A method for improving the quality stability of frozen oysters and frozen oyster meat products

Abstract

This invention discloses a method for improving the quality stability of frozen oysters and a frozen oyster meat product, relating to the field of aquatic product processing technology. The method for improving the quality stability of frozen oysters provided by this invention employs ultrasonic treatment combined with citric acid solution soaking. It utilizes the cavitation effect, microjets, and mechanical vibration generated when ultrasound propagates in a liquid medium to effectively disrupt the mass transfer resistance on the surface of oyster tissue, significantly promoting the penetration and uniform distribution of citric acid within the muscle tissue. This solves the problems of low penetration efficiency of active ingredients and insufficient internal tissue protection in traditional citric acid soaking treatments, achieving effective inhibition of lipid and protein oxidation. This invention features a simple process, high safety, requires no complex equipment, and is suitable for large-scale application in the aquatic product processing industry.

Description

Technical Field

[0001] This invention relates to the field of aquatic product processing technology, and in particular to a method for improving the quality stability of frozen oysters and frozen oyster meat products. Background Technology

[0002] Oysters are an important type of marine shellfish, rich in high-quality protein, polyunsaturated fatty acids, and various minerals, possessing high nutritional and economic value. Freezing is the primary method for long-term preservation of oysters, effectively inhibiting microbial growth and enzyme activity, thus extending shelf life. However, oyster muscle tissue has a high water content and a relatively loose structure, making it highly susceptible to a series of quality changes during freezing, such as lipid oxidation, protein oxidation, and muscle structure damage. This leads to problems like darkening of color, browning, softening of texture, and deterioration of flavor, significantly reducing the product's sensory quality and market value.

[0003] Currently, antioxidant or acidic solution soaking is commonly used in seafood processing to improve frozen storage stability. However, traditional soaking methods suffer from low penetration efficiency and insufficient diffusion within the tissue, resulting in limited protective effects. Previous research has attempted to introduce ultrasound-assisted methods to improve processing. For example, applying ultrasound during the immersion freezing stage can accelerate the freezing rate and reduce ice crystal size, thereby minimizing damage to muscle tissue during freezing. However, the inventors found that this processing method still results in oxidative deterioration during frozen storage, and the oysters, after thawing, still exhibit unsatisfactory quality indicators such as color, texture, and flavor. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that frozen oysters are prone to lipid oxidation, protein oxidation, and deterioration of color and texture during storage in the prior art. The present invention provides a method to improve the quality stability of frozen oysters during storage.

[0005] To address the above problems, the present invention proposes the following technical solution: A method for improving the quality stability of frozen oysters includes the following steps: (1) Immerse the oyster meat in a citric acid solution; (2) The treatment is carried out under ultrasonic conditions, wherein the ultrasonic frequency is 20-40 kHz, the ultrasonic power is 100-500W, and the treatment time is 5-20 min. (3) After ultrasonic treatment, remove the oyster meat, drain off the excess solution on the surface, and vacuum pack it; (4) Store the packaged oyster meat frozen at a temperature not higher than -18°C.

[0006] Further, the citric acid solution in step (1) has a mass fraction of 0.1% to 2.0%.

[0007] Further, the ratio of the mass of the oyster meat to the volume of the citric acid solution in step (1) is 1:3 to 1:10.

[0008] Furthermore, the temperature of the ultrasonic treatment in step (2) is 4 to 20 °C.

[0009] Furthermore, the ultrasonic treatment in step (2) is performed in an intermittent mode.

[0010] Furthermore, the intermittent mode consists of 3-5 seconds of ultrasonic operation followed by 2-4 seconds of interval.

[0011] Further, the oyster meat in step (1) is obtained by removing the shell from the oyster, cleaning the surface impurities, and draining the water.

[0012] The present invention also provides the application of the method in the preparation of frozen oyster meat products.

[0013] The present invention also provides a frozen oyster meat product, which is prepared by the method described above for improving the quality stability of frozen oysters.

[0014] Compared with the prior art, the technical effects achieved by the present invention include: The method for improving the quality stability of frozen oysters provided by this invention employs ultrasonic treatment combined with citric acid solution soaking. By utilizing the cavitation effect, microjets, and mechanical vibration generated when ultrasound propagates in a liquid medium, the mass transfer resistance on the surface of oyster tissue is effectively destroyed, significantly promoting the penetration and uniform distribution of citric acid within the muscle tissue. This solves the problems of low penetration efficiency of active ingredients and insufficient protection of the internal tissue in traditional citric acid soaking treatment, and achieves effective inhibition of lipid oxidation and protein oxidation.

