Method for preserving tilapia mossambica

Abstract

The invention belongs to the technical field of preservation and fresh keeping of low-temperature food, and particularly relates to a fresh keeping method of tilapia mossambica. Specifically, according to the preservation method of the tilapia mossambica provided by the invention, the tilapia mossambica is treated by adopting an ascorbic acid solution with the mass concentration of 0.5-1.5% and is stored at ice temperature. Under the condition that no chemical preservative is added, an existing ice-temperature tilapia storage technology is improved, ascorbic acid is added to reduce the growth speed of putrefying bacteria, and the shelf life of the tilapia stored at the ice temperature is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of low-temperature food preservation and fresh-keeping, and more specifically, relates to a method for preserving tilapia. Background Art

[0002] Tilapia has delicious meat, contains a variety of unsaturated fatty acids and rich proteins, and occupies an important position in people's diet. Due to its high water content and rich nutrition, tilapia is a natural culture medium for spoilage microorganisms and is very easy to spoil. At present, frozen storage is still an effective way to preserve tilapia. Although frozen storage can effectively extend the shelf life of tilapia, the taste of tilapia after frozen storage is poor, and the internal consumption of frozen storage is large, and the energy waste is high.

[0003] Ice temperature storage technology is a new type of preservation technology, which refers to storing aquatic products at a temperature between 0℃ and the freezing point of the product. Aquatic products will not freeze when stored at this temperature, and the quality of aquatic products can be better maintained. The freezing point of cell fluid is generally in the range of -0.5℃ to -3.5℃, so the food can maintain cell activity in the narrow temperature between 0℃ and the freezing point, but respiratory metabolism is inhibited. At ice temperature storage temperature, the quality of tilapia is better, but the shelf life is limited. In order to further extend the shelf life of tilapia, the usual practice is to add preservatives, but consumers find it difficult to accept synthetic preservatives. Using natural ingredients in food to inhibit spoilage bacteria is more in line with consumer requirements.

[0004] Ascorbic acid is a natural ingredient in food and is often known as an antioxidant. Ascorbic acid can also interfere with bacterial quorum sensing and affect the formation of bacterial biofilms. Therefore, ascorbic acid has an antibacterial effect. There have been reports internationally on the use of ascorbic acid to preserve products such as chicken, but due to differences in temperature and the objects to be preserved, the preservation effect of ascorbic acid varies. Combining ice temperature storage technology with ascorbic acid for tilapia preservation has not yet been found. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the prior art and provide a method for preserving tilapia.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] The invention provides a method for preserving tilapia, which comprises treating the tilapia with a preservative liquid and storing the tilapia at an ice temperature;

[0008] The fresh-keeping liquid is an ascorbic acid solution with a mass concentration of 0.5-1.5%.

[0009] The present invention has found through a large number of studies that treating tilapia with an ascorbic acid solution having a mass concentration of 0.5 to 1.5% as a preservative and placing the tilapia in ice temperature storage can significantly improve the shelf life of the tilapia and improve the preservation quality of the tilapia. When a certain amount of iron ions exist in the environment, ascorbic acid can be used as an oxidant to cause a Fenton reaction by reducing transition metals, generate ROS to cause oxidative stress to the spoilage bacteria, and then reduce the spoilage reaction of the spoilage bacteria. Specifically, the total number of colonies during storage can be effectively reduced, the growth of spoilage bacteria of tilapia stored at ice temperature can be inhibited, and the shelf life of tilapia stored at ice temperature can be extended; the accumulation of total volatile basic nitrogen during storage can be effectively delayed; the change of pH during storage can be reduced; the growth and metabolic activity of spoilage bacteria can be inhibited, the decomposition of proteins and amino acids by spoilage bacteria can be reduced, and the production of nitrogen oxides, methyl compounds and sulfides by spoilage bacteria can be inhibited. According to various data of the present invention, the shelf life of tilapia preserved by the preservation method of the present invention can reach 20 to 24 days.

[0010] In the present invention, the ice temperature is a temperature between 0°C and the freezing point of tilapia; specifically, the ice temperature is -2.3 to -0.7°C.

