Preparation process of crayfish fresh-keeping ingredient oil grafted with shrimp shell chitin

Abstract

The application discloses a preparation process of crayfish fresh-keeping ingredient oil grafted with shrimp shell chitin, and relates to the technical field of food preservation.The method uses shrimp shell chitin with a deacetylation degree of greater than or equal to 90% as raw material, carries out quaternary ammonium modification and stearic acid hydrophobic modification, and then carries out grafting reaction with low erucic rapeseed oil in a vacuum environment to form a composite system through lipase catalysis, adds DHA oil for nutrition strengthening, adds gamma oryzanol and bamboo leaf flavonoids for compounding antioxidants for inhibiting oxidation, and finally carries out electrospinning encapsulation to obtain a finished product.The shrimp shell resource utilization realizes green and low-cost raw materials, the chitin multistage modification solves the compatibility problem with oil, the enzyme catalysis grafting, the synergistic antioxidant and the nanometer encapsulation technology can significantly improve the fresh-keeping effect of crayfish at room temperature, delay the oxidation and deterioration of the ingredient oil, and retain the nutritional value of the product.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a process for preparing crayfish-based freshness-locking oil by grafting shrimp shell chitin with oil. Background Technology

[0002] Crayfish meat is tender and nutritious, making it a favorite among consumers. However, due to its high water content and rich protein and fat content, it is prone to microbial growth, oxidation, and flavor loss during room temperature storage, resulting in a short shelf life and limited distribution.

[0003] Currently, most crayfish preservation ingredients on the market rely on single preservatives or physical preservation methods, resulting in problems such as short preservation periods, easy nutrient loss, and insufficient safety. Some preservation ingredients use chemical modifiers to enhance their effect, which may leave harmful residues and fail to meet food safety requirements. Other ingredients use natural polymer materials as barrier agents, but natural materials have poor compatibility with oils, leading to unstable preservation effects and making it difficult to balance preservation performance and product quality. In addition, a large number of crayfish shells generated from aquatic product processing are discarded, which not only wastes resources but also puts pressure on the environment. How to achieve high-value utilization of crayfish shells and develop efficient preservation ingredients based on their characteristics has become an urgent problem to be solved by the industry.

[0004] Therefore, it is necessary to provide a process for preparing crayfish freshness-locking ingredient oil by grafting shrimp shell chitin with oil to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a process for preparing crayfish freshness-locking ingredient oil by grafting shrimp shell chitin with oil, in order to solve the problems of poor compatibility, short freshness-locking period, easy loss of nutrients and waste of resources in existing freshness-locking ingredients.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing crayfish freshness-locking ingredient oil grafted with shrimp shell chitin, comprising the following steps: Step 1: Take chitin from shrimp shells with a degree of deacetylation ≥90%, add it to the reaction vessel and mix it with deionized water, then stir and disperse it to form a uniform suspension; Step 2: Add food-grade anhydrous ethanol as a co-solvent to the suspension and stir to disperse; Step 3: Adjust the pH of the system to 7.2–7.8 using dilute hydrochloric acid or sodium hydroxide solution; Step 4: Add 2,3-epoxypropyltrimethylammonium chloride to the system at a mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride of 1.1 to 1.3:1, and continue stirring until the raw materials are completely mixed; Step 5: Heat the reactor to a constant temperature of 70-80℃ and maintain this temperature for 6-8 hours, using intermittent stirring during the reaction. Step 6: After the reaction is complete, allow the mixture to cool naturally to room temperature. Add deionized water to the reaction vessel, stir, and then transfer it to a centrifuge for centrifugation. Discard the supernatant. Repeat the water washing-centrifugation process to obtain quaternized chitin. Step 7: Transfer the quaternized chitin into the modification vessel, add deionized water and stir to disperse, adjust the solid content of the system to 8% to 12% to form a uniform suspension; Step 8: Weigh out food-grade stearic acid, dissolve it in anhydrous ethanol by heating, and obtain a stearic acid solution; Step 9: Add the stearic acid solution obtained in Step 8 to the suspension obtained in Step 7, and mix thoroughly while stirring. Step 10: Heat the modified reactor to a constant temperature of 55-65℃ and maintain this temperature for 1.5-2.5 hours. Step 11: After the reaction is completed, cool to room temperature, transfer the reaction material in the modified reactor into a centrifuge for centrifugation to obtain modified quaternized chitosan; Step 12: Add the modified quaternized chitin and low erucic acid rapeseed oil to a high-speed shear emulsifier at a mass ratio of 1:4 to 1:6, and mix and disperse to form a uniform system; Step 13: Transfer the system obtained in Step 12 into a vacuum reactor, adjust the vacuum to 0.08-0.10 MPa, and adjust the pH of the system to 5.2-6.2; Step 14: Heat the vacuum reactor to a constant temperature of 50-60°C, add lipase, and maintain this condition for 7-9 hours. Step 15: After the reaction is complete, add DHA oil to the system and stir to mix evenly; Step 16: Add the antioxidant to the system and continue stirring to mix evenly; the antioxidant is a mixture of γ-oryzanol and bamboo leaf flavonoids, with a mass ratio of 2:1. Step 17: The mixed system is subjected to electrospinning to obtain crayfish freshness-locking seasoning oil.

