Method for prolonging shelf life of oysters through combined treatment of weakly acidic electrolyzed water and mulberry leaf extract

Abstract

The invention relates to a method for prolonging the shelf life of oysters through weak acidic electrolyzed water-mulberry leaf extract combined treatment. The method comprises the following steps: preparing a mulberry leaf extract: crushing mulberry leaves, sieving, mixing with an ethanol solution, uniformly stirring, carrying out suction filtration after ultrasonic treatment, evaporating to remove ethanol, and freeze-drying to obtain the mulberry leaf extract; weak acidic electrolyzed water treatment: soaking and cleaning the oysters in weak acidic electrolyzed water; mulberry leaf extract treatment: soaking the oysters in a mulberry leaf extract solution, and taking out the oysters. The combined treatment of the weakly acidic electrolyzed water and the mulberry leaf extract can effectively inhibit spoilage bacteria in and on the surfaces of the oysters, prevent the oysters from spoilage caused by the spoilage bacteria in the storage process, prolong the fresh-keeping period of the oysters by about 3 days, significantly slow down lipid oxidation and key enzyme activity reduction in the storage period of the oysters, and guarantee the edible taste of the oysters.

Description

Technical Field

[0001] The invention belongs to the field of food industry, and particularly relates to a method for prolonging the shelf life of oysters by combined treatment of weakly acidic electrolyzed water and mulberry leaf extract. Background Art

[0002] Oysters belong to the family Ostreidae, order Pectinatus, class Mollusca, phylum Bivalvialis, order Ostreae, and are the largest shellfish in the world. Commonly known as sea oysters and oyster heads, oysters are warm-temperate benthic shellfish with fat meat, delicious taste, rich nutrition, and can be eaten fresh. Oysters are loved by people for their unique flavor. They are rich in protein, amino acids, taurine, vitamins and various trace elements. The content of calcium, phosphorus and iron is more than 10 times that of meat, especially the zinc content, which ranks among the top in shellfish. Oysters also contain taurine, which can enhance the immunity of animals and inhibit tumor growth. At the same time, oysters contain a variety of essential amino acids for the human body, and the amino acid types are complete. Among all the nutrients in oysters, the amino acid composition is very balanced. However, due to the high water content and rich in various unsaturated fatty acids, the microorganisms and enzyme systems are active, which makes it easy for oysters and their products to produce undesirable flavors such as grassy, ​​metallic and fishy in a short time, and even corruption may occur.

[0003] Oyster spoilage is a complex issue, and its essence stems from the interaction of multiple factors. Microorganisms, temperature, pollution, chemicals, heavy metals or other harmful substances may cause oyster spoilage, but in general, microorganisms play the most important role in the oyster spoilage process. As a seafood, oysters may have a large number of microorganisms on their surface and inside. These microorganisms, such as Shewanella, Pseudomonas, Escherichia and Salmonella, may cause oyster spoilage during transportation and storage, thereby affecting the quality and edible safety of oysters. Studies have found that Shewanella is usually one of the main spoilage bacteria in oysters. When oysters are contaminated by Shewanella, it will cause the oyster tissue to soften, emit odor, change color or other abnormal phenomena. These changes will not only affect the taste of oysters, but may also threaten their edible safety. Therefore, it is necessary to develop a new economical and applicable preservation technology to effectively process oysters and prevent and control Shewanella contamination. Thereby achieving the effects of antibacterial, antiseptic and freshness preservation, and improving the utilization rate and economic value of oysters.

[0004] Mulberry leaves are both medicinal and edible. The output of mulberry leaves is seriously in excess of the demand for silkworm breeding, and mulberry leaf resources have not been effectively utilized, which has caused a waste of resources to a certain extent. Summary of the invention

[0005]

Technical issues

[0006] Putrefactive bacteria such as Shewanella present on the surface and inside of oysters can easily cause the oyster tissue to soften, emit an odor, change color, or exhibit other abnormal phenomena. These changes will not only affect the taste of the oysters, but may also pose a threat to their safety for consumption.

