumer acceptance. During refrigeration or freezing, the textural degradation of pre-fried grass carp chunks manifests at multiple levels: ① Protein degradation: Microbial reproduction and metabolism secrete proteases with proteolytic functions, causing myofibril and connective tissue proteins to hydrolyze, resulting in muscle fiber breakage, loose muscle structure, and a continuous decrease in product hardness, elasticity, and chewiness; ② Moisture migration and ice crystal damage: During refrigeration, moisture migrates from the inside of the muscle fibers to the outside, causing the fish meat to become dry and hard; during freezing, ice crystals grow and pierce cell structures, resulting in severe juice loss and tissue collapse after thawing; ③ Fat-protein cross-linking: Fat oxidation products (such as malondialdehyde) covalently cross-link with the amino groups on the side chains of proteins, forming insoluble aggregates. Although this may increase hardness in the short term, it leads to a long-term decrease in protein solubility and digestibility, and the textural degradation is irreversible. Therefore, how to simultaneously inhibit fat oxidation and maintain textural quality during pre-frying and subsequent storage is the core technology and challenge for producing high-quality pre-fried grass carp chunks.

[0005] Previous studies have shown that treating pre-fried products with natural antioxidants, coating them with edible films, or combining both can effectively improve the preservation and quality of pre-fried products. Natural antioxidants possess antioxidant and preservative functions, while edible films effectively isolate oxygen and prevent moisture loss. Introducing natural antioxidants into the edible film system achieves a dual preservation effect of "passive barrier + active antioxidant." Perilla (Perilla frutescens) is a traditional Chinese medicinal and edible plant. Its leaves are rich in rosmarinic acid, caffeic acid, flavonoids, and other phenolic active ingredients, exhibiting excellent free radical scavenging ability and antioxidant activity. Perilla extract, as a natural antioxidant, has been included in the national food safety standard (GB2760) and is highly safe. However, using perilla extract alone as an antioxidant for preserving pre-fried fish pieces has proven ineffective.

[0006] In summary, existing preservation technologies for pre-fried products have the following shortcomings: direct pre-frying followed by packaging and storage lacks effective protective measures against fat oxidation, resulting in short product shelf life; while single edible films (such as sodium alginate or chitosan) have some barrier effect, their resistance to the strong oxidative environment after frying is insufficient, especially their sustained effect in inhibiting fat oxidation during refrigeration is limited; existing coating preservation research focuses mainly on fresh or poultry and livestock products, with limited development of edible film formulations and processes specifically for pre-fried aquatic products, especially freshwater fish products, failing to fully utilize the synergistic advantages of coatings in rapidly setting and forming a protective layer during pre-frying.

[0007] Therefore, developing a processing method that can effectively inhibit fat oxidation during the storage of pre-fried fish pieces, improve their quality, and is simple to operate and safe to eat is of significant industrial demand and technological value. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide an edible coating for improving the quality of pre-fried fish pieces and a method for preparing high-quality pre-fried fish pieces. This invention involves coating the surface of fish pieces with an edible film composed of sodium alginate / chitosan / perilla extract before pre-frying. The physical oxygen barrier effect of the film and the chemical antioxidant effect of perilla extract work synergistically to significantly delay oxidative rancidity, extend shelf life, and improve the quality of the pre-fried fish pieces.

[0009] To achieve the purpose of this invention, the edible composite film of this invention comprises, by weight and volume percentage: 0.8-1.2% sodium alginate, 0.8-1.2% chitosan, 0.15-0.25% perilla extract, and the balance being water.

[0010] Furthermore, in some embodiments of the present invention, the edible composite film comprises, by weight and volume percentage: 0.9-1.1% sodium alginate, 0.9-1.1% chitosan, 0.18-0.22% perilla extract, and the balance being water.

[0011] Furthermore, in some embodiments of the present invention, the edible composite film comprises, by weight and volume percentage: 0.95-1.05% sodium alginate, 0.95-1.05% chitosan, 0.19-0.21% perilla extract, and the balance being water.

[0012] Furthermore, in some embodiments of the present invention, the edible composite film comprises, by weight and volume percentage: 0.98-1.02% sodium alginate, 0.98-1.02% chitosan, 0.195-0.205% perilla extract, and the balance being water.

[0013] Furthermore, in some embodiments of the present invention, the perilla extract is an aqueous extract of perilla leaves, obtained by concentration and drying.