[0007] Preferably, in step 2, the amount of food-grade anhydrous ethanol added is 0.4% to 0.6% of the total mass of the homogeneous suspension obtained in step 1, and the stirring and dispersion time is 5 to 8 minutes.

[0008] In this invention, chitin derived from shrimp shells with a degree of deacetylation ≥90% is used as the core raw material. Its high amino content serves as the reaction site. First, chitin is mixed with deionized water to form a homogeneous suspension. Food-grade anhydrous ethanol is added as a co-solvent to improve the dispersibility of subsequent reaction materials. Then, the pH of the system is adjusted to a weakly alkaline range of 7.2–7.8 using dilute hydrochloric acid or sodium hydroxide solution. This environment promotes the ring-opening of the epoxy groups of 2,3-epoxypropyltrimethylammonium chloride. The reaction mixture is prepared according to a chitin to 2,3-epoxypropyltrimethylammonium chloride ratio of 1.1–1.3:1. After adding the modifier in the specified proportions, the raw materials are thoroughly mixed by continuous stirring. The mixture is then reacted at a constant temperature of 70–80°C for 6–8 hours with intermittent stirring to allow the epoxy groups to undergo nucleophilic addition reactions with the amino groups on the chitin molecular chain, successfully grafting quaternary ammonium salt groups and converting the chitin from hydrophobic to cationic form to enhance its reactivity. Subsequently, the quaternized chitin is transferred to a modification reactor, and the solid content of the system is adjusted to 8%–12% to form a homogeneous suspension. Food-grade stearic acid is dissolved in anhydrous ethanol by heating and then added to the suspension. The reaction is carried out at 55–65°C for 1.5–2.5 hours. By forming ionic bonds between quaternary ammonium groups and stearic acid carboxyl groups, hydrophobic groups of long-chain fatty acids are introduced, significantly reducing the interfacial tension between chitosan and oils and solving the compatibility problem. Then, modified quaternized chitosan and low-erucic acid rapeseed oil are mixed at a mass ratio of 1:4 to 1:6 using a high-speed shear emulsifier to form a homogeneous solid-oil system. This system is then transferred to a vacuum reactor, and the vacuum level is adjusted to 0.08–0.10 MPa to reduce oxygen interference with oil oxidation. The pH of the system is adjusted to 5.2–6.2, and the temperature is raised to 50–60°C. These conditions match the activity range of lipase. After lipase reaction for 7-9 hours, the modified chitin undergoes a transesterification reaction with low-erucic acid rapeseed oil to form a stable chitin-oil graft structure. After the reaction is completed, DHA oil is added for nutritional fortification, followed by the addition of a composite antioxidant composed of γ-oryzanol and bamboo leaf flavonoids in a specific ratio. γ-oryzanol can effectively remove free radicals generated by the auto-oxidation of oils, while bamboo leaf flavonoids can chelate metal ions and block the lipid peroxidation chain reaction. The two work synergistically to exert antioxidant effects. Finally, the mixture is electrospun to form a nanoscale fiber encapsulation structure, constructing a physical barrier.

[0009] Preferably, in step 4, the stirring time is 10–15 minutes. This stirring time ensures that chitosan and 2,3-epoxypropyltrimethylammonium chloride are fully contacted and uniformly mixed, avoiding incomplete quaternization reaction caused by local raw material aggregation, improving the stability of the quaternization rate, and laying a uniform structural foundation for subsequent modification reactions.

[0010] Preferably, in step 5, the intermittent stirring method involves stirring for 8-12 minutes every 25-35 minutes, at a stirring rate of 400-600 r / min. This intermittent stirring method balances reaction uniformity and raw material stability, preventing chitin precipitation that could lead to localized reaction imbalances, while also avoiding excessive hydrolysis of 2,3-epoxypropyltrimethylammonium chloride caused by continuous high-intensity stirring, thus ensuring the purity and reactivity of the quaternized chitin.

[0011] Preferably, in step 6, the amount of deionized water added is 3 to 5 times the volume of the system in the reactor, and the stirring time is 15 to 20 minutes; the centrifugation speed is 2800 to 3200 r / min, and the centrifugation time is 8 to 12 minutes; the water washing-centrifugation operation is repeated at least 3 times. Sufficient water volume and stirring time can efficiently dissolve unreacted raw materials and by-products. These centrifugation parameters and repeated operations can thoroughly separate impurities, thereby increasing the purity of quaternized chitosan to a higher level and reducing the interference of residual impurities on subsequent reactions.