[0007]

Technical solution

[0008] In order to solve the above technical problems, the present invention uses weakly acidic electrolyzed water and plant extracts to jointly treat seafood, inhibit the growth and reproduction of spoilage bacteria during seafood storage, thereby delaying the spoilage of seafood, extending the shelf life of seafood, and maintaining the original nutritional components, taste and flavor of seafood. Compared with traditional chemical preservatives and antibacterial agents, this technology is more natural, environmentally friendly and safe, and meets the pursuit of health and environmental protection by modern consumers.

[0009] Weakly acid electrolyzed water (SAEW) mainly contains chlorine oxides, such as HClO, which have a strong killing effect on bacteria. The pH value of weakly acid electrolyzed water is close to neutral, and the bactericidal components in it are unstable and not easy to remain, so it has little impact on human health and the environment. Its preparation method is relatively simple, the economic cost required for preparation is not high, and compared with other bactericides, it has less impact on food and is suitable for industrial operation.

[0010] Mulberry leaves can be added to food in accordance with regulations. Compared with other antioxidant food additives, mulberry leaves are more natural, cheaper and more likely to be favored by consumers. Mulberry leaves contain a variety of active ingredients, such as flavonoids, tea polyphenols and phenolic compounds. These ingredients have antioxidant, antibacterial and antifungal properties. Using the active ingredients in mulberry leaves to control the growth of microorganisms and food oxidation reactions in food can extend the shelf life of food and maintain food quality.

[0011] The first object of the present invention is to provide a method for prolonging the shelf life of oysters by combined treatment of weakly acidic electrolyzed water and mulberry leaf extract, comprising the steps of:

[0012] (1) Preparing mulberry leaf extract: crushing and sieving mulberry leaves, mixing with ethanol solution, stirring evenly, ultrasonically treating, filtering, evaporating to remove ethanol, and freeze-drying to obtain mulberry leaf extract;

[0013] (2) Weakly acidic electrolyzed water treatment: soaking and washing the oysters in weakly acidic electrolyzed water;

[0014] (3) Treatment with mulberry leaf extract: Soak the oysters treated in step (2) in an aqueous solution of mulberry leaf extract and take them out.

[0015] In one embodiment of the present invention, in step (1), the mulberry leaves are dried mulberry leaves.

[0016] In one embodiment of the present invention, in step (1), the sieving is through a 60-200 mesh sieve.

[0017] In one embodiment of the present invention, in step (1), the sieving is through an 80-mesh sieve.

[0018] In one embodiment of the present invention, in step (1), the ethanol concentration of the ethanol solution is 50-90% v / v.

[0019] In one embodiment of the present invention, in step (1), the ethanol concentration of the ethanol solution is 70% v / v.

[0020] In one embodiment of the present invention, in step (1), the mixing mass ratio of mulberry leaves to ethanol solution is 1:20 to 1:40.

[0021] In one embodiment of the present invention, in step (1), the mixing mass ratio of mulberry leaves to ethanol solution is 1:30.

[0022] In one embodiment of the present invention, in step (1), the temperature of the ultrasonic treatment is 45-65° C., the frequency is 30-60 kHz, the power output is 200-400 W, and the time is 40-100 min.

[0023] In one embodiment of the present invention, in step (1), the temperature of ultrasonic treatment is 55° C., the frequency is 40 kHz, the power output is 270 W, and the time is 60 min.

[0024] In one embodiment of the present invention, in step (1), the suction filtration is to remove solids and retain liquid.

[0025] In one embodiment of the present invention, in step (1), the method for removing ethanol by evaporation is rotary evaporation.

[0026] In one embodiment of the present invention, the rotary evaporation temperature is 40-55° C. and the time is 50-80 min.

[0027] In one embodiment of the present invention, in step (1), the freeze-drying temperature is -40 to -10°C, the pressure is 0.13 to 0.26 mbar, and the time is 1440 to 1800 min.

[0028] In one embodiment of the present invention, in step (2), the pH value of the weakly acidic electrolyzed water is 5.8±0.1; and the effective chlorine content is 45-65 mg / L.

[0029] In one embodiment of the present invention, in step (2), the pH value of the weakly acidic electrolyzed water is 5.87±0.02; and the effective chlorine content is 60 mg / L.

[0030] In one embodiment of the present invention, in step (2), weakly acidic electrolyzed water is prepared using the Want Want Group hypochlorous acid water generator HD-240L.

