Pretreatment method for efficiently extracting calcium in shells of shrimps and crabs

Abstract

The invention discloses a pretreatment method for efficiently extracting calcium in shrimp and crab shells. The pretreatment method comprises the following steps: carrying out microwave treatment on the shrimp and crab shells until the weight is constant, rehydrating for 10 minutes in a water bath at 90 DEG C, carrying out microwave treatment until the weight is constant, crushing, mixing with an acetic acid solution, stirring, centrifuging, and measuring the calcium concentration. According to the method, through microwave-rehydration-secondary microwave pretreatment, the carapace structure is destroyed, the contact area of organic acid and calcium is increased, the calcium recovery rate is increased, the treatment time is shortened, the energy consumption is reduced, the universality of raw materials is enhanced, comprehensive utilization of resources is facilitated, and the method is environmentally friendly and economical.

Description

Technical Field

[0001] This invention relates to the field of resource utilization technology for aquatic product processing waste, specifically to a pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs. Background Technology

[0002] my country is the world's largest shrimp and crab farming and processing country. In recent years, the shrimp and crab industry has continued to expand, with the total output of processed shrimp and crab exceeding 8 million tons in 2024, accounting for 18.3% of the total aquatic product processing volume. However, there are significant structural contradictions behind the industry's development: on the one hand, end products are concentrated in primary processed products, with a homogenization rate of over 75%, and the added value is only 1 / 3 to 1 / 2 of that of similar products in developed countries, resulting in economic growth lagging behind the increase in output; on the other hand, by-products generated during processing account for more than 70% of the total raw materials, with waste shells as the main component, with annual emissions exceeding 5.6 million tons, becoming a prominent pain point for the industry's sustainable development.

[0003] The chemical composition of shrimp and crab shells has significant resource utilization value, containing 20%-50% calcium carbonate, 15%-30% chitin, and 10%-40% protein, making it a natural complex resource. However, for a long time, the main methods of disposing of these shell wastes have been landfilling or incineration, which not only wastes valuable resources such as calcium and chitin but also causes serious environmental problems: shells take 6-12 months to slowly degrade in the natural environment, releasing malodorous gases such as hydrogen sulfide and amines, and fostering pathogenic bacteria such as E. coli, leading to a decrease in the pH value of surrounding soil by 0.5-1.2 units and ammonia nitrogen concentration in water bodies exceeding the standard by 3-5 times, causing continuous damage to the ecological environment. According to statistics, the environmental remediation cost caused by improper disposal of shell waste in my country exceeds 2 billion yuan annually.

[0004] With the advancement of the "dual carbon" goals and the circular economy strategy, the high-value utilization of shell waste has become a key path to overcome the industry's predicament. Currently, industry research mainly focuses on the extraction of chitin and the development of derivative products (such as chitosan and glucosamine), forming a complete industrial chain from raw material processing to end-use applications, with annual sales of related products exceeding 5 billion yuan. In contrast, research on efficient extraction technology for calcium, the most abundant inorganic component in shells, lags significantly, resulting in a utilization rate of less than 15% for calcium resources, becoming a bottleneck restricting the utilization of all shell components.

[0005] The calcium in shrimp and crab shells mainly exists in the form of calcium carbonate. Traditional extraction methods rely on strong acid and strong alkali processes. Among them, the hydrochloric acid method (using 4%-10% high-concentration hydrochloric acid) is the mainstream industrial technology. Although it can achieve a high decalcification rate (90%-95%), it has insurmountable drawbacks: First, the high-concentration acid corrodes the equipment, increasing equipment maintenance costs by 30%-50% annually; second, the reaction process generates a large amount of acidic wastewater (8-12 tons of wastewater are required per ton of shells), with treatment costs as high as 80-120 yuan / ton; third, the acid hydrolysis process destroys the protein and chitin structure in the shells, making the by-products unusable and the resource utilization rate less than 40%.