[0012] Preferably, in step 8, the amount of stearic acid added is 0.2% to 0.4% of the total mass of the suspension obtained in step 7; the amount of anhydrous ethanol used is 5 to 8 times the mass of stearic acid; and the heating and dissolution temperature is 50 to 60°C. This amount of stearic acid added can avoid insufficient or excessive modification, and sufficient ethanol and a suitable temperature can ensure that the stearic acid is completely dissolved to form a homogeneous solution, thus ensuring the uniformity of the hydrophobic modification reaction.

[0013] Preferably, in step 9, the stearic acid solution is added at a rate of 1–2 mL / min, and the stirring rate is 300–500 r / min. After the addition is complete, stirring continues for 20–30 min. Slow addition and moderate stirring can prevent excessively high local concentrations of stearic acid from causing agglomeration. Continuous stirring afterwards can promote the full reaction between stearic acid and quaternized chitosan, improve the consistency of hydrophobic modification, and enhance the compatibility of chitosan with oils.

[0014] Preferably, in step 11, the centrifugation speed is 2800–3200 r / min, and the centrifugation time is 8–12 min. Under these parameters, unreacted stearic acid and other impurities can be efficiently separated to obtain high-purity modified quaternized chitosan, avoiding the impact of impurities on the efficiency and product quality of subsequent oil grafting reactions.

[0015] Preferably, in step 12, the high-speed shear emulsifier operates at a speed of 9000–11000 r / min, and the dispersion time is 18–22 min. The high speed and suitable dispersion time break the interfacial tension between the modified quaternized chitosan and the low-erucic acid rapeseed oil, forming a microscopically uniform mixture and increasing the contact area between the two, thus creating favorable conditions for the subsequent enzyme-catalyzed grafting reaction.

[0016] Preferably, in step 14, the amount of lipase added is 0.4% to 0.6% of the total mass of the system obtained in step 12; in step 15, the amount of DHA oil added is 3% to 5% of the total mass of the system obtained in step 14, the stirring speed is 400 to 600 r / min, and the stirring time is 8 to 12 min; in step 16, the amount of antioxidant added is 0.08% to 0.10% of the total mass of the system obtained in step 14. Appropriate lipase addition maximizes catalytic efficiency, precise DHA oil addition ensures nutritional fortification while avoiding waste, these stirring parameters ensure uniform dispersion of DHA oil and antioxidants, and optimal antioxidant addition fully exerts synergistic antioxidant effects, delaying the oxidative deterioration of oils and DHA.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses chitin derived from shrimp shells as the core raw material, fully utilizing its structural advantages of a natural polymer backbone and abundant amino sites, as well as its natural biocompatibility and barrier properties. After modification, it can be transformed into a highly efficient freshness-locking ingredient. First, quaternization modification allows the epoxy groups of 2,3-epoxypropyltrimethylammonium chloride to undergo a nucleophilic addition reaction with the amino groups on the chitin molecular chain, grafting cationic groups and endowing chitin with reactivity and polarity regulation capabilities. Then, hydrophobic modification with stearic acid allows the quaternary ammonium groups to form ionic bonds with the carboxyl groups of stearic acid, introducing a lipophilic long chain and constructing an amphiphilic structure. Through two-stage modification, the polarity and compatibility of chitin are regulated, overcoming the interfacial tension problem caused by the polarity difference between natural chitin and oils, and overcoming the defects of traditional natural polymer materials that are prone to aggregation and uneven dispersion in oil systems, providing a uniform and stable structural basis for subsequent grafting reactions.

[0018] 2. This invention employs a vacuum reactor to create a low-oxygen environment, reducing oxidative loss of oils during the reaction process. Simultaneously, the system pH is adjusted to 5.2–6.2, and the temperature is controlled at 50–60°C, matching the optimal activity range of lipase. The vacuum environment reduces oxygen interference with oil oxidation, and the suitable acid-base and temperature conditions ensure lipase catalytic activity, promoting the transesterification reaction between modified chitosan and low-erucic acid rapeseed oil to form a stable chitosan-oil graft structure. This process is gentler than traditional chemical grafting, improving grafting efficiency and product purity while avoiding the risk of chemical catalyst residue.

[0019] 3. This invention utilizes a combination of γ-oryzanol and bamboo leaf flavonoids to form an antioxidant system. γ-oryzanol can efficiently scavenge free radicals generated by the auto-oxidation of oils, while bamboo leaf flavonoids can chelate metal ions and block the chain reaction of lipid peroxidation. The two work synergistically to inhibit the oxidation process at different stages. This solves the problem of limited antioxidant components and single effects in traditional freshness-preserving ingredients, significantly improving oxidation inhibition efficiency, effectively delaying the oxidative deterioration of ingredient oils and DHA, and extending the product's shelf life.

