Natural compound preservative for crayfish as well as preparation method and application of natural compound preservative
By developing a natural composite preservative with lotus leaf and oak leaf extract combined with chitosan, the existing natural preservatives have been solved, which significantly extends the shelf life of crayfish and reduces the cost.
Patent Information
- Application Number
- CN202411950048.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-27
- Publication Date
- 2025-03-21
AI Technical Summary
The existing natural fresh preservatives have high preparation costs, narrow antibacterial range, poor fresh preservation effect, and difficult to effectively extend the shelf life of crayfish.
A natural composite preservative for crayfish was developed. Through the synergistic effect of lotus leaves and oak leaf extract, combined with chitosan, a preservative with broad-spectrum antibacterial and antioxidant effects was prepared.
The shelf life of crayfish is significantly extended from 8 days to 32 days, reducing the cost of using natural composite preservatives, while improving the preservation effect and stability.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of food preservation, and in particular to a natural composite preservative for crayfish, a preparation method thereof and application thereof. Background Art
[0002] Crayfish contains a variety of essential amino acids for the human body, has the advantages of high protein, low fat and low calories, and its meat is tender and delicious. It is one of the best-selling freshwater shrimps in my country. However, due to the rich nutrition of crayfish, it is easily invaded by bacteria or spoiled by fat oxidation, so the shelf life during storage is not long. At present, the preservation methods of crayfish mainly include low temperature, gas conditioning, radiation, chemical preservation, natural preservation, etc. Compared with chemical preservatives, natural preservatives have the characteristics of green environmental protection, non-toxic and harmless, so they have greater application prospects. Existing aquatic natural preservatives usually contain lysozyme, chitosan, polyphenols, nisin and plant extracts, but the preparation cost is relatively expensive, the antibacterial range is narrow, and the preservation effect is insufficient. The present invention aims to develop natural food packaging materials with abundant materials such as lotus leaves and oak leaves, which are easy to extract, and develop a new natural composite preservative, which uses its mutual synergistic effect to extend the shelf life of crayfish and reduce the use cost of natural composite preservatives.
[0003] Lotus leaves contain a variety of bioactive ingredients, such as polyphenols, volatile oils, and terpenoids. These ingredients have the effect of inhibiting the growth of microorganisms such as bacteria, molds, and fungi. They can also inhibit the activity of lipid peroxidase, scavenge various free radicals, and exhibit antioxidant functions. These characteristics make lotus leaf extract a potential natural preservative. Studies have shown that lotus leaf extract has a significant preservative effect on fish. By measuring the total colony count, pH value, volatile basic nitrogen (TVB-N) value, and thiobarbituric acid (TBA) value of raw fish slices during the refrigerated period, it was found that lotus leaf extract can effectively inhibit the growth of microorganisms in fish, delay the increase in pH value and the appearance of TVB-N limit value, and delay the increase in TBA value. In addition, lotus leaf extract can also improve the smell and texture of fish slices, which is significantly better than some commonly used natural antibacterial agents such as chitosan and lysozyme. However, its optimal concentration and the effect of compounding with other preservatives still need to be further studied.
[0004] Oak leaves are often used as food packaging materials because of their broad leaves and natural antiseptic properties. For example, in the production of traditional foods such as rice dumplings, steamed buns and dumplings, oak leaves are often used as wrapping materials, which can not only protect the food from external pollution, but also add a fresh flavor to the food. During the storage process of foods packaged with oak leaves, the taste and quality of the food can be effectively maintained due to the preservation effect of oak leaves. In addition to being used directly as packaging materials, oak leaves can also be used to extract their active ingredients for food preservation. Studies have shown that oak leaf extract has an inhibitory effect on a variety of microorganisms and can effectively extend the shelf life of food. Oak leaf extract can also be used in combination with other preservatives to improve the preservation effect. For example, the combination of oak leaf extract with salt, acetic acid, etc. can further enhance its preservation effect.