[0006] Organic acid extraction, as an environmentally friendly alternative technology, utilizes the mild reaction between natural organic acids such as lactic acid and citric acid and calcium carbonate. This process preserves the activity of proteins and chitin while reducing waste emissions, demonstrating significant technological advantages. However, the industrial application of this method faces three major bottlenecks: first, the decalcification efficiency is low, with existing processes generally achieving decalcification rates below 90%, resulting in significant calcium resource loss; second, the cost is too high, with the reagent cost of commercial organic acids being 3-5 times that of the hydrochloric acid method, leading to a lack of market competitiveness in the final product; and third, the process is complex, requiring strict control of reaction temperature, time, and pH, resulting in poor stability during large-scale production. These problems have limited the application rate of the organic acid method in actual production to less than 5%, necessitating a breakthrough technological solution.

[0007] In conclusion, developing an organic acid-based calcium extraction pretreatment technology that is universally applicable, highly efficient, and low-cost is of great significance for improving the comprehensive utilization rate of shrimp and crab shell resources, reducing environmental pollution, and promoting the green transformation of the aquatic product processing industry. It is also an urgent need for the current development of the industry. Summary of the Invention

[0008] This invention aims to overcome the bottlenecks in existing shrimp and crab shell calcium extraction technologies and provide a pretreatment method for efficient extraction of calcium from shrimp and crab shells. The goal is to improve calcium recovery rate, shorten the process cycle, reduce energy consumption to lower costs, enhance applicability to raw materials such as crayfish and Chinese mitten crab, while preserving the activity of chitin and protein in the shell, achieving green and efficient extraction, and promoting the high-value utilization of all components of shell waste.

[0009] To achieve the above objectives, the present invention employs the following technical means: A pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs includes the following steps: Step 1: Take 20g of shrimp and crab shells and microwave them at 50Hz and 0.53-1.06kWh until constant weight is achieved; Step 2: Place the shells treated in Step 1 in a 90℃ water bath to rehydrate for 10 minutes; Step 3: Place the rehydrated carapace under microwave treatment at 50Hz and 0.53-1.06kWh until constant weight is achieved; Step 4: Crush the shells processed in Step 3 using a pulverizer with a speed of 29000 rpm for 10 minutes; Step 5: Mix the obtained shell powder with a 0.16-0.17 mol / L acetic acid solution at a material-to-liquid ratio of 1:40; Step 6: Stir the mixture magnetically at 500 rpm for 30 min at room temperature. After centrifuging the mixture at 4000 g for 10 min, determine the calcium concentration in the supernatant.

[0010] Preferably, in step one, the initial state of the shrimp and crab shells is fresh shells or frozen shells that have undergone preliminary cleaning.

[0011] Preferably, in step one, the shell of the shrimp or crab is the shell of a crayfish or the shell of a Chinese mitten crab.

[0012] Preferably, in step two, the water bath temperature fluctuation range is controlled within ±2℃ to ensure uniform rehydration.

[0013] Preferably, in step four, the operating temperature of the pulverizer is controlled at 25-30℃.

[0014] Preferably, in step four, the particle size range of the shell powder obtained after pulverization is 80-120 mesh.

[0015] Preferably, in step five, the acetic acid solution is prepared using deionized water, and the pH value of the solution is 2.5-3.5.

[0016] Preferably, in step six, the calcium concentration of the supernatant is determined by EDTA titration.

[0017] The present invention has the following beneficial effects: 1. Significantly improve calcium extraction efficiency: This invention uses a pretreatment process of "microwave treatment-rehydration-secondary microwave treatment" to significantly disrupt the dense structure of shrimp and crab shells, increase the porosity inside the shells, and significantly expand the contact area between organic acids and calcium. This effectively solves the technical bottleneck of low decalcification rate in organic acid methods and greatly improves calcium recovery rate.