[0020] 4. This invention uses electrospinning technology to process the mixed system into a nanoscale fiber structure. The dense network structure formed by the nanofibers can construct a physical barrier, significantly reducing the penetration rate of oxygen, moisture, and microorganisms, and minimizing the contact between crayfish and adverse external factors. Compared with traditional processes, this significantly extends the shelf life of crayfish at room temperature, solving the problems of easy spoilage and limited circulation of aquatic food products during room temperature storage. Attached Figure Description

[0021] Figure 1 Line graph comparing the DHA retention rate of crayfish freshness-locking oil prepared by the processes provided in Examples 1-3 and Comparative Examples 1-6 after 6 months of storage at room temperature. Figure 2 The bar chart shows the comparison of peroxide values ​​of crayfish freshness-locking oils prepared by the processes provided in Examples 1-3 and Comparative Examples 1-6 after 6 months of storage at room temperature. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0023] Example 1 This embodiment provides a process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil, including the following steps: 1. Take chitin derived from shrimp shells with a degree of deacetylation of 90%, add it to a reaction vessel and mix it with deionized water, stirring and dispersing to form a uniform suspension; 2. Add food-grade anhydrous ethanol as a co-solvent to the suspension. The amount of food-grade anhydrous ethanol added is 0.4% of the total mass of the homogeneous suspension obtained in step 1. Stir and disperse for 5 minutes. 3. Adjust the pH of the system to 7.2 using dilute hydrochloric acid; 4. Add 2,3-epoxypropyltrimethylammonium chloride to the system at a mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride of 1.1:1, and stir continuously for 10 minutes until the raw materials are completely mixed. 5. Heat the reactor to a constant temperature of 70℃ and maintain this temperature for 6 hours. During the reaction, stir intermittently for 8 minutes every 25 minutes at a stirring rate of 400 r / min. 6. After the reaction is complete, allow the mixture to cool naturally to room temperature. Add three times the apparent volume of the quaternization reaction suspension in the reactor to the reactor, add deionized water, stir for 15 minutes, and then transfer to a centrifuge for centrifugation at a speed of 2800 r / min for 8 minutes. Discard the supernatant. Repeat the water washing-centrifugation operation three times to obtain quaternized chitosan. 7. Transfer the quaternized chitin to a modification reactor, add deionized water and stir to disperse, adjust the solid content of the system to 8%, and form a uniform suspension; 8. Weigh out food-grade stearic acid, the amount of stearic acid added is 0.2% of the total mass of the suspension obtained in step 7, and dissolve it in anhydrous ethanol at 50°C with 5 times the mass of stearic acid to obtain a stearic acid solution. 9. Add the stearic acid solution to the suspension obtained in step 7 at a dropping rate of 1 mL / min, while maintaining a stirring rate of 300 r / min. After the addition is complete, continue stirring for 20 min until the mixture is homogeneous. 10. Heat the modified reactor to a constant temperature of 55°C and maintain this temperature for 1.5 hours. 11. After the reaction is complete, cool to room temperature, transfer the reaction material in the modified reactor into a centrifuge, and centrifuge at 2800 r / min for 8 min to obtain modified quaternized chitosan; 12. Add the modified quaternized chitin and low erucic acid rapeseed oil to a high-speed shear emulsifier at a mass ratio of 1:4 and shear and disperse them at a speed of 9000 r / min for 18 min to form a uniform system. 13. Transfer the system obtained in step 12 into a vacuum reactor, adjust the vacuum to 0.08 MPa, and adjust the pH of the system to 5.2; 14. Heat the vacuum reactor to a constant temperature of 50°C, add lipase, the amount of lipase added is 0.4% of the total mass of the homogeneous system obtained in step 12, and maintain this condition for 7 hours. 15. After the reaction is complete, add DHA oil to the system. The amount of DHA oil added is 3% of the total mass of the system after the grafting reaction in step 14. Stir at 400 r / min for 8 min to mix evenly. 16. Add an antioxidant to the system. The amount of antioxidant added is 0.08% of the total mass of the system after the grafting reaction in step 14. Continue stirring and mixing until homogeneous. The antioxidant is a mixture of γ-oryzanol and bamboo leaf flavonoids in a mass ratio of 2:1. 17. The uniformly mixed system is subjected to electrospinning to obtain crayfish freshness-locking seasoning oil.