[0014] On the other hand, the present invention provides a method for preparing high-quality fish fillets using the aforementioned edible composite film combined with a pre-frying process, the method comprising the following steps: S1. Raw material pretreatment: After slaughtering the fish, scrape off the surface scales, remove the head, fins, tail and internal organs, rinse the fish thoroughly, and cut it into uniform pieces. S2. Mix sodium alginate, chitosan, perilla extract and water to obtain a coating solution; S3. Completely immerse the fish pieces in the coating solution; S4. Deep-fry the coated fish pieces; S5. After the fish pieces have cooled, put them into a vacuum bag and store them in a refrigerator at 4°C.

[0015] Furthermore, in some embodiments of the present invention, in step S3, the fish pieces are completely immersed in the coating solution for 4-7 minutes.

[0016] Furthermore, in some embodiments of the present invention, the frying conditions in step S4 are frying at 170-190°C.

[0017] Furthermore, in some embodiments of the present invention, the frying time in step S4 is 75-105 seconds.

[0018] Furthermore, in some embodiments of the present invention, the frying in step S4 is performed at 175-185°C for 85-95 seconds.

[0019] Furthermore, in some embodiments of the present invention, the fish is grass carp.

[0020] Compared with the prior art, the advantages of the present invention are as follows: (1) Significantly inhibits lipid oxidation and effectively improves the quality of pre-fried fish pieces Experiments showed that the composite coating of sodium alginate / chitosan / perilla extract combined with pre-frying treatment could continuously and significantly inhibit the oxidation of fish fat throughout the entire refrigeration period. Using peroxide value (POV) as the evaluation index, under refrigeration conditions at 4℃: On day 6, the POV of the mixed group was 0.0174 g / 100g, the control group was 0.0236 g / 100g, the chitosan-perilla extract group was 0.0194 g / 100g, and the sodium alginate-perilla extract group was 0.0198 g / 100g. The POV of the mixed group was 26.3%, 10.3%, and 12.1% lower than that of the control group, chitosan-perilla extract group, and sodium alginate-perilla extract group, respectively. On day 11, the POV of the mixed group was 0.0187 g / 100g, while that of the control group, chitosan-perilla extract group, and sodium alginate-perilla extract group was 0.0248 g / 100g. The peroxide values ​​of the mixed groups (0.0215 g / 100g, 0.0225 g / 100g, and 0.0225 g / 100g) were reduced by 24.6%, 13.0%, and 16.9% respectively compared to the individual groups. This indicates that the combination of sodium alginate, chitosan, and perilla extract can produce a significant synergistic effect, and its effect in inhibiting fat oxidation in pre-fried fish pieces is superior to any two combinations, effectively improving product quality.

[0021] (2) Effectively maintains the product's texture and quality, and keeps the taste good during storage. Texture is an important indicator for evaluating the quality of pre-fried fish fillets. During refrigeration, degradation of muscle protein, moisture loss, and fat oxidation in fish fillets lead to deterioration of texture. The composite coating of this invention has an outstanding effect on maintaining texture: The control group experienced drastic changes in texture during refrigeration. By day 11, its hardness had decreased from 1404.01±117.24 to 2041.58±104.57, and its chewiness had decreased from 196.56±2.01 to 379.6±63.19, indicating loose fish meat and severely deteriorated taste. In contrast, the mixed group, due to the protective effect of the edible film, exhibited significantly better textural stability, with a much smaller decrease in hardness compared to the control group, and the fish meat maintained good elasticity and chewiness. This indicates that the composite coating not only inhibits chemical oxidation but also slows down physical deterioration by forming a protective layer, maintaining the excellent taste of pre-fried fish pieces.

[0022] (3) Physical barriers and chemical antioxidants work synergistically to provide comprehensive preservation. This invention innovatively combines sodium alginate, chitosan, and perilla extract to achieve a synergistic effect of multiple preservation mechanisms: Sodium alginate and chitosan form a dense polyelectrolyte composite film through electrostatic interaction, which is rapidly set after pre-frying, constructing a robust oxygen and moisture barrier on the surface of the fish pieces, physically isolating external oxygen and inhibiting oxidation reactions; Perilla extract, rich in natural antioxidant active ingredients such as rosmarinic acid and flavonoids, is uniformly dispersed in the film matrix, continuously releasing and capturing free radicals and chelating metal ions, actively interrupting the oxidation chain reaction at a chemical level; The pre-frying process instantly solidifies and sets the coating, locking the active ingredients onto the surface of the fish pieces, enhancing the adhesion and integrity of the film layer, while the high temperature partially passivates endogenous lipases and lipoxygenases in the fish meat, reducing the risk of enzymatic oxidation. The synergy of these three factors provides the product with dual protection during storage, including passive oxygen barrier and active antioxidant effects, resulting in a preservation effect far superior to single coating or pre-frying treatments.