[0011] Preferably, the treatment is carried out by spraying or soaking. In the present invention, the fresh-keeping liquid spraying or soaking the tilapia must cover the entire surface of the tilapia.

[0012] Preferably, the soaking time is 1.5 to 2.5 minutes.

[0013] More preferably, the soaking time is 1.8 to 2.2 minutes; specifically, the soaking time is 2 minutes.

[0014] Preferably, the treatment temperature is at ice temperature, that is, at -2.3 to -0.7°C.

[0015] Preferably, the mass concentration of the ascorbic acid solution is 0.8-1.2%. Specifically, the mass concentration of the ascorbic acid solution is 1%.

[0016] Preferably, the solvent in the ascorbic acid solution is 0.9% saline.

[0017] Preferably, the tilapia is first cleaned, headed, eviscerated, skinned and cut into pieces.

[0018] Preferably, the fresh-keeping liquid is drained after treatment, packaged, and finally stored at ice temperature.

[0019] In the present invention, the draining is to remove the excess fresh-keeping liquid so that the tilapia does not drip liquid.

[0020] Preferably, the packaging is carried out in a sterilized plastic bag.

[0021] The present invention has the following beneficial effects:

[0022] The present invention provides a method for preserving tilapia. Without using any chemical preservative, the tilapia is soaked or sprayed with low-concentration ascorbic acid to preserve the tilapia. The present invention provides a new method for preserving ice-temperature stored food, especially tilapia. The method provided by the present invention can not only significantly extend the shelf life of ice-temperature stored tilapia, effectively reduce the accumulation of volatile basic nitrogen during storage, but also delay the decline of sensory qualities such as color and smell of fish meat. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Changes in the total colony count of tilapia with different preservation treatments during storage.

[0024] Figure 2 Changes of TVB-N value during storage of tilapia with different preservation treatments.

[0025] Figure 3 Changes of pH value during storage of tilapia with different preservation treatments.

[0026] Figure 4 Changes in sensory evaluation scores of tilapia with different preservation treatments during storage.

[0027] Figure 5 This is a radar chart of the spoilage odor of tilapia with different preservation treatments after storage at -1.5±0.8℃ for 24 days.

[0028] Figure 6 Changes in the contents of nitrogen oxides, methyl compounds and sulfides in tilapia with different preservation treatments after storage at -1.5±0.8℃ for 24 days. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0030] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0031] Example 1

[0032] 1. Preparation of Ascorbic Acid Solution

[0033] Ascorbic acid was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with a purity of 99%. Ascorbic acid was prepared into an ascorbic acid solution with a mass concentration of 1% using sterile 0.9% physiological saline, and after being fully dissolved, it was sterilized using a filter membrane with a pore size of 0.22 μm that had been sterilized at 121° C. and set aside.

[0034] 2. Tilapia preservation

[0035] Fresh tilapia were washed with sterile water, headed, gutted, skinned, and cut into pieces (2cm*3cm). The tilapia pieces were randomly divided into two groups:

[0036] 0.9% saline (blank control group): Soak the fish pieces in 0.9% saline at -1.5±0.8℃ for 2 minutes to make sure the fish pieces are fully in contact with the soaking solution, then remove and drain for 5 minutes until the fish pieces do not drip. Then package the fish pieces in a sterile packaging bag and store at -1.5±0.8℃;

[0037] 1% ascorbic acid solution group: Soak the fish pieces in 1% ascorbic acid solution at -1.5±0.8℃ for 2 minutes to make the fish pieces fully contact with the soaking solution, then take them out and drain for 5 minutes until the fish pieces do not drip water. Then put the fish pieces in sterile packaging bags and store them at -1.5±0.8℃.

[0038] Example 2

[0039] Experimental materials: Tilapia after the preservation treatment in Example 1.

[0040] Experimental sampling method:

[0041] Part of the fish meat was immediately taken out from the sample after the preservation treatment in Example 1 for analysis, and the data was recorded as day 0. The remaining fish meat was stored at -1.5±0.8°C, and samples were taken and analyzed on the 4th, 8th, 12th, 16th, 20th, and 24th days of storage. Three bags were taken from each treatment group for measurement, and the measurement results were averaged.