[0031] In one embodiment of the present invention, in step (2), the mass ratio of oysters to weakly acidic electrolyzed water is 1:2 to 1:2.5; and the soaking time is 2 to 8 minutes.

[0032] In one embodiment of the present invention, in step (2), the cleaning is performed by rinsing with clean water for 20 to 60 seconds.

[0033] In one embodiment of the present invention, in step (3), the concentration of mulberry leaf extract in the mulberry leaf extract aqueous solution is 1 to 4 mg / mL.

[0034] In one embodiment of the present invention, in step (3), the mass ratio of the oyster to the mulberry leaf extract aqueous solution is 1:2 to 1:2.5; and the soaking time is 2 to 8 minutes.

[0035] In one embodiment of the present invention, the oysters obtained in step (3) are dried on the surface with absorbent paper and then placed in a refrigerator at 0 to 4°C for refrigeration.

[0036] The second object of the present invention is to provide oysters treated by the above method.

[0037] Beneficial effects:

[0038] 1. Weakly acidic electrolyzed water and mulberry leaf extract can effectively inhibit the putrefactive bacteria in and on the surface of oysters, preventing the oysters from spoiling due to putrefactive bacteria during storage.

[0039] 2. The combined treatment of weakly acidic electrolyzed water and mulberry leaf extract can extend the shelf life of oysters by about 3 days.

[0040] 3. The combined treatment of weakly acidic electrolyzed water and mulberry leaf extract significantly slowed down lipid oxidation and the decrease of key enzyme activities during oyster storage.

[0041] 4. After the oysters are treated with weakly acidic electrolyzed water and mulberry leaf extract and then refrigerated at 4°C, the growth of putrefactive bacteria in the oysters can be inhibited while ensuring the edible taste of the oysters. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The total bacterial colony count changes during storage of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0043] Figure 2 The TVB-N value changes during storage of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3;

[0044] Figure 3The total thiol content changes during storage of Example 1 and Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0045] Figure 4 The POV value changes during storage of Example 1 and Comparative Examples 1, 2 and 3 are shown. DETAILED DESCRIPTION

[0046] Determination of total colony count during oyster storage:

[0047] Dilute the homogenate of the oyster sample with saline in a ratio of 1:9 and mix them evenly. Next, prepare a 10-fold series of dilutions from the diluted sample. Select the dilution with the appropriate concentration, inoculate it on PCA (plate count agar) medium, and culture it according to the corresponding conditions. After the culture is completed, count the colonies on the culture medium. Based on the number of colonies, the total number of colonies in the original sample can be inferred.

[0048] TVB-N determination:

[0049] Take 20g of oysters and accurately add 100.0mL of water to soak for 30min, then filter. Apply water-soluble glue to the edge of the diffusion dish, add 1mL of boric acid solution and 1 drop of mixing indicator to the center chamber of the dish. Accurately add 1.0mL of filtrate to the outer chamber of the dish, cover with frosted glass cover, and then quickly add 1mL of saturated potassium carbonate solution from the gap, immediately push the frosted glass cover flat to fully mix the sample solution and saturated potassium carbonate solution, then place in a 37±1℃ constant temperature box for 2h, then cool to room temperature, and titrate with hydrochloric acid or sulfuric acid standard titration solution.

[0050]

[0051] Wherein: V1 is the volume of hydrochloric acid or sulfuric acid standard titration solution consumed by the test solution, in milliliters (mL); V2 is the volume of hydrochloric acid or sulfuric acid standard titration solution consumed by the reagent blank, in milliliters (mL); c is the concentration of hydrochloric acid or sulfuric acid standard titration solution, in moles per liter (mol / L); 14 is the mass of nitrogen equivalent to titrating 1.0mL of hydrochloric acid [c(HCl)=1.000mol / L] or sulfuric acid [c(1 / H2SO4)=1.000mol / L] standard titration solution, in grams per mole (g / mol); m is the mass of the sample, in grams (g), or the sample volume, in mL; V is the volume of the filtrate accurately aspirated, in milliliters (mL), and in this method V=1mL; V0 is the total volume of the sample solution, in milliliters (mL), and in this method V0=100mL; 100 is the conversion factor for converting the calculated result into milligrams per hundred grams (mg / 100g).