[0015] Furthermore, the treatment solution of this invention is only a citric acid solution, without the need for compounding other antioxidants or additives. Through the chelating effect of citric acid on pro-oxidative metal ions, combined with the moderate improvement of tissue microstructure by ultrasonic treatment, a stable antioxidant protection system is built before frozen storage, thereby significantly slowing down the oxidative degradation of polyunsaturated fatty acids during frozen storage, effectively maintaining the integrity of protein structure, and achieving good preservation of color stability and muscle texture characteristics of frozen oysters.

[0016] In summary, this invention provides a simple, safe, and convenient technical solution for maintaining the quality of frozen oysters. It is suitable for preparing high-quality frozen oyster meat products and can effectively maintain the sensory quality and nutritional value of the products during long-term frozen storage. This provides the aquatic product processing industry with a green, convenient, and cost-controllable freezing and preservation strategy. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A process flow diagram of the method for improving the quality stability of frozen oysters provided by the present invention.

[0019] Figure 2 The graph shows the changes in lipid oxidation index (TBARS value) of oysters during frozen storage under different treatment conditions.

[0020] Figure 3 The graph shows the changes in DHA and EPA content in oysters during frozen storage under different treatment conditions.

[0021] Figure 4 The graph shows the changes in protein oxidation indicators (protein carbonyl content and free thiol content) during frozen storage of oysters under different treatment conditions. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0024] It should also be understood that the terminology used in the specification of embodiments of the present invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the present invention. As used in the specification of embodiments of the present invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0025] See Figure 1 This is a process flow diagram of a method for improving the quality stability of frozen oysters provided by an embodiment of the present invention. The method of the present invention specifically includes the following steps: (1) Preparation of oyster raw materials.

[0026] In practice, fresh oysters must first be selected as raw material. The oyster shells are cleaned, the meat is removed, and excess water is drained off. The initial freshness of the oyster meat directly affects its quality stability during subsequent frozen storage; therefore, fresh, odorless oysters with intact muscle tissue should be selected. If the raw material is not fresh, its endogenous enzyme activity is high and its initial microbial load is large, making it difficult to effectively inhibit quality deterioration even after subsequent treatment. Therefore, raw material processing is a fundamental prerequisite for ensuring the overall effectiveness of the method.

[0027] (2) Immerse the oyster meat in a citric acid solution.

[0028] After obtaining the oyster meat, a citric acid solution needs to be prepared as a treatment solution, and the oyster meat is immersed in the citric acid solution. Citric acid is a food-grade organic acid, and the carboxyl group in its molecular structure can effectively chelate oxidizing metal ions (such as iron ions, copper ions, etc.), thereby cutting off the initiation link of the lipid oxidation chain reaction. In practice, the mass fraction of the citric acid solution is controlled within the range of 0.1% to 2.0%, for example, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, etc. If the citric acid concentration is too low (below 0.1%), the chelating ability is insufficient, and it is difficult to effectively inhibit the oxidation reaction; if the concentration is too high (above 2.0%), it may lead to excessive acidification of the protein on the surface of the oyster meat, resulting in an unpleasant sour taste or texture change, while increasing costs and potentially affecting the product flavor.

[0029] In practice, the ratio of oyster meat mass to citric acid solution volume (material-to-liquid ratio) should be controlled within the range of 1:3 to 1:10, such as 1:3, 1:4, 1:5, 1:8, 1:10, etc. A material-to-liquid ratio that is too low (too much oyster meat) will result in insufficient citric acid and inadequate penetration; a material-to-liquid ratio that is too high will waste the solution, and an excessively large solution volume may dilute the endogenous antioxidants dissolved from the oyster meat, which is detrimental to the overall protective effect.

[0030] (3) Processing under ultrasonic conditions.