[0042] Analysis of microbial changes in fish fillets from different treatment groups:

[0043] The experimental method was based on GB / T 4789.2-2016. Under sterile conditions, 10 g of tilapia meat was placed in 90 mL of sterile saline (0.9%, w / v) and shaken at 120 r / min for 30 min. 1 mL of the bacterial suspension was diluted gradiently and cultured in PCA medium at 30 °C for 48 h. The number of colonies was calculated and the results were taken as logarithmic values. The experiment was repeated 3 times.

[0044] Experimental results:

[0045] Figure 1The figure shows the changes in the total number of bacteria in the fish blocks treated with 1% ascorbic acid or saline during ice storage. As can be seen from the figure, the initial total number of colonies (total number of colonies on day 0) of the two groups of tilapia blocks was in the range of 3.85-4.05lgCFU / mL, with no significant difference (p < 0.05). The total number of bacteria in the two groups of samples increased significantly during storage compared with the initial colony summary (p < 0.05). On the 8th day of storage, the total number of colonies in the blank control group was 7.61lg CFU / mL, which exceeded the maximum safety limit of 7.00lgCFU / mL for the total number of fish colonies specified by the International Microbiological Specifications Committee. The total number of colonies in the 1% ascorbic acid solution group exceeded the safety limit only on the 12th day, which was 7.54lg CFU / mL. The results show that 1% ascorbic acid can inhibit the growth of spoilage bacteria in tilapia stored at ice temperature and extend the shelf life of tilapia stored at ice temperature.

[0046] Example 3

[0047] Experimental materials: Tilapia treated with the preservation method in Example 1 was sampled and analyzed on the 0th, 4th, 8th, 12th, 16th, 20th and 24th days of storage.

[0048] (1) Changes in total volatile basic nitrogen (TVB-N)

[0049] The experimental method refers to the microdiffusion method of GB / T 5009.228-2016, which is briefly described as follows: 10g of tilapia stored on days 0, 4, 8, 12, 16, 20, and 24 of Example 1 are weighed in 100mL of water, shaken evenly, immersed for 30min and filtered, and the filtrate is used for standby. The water-soluble glue is applied to the edge of the diffusion dish, and 1mL of boric acid solution and 1 drop of mixed indicator are added to the central inner chamber of the dish. 1.0mL of filtrate is added to the outer chamber of the dish, covered with a frosted glass cover, 1mL of saturated potassium carbonate solution is added from the gap, the frosted glass cover is immediately pushed flat, and the diffusion dish is gently rotated to fully mix the sample solution and the saturated potassium carbonate solution, and then placed in a 37℃±1℃ incubator for 2h, cooled to room temperature, and the cover is removed. It is titrated with a standard titration solution of hydrochloric acid or sulfuric acid (0.0100mol / L), and the end point color is blue-purple. Distilled water is used as a blank. The experimental results were expressed as the arithmetic mean of two independent determination results obtained under repeatability conditions, and the results were rounded to three significant figures.

[0050] Result calculation: The content of volatile basic nitrogen in the sample is calculated according to formula (1):

[0051] Formula (1): X = [(V1-V2) × c × 14] / (m × V / V0) × 100;

[0052] Where:

[0053] X——the content of volatile basic nitrogen in the sample, in milligrams per 100 grams (mg / 100g) or milligrams per 100 milliliters (mg / 100mL);

[0054] V1————The volume of hydrochloric acid or sulfuric acid standard titration solution consumed by the test solution, in milliliters (mL);

[0055] V2——the volume of hydrochloric acid or sulfuric acid standard titration solution consumed by the reagent blank, in milliliters (mL);

[0056] c————Concentration of hydrochloric acid or sulfuric acid standard titration solution, in moles per liter (mol / L);

[0057] m——sample mass, in grams (g), or sample volume, in mL;

[0058] V————accurately drawn filtrate volume, in milliliters (mL), in this method V=1;

[0059] V0——Total volume of sample solution, in milliliters (mL). In this method, V0=100;