[0005] The polyphenol compounds in lotus leaf extract and oak leaf have antibacterial and antioxidant effects, and can inhibit the growth and reproduction of microorganisms in food. When the two work synergistically, stronger antibacterial and antioxidant effects may be produced, thereby extending the shelf life of food. At present, there is no literature on the use of a composite preservative of lotus leaf combined with oak leaf to extend the shelf life of refrigerated crayfish. In this technology, we have developed a natural composite preservative based on lotus leaf and oak leaf extracts and added chitosan, which can not only ensure the quality of crayfish, but also significantly extend its shelf life, thereby providing a green, novel and efficient technical solution for the natural preservation of crayfish. The product formula of the present invention can effectively improve the shelf life of crayfish, and can control the preparation cost, while opening up the possibility of lotus leaf and oak leaf in the field of aquatic product preservation. Summary of the invention
[0006] In order to solve the problems of high preparation cost, narrow antibacterial range and insufficient preservation effect of existing natural preservatives, the present invention develops natural food packaging materials such as lotus leaves and oak leaves that are abundant and easy to extract. The new natural composite preservative provided by the present invention utilizes the synergistic effect of lotus leaf extract and oak leaf extract to extend the shelf life of crayfish and reduce the use cost of the natural composite preservative.
[0007] The first aspect of the present invention provides a natural composite preservative for crayfish, the natural composite preservative comprising lotus leaf extract, oak leaf extract, chitosan and distilled water, wherein the mass ratio of lotus leaf extract to oak leaf extract is 1:0.5-2. The present invention utilizes the synergistic effect of lotus leaf extract and oak leaf extract to effectively inhibit the growth of microorganisms and the increase of volatile basic nitrogen (TVB-N) in crayfish during storage, thereby maintaining the freshness of crayfish and extending the shelf life. The present invention first determines the optimal preservation concentration of lotus leaf extract and oak leaf extract, and on this basis, the lotus leaf extract and oak leaf extract are prepared in a variety of proportions such as 1:2, 1:1.5, 1:1.2, 1:1, 1:0.5, and then used in combination with chitosan to preserve crayfish.
[0008] Furthermore, the composition of the above-mentioned natural composite preservative for crayfish includes 2% lotus leaf extract, 1-4% oak leaf extract and 1% chitosan.
[0009] Furthermore, the lotus leaf extract is prepared by the following method: the lotus leaves are dried and crushed, an appropriate amount of sample is weighed, 70% ethanol is added at a solid-liquid ratio of 1:20, ultrasonic oscillation is performed at 70°C, and the sample is filtered. The supernatant is vacuum-rotated and evaporated to dryness, and the sample is diluted to 3 g / L with sterile distilled water to obtain the lotus leaf extract.
[0010] Furthermore, the method for preparing the oak leaf extract is to dry and crush the oak leaves, weigh an appropriate amount of sample, add 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically oscillate at 60°C, filter, take the supernatant and vacuum rotary evaporate to dryness, and dilute it to 3g / L with sterile distilled water to obtain the oak leaf extract.
[0011] Furthermore, the natural composite preservative is obtained by directly mixing lotus leaf extract, oak leaf extract, chitosan and distilled water.
[0012] The second aspect of the present invention provides a method for preparing a natural composite preservative for crayfish, the method comprising the following steps:
[0013] Preparation of lotus leaf extract: Take lotus leaves, dry and crush them, weigh an appropriate amount of sample, add 70% ethanol at a solid-liquid ratio of 1:20, ultrasonically vibrate at 70°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain lotus leaf extract;
[0014] Preparation of oak leaf extract: dry and crush oak leaves, weigh an appropriate amount of sample, add 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically vibrate at 60°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain the oak leaf extract;
[0015] According to the mass and dosage of the natural composite preservative, lotus leaf extract, oak leaf extract, chitosan and distilled water are directly mixed to obtain the natural composite preservative.
[0016] Furthermore, there is no particular order in which the lotus leaf extract and the oak leaf extract are prepared.
[0017] Furthermore, in the preparation step of the lotus leaf extract, the ultrasonic oscillation process is 300W ultrasonic oscillation for 40 minutes. In the preparation step of the oak leaf extract, the ultrasonic oscillation process is 250W ultrasonic oscillation for 40 minutes. By using ultrasound-assisted extraction, the effective ingredients are efficiently extracted from lotus leaves and oak leaves. After the extraction process parameters are optimized, the extraction efficiency can be significantly improved, the energy consumption can be reduced, the extraction cost can be saved, and the purity and activity of the extract can be guaranteed at the same time.