[0024] Example 2 This embodiment provides a process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil, including the following steps: 1. Take chitin derived from shrimp shells with a degree of deacetylation of 92%, add it to a reaction vessel and mix it with deionized water, stirring and dispersing to form a uniform suspension; 2. Add food-grade anhydrous ethanol as a co-solvent to the suspension. The amount of food-grade anhydrous ethanol added is 0.5% of the total mass of the homogeneous suspension obtained in step 1. Stir and disperse for 6 minutes. 3. Adjust the pH of the system to 7.5 using sodium hydroxide solution; 4. Add 2,3-epoxypropyltrimethylammonium chloride to the system at a mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride of 1.2:1, and stir continuously for 12 minutes until the raw materials are completely mixed; 5. Heat the reactor to a constant temperature of 75°C and maintain this temperature for 7 hours. During the reaction, stir intermittently for 10 minutes every 30 minutes, at a stirring rate of 500 r / min. 6. After the reaction is complete, allow the mixture to cool naturally to room temperature. Add deionized water at a volume of 4 times the apparent volume of the quaternization reaction suspension in the reactor. Stir for 18 minutes and then transfer the mixture to a centrifuge for centrifugation at a speed of 3000 r / min for 10 minutes. Discard the supernatant. Repeat the water washing-centrifugation operation 4 times to obtain quaternized chitosan. 7. Transfer the quaternized chitin to the modification vessel, add deionized water and stir to disperse, adjust the solid content of the system to 10%, and form a uniform suspension; 8. Weigh out food-grade stearic acid, the amount of stearic acid added is 0.3% of the total mass of the suspension obtained in step 7, and dissolve it in anhydrous ethanol at 55°C with 6 times the mass of stearic acid to obtain a stearic acid solution. 9. Add the stearic acid solution to the suspension obtained in step 7 at a dropping rate of 1.5 mL / min, while maintaining a stirring rate of 400 r / min. After the addition is complete, continue stirring for 25 min until the mixture is homogeneous. 10. Heat the modified reactor to a constant temperature of 60°C and maintain this temperature for 2 hours. 11. After the reaction is complete, cool to room temperature, transfer the reaction material in the modified reactor into a centrifuge, and centrifuge at 3000 r / min for 10 min to obtain modified quaternized chitosan; 12. Add the modified quaternized chitin and low erucic acid rapeseed oil to a high-speed shear emulsifier at a mass ratio of 1:5 and shear and disperse them at a speed of 10000 r / min for 20 min to form a homogeneous system. 13. Transfer the system obtained in step 12 into a vacuum reactor, adjust the vacuum to 0.09 MPa, and adjust the pH of the system to 5.7; 14. Heat the vacuum reactor to a constant temperature of 55°C, add lipase, the amount of lipase added is 0.5% of the total mass of the homogeneous system obtained in step 12, and maintain this condition for 8 hours. 15. After the reaction is complete, add DHA oil to the system. The amount of DHA oil added is 4% of the total mass of the system after the grafting reaction in step 14. Stir at 500 r / min for 10 min to mix evenly. 16. Add an antioxidant to the system. The amount of antioxidant added is 0.09% of the total mass of the system after the grafting reaction in step 14. Continue stirring and mixing until homogeneous. The antioxidant is a mixture of γ-oryzanol and bamboo leaf flavonoids in a mass ratio of 2:1. 17. The uniformly mixed system is subjected to electrospinning to obtain crayfish freshness-locking seasoning oil.

[0025] Example 3 This embodiment provides a process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil, including the following steps: 1. Take chitin derived from shrimp shells with a degree of deacetylation of 95%, add it to a reaction vessel and mix it with deionized water, stirring and dispersing to form a uniform suspension; 2. Add food-grade anhydrous ethanol as a co-solvent to the suspension. The amount of food-grade anhydrous ethanol added is 0.6% of the total mass of the homogeneous suspension obtained in step 1. Stir and disperse for 8 minutes. 3. Adjust the pH of the system to 7.8 using dilute hydrochloric acid; 4. Add 2,3-epoxypropyltrimethylammonium chloride to the system at a mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride of 1.3:1, and stir continuously for 15 minutes until the raw materials are completely mixed. 5. Heat the reactor to a constant temperature of 80℃ and maintain this temperature for 8 hours. During the reaction, stir intermittently for 12 minutes every 35 minutes at a stirring rate of 600 r / min. 6. After the reaction is complete, allow the mixture to cool naturally to room temperature. Add five times the apparent volume of the quaternization reaction suspension in the reactor to the reactor, add deionized water, stir for 20 minutes, and then transfer to a centrifuge for centrifugation at 3200 r / min for 12 minutes. Discard the supernatant. Repeat the water washing-centrifugation operation five times to obtain quaternized chitosan. 7. Transfer the quaternized chitin to the modification vessel, add deionized water and stir to disperse, adjust the solid content of the system to 12%, and form a uniform suspension; 8. Weigh out food-grade stearic acid, the amount of stearic acid added is 0.4% of the total mass of the suspension obtained in step 7, and dissolve it in anhydrous ethanol at 60°C with 8 times the mass of stearic acid to obtain a stearic acid solution. 9. Add the stearic acid solution to the suspension obtained in step 7 at a dropping rate of 2 mL / min, while maintaining a stirring rate of 500 r / min. After the addition is complete, continue stirring for 30 min until the mixture is homogeneous. 10. Heat the modified reactor to a constant temperature of 65°C and maintain this temperature for 2.5 hours. 11. After the reaction is complete, cool to room temperature, transfer the reaction material in the modified reactor into a centrifuge, and centrifuge at 3200 r / min for 12 min to obtain modified quaternized chitosan; 12. Add the modified quaternized chitin and low erucic acid rapeseed oil to a high-speed shear emulsifier at a mass ratio of 1:6 and shear and disperse them at a speed of 11000 r / min for 22 min to form a homogeneous system. 13. Transfer the system obtained in step 12 into a vacuum reactor, adjust the vacuum to 0.10 MPa, and adjust the pH of the system to 6.2; 14. Heat the vacuum reactor to a constant temperature of 60°C, add lipase, the amount of lipase added is 0.6% of the total mass of the homogeneous system obtained in step 12, and maintain this condition for 9 hours. 15. After the reaction is complete, add DHA oil to the system. The amount of DHA oil added is 5% of the total mass of the system after the grafting reaction in step 14. Stir at 600 r / min for 12 min to mix evenly. 16. Add an antioxidant to the system. The amount of antioxidant added is 0.10% of the total mass of the system after the grafting reaction in step 14. Continue stirring and mixing until homogeneous. The antioxidant is a mixture of γ-oryzanol and bamboo leaf flavonoids in a mass ratio of 2:1. 17. The uniformly mixed system is subjected to electrospinning to obtain crayfish freshness-locking seasoning oil.