[0060] TVB-N value is a common evaluation index for fish freshness. TVB-N value is the alkaline nitrogen-containing substances such as amines and ammonia produced by bacteria through the degradation of proteins and other nitrogen-containing compounds. The changes in TVB-N value of tilapia with different preservation treatments during storage are shown in Figure 2. Figure 2 As shown. The TVB-N value of the blank control group on the 20th day of storage was 48.56 mg / 100g, which is higher than the acceptable upper limit of fish spoilage of 35 mg / 100g stipulated by the European Commission. The TVB-N value of tilapia treated with ascorbic acid on the 20th day of storage was only 21.04 mg / 100g, which means that the tilapia can be stored for at least 20 days using the method described in the present invention. The TVB-N value only exceeded 35 mg / 100g when stored for 24 days, which was 36.07 mg / 100g. During the ice temperature storage period of 12 to 24 days, the TVB-N value of tilapia treated with ascorbic acid was significantly lower than that of tilapia in the blank control group (p<0.05), indicating that 1% ascorbic acid treatment can inhibit the corruption of spoilage bacteria, effectively delay the accumulation of TVB-N in tilapia, and extend the shelf life of tilapia stored at ice temperature, which can be stored for at least 20 days.

[0061] (2) Changes in pH

[0062] The experimental method refers to GB5009.237-2016 and is briefly described as follows: weigh 5.00g of sample, add 50mL of 0.1mol / L potassium chloride solution, and homogenize at 15000r / min for 2min. Pipette a sample that can immerse the electrode into a beaker, and ensure that the sample temperature is within the range of 20℃±2℃. Immerse the pH meter electrode in the sample solution, follow the measurement steps of the pH meter, and record the reading after it stabilizes. The value is accurate to 0.01, and the experiment is repeated 3 times.

[0063] The change in pH value is one of the criteria for measuring the freshness of fish. After slaughter, the carbohydrate metabolism pathway in fish is anaerobic respiration. Glycogen decomposition produces a large amount of lactic acid, and ATP decomposition produces a certain amount of phosphoric acid, which will cause the pH value of fish muscle to decrease. As the freshness decreases, the fish protein autolyzes, causing the protein, amino acids and some other nitrogen-containing substances in the fish to be decomposed into ammonia and amines, and the pH value gradually increases. At the same time, as the storage time increases, bacterial activity gradually increases, and the various enzymes secreted by bacteria accelerate the decomposition of proteins and other substances, causing the pH value to further increase. The changes in pH value of tilapia under different treatment conditions are as follows: Figure 3 As shown. In the initial storage period of 0 to 12 days, the pH values ​​of the two groups did not change significantly (p>0.05). After 12 days, the pH values ​​of both groups increased significantly. During the storage period of 12 to 24 days, the pH value of the fish fillets in the blank control group was always significantly higher than that of the tilapia in the ascorbic acid treatment group, indicating that 1% ascorbic acid can effectively inhibit the metabolic activity of spoilage bacteria, which is consistent with the results of the TVB-N value.

[0064] (3) Analysis of changes in sensory characteristics

[0065] Quantitative Descriptive Analysis (QDA) was used to analyze the

[0066] The sensory evaluation team consists of 5 trained people. They use a combination of scoring and description to score the smell, color, and texture of tilapia. The scores are 0 for very fresh, 1 for fresh, 2 for average, 3 for slightly corrupt, 4 for obviously corrupt, and 5 for completely unacceptable. The characteristics of corruption are described. The description of smell characteristics includes normal fragrance, fresh fragrance, hydrogen sulfide smell, ammonia smell, sour smell, and fishy smell. The description of color appearance includes dark, red, shiny, and the presence or absence of mucus. The description of texture includes softness, elasticity, tissue tightness, and texture clarity. Finally, the average score is calculated.

[0067] Changes in sensory scores of tilapia treated with different methods during ice storage Figure 4As shown. The sensory scores of all tilapia increased significantly during storage (P<0.05), indicating that the tilapia was gradually corrupting. As the storage time increased, the tilapia mainly showed soft texture, increased mucus, dark color and increased rancidity. The sensory evaluation score of untreated tilapia was greater than 3 during the 16-20 days of storage. At this time, the sensory quality of tilapia declined seriously and was slightly corrupted. However, the sensory evaluation score of tilapia treated with ascorbic acid was still less than 3 at 20 days, indicating that ascorbic acid treatment can effectively delay the deterioration of the sensory quality of tilapia and effectively extend the shelf life of tilapia stored at ice temperature.