[0031] After draining the surface moisture, the oyster meat is immersed in a citric acid solution and then subjected to ultrasonic treatment. When ultrasound propagates in a liquid medium, it generates cavitation, microjet, and mechanical vibration. The microbubbles generated by cavitation, upon rupture, create localized high temperatures, high pressures, and shock waves, effectively disrupting the mass transfer boundary layer on the oyster tissue surface and opening intercellular channels. This significantly promotes the penetration and diffusion of citric acid molecules into the muscle tissue. Simultaneously, moderate ultrasonic vibration improves the tissue microstructure, resulting in a more uniform distribution of citric acid within the tissue, overcoming the shortcomings of traditional soaking treatments where active ingredients remain only on the surface and lack adequate internal protection.

[0032] In practice, the ultrasound frequency is controlled within the range of 20–40 kHz, such as 20 kHz, 22 kHz, 25 kHz, 30 kHz, and 40 kHz. Too low a frequency (below 20 kHz) can easily generate large cavitation bubbles, potentially causing excessive mechanical damage to the tissue; too high a frequency (above 40 kHz) weakens the cavitation effect, resulting in insignificant penetration promotion. The ultrasound power is controlled within the range of 100–500 W, such as 100 W, 150 W, 200 W, 250 W, 300 W, 400 W, and 500 W. Too low a power (below 100 W) results in a weak cavitation effect, making it difficult to effectively promote mass transfer; too high a power (above 500 W) may cause local overheating or excessive mechanical impact, leading to muscle fiber rupture and increased fluid loss. The treatment time is controlled within the range of 5–20 min, such as 5 min, 8 min, 10 min, 15 min, and 20 min. If the ultrasonic treatment time is too short (less than 5 minutes), the citric acid penetration will be insufficient; if the time is too long (more than 20 minutes), the continuous ultrasonic action may cause excessive softening of the tissue or dissolution of nutrients. Furthermore, the ultrasonic treatment temperature should be controlled within the range of 4–20 °C, such as 4 °C, 10 °C, 15 °C, and 20 °C. It is preferable to use an ice-water bath to maintain a low temperature (approximately 4 °C) to avoid the temperature rise caused by ultrasonic energy conversion during the treatment process, which could adversely affect the freshness of the oyster meat. If the temperature exceeds 20 °C, the risk of microbial growth increases, and proteins may undergo thermal denaturation, thus affecting the quality of subsequent frozen storage.

[0033] Ultrasonic treatment can be performed in an intermittent mode, such as working for 3-5 seconds and then pausing for 2-5 seconds (e.g., working for 4 seconds and pausing for 2 seconds). The intermittent mode helps to avoid the excessive heat effect caused by continuous ultrasound, while giving the cavitation bubbles time to reform, thereby improving cavitation efficiency.

[0034] In practical applications, the parameters such as ultrasonic frequency, power, time, temperature, and intermittent mode can be adjusted according to the equipment model, processing capacity, and raw material characteristics.

[0035] (4) After ultrasonic treatment, remove the oyster meat, drain off the excess solution on the surface, and vacuum pack it.

[0036] In practice, after ultrasonic treatment, the oyster meat needs to be removed from the citric acid solution and excess solution drained from its surface. This draining process prevents excessive surface solution from causing poor sealing or uneven concentration during vacuum packaging, and also reduces excessive ice crystal formation during frozen storage. Vacuum packaging then follows, effectively removing oxygen from the packaging bag, reducing the rate of aerobic oxidation, and preventing the product surface from drying out and oxidizing due to direct contact with cold air during freezing.

[0037] (5) Store the packaged oyster meat frozen at a temperature not higher than -18°C.

[0038] In practice, vacuum-packed oyster meat is frozen and stored at a temperature not exceeding -18°C. -18°C is a commonly used benchmark temperature for food freezing and storage. At this temperature, microbial activity essentially ceases, enzyme activity is significantly reduced, and the oxidation reaction rate is greatly slowed down. During freezing and storage, citric acid, which has pre-penetrated into the tissue, continuously chelates oxidizing metal ions, thereby effectively inhibiting lipid and protein oxidation during long-term freezing and storage, maintaining the color, texture, and nutritional value of the oyster meat.

[0039] Example 1 This embodiment provides a method for improving the quality stability of frozen oysters, specifically including the following steps: (1) Raw material processing: Select fresh live oysters weighing 160-200 g, clean the impurities on the surface of the oyster shells, remove the oyster meat with a shell-opening tool, and drain the surface water for later use.

[0040] (2) Preparation of citric acid solution: Prepare a 0.5% citric acid aqueous solution as a pretreatment solution.