[0018] The third aspect of the present invention provides a use of a natural composite preservative for crayfish, wherein the natural composite preservative is used for preserving crayfish by soaking, spraying or coating.
[0019] Furthermore, the soaking method adopted is to select fresh crayfish, rinse them with sterile water, put them into crushed ice water for sudden death, soak them with a natural composite preservative, drain the water, pack them with a polyethylene fresh-keeping bag, and seal them after exhausting the air.
[0020] Compared with the prior art, the present invention has the following beneficial technical effects:
[0021] 1. The present invention combines the mixed extract of lotus leaf and oak leaf with chitosan for crayfish preservation, which can significantly improve the preservation effect. Both lotus leaf and oak leaf are rich in natural antibacterial and antioxidant ingredients. The mixed extract can play a synergistic role, significantly enhancing the preservation effect on crayfish, and its shelf life can be extended from 8 days to 32 days. The polyphenols and other ingredients in lotus leaf have broad-spectrum antibacterial properties, while the antioxidant enzymes and active ingredients in oak leaf can effectively improve the antioxidant capacity of crayfish. The addition of chitosan further enhances the antibacterial ability of the preservative, and its film-forming property also improves the adhesion and stability of the preservative. Compared with chemically synthesized preservatives, the preservative of the present invention is safer and healthier, meets the pursuit of food safety by modern consumers, and lotus leaf and oak leaf are easy to obtain and have low cost.
[0022] 2. The present invention utilizes ultrasound to assist in the efficient extraction of effective ingredients from lotus leaves and oak leaves. After optimizing the extraction process parameters, the extraction efficiency can be significantly improved, energy consumption can be reduced, and extraction costs can be saved while ensuring the purity and activity of the extract. The lotus leaf and oak leaf mixed extract obtained by extraction is evenly mixed with a chitosan solution to obtain a stable preservative. The preparation process is simple and controllable, and the quality and stability of the preservative can be ensured. At the same time, by optimizing the process conditions, the preservation effect and stability of the composite preservative can be further improved.
[0023] 3. The preservative of the present invention can be used in the packaging and storage process of crayfish, and can be used by soaking, spraying or coating. Experiments have shown that the use of the preservative of the present invention can significantly extend the shelf life of crayfish, reduce quality loss, and maintain its color, taste and nutritional value. The use process is simple and easy, and does not require complex equipment and technology. At the same time, by accurately controlling the amount and use of the preservative, its uniform distribution and stability in crayfish can be ensured, thereby improving the preservation effect and control accuracy. In summary, the present invention combines the mixed extract of lotus leaf and oak leaf with chitosan for crayfish preservation, which has broad application prospects and market competitiveness. DETAILED DESCRIPTION
[0024] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. Additional aspects and advantages of the present invention will be given in part in the following description, and part will become apparent from the following description, or will be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.
[0025] As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.
[0026] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.
[0027] In some examples, approximate terms may correspond to the precision of the instrument used to measure the value. In the present specification and claims, range limits may be combined and / or interchanged. If not otherwise specified, these ranges include all subranges contained therein.
[0028] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.
[0029] The terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described in the present invention mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to 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.
[0030] Unless otherwise specified, the raw materials and equipment used in the present invention can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.
[0031] In some embodiments, the present invention provides a natural composite preservative for crayfish, the natural composite preservative comprising lotus leaf extract, oak leaf extract, chitosan and distilled water, wherein the mass ratio of lotus leaf extract to oak leaf extract is 1:0.5-2. The mass ratio of lotus leaf extract to oak leaf extract is 1:2, 1:1.5, 1:1.2, 1:1 or 1:0.5.
[0032] In some embodiments, the composition of the above-mentioned natural composite preservative for crayfish includes 2% lotus leaf extract, 1-4% oak leaf extract, and 1% chitosan. Furthermore, the oak leaf extract is 1%, 1.5%, 2%, 2.5%, 3%, 3.5% or 4%.
[0033] In some embodiments, lotus leaf extract is prepared by the following method: dry and crush the lotus leaves, weigh an appropriate amount of sample, add 70% ethanol at a solid-liquid ratio of 1:20, ultrasonically oscillate at 70°C, filter, take the supernatant and vacuum rotary evaporate to dryness, and dilute it to 3 g / L with sterile distilled water to obtain the lotus leaf extract.