[0023] (4) The ingredients are natural and edible, and have high safety. The sodium alginate and chitosan used in this method are both natural polysaccharides, and the perilla extract is an extract from a plant that is both medicinal and edible. All materials are food-grade or permitted for use in food, and comply with national food safety standards (such as GB2760). The composite coating can be eaten directly after being fried with the fish pieces without peeling, and it does not introduce any toxic or harmful substances, making it highly acceptable to consumers.

[0024] (5) The process is simple and easy to industrialize. This invention adds only a coating step to the traditional pre-frying process, requiring no complex equipment modifications. The coating solution is simple to prepare, the immersion coating operation is quick, and it seamlessly integrates with existing aquatic product processing lines. The pre-fried product can be immediately packaged and stored, the processing flow is short, and the cost increase is limited, making it highly suitable for large-scale industrial application.

[0025] In summary, this invention addresses the industry pain points of fish chunks being easily oxidized and pre-fried products having a short shelf life. By organically combining a sodium alginate / chitosan / perilla extract composite edible film with the pre-frying process, it significantly delays fat oxidation and textural deterioration, greatly extends the refrigerated shelf life, and improves the quality of pre-fried fish chunks. Moreover, the process is simple, safe, and reliable, possessing significant economic value and promising prospects for widespread application. Attached Figure Description

[0026] Figure 1 Line graphs showing the changes in peroxide value of pre-fried grass carp pieces after refrigeration for 0, 6, and 11 days, respectively, for the blank control group, the group with 1% chitosan-0.2% perilla extract alone (1% chitosan group), the group with 1% sodium alginate-0.2% perilla extract alone (1% sodium alginate group), the group with 1% chitosan-1% sodium alginate-0.2% perilla extract alone (Group D), the group with 0.5% chitosan-1% sodium alginate-0.2% perilla extract alone (Group A), the group with 1% chitosan-0.5% sodium alginate-0.2% perilla extract alone (Group B), and the group with 1% chitosan-1% sodium alginate-0.1% perilla extract alone (Group C). Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0028] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0029] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0030] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0031] Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0032] This invention uses a texture analyzer to determine the hardness, elasticity, cohesiveness, and chewiness of samples. Instrument parameters: TPA analysis mode selected, P / 36R probe. Test conditions: probe speed before measurement 3 mm / s, speed during measurement 1 mm / s, speed after measurement 3 mm / s, deformation degree 50%, trigger force 5 g. Peroxide value was determined according to GB 5009.227-2023.

[0033] The perilla extract described in this invention is an aqueous extract of perilla leaves, which is concentrated and dried to obtain a powder. The perilla extract was purchased from Henan Longteng Bioengineering Co., Ltd., and is a 30-fold concentrated product.

[0034] Example 1 To determine the optimal blending ratio of sodium alginate, chitosan, and perilla extract, this example uses the peroxide value (POV) on days 0, 6, and 11 of refrigeration as the primary evaluation indicator. The total volume of the coating solution was fixed at 400 mL. The components were divided into groups A, B, C, and D according to the following ratios (w / v): 0.5% chitosan-1% sodium alginate-0.2% perilla extract, 1% chitosan-0.5% sodium alginate-0.2% perilla extract, 1% chitosan-1% sodium alginate-0.1% perilla extract, and 1% chitosan-1% sodium alginate-0.2% perilla extract. The peroxide values ​​of each group were determined according to GB 5009.227-2023. The peroxide values ​​of groups A, B, C, and D on days 0, 6, and 11 were recorded as A0, A6, A11, B0, B6, B11, C0, C6, C11, D0, D6, and D11, respectively. The peroxide values ​​of A0, A6, A11, B0, B6, B11, C0, C6, C11, D0, D6, and D11 were 0.0114, 0.0195, 0.0221, 0.0112, 0.0189, 0.0215, 0.0110, 0.0182, 0.0206, 0.0109, 0.0174, and 0.0187 g / 100g, respectively. Figure 1 It can be seen that the composite edible coating liquid formulation of group D is better, so this formulation was selected.

[0035] Example 2 Preparation of composite edible film coating solution and pre-fried grass carp chunks: (1) Raw material processing After killing the grass carp, scrape off the surface scales, remove the head, fins, tail and internal organs, rinse the fish thoroughly, and cut it into uniform pieces of 3cm×3cm×1cm.

