Nano-selenium composite antioxidant composition based on sodium alginate coating and preparation method thereof

Abstract

The application discloses a nano-selenium composite antioxidant composition based on sodium alginate coating and a preparation method thereof. The composition is made of sodium alginate, sodium selenite, L-ascorbic acid, DL-alpha-tocopherol, edible ethanol and deionized water and the like. In the sodium alginate aqueous phase network, L-ascorbic acid is used to reduce sodium selenite in situ to nano-selenium, the pH value is reduced in the reaction process to induce the protonation and conformational contraction of sodium alginate molecular chains, and micro-area coating is formed. Meanwhile, with the help of the ethanol cosolvent, DL-alpha-tocopherol is guided to migrate to the interface, and after nitrogen stripping desolventizing, a lipid protection layer is formed on the surface of the nano-selenium, and then powder is obtained through ultrafiltration washing and spray drying. The application inhibits the agglomeration and settlement of nano-selenium particles, reduces the oxidation rate of zero-valent selenium, and improves the storage stability and rehydration dispersibility of the composition.

Description

Technical Field

[0001] This invention relates to the field of functional nanomaterials and antioxidant preparation technology, specifically to a nano-selenium composite antioxidant composition based on sodium alginate coating and its preparation method. Background Technology

[0002] Nano-selenium, as a low-toxicity, highly bioavailable selenium supplement and antioxidant, has broad application prospects in food, medicine, and cosmetics. However, nano-zero-valent selenium particles possess extremely high surface free energy, making them thermodynamically unstable in aqueous systems. During storage or rehydration dispersion, they are prone to spontaneous aggregation, crystallization, and sedimentation, leading to a significant decrease in dispersibility and bioavailability. Furthermore, the surface of active zero-valent selenium lacks an effective physical barrier, making it highly susceptible to oxidative degradation and deactivation under the influence of dissolved oxygen and moisture.

[0003] To improve the dispersion stability and antioxidant properties of nano-selenium, existing technologies often employ single water-soluble polymeric materials (such as polysaccharides or proteins) to coat and modify nano-selenium. However, during actual processing and long-term storage, these single polymeric modification layers, due to their relatively loose structure and strong hydrophilicity, are unable to prevent the penetration of water and dissolved oxygen into the internal selenium core, making it difficult to fundamentally solve the problem of oxidative deterioration of zero-valent selenium. Furthermore, when introducing protective layers using organic solvents or lipid-soluble protective agents, the problem of lipid-soluble components migrating unevenly and accumulating at phase boundaries in the aqueous system is often encountered. If conventional methods such as vacuum evaporation are used to remove the solvent, severe foaming and shoving phenomena can easily occur in the presence of surface-active polymers. Moreover, drastic changes in local acidity or reducing agent concentration can easily lead to localized gelation and irreversible flocculation of the polymer matrix, affecting the uniformity of the product and the stability of the processing. Therefore, developing a nano-selenium composite antioxidant composition and its preparation technology that can simultaneously inhibit physical sedimentation and protect against chemical oxidation with a stable and controllable production process is of great significance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a nano-selenium composite antioxidant composition based on sodium alginate coating and its preparation method, which solves the problems of easy aggregation and sedimentation of existing nano-selenium systems during storage or rehydration, and the lack of interface protection leading to easy oxidation and deterioration of zero-valent selenium.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The nano-selenium composite antioxidant composition based on sodium alginate coating is made from raw materials comprising the following parts by weight:

[0007] Sodium alginate 2.0–5.0 parts;

[0008] Sodium selenite 1.0–3.0 parts;

[0009] L-Ascorbic acid 7.0–11.0 parts;

[0010] DL-α-tocopherol 0.5–2.0 parts;

[0011] 5.0–15.0 parts of edible ethanol;

[0012] 150.0 to 300.0 parts of deionized water.

[0013] By employing the above technical solution, sodium alginate forms a polymeric network matrix containing hydrophilic groups in an aqueous phase and is mixed with sodium selenite. L-ascorbic acid is used as an aqueous phase reducing agent to reduce tetravalent selenium to zero-valent selenium nanoparticles in situ. The newly generated selenium nanoparticles are limited in their rapid growth and aggregation due to the coating of sodium alginate molecular chains and the steric hindrance of the network.