[0052] Determination of total thiol content:

[0053] The total thiol content of oysters was determined using a total thiol content detection kit manufactured by Solebow. About 0.1 g of oysters were weighed, 1 ml of extract was added, and then homogenized in an ice bath. Next, centrifugation was performed at room temperature at a centrifugal speed of 8000 g for 10 minutes, and the supernatant was taken for testing.

[0054] POV value determination:

[0055] Take 1.000 g of oyster sample and add 10 ml of chloroform-methanol solution (the volume ratio of chloroform to methanol is 1:1) and homogenize for 15 seconds. Then mix the homogenate with 3 ml of sodium chloride solution (concentration is 5 g / L) and centrifuge at 5000 rpm for 10 minutes at 4°C. Collect the chloroform layer (2.5 ml) and mix with 2.5 ml of chloroform-methanol solution. Then add 25 ml of ammonium thiocyanate (concentration is 3.94 M) and 25 ml of ferrous chloride (concentration is 20 mM). Let the sample stand at 20°C for 20 minutes and measure the absorbance at 500 nm.

[0056] The weakly acidic electrolyzed water used in the embodiments and comparative examples was prepared by the Want Want Group hypochlorous acid water generator HD-240L, with a pH value of 5.87±0.02 and an effective chlorine content of 60 mg / L.

[0057] Example 1

[0058] (1) Raw material pretreatment

[0059] Use freshly caught oysters as the raw material, shuck them and rinse them briefly before use;

[0060] (2) Preparation of mulberry leaf extract

[0061] The dried mulberry leaves were crushed by a pulverizer, and fine powder was screened out through 80 meshes. The mulberry leaf powder was mixed with 70% v / v ethanol solution at a mass ratio of 1:30, and fully stirred and evenly treated with ultrasound. The ultrasound temperature was 55°C, the ultrasound frequency was 40kHz, the power output was 270W, and the ultrasound time was 60 minutes. The mixture obtained by ultrasound treatment was filtered through a vacuum filter, the solid was discarded and the liquid was retained, and the ethanol in the obtained liquid was evaporated using a rotary evaporator. The mixture was placed in a vacuum freeze dryer and dehydrated and dried under vacuum conditions to obtain a mulberry leaf extract.

[0062] (3) Weakly acidic electrolyzed water treatment

[0063] The oysters obtained in step (1) are soaked in weakly acidic electrolyzed water for 5 minutes, with the mass ratio of oysters to weakly acidic electrolyzed water being 1:2, and then rinsed with clean water for 30 seconds.

[0064] (4) Mulberry leaf extract treatment

[0065] Prepare a 2 mg / mL aqueous solution of mulberry leaf extract, soak the oysters obtained in step (3) in the aqueous solution of mulberry leaf extract for 5 minutes, the mass ratio of oysters to the aqueous solution of mulberry leaf extract being 1:2, and take them out.

[0066] (5) Refrigerate at 4℃

[0067] The oysters obtained in step (4) were dried with absorbent paper to remove surface moisture and placed in a refrigerator at 4°C.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that steps (2), (3) and (4) are not performed.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that step (3) is not performed.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that steps (2) and (4) are not performed.

[0074] The test results are as follows:

[0075] The total colony count test results are as follows Figure 1 As shown, with the increase of storage time, the total colony count of each group of samples showed an upward trend, among which the total colony count of Comparative Example 1 was higher than that of the other three groups. On the 6th day of storage, the total colony count of the oyster sample of Comparative Example 1 exceeded the threshold of 8.00logCFU / g, which is the limit of microbial growth commonly used in food safety standards. In contrast, the total colony count of Example 1 exceeded this threshold only on the 9th day of storage, and remained at a low level throughout the experiment. This shows that the treatment method of weakly acidic electrolyzed water combined with mulberry leaf extract can effectively inhibit the reproduction of microorganisms in oysters.