[0034] Furthermore, the method for preparing the oak leaf extract is to dry and crush the oak leaves, weigh an appropriate amount of sample, add 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically oscillate at 60°C, filter, take the supernatant and vacuum rotary evaporate to dryness, and dilute it to 3g / L with sterile distilled water to obtain the oak leaf extract.
[0035] Furthermore, the natural composite preservative is obtained by directly mixing lotus leaf extract, oak leaf extract, chitosan and distilled water.
[0036] In some embodiments, the present invention provides a method for preparing a natural composite preservative for crayfish, the preparation method comprising the following steps:
[0037] Preparation of lotus leaf extract: Take lotus leaves, dry and crush them, weigh an appropriate amount of sample, add 70% ethanol at a solid-liquid ratio of 1:20, ultrasonically vibrate at 70°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain lotus leaf extract;
[0038] Preparation of oak leaf extract: dry and crush oak leaves, weigh an appropriate amount of sample, add 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically vibrate at 60°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain the oak leaf extract;
[0039] According to the mass and dosage of the natural composite preservative, lotus leaf extract, oak leaf extract, chitosan and distilled water are directly mixed to obtain the natural composite preservative.
[0040] Furthermore, there is no particular order in which the lotus leaf extract and the oak leaf extract are prepared.
[0041] Furthermore, in the preparation step of the lotus leaf extract, the ultrasonic oscillation process is 300W ultrasonic oscillation for 40 minutes. In the preparation step of the oak leaf extract, the ultrasonic oscillation process is 250W ultrasonic oscillation for 40 minutes.
[0042] In some embodiments, the present invention provides a use of a natural composite preservative for crayfish, wherein the natural composite preservative is used for crayfish preservation by soaking, spraying or coating.
[0043] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0044] The present invention is further described below in conjunction with specific embodiments:
[0045] Example 1
[0046] Step 1: Preparation of lotus leaf extract
[0047] The lotus leaf was dried and crushed at 60℃ and passed through 60 mesh. Weigh 10g sample, add 70% ethanol at a solid-liquid ratio of 1:20, and ultrasonically vibrate at 300W for 40min at 70℃. After filtering, the supernatant was vacuum-rotated and evaporated to dryness, and diluted to 3g / L with sterile distilled water to obtain the lotus leaf extract. Lotus leaf extracts of different concentrations were prepared by percentage using mother liquor.
[0048] Step 2: Preparation of oak leaf extract
[0049] Dry and crush the oak leaves at 60℃ and pass through 60 mesh. Weigh 10g of sample, add 60% ethanol at a solid-liquid ratio of 1:30, and ultrasonically vibrate at 250W for 40min at 60℃. After filtering, take the supernatant and vacuum-rotate and evaporate to dryness, and dilute to 3g / L with sterile distilled water to obtain the oak leaf extract mother liquor. Oak leaf extracts of different concentrations are prepared by percentage using the mother liquor.
[0050] Step 3: Preparation of natural composite preservative
[0051] The composite preservative is obtained by mixing 2% lotus leaf extract, 4% oak leaf extract and 1% chitosan.
[0052] Step 4: Preservation of crayfish
[0053] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0054] Step 5: Evaluation of the preservation effect of crayfish
[0055] After packaging, the crayfish were stored in a 4°C refrigerator and tested every four days for the total colony count, pH value, volatile basic nitrogen (TVB-N) value, thiobarbituric acid (TBA) value, and sensory indicators.
[0056] Example 2
[0057] Step 1: Preparation of lotus leaf extract
[0058] The lotus leaf was dried and crushed at 60℃ and passed through 60 mesh. Weigh 10g sample, add 70% ethanol at a solid-liquid ratio of 1:20, and ultrasonically vibrate at 300W for 40min at 70℃. After filtering, the supernatant was vacuum-rotated and evaporated to dryness, and diluted to 3g / L with sterile distilled water to obtain the lotus leaf extract. Lotus leaf extracts of different concentrations were prepared by percentage using mother liquor.