[0026] Comparative Example 1 The only difference between this comparative example and Example 2 is that the degree of deacetylation of chitin in step 1 is 85%.

[0027] Expected performance: Insufficient number of amino groups on the chitin molecular chain, reduced quaternization rate, lack of sufficient binding sites for subsequent hydrophobic modification of stearic acid, poor compatibility between chitin and oils, decreased freshness-locking effect of the final ingredient oil, accelerated DHA oxidation rate, and insufficient stability at room temperature.

[0028] Comparative Example 2 The only difference between this comparative example and Example 2 is that the pH value of the system is adjusted to 6.5 in step 3.

[0029] Expected performance: Deviating from the optimal weakly alkaline environment for the ring-opening reaction of the 2,3-epoxypropyltrimethylammonium chloride epoxy group, the epoxy group is prone to protonation and hydrolysis, the efficiency of the quaternization reaction is reduced, the yield of quaternized chitin decreases, the uniformity of subsequent grafting reactions deteriorates, and the freshness-locking and nutrient retention effects of the compound oil are affected.

[0030] Comparative Example 3 The only difference between this comparative example and Example 2 is that the mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride in step 4 is 1.0:1.

[0031] Expected performance: Insufficient dosage of 2,3-epoxypropyltrimethylammonium chloride leads to incomplete quaternization of chitin, with a quaternization rate below 80%. This results in decreased subsequent binding efficiency with stearic acid, poor hydrophobic modification of chitin, and easy stratification when mixed with oils, leading to poor stability of the formulated oil.

[0032] Comparative Example 4 The only difference between this comparative example and Example 2 is that in step 8, anhydrous ethanol was not used to dissolve stearic acid; instead, solid stearic acid was directly added to the suspension.

[0033] Expected performance: Stearic acid cannot be evenly dispersed, and clumping and aggregation are prone to occur. The local stearic acid concentration is too high, the modification reaction is uneven, some quaternized chitin is not effectively hydrophobically modified, the compatibility with low erucic acid rapeseed oil is poor, the grafting reaction efficiency is reduced, and the freshness-locking performance of the blended oil is impaired.

[0034] Comparative Example 5 The only difference between this comparative example and Example 2 is that in step 16, only γ-oryzanol was used as the antioxidant, and no bamboo leaf flavonoids were added.

[0035] Expected performance: Lacking the synergistic effect of bamboo leaf flavonoids, single antioxidants are difficult to effectively inhibit the oxidation of oils and DHA, resulting in limited antioxidant effects. The oxidation rate of DHA in the ingredient oil increases, the peroxide value increases rapidly during room temperature storage, and the freshness-locking period is shortened.

[0036] Comparative Example 6 The only difference between this comparative example and Example 2 is that electrospinning was not performed in step 17, and the ingredient oil was obtained directly.

[0037] Expected performance: Unable to form a nanoscale encapsulation structure, the oils and DHA are directly exposed to the air, making them susceptible to oxidation and deterioration upon contact with oxygen and moisture. This significantly reduces the freshness-locking effect, causes rapid loss of nutrients during room temperature storage, and significantly shortens the product's shelf life.