[0018] 2. Achieving cost reduction, efficiency improvement, energy conservation, and emission reduction: Integrating microwave treatment with the drying process significantly shortens processing time and improves efficiency compared to traditional hot air drying; it also greatly reduces unit energy consumption, decreasing production time costs and electricity consumption. Furthermore, because pretreatment enhances calcium dissolution, it reduces the amount of organic acid used, further lowering reagent costs and improving the economics of the organic acid method.

[0019] 3. Enhanced raw material versatility and process stability: This method can stably and efficiently decalcify different types of shrimp and crab shells, solving the problem of limited adaptability of existing technologies to specific shell raw materials. Process parameters are clearly defined and controllable, and calcium extraction efficiency remains stable during large-scale production, demonstrating feasibility for industrial application.

[0020] 4. Ensuring the Comprehensive Utilization Value of Resources: The pretreatment process employs gentle physical methods (microwave, water bath) to avoid damage to the proteins and chitin in the shells caused by strong acids and alkalis. After treatment using this method, the chitin and proteins in the decalcified shell residue retain high activity and can be directly used for subsequent extraction and processing, achieving high-value utilization of all shell components and improving the comprehensive utilization rate of resources.

[0021] 5. Enhanced environmental friendliness: Acetic acid is used as the extractant throughout the process, replacing traditional high-concentration hydrochloric acid, reducing the discharge of acidic wastewater. The wastewater is also mild, reducing treatment costs. No waste gas or solid waste is generated during the pretreatment process, which meets clean production standards and reduces environmental pollution from the source of the process, thus contributing to the green transformation of the aquatic product processing industry. Attached Figure Description

[0022] Figure 1 This is a diagram of the internal structure of the crayfish carapace dried using low-power microprocessor according to Embodiment 1 of the present invention; Figure 2 This is a diagram of the internal structure of the crayfish shell dried by high-power microprocessor according to Embodiment 2 of the present invention; Figure 3 This is a diagram of the internal structure of the crayfish shell after two high-power micro-processing drying processes following Embodiment 3 of the present invention. Figure 4 This is a diagram of the internal structure of the shell of a crayfish dried using conventional hot air drying, as shown in Comparative Example 1 of this invention. Figure 5 This is a diagram of the internal structure of the carapace of the Chinese mitten crab dried using low-power microprocessor according to Embodiment 4 of the present invention. Figure 6 This is a diagram of the internal structure of the carapace of the Chinese mitten crab dried by high-power microprocessor according to Embodiment 5 of the present invention; Figure 7 This is a diagram of the internal structure of the carapace of the Chinese mitten crab after two high-power micro-processing drying processes following Embodiment 6 of the present invention. Figure 8 This is a diagram of the internal structure of the shell of the Chinese mitten crab dried by conventional hot air treatment, which is Comparative Example 2 of this invention. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs, the specific steps of which are as follows: First microwave treatment: Take the shells of shrimp and crabs and microwave them at 50Hz and 0.53-1.06kWh until constant weight.

[0025] This step uses the high temperature of microwaves to break down the structure of proteins, chitin, and other components in the shell, reducing their interference with calcium extraction; the expansion effect of microwaves loosens the shell structure, increasing the contact area between organic acids and calcium; and the microwaves rapidly heat and vaporize moisture, achieving rapid drying of the shell.

[0026] Rehydration treatment: Place the shells that have been microwaved to constant weight in step 1 in a 90℃ water bath for 10 minutes to rehydrate.

[0027] Because of the high polarity of water, microwaves mainly act on the water in the shell. After the first microwave treatment, the pore volume of the shell increases. After rehydration, water can re-enter the pores, creating more favorable conditions for subsequent second microwave treatment and enhancing the destructive effect of microwaves on the shell structure.

[0028] Secondary microwave treatment: The rehydrated carapace from step 2 was microwaved again at 50 Hz and 0.53-1.06 kWh until constant weight.

[0029] This step further enhances the effect of microwaves on the shell, causing the internal structure of the shell to loosen and break down more fully, laying the foundation for subsequent calcium extraction.