[0076] TVBN (Total Volatile Basic Nitrogen) value is an indicator commonly used to evaluate the freshness of meat. Its change reflects the degree of protein degradation in meat. The change of TVBN value can be regarded as an indicator of protein degradation. The sanitary standard limit is usually 20mg / 100g. TVB-N value test results are as follows: Figure 2As shown. The initial TVBN values ​​of the four groups of samples were relatively low, about 4.2 mg / 100 g, which shows that these oyster samples have a high degree of freshness. However, with the passage of time, the TVBN content gradually increased during storage, reflecting the degradation process of internal protein. During this process, the TVBN value of Comparative Example 1 increased significantly faster than that of the other treatment groups, especially on the 3rd day, it quickly increased to 11.84 mg / 100g, while Example 1 only reached 10.46 mg / 100g on the 6th day. This shows that the protein degradation rate of the sample in Comparative Example 1 is faster and the corruption process is faster. It shows that the treatment method of weakly acidic electrolyzed water combined with mulberry leaf extract can effectively delay the corruption of oysters and extend the shelf life of oysters.

[0077] The total thiol content can be regarded as an indicator of the degree of protein oxidation and also reflects the degree of protein denaturation. Figure 3 As shown, the total thiol content of the samples in Comparative Example 1 and Comparative Example 2 decreased significantly during storage, while the total thiol content in the samples in Comparative Example 3 and Example 1 decreased less during storage and still maintained a high content in the later stage of storage, indicating that the combined treatment can effectively delay the denaturation of oyster protein.

[0078] POV value can reflect the degree of fat oxidation in aquatic products during storage. Figure 4 The results showed that on the 3rd day, there were no significant differences between the groups (P>0.05). Subsequently, the POV values ​​of Comparative Examples 1, 2, and 3 increased significantly on the 6th day and then gradually decreased (P<0.05). However, Example 1 did not change significantly during the first 6 days of refrigeration (P>0.05), but increased slightly in the next 6 days. By the 12th day, the POV values ​​of all groups were relatively stable, which may be because the decomposition and generation rates of hydrogen peroxide in the samples were similar. In general, the POV value of Example 1 had the lowest degree of change, indicating that the combined treatment played a significant role in inhibiting lipid oxidation.

[0079] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for extending the shelf life of oysters by combined treatment of weakly acidic electrolyzed water and mulberry leaf extract, characterized in that: Includes steps: (1) Preparing mulberry leaf extract: crushing and sieving mulberry leaves, mixing with ethanol solution, stirring evenly, ultrasonically treating, filtering, evaporating to remove ethanol, and freeze-drying to obtain mulberry leaf extract; (2) Weakly acidic electrolyzed water treatment: soaking and washing the oysters in weakly acidic electrolyzed water; (3) Treatment with mulberry leaf extract: Soak the oysters treated in step (2) in an aqueous solution of mulberry leaf extract and take them out.

2. The method according to claim 1, characterized in that: In step (1), the mulberry leaves are dried mulberry leaves; and the sieving is through a 60-200 mesh sieve.

3. The method according to claim 1, characterized in that In step (1), the ethanol concentration of the ethanol solution is 50 to 90% v / v.

4. The method according to claim 1, characterized in that: In step (1), the mixing mass ratio of mulberry leaves to ethanol solution is 1:20 to 1:

40.

5. The method according to claim 1, characterized in that: In step (1), the temperature of the ultrasonic treatment is 45-65° C., the frequency is 30-60 kHz, the power output is 200-400 W, and the time is 40-100 min.

6. The method according to claim 1, characterized in that In step (1), the suction filtration is used to remove solids and retain liquids; and the method for removing ethanol by evaporation is rotary evaporation.

7. The method according to claim 1, characterized in that In step (2), the pH value of the weakly acidic electrolyzed water is 5.8±0.1; the effective chlorine content is 45-65 mg / L; the mass ratio of oyster to weakly acidic electrolyzed water is 1:2-1:2.5; and the soaking time is 2-8 min.

8. The method according to claim 1, characterized in that In step (3), the concentration of the mulberry leaf extract in the mulberry leaf extract aqueous solution is 1 to 4 mg / mL; the mass ratio of the oyster to the mulberry leaf extract aqueous solution is 1:2 to 1:2.5; and the soaking time is 2 to 8 minutes.

9. The method according to claim 1, characterized in that: The oysters obtained in step (3) were dried with absorbent paper to remove surface moisture and placed in a refrigerator at 0-4°C.

10. Oysters treated by the method according to any one of claims 1 to 9.

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