[0038] To compare the performance differences in the preparation processes of crayfish freshness-locking ingredient oils using shrimp shell chitin-grafted oils provided in Examples 1-3 and Comparative Examples 1-6, the present invention provides the following experimental methods:

[0039] 1. Freshness-locking performance test: The ingredient oils prepared in each example and comparative example were applied to the surface of crayfish and stored at room temperature (25°C). The sensory quality (color, odor, meat elasticity) and microbial count of the crayfish were tested periodically. 2. DHA retention rate test: After 6 months of storage at room temperature, the remaining DHA content in each ingredient oil was determined by high performance liquid chromatography, and the DHA retention rate was calculated. 3. Peroxide value test: Measure the peroxide value of the oil after 6 months of storage at room temperature to assess the degree of oil oxidation.

[0040] The experimental data are as follows:

[0041] Based on the experimental data, regarding the core nutritional indicator DHA retention rate, after 6 months of storage at room temperature, the DHA retention rate of all three examples remained stable at over 89.2%. Among them, Example 2, as the optimal synergistic combination of various process parameters, achieved a DHA retention rate as high as 93.5%, fully demonstrating the optimization of process parameters and technical advantages of the present invention. In contrast, the DHA retention rates of Comparative Examples 1-6 were only between 58.3% and 75.3%, representing an average decrease of over 20% compared to the examples. Specifically, Comparative Example 1, due to the use of chitosan with a deacetylation degree of 85%, resulted in insufficient quaternization modification, limiting subsequent grafting and protection, with a DHA retention rate of only 72.6%. Comparative Example 5, lacking a compound synergistic antioxidant system, found that a single antioxidant was insufficient to comprehensively block the oxidation pathway, reducing the DHA retention rate to 65.7%. Comparative Example 6, lacking electrospinning encapsulation, exposed DHA directly to oxygen, moisture, and other environments, resulting in the most severe oxidation loss and the lowest retention rate of only 58.3%. This directly demonstrates the crucial supporting role of chitosan multi-stage modification, synergistic antioxidant, and electrospinning encapsulation technologies in DHA nutrient retention.

[0042] Regarding the peroxide value, a key indicator of oxidative stability, the examples demonstrated excellent antioxidant performance, with peroxide values ​​all below 0.062 g / 100 g, and Example 2 even as low as 0.048 g / 100 g, indicating that the oxidation chain reaction of oils in the system was effectively inhibited. In contrast, the peroxide values ​​of the comparative examples ranged from 0.088 g / 100 g to 0.132 g / 100 g, significantly increasing the risk of oxidative deterioration. Among them, Comparative Example 6, lacking electrospinning encapsulation and physical barrier, had sufficient contact between the oil and external oxygen, resulting in a peroxide value as high as 0.132 g / 100 g. Comparative Example 5, lacking the synergistic antioxidant effect of γ-oryzanol and bamboo leaf flavonoids, could only inhibit oxidation at a single stage, with a peroxide value of 0.115 g / 100 g. This fully demonstrates that the synergistic antioxidant system, through multiple effects of free radical scavenging, metal ion chelation, and chain reaction blocking, combined with the dense physical barrier formed by electrospinning encapsulation, can effectively cut off the oxidation chain of oils, significantly improving the storage stability and shelf life of the product.

[0043] In terms of sensory quality score and microbial count, key evaluation indicators for crayfish freshness preservation, the first example demonstrates an absolute technical advantage: after 15 days of storage at room temperature, the sensory quality score remained above 8.5 points (out of 10), with Example 2 reaching as high as 9.2 points, and the microbial count was strictly controlled at 1.8 × 10⁻⁶. 3 ~3.2×10 3 CFU / g; while the sensory quality scores of the comparative samples were only 4.8–6.7 points, with the highest microbial count reaching 2.5 × 10⁻⁶. 4 The CFU / g level far exceeded that of the examples. Specifically, Comparative Example 6, lacking electrospinning encapsulation protection, allowed microorganisms to easily penetrate the system and multiply, resulting in accelerated moisture loss and flavor deterioration in the crayfish, leading to a sensory quality score as low as 4.8. Comparative Example 3, due to a deviation from the optimal mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride, insufficient quaternization modification, resulting in insufficient compatibility between chitosan and oils, poor graft structure stability, and weakened freshness-locking and barrier effects, achieved a sensory quality score of 5.9 and a microbial count of 9.5 × 10⁻⁶. 3 CFU / g. This data clearly shows that after quaternization and hydrophobic multi-level modification with stearic acid, the stable graft structure formed by chitin and low-erucic acid rapeseed oil, combined with the nanoscale physical barrier layer constructed by electrospinning encapsulation, can effectively block the invasion and migration of external microorganisms, inhibit the loss of water in crayfish muscle tissue, protein degradation and volatilization of flavor substances, significantly delay the deterioration of its sensory quality, and greatly extend the room temperature storage period and circulation radius of crayfish.