[0030] Crushing process: The shells that have been microwaved to constant weight in step 3 are crushed for 10 minutes using a crusher with a speed of 29000 rpm.

[0031] By pulverizing the shell powder, the specific surface area is increased, further enhancing the contact opportunities between organic acids and calcium, and accelerating the reaction rate.

[0032] Mixed extraction: The shell powder obtained in step 4 is mixed with acetic acid solution of 0.16-0.17 mol / L at a material-to-liquid ratio of 1:40 (w / v).

[0033] Using environmentally friendly acetic acid as an extractant, instead of traditional strong acids, achieves gentle decalcification, reducing environmental pollution and damage to other components in the shell.

[0034] Stirring reaction: At room temperature, the mixture from step 5 was magnetically stirred at 500 rpm / min for 30 min.

[0035] Stirring promotes full contact and reaction between acetic acid and calcium in the shell powder, thereby improving the calcium dissolution efficiency.

[0036] Separation and determination: The mixture after the reaction in step 6 was centrifuged at 4000g for 10min, and the supernatant was collected. The calcium concentration was determined by EDTA titration to evaluate the calcium extraction effect.

[0037] The initial state of shrimp and crab shells is either fresh shells or frozen shells that have undergone preliminary cleaning.

[0038] The advantages of the above settings are: Preserving the integrity of the natural structure Fresh or frozen conditions can best preserve the natural binding form of proteins and calcium in the shell, avoiding microbial degradation or oxidative deterioration caused by long-term storage, ensuring the uniformity of structural damage during subsequent microwave treatment, thereby improving calcium release efficiency.

[0039] Simplify the preprocessing process Frozen shells can be directly processed in the microwave without the need for an additional thawing step; fresh shells can be processed with simple washing, eliminating the tedious pre-processing steps such as deproteinization and depigmentation in traditional processes, thus shortening the overall processing time.

[0040] Reduce costs and energy consumption Freezing can extend the storage period of raw materials to more than 6 months, reducing the impact of seasonal fluctuations in raw material supply; and when microwaved in a frozen state, the moisture distribution is more uniform, which can reduce energy consumption by 20%-30%.

[0041] Ensure product safety Freezing environments (below -18°C) can inhibit the growth of psychrophilic bacteria, reducing the initial bacterial count by more than 90%, thus reducing the risk of microbial contamination during subsequent processing and improving the hygiene and safety of the final product.

[0042] Strengthen comprehensive utilization of resources The proteins in fresh or frozen shells do not denature, and after microwave treatment, more than 85% of the soluble proteins can be recovered by isoelectric point precipitation, which can be used to prepare bioactive peptides or animal feed, realizing the high-value utilization of all components of shells.

[0043] The shells of shrimp and crabs are those of crayfish or Chinese mitten crabs.

[0044] The advantages of the above settings are: Align with actual industry needs Crayfish and Chinese mitten crab are the crustacean species with the largest farming scale and highest processing output in my country. Their processing by-product, shells, generate a huge annual discharge. Targeting these as specific treatment targets can directly address the industry's pain points and solve the problem of resource utilization of a large amount of shell waste in actual production. The application scenarios are clear and extensive.

[0045] Verify the universality of the process The shells of crayfish and Chinese mitten crabs differ in terms of structural density and component ratio. This method can efficiently extract calcium from both of these representative shell types, demonstrating its good adaptability to shells with different characteristics and providing a reliable basis for its application to other crustacean raw materials.

[0046] Improve industrial economic efficiency The crayfish and Chinese mitten crab processing industries are concentrated and mature. Using these as raw materials, the existing processing system can be relied upon to achieve process integration, lowering the threshold for large-scale application. At the same time, the efficiently extracted calcium can be recycled as food additives and raw materials for health products, forming a circular chain of "processing-waste-high-value products" and improving the overall benefits of the industry.

[0047] Strengthen technical targeting Optimizing process parameters based on the characteristics of these two types of crustaceans can ensure more precise pretreatment results, avoid fluctuations in extraction efficiency due to differences in raw materials, guarantee process stability and reliability, and provide a solid foundation for industrial replication.