[0059] Step 2: Preparation of oak leaf extract
[0060] Dry and crush the oak leaves at 60℃ and pass through 60 mesh. Weigh 10g of sample, add 60% ethanol at a solid-liquid ratio of 1:30, and ultrasonically vibrate at 250W for 40min at 60℃. After filtering, take the supernatant and vacuum-rotate and evaporate to dryness, and dilute to 3g / L with sterile distilled water to obtain the oak leaf extract mother liquor. Oak leaf extracts of different concentrations are prepared by percentage using the mother liquor.
[0061] Step 3: Preparation of natural composite preservative
[0062] 2% lotus leaf extract, 3% oak leaf extract and 1% chitosan are mixed to obtain a composite preservative.
[0063] Step 4: Preservation of crayfish
[0064] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0065] Step 5: Evaluation of the preservation effect of crayfish
[0066] After packaging, the crayfish were stored in a 4°C refrigerator and tested every four days for the total colony count, pH value, volatile basic nitrogen (TVB-N) value, thiobarbituric acid (TBA) value, and sensory indicators.
[0067] Example 3
[0068] Step 1: Preparation of lotus leaf extract
[0069] The lotus leaf was dried and crushed at 60℃ and passed through 60 mesh. Weigh 10g sample, add 70% ethanol at a solid-liquid ratio of 1:20, and ultrasonically vibrate at 300W for 40min at 70℃. After filtering, the supernatant was vacuum-rotated and evaporated to dryness, and diluted to 3g / L with sterile distilled water to obtain the lotus leaf extract. Lotus leaf extracts of different concentrations were prepared by percentage using mother liquor.
[0070] Step 2: Preparation of oak leaf extract
[0071] Dry and crush the oak leaves at 60℃ and pass through 60 mesh. Weigh 10g of sample, add 60% ethanol at a solid-liquid ratio of 1:30, and ultrasonically vibrate at 250W for 40min at 60℃. After filtering, take the supernatant and vacuum-rotate and evaporate to dryness, and dilute to 3g / L with sterile distilled water to obtain the oak leaf extract mother liquor. Oak leaf extracts of different concentrations are prepared by percentage using the mother liquor.
[0072] Step 3: Preparation of natural composite preservative
[0073] 2% lotus leaf extract, 2.4% oak leaf extract and 1% chitosan are mixed to obtain a composite preservative.
[0074] Step 4: Preservation of crayfish
[0075] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0076] Step 5: Evaluation of the preservation effect of crayfish
[0077] After packaging, the crayfish were stored in a 4°C refrigerator and tested every four days for the total colony count, pH value, volatile basic nitrogen (TVB-N) value, thiobarbituric acid (TBA) value, and sensory indicators.
[0078] Example 4
[0079] Step 1: Preparation of lotus leaf extract
[0080] The lotus leaf was dried and crushed at 60℃ and passed through 60 mesh. Weigh 10g sample, add 70% ethanol at a solid-liquid ratio of 1:20, and ultrasonically vibrate at 300W for 40min at 70℃. After filtering, the supernatant was vacuum-rotated and evaporated to dryness, and diluted to 3g / L with sterile distilled water to obtain the lotus leaf extract. Lotus leaf extracts of different concentrations were prepared by percentage using mother liquor.
[0081] Step 2: Preparation of oak leaf extract
[0082] Dry and crush the oak leaves at 60℃ and pass through 60 mesh. Weigh 10g of sample, add 60% ethanol at a solid-liquid ratio of 1:30, and ultrasonically vibrate at 250W for 40min at 60℃. After filtering, take the supernatant and vacuum-rotate and evaporate to dryness, and dilute to 3g / L with sterile distilled water to obtain the oak leaf extract mother liquor. Oak leaf extracts of different concentrations are prepared by percentage using the mother liquor.
[0083] Step 3: Preparation of natural composite preservative
[0084] 2% lotus leaf extract, 2% oak leaf extract and 1% chitosan are mixed to obtain a composite preservative.
[0085] Step 4: Preservation of crayfish
[0086] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0087] Step 5: Evaluation of the preservation effect of crayfish
[0088] After packaging, the crayfish were stored in a 4°C refrigerator and tested every four days for the total colony count, pH value, volatile basic nitrogen (TVB-N) value, thiobarbituric acid (TBA) value, and sensory indicators.