[0044] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A process for preparing crayfish-based freshness-locking oil using shrimp shell chitin-grafted oil, characterized in that, Includes the following steps: Step 1: Take chitin from shrimp shells with a degree of deacetylation ≥90%, add it to the reaction vessel and mix it with deionized water, then stir and disperse it to form a uniform suspension; Step 2: Add food-grade anhydrous ethanol as a co-solvent to the suspension and stir to disperse; Step 3: Adjust the pH of the system to 7.2–7.8 using dilute hydrochloric acid or sodium hydroxide solution; Step 4: Add 2,3-epoxypropyltrimethylammonium chloride to the system at a mass ratio of chitosan to 2,3-epoxypropyltrimethylammonium chloride of 1.1 to 1.3:1, and continue stirring until the raw materials are completely mixed; Step 5: Heat the reactor to a constant temperature of 70-80℃ and maintain this temperature for 6-8 hours, using intermittent stirring during the reaction. Step 6: After the reaction is complete, allow the mixture to cool naturally to room temperature. Add deionized water to the reaction vessel, stir, and then transfer it to a centrifuge for centrifugation. Discard the supernatant. Repeat the water washing-centrifugation process to obtain quaternized chitin. Step 7: Transfer the quaternized chitin into the modification vessel, add deionized water and stir to disperse, adjust the solid content of the system to 8% to 12% to form a uniform suspension; Step 8: Weigh out food-grade stearic acid, dissolve it in anhydrous ethanol by heating, and obtain a stearic acid solution; Step 9: Add the stearic acid solution obtained in Step 8 to the suspension obtained in Step 7, and mix thoroughly while stirring. Step 10: Heat the modified reactor to a constant temperature of 55-65℃ and maintain this temperature for 1.5-2.5 hours. Step 11: After the reaction is completed, cool to room temperature, transfer the reaction material in the modified reactor into a centrifuge for centrifugation to obtain modified quaternized chitosan; Step 12: Add the modified quaternized chitin and low erucic acid rapeseed oil to a high-speed shear emulsifier at a mass ratio of 1:4 to 1:6, and mix and disperse to form a uniform system; Step 13: Transfer the system obtained in Step 12 into a vacuum reactor, adjust the vacuum to 0.08-0.10 MPa, and adjust the pH of the system to 5.2-6.2; Step 14: Heat the vacuum reactor to a constant temperature of 50-60°C, add lipase, and maintain this condition for 7-9 hours. Step 15: After the reaction is complete, add DHA oil to the system and stir to mix evenly; Step 16: Add the antioxidant to the system and continue stirring to mix evenly; the antioxidant is a mixture of γ-oryzanol and bamboo leaf flavonoids, with a mass ratio of 2:

1. Step 17: The mixed system is subjected to electrospinning to obtain crayfish freshness-locking seasoning oil.

2. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 2, the amount of food-grade anhydrous ethanol added is 0.4% to 0.6% of the total mass of the homogeneous suspension obtained in step 1, and the stirring and dispersion time is 5 to 8 minutes.

3. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 4, the stirring time is 10 to 15 minutes.

4. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 5, the intermittent stirring method is to stir for 8-12 minutes every 25-35 minutes, and the stirring rate is 400-600 r / min.

5. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 6, the amount of deionized water added is 3 to 5 times the volume of the system in the reactor, and the stirring time is 15 to 20 minutes; the centrifugation speed is 2800 to 3200 r / min, the centrifugation time is 8 to 12 minutes, and the water washing-centrifugation operation is repeated at least 3 times.

6. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 8, the amount of stearic acid added is 0.2% to 0.4% of the total mass of the suspension obtained in step 7; the amount of anhydrous ethanol used is 5 to 8 times the mass of stearic acid; and the heating and dissolution temperature is 50 to 60°C.

7. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 9, the stearic acid solution is added at a rate of 1-2 mL / min, the stirring rate is 300-500 r / min, and stirring continues for 20-30 min after the addition is complete.

8. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 11, the centrifugation speed is 2800-3200 r / min and the centrifugation time is 8-12 min.

9. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 12, the high-speed shear emulsifier operates at a speed of 9000–11000 r / min and a dispersion time of 18–22 min.

10. The process for preparing crayfish freshness-locking ingredient oil using shrimp shell chitin-grafted oil according to claim 1, characterized in that, In step 14, the amount of lipase added is 0.4% to 0.6% of the total mass of the system obtained in step 12; in step 15, the amount of DHA oil added is 3% to 5% of the total mass of the system obtained in step 14, the stirring speed is 400 to 600 r / min, and the stirring time is 8 to 12 min; in step 16, the amount of antioxidant added is 0.08% to 0.10% of the total mass of the system obtained in step 14.

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