[0068] (4) Electronic nose measurement of tilapia spoilage odor

[0069] The experimental method is as follows: 3.50 g of tilapia meat that has been stored at ice temperature for 24 days after the preservation treatment in Example 1 was taken, minced, and then placed in a 40 mL injection bottle, with a headspace equilibrium temperature of 60°C and an equilibrium time of 20 min. The electronic nose measurement conditions are as follows: injection needle temperature of 50°C, cleaning time of 100 s, air intake of 150 mL / min, measurement time of 120 s, and the characteristic value extraction time point is set to 110-115 s. The information within the characteristic time period is analyzed, and 3 parallel samples are prepared for each sample. The results remove abnormal values ​​to ensure the accuracy of the experimental data.

[0070] The electronic nose was used to analyze the spoilage odor of tilapia treated with different methods. The results are as follows: Figure 5 and Figure 6 As shown in the figure, fresh refers to fresh fish, CK refers to blank control, and VC refers to tilapia treated with 1% ascorbic acid. Figure 5 As shown in the radar chart, after 24 days of storage, compared with fresh tilapia, the nitrogen oxides, organic sulfides, aldehydes, ketones and alcohols, methyl compounds and sulfides in the fish fillets of the blank control group increased significantly (p < 0.05), indicating that the corruption smell of tilapia stored at ice temperature is mainly composed of these five substances. Figure 6 It can be seen that after tilapia was treated with ascorbic acid, its nitrogen oxides, methyl compounds and sulfide contents were significantly lower than those in the blank control group (p < 0.05). Among them, the response value of nitrogen oxides was basically consistent with that of fresh tilapia, indicating that ascorbic acid can effectively inhibit the metabolic activity of putrefactive bacteria, inhibit the production of volatile putrefactive substances, and delay the sensory spoilage of tilapia stored at ice temperature. The results are consistent with the sensory evaluation.

[0071] In summary, the embodiment of the present invention uses a preservative solution (an ascorbic acid solution with a mass concentration of 1%) to effectively extend the shelf life of tilapia without freezing the tilapia. Adding ascorbic acid can inhibit the growth of spoilage bacteria and their metabolic activities, reduce the decomposition of proteins and amino acids by spoilage bacteria, reduce the decomposition products of nitrogen-containing compounds such as amines and ammonia to a certain extent, and extend the shelf life of tilapia stored at ice temperature. In addition, ascorbic acid can inhibit the production of nitrogen oxides, methyl compounds and sulfides by spoilage bacteria, and delay the sensory corruption of tilapia stored at ice temperature. The ascorbic acid used in the embodiment of the present invention is a natural food ingredient. Using it to preserve tilapia avoids the use of preservatives, improves the edibility of food, reduces the use of preservatives, and can meet the needs of certain consumers to resist preservatives.

[0072] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preserving tilapia, characterized in that: Tilapia was treated with preservative solution and stored at ice temperature; The fresh-keeping liquid is an ascorbic acid solution with a mass concentration of 0.5-1.5%.

2. The method according to claim 1, characterized in that: The ice temperature is -2.3 to -0.7°C.

3. The method according to claim 1, characterized in that: The treatment is carried out by spraying or soaking.

4. The method according to claim 3, characterized in that: The soaking time is 1.5 to 2.5 minutes.

5. The method according to claim 3, characterized in that: The soaking time is 1.8 to 2.2 minutes.

6. The method according to claim 1, characterized in that: The treatment temperature is -2.3 to -0.7°C.

7. The method according to claim 1, characterized in that: The mass concentration of the ascorbic acid solution is 0.8-1.2%.

8. The method according to claim 1, characterized in that: The solvent in the ascorbic acid solution is 0.9% physiological saline.

9. The method according to claim 1, characterized in that: The tilapia is first cleaned, headed, eviscerated, skinned and cut into pieces.

10. The method according to claim 1, characterized in that: After the fresh-keeping liquid is treated, it is drained, packaged, and finally stored at ice temperature.

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