[0036] (2) Preparation of coating solution Weigh out 4.0g of chitosan, 4.0g of sodium alginate, and 0.8g of perilla extract. Add the components in the coating solution according to the following mass-volume percentage (w / v): sodium alginate 1%, chitosan 1%, and perilla extract 0.2%. Add the mixture to drinking water at 80℃ and stir until homogeneous to obtain the composite coating solution.

[0037] (3) Pre-frying Place the coated fish pieces into soybean oil heated to 180°C and fry for 90 seconds, until the surface turns light golden brown and the fish is basically cooked through. Remove and drain off excess oil.

[0038] (4) Save Place the cooled fish pieces in a vacuum bag and store them in a refrigerator at 4°C.

[0039] Example 3 The effect of different coating treatments on peroxide value during cold storage: This embodiment sets up the following four treatment groups, and the peroxide value (POV) is measured on days 0, 6, and 11 after refrigeration at 4℃ to evaluate the oxidation inhibition effect. POV determination is performed according to GB 5009.227-2016, and the results are expressed as g / 100g. Control group: Fish pieces are directly pre-fried without coating; Chitosan group: The coating solution contains only 1.0% chitosan and 0.2% perilla extract, without sodium alginate; Sodium alginate group: The coating solution contains only 1.0% sodium alginate and 0.2% perilla extract, without chitosan; Mixed group: The composite coating solution of Example 2 is used. Results are as follows: Figure 1 As shown.

[0040] Example 4 The effects of different coating treatments on texture during cold storage: In this embodiment, the grouping and processing were the same as in Example 3. The hardness, elasticity, cohesiveness, and chewiness of the samples were measured using a texture analyzer on days 0, 6, and 11 after refrigeration at 4℃. Instrument parameters were set as follows: TPA analysis mode, P / 36R probe. Test conditions: probe velocity 3 mm / s before measurement, 1 mm / s during measurement, 3 mm / s after measurement, deformation degree 50%, trigger force 5 g. The results are shown in Table 1.

[0041] Table 1. Effects of different coating treatments on texture during cold storage. Those skilled in the art will readily understand that the above description is merely a partial example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An edible composite film, characterized in that, The edible composite film contains, by weight and volume percentage: 0.8-1.2% sodium alginate, 0.8-1.2% chitosan, 0.15-0.25% perilla extract, and the balance being water.

2. The edible composite film according to claim 1, characterized in that, The edible composite film contains, by weight and volume percentage: 0.9-1.1% sodium alginate, 0.9-1.1% chitosan, 0.18-0.22% perilla extract, and the balance being water.

3. The edible composite film according to claim 1, characterized in that, The edible composite film contains, by weight and volume percentage: 0.95-1.05% sodium alginate, 0.95-1.05% chitosan, 0.19-0.21% perilla extract, and the balance being water.

4. The edible composite film according to claim 1, characterized in that, The edible composite film contains, by weight and volume percentage: 0.98-1.02% sodium alginate, 0.98-1.02% chitosan, 0.195-0.205% perilla extract, and the balance being water.

5. The edible composite film according to any one of claims 1-4, characterized in that, The perilla extract is an aqueous extract of perilla leaves, obtained by concentration and drying.

6. A method for preparing high-quality fish fillets using the edible composite film according to any one of claims 1-5 combined with a pre-frying process, characterized in that, The method includes the following steps: S1. Raw material pretreatment: After slaughtering the fish, scrape off the surface scales, remove the head, fins, tail and internal organs, rinse the fish thoroughly, and cut it into uniform pieces. S2. Mix sodium alginate, chitosan, perilla extract and water to obtain a coating solution; S3. Completely immerse the fish pieces in the coating solution; S4. Deep-fry the coated fish pieces; S5. After the fish pieces have cooled, put them into a vacuum bag and store them in a refrigerator at 4°C.

7. The method for preparing high-quality fish fillets using an edible composite film combined with a pre-frying process according to claim 6, characterized in that, In step S3, the fish pieces are completely immersed in the coating solution for 4-7 minutes.

8. The method for preparing high-quality fish fillets using an edible composite film combined with a pre-frying process according to claim 6, characterized in that, In step S4, the frying conditions are frying at 170-190℃.

9. The method for preparing high-quality fish fillets using an edible composite film combined with a pre-frying process according to claim 6, characterized in that, The frying time in step S4 is 75-105 seconds.

10. The method for preparing high-quality fish fillets using an edible composite film combined with a pre-frying process according to claim 6, characterized in that, In step S4, frying is performed at 175-185℃ for 85-95 seconds.

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