[0041] (3) Ultrasonic assisted treatment: Oyster meat was immersed in citric acid solution at a material-to-liquid ratio of 1:5 and ultrasonic assisted treatment was carried out under ice-water bath conditions (treatment temperature of about 4 ℃). The ultrasonic frequency was 22 kHz, and the ultrasonic power was set to 100 W, 200 W and 300 W respectively for comparative experiments. The intermittent working mode was adopted (ultrasonic working for 4 s, intermittent for 2 s), and the total treatment time was 10 min.

[0042] (4) Draining treatment: After ultrasonic treatment, remove the oyster meat, drain off the excess solution on the surface, and then vacuum pack it.

[0043] (5) Frozen storage: Vacuum-packed oyster meat was frozen and stored at a temperature not higher than -18℃ for 6 months, and samples were taken at different time points to determine various indicators.

[0044] Experiment 1 To verify the inhibitory effect of the method of the present invention on lipid oxidation of frozen oysters, oyster samples (US100+CA, US200+CA, US300+CA) that were treated with different ultrasonic powers (100 W, 200 W, 300 W) in Example 1 and then frozen and stored for 6 months were taken. At the same time, fresh oyster meat without any treatment was set as the fresh control group (Fresh), frozen oysters soaked in citric acid only (without ultrasonic treatment) were set as the citric acid control group (CA), and frozen oysters without any pretreatment were set as the frozen control group (FC). The thiobarbituric acid reactive substances (TBARS) values ​​of each sample were measured.

[0045] The measurement results are as follows Figure 2 As shown in the figure, compared with fresh oyster meat, the TBARS value of the frozen control group was significantly increased after 6 months of frozen storage, indicating that a significant lipid oxidation reaction occurred during frozen storage. The TBARS value of the citric acid control group was lower than that of the frozen control group, indicating that citric acid treatment alone has a certain antioxidant effect. The TBARS values ​​of all samples treated with ultrasound-assisted citric acid were further significantly reduced, with the 200 W ultrasound power group showing the best effect and the lowest TBARS value. The results indicate that the method of this invention can effectively inhibit lipid oxidation of oyster meat during frozen storage, and the effect is most significant at an ultrasound power of around 200 W.

[0046] Experiment 2 To further verify the protective effect of the method of the present invention on polyunsaturated fatty acids, the contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were determined by gas chromatography for each group of samples in Example 1.

[0047] The measurement results are as follows Figure 3 As shown in the figure, compared with fresh oyster meat, the DHA and EPA contents of the frozen control group were significantly reduced after 6 months of frozen storage, indicating that polyunsaturated fatty acids underwent significant oxidative degradation during frozen storage. The DHA and EPA contents of the citric acid control group were higher than those of the frozen control group. Furthermore, the DHA and EPA contents of all samples treated with ultrasound-assisted citric acid were significantly increased, with the 200 W ultrasound power group showing the best effect and the highest fatty acid retention rate. The results indicate that the method of this invention can effectively inhibit the oxidative degradation of polyunsaturated fatty acids during frozen storage, thus better preserving the nutritional value of oyster meat.

[0048] Experiment 3 To verify the inhibitory effect of the method of the present invention on protein oxidation in frozen oysters, samples from each group in Example 1 were taken, and the protein carbonyl content and free thiol content were measured respectively.

[0049] The measurement results are as follows Figure 4As shown in the figure, compared with fresh oyster meat, after 6 months of frozen storage, the protein carbonyl content in the frozen control group increased significantly, while the free sulfhydryl content decreased significantly, indicating a significant protein oxidation reaction. The degree of protein oxidation in the citric acid control group was less than that in the frozen control group. However, after ultrasound-assisted citric acid treatment, the protein carbonyl content in all groups decreased significantly, while the free sulfhydryl content remained at a high level, with the 200 W ultrasound power treatment group showing the best effect. The results indicate that the method of this invention can effectively inhibit protein oxidation during frozen storage and maintain the stability of protein structure.

[0050] Experiment 4 To verify the effect of the method of the present invention on improving the color stability of frozen oysters, samples from each group in Example 1 were taken, and the brightness value of the oyster samples was measured using a colorimeter. L* ), red-green value ( a* ), Blue-Yellow Value ( b* ), whiteness value ( W* ) and overall color difference ( ΔE ).