[0089] Example 5
[0090] Step 1: Preparation of lotus leaf extract
[0091] The lotus leaf was dried and crushed at 60℃ and passed through 60 mesh. Weigh 10g sample, add 70% ethanol at a solid-liquid ratio of 1:20, and ultrasonically vibrate at 300W for 40min at 70℃. After filtering, the supernatant was vacuum-rotated and evaporated to dryness, and diluted to 3g / L with sterile distilled water to obtain the lotus leaf extract. Lotus leaf extracts of different concentrations were prepared by percentage using mother liquor.
[0092] Step 2: Preparation of oak leaf extract
[0093] Dry and crush the oak leaves at 60℃ and pass through 60 mesh. Weigh 10g of sample, add 60% ethanol at a solid-liquid ratio of 1:30, and ultrasonically vibrate at 250W for 40min at 60℃. After filtering, take the supernatant and vacuum-rotate and evaporate to dryness, and dilute to 3g / L with sterile distilled water to obtain the oak leaf extract mother liquor. Oak leaf extracts of different concentrations are prepared by percentage using the mother liquor.
[0094] Step 3: Preparation of natural composite preservative
[0095] 2% lotus leaf extract, 1% oak leaf extract and 1% chitosan are mixed to obtain a composite preservative.
[0096] Step 4: Preservation of crayfish
[0097] Select crayfish with good carapace color, intact limbs and uniform size, rinse with sterile water, and put into crushed ice water to die suddenly. Soak in the above-mentioned lotus leaf, oak leaf and chitosan composite preservative in a ratio of 1:2 for 15 minutes, drain the water, pack in polyethylene fresh-keeping bags, and seal after exhausting all the air.
[0098] Step 5: Evaluation of the preservation effect of crayfish
[0099] After packaging, the crayfish were stored in a 4°C refrigerator and tested every four days for the total colony count, pH value, TVB-N value, TBA value and sensory index.
[0100] Comparative Example 1
[0101] The difference between this comparative example and Example 1 is that the preservative in step 3 contains only 2% lotus leaf extract.
[0102] Comparative Example 2
[0103] The difference between this comparative example and Example 1 is that the preservative in step 3 contains only 4% of oak leaf extract.
[0104] Comparative Example 3
[0105] The difference between this comparative example and Example 1 is that the preservative in step 3 contains 2% lotus leaf extract and 4% oak leaf extract.
[0106] Comparative Example 4
[0107] The difference between this comparative example and Example 1 is that the preservative in step 3 contains only 1% chitosan.
[0108] Comparative Example 5
[0109] The difference between this comparative example and Example 1 is that in step 4, sterile water is used instead of the natural composite preservative to treat the crayfish.
[0110] Comparative Example 6
[0111] The difference between this comparative example and Example 1 is that the preservative in step 3 contains 6% lotus leaf extract and 1% chitosan.
[0112] Comparative Example 7
[0113] The difference between this comparative example and Example 1 is that the preservative in step 3 contains 6% oak leaf extract and 1% chitosan.
[0114] All specific data of the embodiments and comparative examples are shown in Tables 1 to 6, wherein.
[0115] Table 1 shows the effects of different concentrations of natural composite preservatives on the total colony count of crayfish;
[0116] Table 2 shows the effects of different concentrations of natural composite preservatives on the pH value of crayfish;
[0117] Table 3 shows the effects of different concentrations of natural composite preservatives on the barbiturate content of crayfish;
[0118] Table 4 shows the effects of different concentrations of natural composite preservatives on the TVB-N content of crayfish;
[0119] Table 5 shows the sensory evaluation indexes of crayfish;
[0120] Table 6 shows the sensory evaluation of crayfish treated with natural composite preservatives at different concentrations.
[0121]
[0122]
[0123]
[0124]
[0125]
[0126] From the experimental data in the above table, it can be seen that the natural preservative of 2% lotus leaf extract, 3% oak leaf extract and 1% chitosan used in Example 2 has the best preservation effect on crayfish, and the shelf life can reach 32 days. In Examples 1, 3, 4, and 5, the shelf life of crayfish can also reach 24-28 days.