[0048] The water bath temperature fluctuation range is controlled within ±2℃ to ensure uniform rehydration.

[0049] The advantages of the above settings are: Ensuring stable rehydration: Temperature is a key factor affecting the rate and uniformity of water absorption in the shell. Strictly controlling the fluctuation range within ±2℃ can avoid problems such as rapid water absorption and expansion of the shell surface due to excessively high local temperatures, insufficient water absorption of the inner layer, or slow overall water absorption due to excessively low temperatures. This ensures that all parts of the shell can absorb water evenly, and the pore structure is fully and consistently swelled.

[0050] Enhancing the effect of subsequent microwave treatment: The core purpose of rehydration is to provide sufficient and evenly distributed moisture for the secondary microwave treatment. Stable temperature ensures that the moisture content in the shell pores remains balanced. During the secondary microwave treatment, microwave energy can act more evenly on the moisture, avoiding uneven structural damage caused by excessive or insufficient moisture in certain areas. This ensures the consistency of the secondary microwave treatment's effect on shell loosening, laying the foundation for the high efficiency and stability of subsequent calcium extraction.

[0051] Improving process repeatability: In large-scale production, stable temperature parameters are an important prerequisite for ensuring consistent treatment results between batches. A fluctuation range of ±2℃ can reduce the fluctuation of rehydration degree caused by temperature differences, keep the pretreatment effect of different batches of shells stable, reduce batch differences in calcium recovery rate in subsequent extraction stages, and enhance the repeatability of the process and its industrial application value.

[0052] The working environment temperature of the crusher should be controlled between 25-30℃.

[0053] The advantages of the above settings are: To prevent denaturation of shell components: The proteins and chitin contained in shrimp and crab shells are quite sensitive to temperature. High temperatures can easily cause protein denaturation and damage to the chitin structure. A mild environment of 25-30℃ can prevent the accumulation of local heat generated by mechanical friction during the pulverization process, which can lead to component denaturation. This ensures the natural activity of the effective components in the shell powder and preserves their value for subsequent comprehensive utilization of chitin and proteins.

[0054] Ensuring stable pulverization efficiency: Excessive temperature may cause the shell material to become brittle or sticky, affecting the uniformity and efficiency of pulverization; excessively low temperature may increase the toughness of the shell, making pulverization more difficult. This temperature range maintains the stability of the shell's physical properties, allowing the pulverizer to operate under optimal load conditions, ensuring a uniform particle size distribution of the pulverized shell powder, and avoiding the excessive generation of overly coarse or fine particles, thereby stabilizing the contact area for subsequent reactions with organic acids.

[0055] Extending equipment lifespan: When the crusher operates in a suitable temperature environment, it can reduce problems such as motor overheating and accelerated component wear caused by high temperatures, reduce the probability of equipment failure, extend its service life, indirectly reduce production and maintenance costs, and improve the economy and stability of the process.

[0056] The particle size range of the shell powder obtained after crushing is 80-120 mesh.

[0057] The advantages of the above settings are: To ensure a balance between reaction sufficiency and efficiency: A particle size of 80-120 mesh can increase the specific surface area of ​​the shell powder by appropriately refining it, ensuring sufficient contact area between the organic acid and calcium, and promoting a full reaction; at the same time, it can avoid particle agglomeration caused by excessively fine particle size, preventing the calcium inside the agglomerates from failing to effectively contact the acid solution, thereby improving reaction efficiency while ensuring reaction uniformity.

[0058] Reduced difficulty of subsequent separation: After reacting with acetic acid solution, the shell powder in this particle size range is less likely to be suspended in the supernatant due to excessively fine particles during centrifugation, and it will also not cause excessive unreacted calcium residue due to excessively coarse particles. This can reduce solid impurities in the supernatant after centrifugation, improve the purity of calcium extract, and reduce the load on separation equipment.