[0051] The test results are shown in Table 1. Compared with fresh oyster meat, after 6 months of frozen storage, the frozen control group... a* and b* Significantly increased L* and W* Significantly reduced, ΔE The significantly increased value indicates that the oyster meat underwent obvious darkening and browning during frozen storage. The degree of color deterioration in the citric acid control group was less than that in the frozen control group. However, the samples treated with ultrasound-assisted citric acid showed... L* and W* Significantly improved a* and b* Significantly reduced, ΔE The color values ​​decreased significantly, with the color index of the 200 W ultrasonic power treatment group being closest to that of the fresh sample. The results indicate that the method of this invention can effectively inhibit color deterioration of frozen oysters during storage and maintain good appearance quality.

[0052] Experiment 5 To verify the effect of the method of the present invention on maintaining the textural stability of frozen oysters, samples from each group in Example 1 were taken, and the textural properties parameters such as hardness, elasticity, cohesiveness, chewiness, and resilience of the oyster samples were measured using a texture analyzer.

[0053] The results are shown in Table 1. Compared with fresh oyster meat, after 6 months of frozen storage, all textural indices of the frozen control group decreased significantly, indicating a significant softening of the oyster muscle tissue. The degree of textural deterioration in the citric acid control group was alleviated compared with the frozen control group. However, the decrease in all textural indices was significantly reduced in all groups treated with ultrasound-assisted citric acid, with the 100–200 W ultrasound power group showing the best textural preservation effect. The results indicate that the method of this invention can effectively slow down the softening of frozen oysters during storage and better maintain the texture characteristics of the muscle tissue.

[0054] Table 1. Results of color and texture changes in oysters under different treatment conditions. Note: The data in the table are "mean ± standard deviation"; different superscript letters in the same row indicate significant differences between groups (p<0.05), and the same letter indicates no significant difference.

[0055] Based on the above test results, the method for improving the quality stability of frozen oysters provided by this invention only requires the use of citric acid treatment solution, without the need for additional antioxidants or additives. The raw materials are simple and safe. Combined with the ultrasonic cavitation effect, it can promote the efficient penetration and uniform distribution of citric acid in oyster tissue, significantly enhancing the antioxidant protective effect of citric acid. This invention can effectively inhibit lipid oxidation reactions during frozen storage, reduce the formation of thiobarbituric acid reactants, while retaining the content of polyunsaturated fatty acids (DHA and EPA); it can also reduce protein oxidation reactions, lower protein carbonyl content, and maintain a high thiol content. Furthermore, this invention can significantly improve the color stability of frozen oysters and delay the softening of muscle texture.

[0056] The invention features a simple process, high safety, and requires no complex equipment, making it suitable for large-scale application in the aquatic product processing industry.

[0057] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0058] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for improving the quality stability of frozen oysters, characterized in that, Includes the following steps: (1) Immerse the oyster meat in a citric acid solution; (2) The treatment is carried out under ultrasonic conditions, wherein the ultrasonic frequency is 20-40 kHz, the ultrasonic power is 100-500 W, and the treatment time is 5-20 min; (3) After ultrasonic treatment, remove the oyster meat, drain off the excess solution on the surface, and vacuum pack it; (4) Store the packaged oyster meat frozen at a temperature not higher than -18°C.

2. The method as described in claim 1, characterized in that, The citric acid solution in step (1) has a mass fraction of 0.1% to 2.0%.

3. The method as described in claim 1, characterized in that, The ratio of the mass of oyster meat to the volume of citric acid solution in step (1) is 1:3 to 1:

10.

4. The method as described in claim 1, characterized in that, The temperature of the ultrasonic treatment in step (2) is 4 to 20 °C.

5. The method as described in claim 1, characterized in that, The ultrasonic treatment in step (2) is performed in an intermittent mode.

6. The method as described in claim 5, characterized in that, The intermittent mode consists of ultrasound working for 3–5 seconds, followed by an interval of 2–4 seconds.

7. The method as described in claim 1, characterized in that, The oyster meat in step (1) is obtained by removing the shells from oysters, cleaning the surface impurities, and draining the water.

8. The use of the method according to any one of claims 1 to 7 in the preparation of frozen oyster meat products.

9. A frozen oyster meat product, characterized in that, It was prepared using the method for improving the quality stability of frozen oysters as described in any one of claims 1-7.

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