[0127] Comparative Examples 1, 2, and 4 contain only one preservative ingredient, and the shelf life of crayfish is 16-20 days. Comparative Example 3 contains 2% lotus leaf extract and 4% oak leaf extract, and the shelf life of crayfish can be further extended to 24 days. This shows that as the ingredients in the preservative increase, the preservation effect can be further enhanced.
[0128] In Comparative Example 5, no preservative was added and the shelf life of the crayfish was only 8 days.
[0129] Although Comparative Examples 6 and 7 contain two preservative ingredients and the concentrations of lotus leaf extract and oak leaf extract are increased to 6%, their preservation effects on crayfish are not as good as those of Comparative Example 3 and all the embodiments, which shows that the lotus leaf and oak leaf extracts have a significant synergistic effect after mixing.
[0130] By adjusting the ratio of lotus leaf extract to oak leaf extract, we optimized the formula of the natural composite preservative, thereby significantly increasing the shelf life of crayfish. The present invention further reduces the cost of the natural composite preservative while improving the crayfish preservation effect by developing lotus leaf and oak leaf resources.
[0131] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the composition and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A natural composite preservative for crayfish, characterized in that: The natural composite preservative comprises lotus leaf extract, oak leaf extract, chitosan and distilled water, wherein the mass ratio of the lotus leaf extract to the oak leaf extract is 1:0.5-2.
2. The natural composite preservative for crayfish according to claim 1, characterized in that: The composition and mass content of the natural composite preservative are: 2% lotus leaf extract, 1-4% oak leaf extract and 1% chitosan.
3. A natural composite preservative for crayfish according to any one of claims 1-2, characterized in that: The lotus leaf extract is prepared by the following method: drying and crushing lotus leaves, weighing an appropriate amount of sample, adding 70% ethanol at a solid-liquid ratio of 1:20, ultrasonically oscillating at 70°C, filtering, taking the supernatant and vacuum rotary evaporating to dryness, and diluting it to 3g / L with sterile distilled water to obtain the lotus leaf extract.
4. A natural composite preservative for crayfish according to any one of claims 1 to 3, characterized in that: The method for preparing the oak leaf extract comprises drying and crushing the oak leaves, weighing an appropriate amount of sample, adding 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically oscillating at 60°C, filtering, taking the supernatant and vacuum rotary evaporating to dryness, and diluting it to 3g / L with sterile distilled water to obtain the oak leaf extract.
5. A natural composite preservative for crayfish according to any one of claims 1 to 4, characterized in that: The natural composite preservative is obtained by directly mixing lotus leaf extract, oak leaf extract, chitosan and distilled water.
6. The method for preparing the natural composite preservative for crayfish according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: Preparation of lotus leaf extract: Take lotus leaves, dry and crush them, weigh an appropriate amount of sample, add 70% ethanol at a solid-liquid ratio of 1:20, ultrasonically vibrate at 70°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain lotus leaf extract; Preparation of oak leaf extract: dry and crush oak leaves, weigh an appropriate amount of sample, add 60% ethanol at a solid-liquid ratio of 1:30, ultrasonically vibrate at 60°C, filter, take the supernatant and vacuum rotary evaporate to dryness, dilute with sterile distilled water to 3g / L, and obtain the oak leaf extract; According to the mass and dosage of the natural composite preservative, lotus leaf extract, oak leaf extract, chitosan and distilled water are directly mixed to obtain the natural composite preservative.
7. The preparation method according to claim 6, characterized in that: In the preparation step of the lotus leaf extract, the ultrasonic oscillation process is 300W ultrasonic oscillation for 40 minutes.
8. The preparation method according to any one of claims 6-7, characterized in that: In the preparation step of the oak leaf extract, the ultrasonic oscillation process is 250W ultrasonic oscillation for 40 minutes.
9. Use of the natural composite preservative for crayfish according to any one of claims 1 to 5 or the natural composite preservative for crayfish prepared by the preparation method according to any one of claims 6 to 7, characterized in that: The natural composite preservative is used for preserving crayfish, and can be used in the form of immersion, spraying or coating.
10. The use according to claim 9, characterized in that: Fresh crayfish were selected, washed with sterile water, put into crushed ice water for sudden death, soaked in a natural composite preservative, drained, packed in polyethylene fresh-keeping bags, and sealed after exhausting all the air.