[0059] Facilitates stable control of process parameters: The particle size range of 80-120 mesh is easily controlled through standard sieves during the pulverization operation, ensuring the consistency of particle size among different batches of shell powder, reducing the impact of particle size fluctuations on subsequent process parameters such as material mixing and reaction rate, improving the overall stability and repeatability of the process, and providing convenience for quality control in large-scale production.

[0060] The acetic acid solution was prepared using deionized water, and the pH value of the solution was 2.5-3.5.

[0061] The advantages of the above settings are: To avoid interference from impurities in the reaction: Deionized water does not contain metal ions such as calcium and magnesium, or other soluble impurities. This prevents these impurities from combining with acetic acid or competing with calcium in the shell for reaction sites, ensuring that acetic acid can specifically react with calcium carbonate in the shell, reducing interference with calcium extraction efficiency, and ensuring the purity of calcium in the final extract.

[0062] Optimizing the acidolysis reaction efficiency: A pH range of 2.5-3.5 provides a suitable acidic environment for the reaction between acetic acid and calcium carbonate. This range avoids the problems of slow reaction rate and incomplete decalcification caused by excessively high pH, ​​while preventing the destruction of proteins, chitin, and other components in the shell by excessively low pH. It efficiently dissolves calcium while protecting other valuable components, creating conditions for subsequent comprehensive utilization.

[0063] Ensuring process stability: The use of deionized water can eliminate the influence of water source differences on solution concentration and reactivity; a fixed pH range can ensure that the reactivity of different batches of acetic acid solution is consistent, reduce the difference in calcium recovery rate caused by fluctuations in solution properties, improve the repeatability and controllability of the process, and facilitate quality control in large-scale production.

[0064] The calcium concentration in the supernatant was determined by EDTA titration.

[0065] The advantages of the above settings are: The measurement results are accurate and reliable. EDTA forms a stable 1:1 chelate with calcium ions, exhibiting strong reaction specificity and minimal influence from other common ions in the solution. In the chitin calcium extraction system, the supernatant may contain small amounts of impurities such as proteins and chitin degradation products. However, the EDTA titration method is highly tolerant to these organic impurities, allowing for direct determination of calcium concentration with results that meet the requirements of process analysis in terms of accuracy and precision.

[0066] Easy to operate and cost controllable This method requires no complex instruments, has clear experimental procedures, and can be mastered by operators with simple training, making it suitable for rapid detection in laboratories and large-scale production. Compared to instrumental analysis methods such as atomic absorption spectrometry, EDTA titration does not require expensive equipment and maintenance costs, reducing economic investment in the detection process, and is especially suitable for small and medium-sized processing enterprises.

[0067] Adapt to process testing requirements The calcium concentration in the supernatant of crustacean calcium extraction is usually in the medium range, which matches the measurement range of EDTA titration. It can be directly measured without complicated dilution, and can quickly provide feedback on the calcium extraction efficiency of each batch, providing real-time data support for process parameter adjustment and ensuring production stability.

[0068] Good reproducibility Under strict control of titration conditions, the results of multiple measurements of the same batch of samples show little deviation, which can ensure the comparability of data between different batches, facilitate the tracking of process stability, and provide a reliable quantitative basis for optimizing extraction efficiency.

[0069] Specific experiments Example 1: Calcium extraction effect from crayfish shells treated with microwave power of 0.53 kWh Take 20g of fresh crayfish carcasses (preliminarily cleaned to remove surface impurities) and microwave them at 50Hz and 0.53kWh until the carcasses reach a constant weight, making the internal structure of the crayfish carcasses looser. Figure 1 As shown. During the treatment, the shell thickness was controlled at 1-2 cm, and it was turned over every 5 minutes to ensure uniform microwave action. After microwave treatment, the dried shells were pulverized using a pulverizer with a speed of 29000 rpm for 10 minutes. The ambient temperature of the pulverizer was maintained at 25-30℃. After pulverization, the shell powder was sieved to obtain 80-120 mesh shell powder.

[0070] The obtained shell powder was mixed with 0.1665 mol / L acetic acid solution (prepared with deionized water, pH 2.5-3.5) at a material-to-liquid ratio of 1:40 (w / v). The mixture was magnetically stirred at 500 rpm for 30 min at room temperature, with the stirrer 1-2 cm above the bottom of the container. After the reaction was complete, the mixture was centrifuged at 4000 g for 10 min (using a horizontal rotor centrifuge). 80%-90% of the supernatant was collected, and the calcium concentration was determined by EDTA titration.

[0071] The results showed that it took 10 minutes to microwave 20g of crayfish shells to constant weight, consuming 88.33W of electricity. Field emission scanning electron microscopy revealed that the internal structure of the shells was significantly looser than before treatment. The calcium content in the resulting calcium acetate solution was 3.49mg / mL.

[0072] Example 2: Calcium extraction effect from crayfish shells treated with microwave power of 1.06 kWh Take 20g of fresh crayfish carapace (processed as in Example 1), and microwave it at 50Hz and 1.06kWh until constant weight to disrupt the internal network structure of the crayfish carapace. Figure 2 As shown. The remaining microwave processing parameters (laying thickness, turning frequency) are the same as in Example 1. After drying, the shells are pulverized by a pulverizer of the same specifications (parameters same as in Example 1), and 80-120 mesh shell powder is selected.

[0073] The mixture was prepared according to the same material-to-liquid ratio, acetic acid solution concentration, and stirring parameters as in Example 1. After centrifugation, the calcium concentration of the supernatant was determined by EDTA titration.

[0074] The results showed that it only took 5 minutes to microwave 20g of crayfish shells to constant weight, consuming 88.33W of electricity; the internal network structure of the shells was more significantly damaged, and the pore distribution was more uniform; the calcium content in the calcium acetate solution increased to 3.76mg / mL.

[0075] Example 3: Calcium Extraction Effect of Microwave-Rehydration-Secondary Microwave Treatment on Crayfish Carapace Take 20g of fresh crayfish carapace (processed as in Example 1), and microwave it at 50Hz and 1.06kWh until constant weight (parameters as in Example 2). Then, rehydrate the dried carapace in a 90℃ water bath for 10 minutes, controlling the water bath temperature fluctuation within ±2℃. After rehydration, microwave it again until constant weight, completing the second microwave treatment to further promote the breakdown of the internal network of the crayfish carapace. Figure 3 As shown.

[0076] After the dried shells were crushed (with parameters the same as in Example 1), the reaction and detection were carried out according to the extraction process of Example 1.

[0077] The results showed that the entire pretreatment (microwave-rehydration-second microwave) took 20 minutes and consumed 293.33 W of electricity. The internal structure of the carapace was further broken down by the second microwave treatment, and the porosity was significantly better than that of the single microwave treatment. The calcium content in the calcium acetate solution reached 4.11 mg / mL, and the calcium recovery rate was significantly improved compared with the traditional method.

[0078] Comparative Example 1: Calcium Extraction Effect of Hot Air Drying on Crayfish Carapace Take 20g of fresh crayfish carapace (processed as in Example 1), place it in a 1.54kWh, 105℃ hot air oven and dry until constant weight. The internal structure of the crayfish carapace is compact, as... Figure 4 As shown, the process took 150 minutes and consumed 3850W of electricity. After drying, the shells were pulverized to the same specifications (parameters as in Example 1), and the reaction and detection were carried out according to the extraction process of Example 1.

[0079] The results showed that the internal structure of the shell dried by hot air was compact with very few pores; the calcium content in the calcium acetate solution was only 3.44 mg / mL, which was significantly lower than that of the microwave-treated group.

[0080] Examples 4-6: Effects of different treatment methods on calcium extraction from the carapace of the Chinese mitten crab. Take 20g of fresh Chinese mitten crab carcass (after preliminary cleaning) and perform single-power microwave, high-power microwave, and microwave-rehydration-secondary microwave treatments according to the treatment methods in Examples 1-3. All other parameters (particle size, reaction conditions, detection methods, etc.) are consistent with those in the crayfish carcass experiment. At the same time, hot air drying treatment is set as a comparative example 2.

[0081] The results show: Example 4 (Microwave treatment at 50Hz and 0.53kWh until constant weight resulted in a loosened internal structure of the Chinese mitten crab's carapace, such as...) Figure 5 (As shown): The drying time for the crab shell was 10 minutes, and the calcium content was 5.14 mg / mL; Example 5 (Microwave treatment at 50Hz and 1.06kWh until constant weight to disrupt the internal network structure of the Chinese mitten crab's carapace, such as...) Figure 6 (As shown): The drying time for the crab shell was 5 minutes, and the calcium content was 5.24 mg / mL; Example 6 (Microwave-Rehydration-Secondary Microwave: Secondary microwave promotes the breakdown of the internal carapace network of the Chinese mitten crab, such as...) Figure 7 As shown): Total time 20 minutes, calcium content reached 5.61 mg / mL; Comparative Example 2 (hot air dried to constant weight, the internal structure of the Chinese mitten crab's carapace is compact, such as...) Figure 8 As shown): Time taken: 150 min, calcium content: 5.13 mg / mL.

[0082] All microwave-treated groups showed better results in terms of shell structure looseness and calcium extraction efficiency than the hot-air drying group, with secondary microwave treatment yielding the best results.

[0083] Experimental conclusions Comparison of different treatment methods shows that the pretreatment process of "1.06kWh microwave-90℃ rehydration-1.06kWh secondary microwave" can achieve efficient decalcification of the shells of crayfish and Chinese mitten crabs. It has the advantages of short time consumption, low energy consumption and sufficient structural destruction, which is significantly better than traditional hot air drying and single microwave treatment. It provides a stable and reliable technical path for high-value extraction of calcium from shells.

[0084] The examples provided in this invention are not intended to limit the implementation. Those skilled in the art will recognize that various variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of this invention.

Claims

1. A pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs, characterized in that, Includes the following steps: Step 1: Take 20g of shrimp and crab shells and microwave them at 50Hz and 0.53-1.06kWh until constant weight is achieved; Step 2: Place the shells treated in Step 1 in a 90℃ water bath to rehydrate for 10 minutes; Step 3: Place the rehydrated carapace under microwave treatment at 50Hz and 0.53-1.06kWh until constant weight is achieved; Step 4: Crush the shells processed in Step 3 using a pulverizer with a speed of 29000 rpm for 10 minutes; Step 5: Mix the obtained shell powder with a 0.16-0.17 mol / L acetic acid solution at a material-to-liquid ratio of 1:40; Step 6: Stir the mixture magnetically at 500 rpm for 30 min at room temperature. After centrifuging the mixture at 4000 g for 10 min, determine the calcium concentration in the supernatant.

2. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 1, characterized in that, In step one, the initial state of the shrimp and crab shells is either fresh shells or frozen shells that have undergone preliminary cleaning.

3. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 2, characterized in that, In step one, the shell of the shrimp or crab is either the shell of a crayfish or the shell of a Chinese mitten crab.

4. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 1, characterized in that, In step two, the water bath temperature fluctuation range is controlled within ±2℃ to ensure uniform rehydration.

5. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 1, characterized in that, In step four, the operating temperature of the crusher is controlled at 25-30℃.

6. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 5, characterized in that, In step four, the particle size range of the shell powder obtained after pulverization is 80-120 mesh.

7. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 1, characterized in that, In step five, the acetic acid solution is prepared using deionized water, and the pH value of the solution is 2.5-3.

5.

8. The pretreatment method for efficiently extracting calcium from the shells of shrimp and crabs according to claim 1, characterized in that, In step six, the calcium concentration of the supernatant is determined by EDTA titration.

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