[0014] During the reduction reaction, L-ascorbic acid participates in the redox reaction and releases hydrogen ions, as shown in the following reaction equation:

[0015] H₂SeO₃ + 2C₆H₈O₆ → Se 0 ↓ + 2C6H6O6 + 3H2O;

[0016] As the reaction progresses, the hydrogen ion concentration in the system increases, and the pH value of the system gradually decreases. The carboxyl group (-COO) on the sodium alginate molecular chain... - The group undergoes protonation to transform into a carboxyl group (-COOH), and the reaction formula is as follows:

[0017] R-COO − +H + →R-COOH;

[0018] As a result, the electrostatic repulsion between chains weakens, and the sodium alginate polymer chains transform from an extended form to a compact coiled form. This conformational contraction process creates microcavities with relatively hydrophobic properties within the molecular network, encapsulating the nano-selenium within them.

[0019] Based on this, a premixed solution composed of DL-α-tocopherol and edible ethanol was introduced. Edible ethanol, as a co-solvent, reduces the migration resistance of hydrophobic DL-α-tocopherol in the aqueous network, promoting the enrichment of hydrophobic microdomains formed by the conformational contraction of lipid-soluble DL-α-tocopherol towards sodium alginate and the nano-selenium interface. Subsequently, the co-solvent ethanol was removed by physical stripping, disrupting the dissolution effect of the ethanol-water system on the hydrophobic component, causing DL-α-tocopherol to settle on the surface of the nano-selenium particles, forming a lipid physical barrier layer. This barrier layer slows the penetration of external dissolved oxygen and water molecules into the internal selenium particle surface, reduces the oxidation rate of zero-valent selenium, and helps improve the chemical stability and rehydration dispersion stability of the composite powder during storage.

[0020] Preferably, the weight parts of each raw material are: 3.5 parts sodium alginate, 2.0 parts sodium selenite, 9.0 parts L-ascorbic acid, 1.25 parts DL-α-tocopherol, 10.0 parts edible ethanol, and 225.0 parts deionized water.

[0021] By adopting the above technical solution, under the given ratio conditions, the network coating amount of sodium alginate is adapted to the amount of nano-selenium generated, the degree of conformational shrinkage caused by protonation is more suitable, and DL-α-tocopherol can be enriched more uniformly in the system. While maintaining a high yield, the risk of phase separation caused by excessive lipophilic components is reduced.

[0022] Preferably, the sodium alginate has a weight-average molecular weight of 100,000 Da to 300,000 Da, and a dynamic viscosity of 200 mPa·s to 400 mPa·s for a 1 wt% aqueous solution at 20°C; and the edible ethanol has a mass percentage purity of ≥95.0 wt%.

[0023] By adopting the above technical solution and selecting sodium alginate with the specified molecular weight and viscosity range, a polyanionic network with appropriate entanglement density and steric hindrance can be constructed in the aqueous phase. This network can maintain good sol flowability and provide sufficient conformational shrinkage capacity when the pH decreases. Using food-grade ethanol with a purity of ≥95.0 wt% can promote the dissolution and dispersion of DL-α-tocopherol and reduce the interference of impurities on solvent replacement and stripping desolvation processes.

[0024] Preferably, the raw materials also contain sodium hydroxide, which is added in the form of a 0.05 mol / L aqueous solution to adjust the pH of the initial sodium alginate sol system to 6.8–7.2.

[0025] By adopting the above technical solution, adding dilute sodium hydroxide solution during the sodium alginate dissolution stage can promote the full ionization of carboxyl groups on the sodium alginate molecular chain into carboxylate ions, so that the molecular chain is in a more fully extended state before the reaction. This is beneficial for the uniform dispersion of sodium selenite in the aqueous network, providing a consistent initial environment for subsequent in-situ reduction and pH-induced conformational transformation.

[0026] Secondly, the present invention provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, using the following technical solution:

[0027] A method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating includes the following steps:

[0028] (1) Prepare an aqueous solution of sodium alginate, adjust the pH value to 6.8-7.2, add sodium selenite and stir evenly to obtain a homogeneous mixed sol;

[0029] (2) The aqueous reducing agent premix containing L-ascorbic acid is pumped into the homogeneous mixed sol to carry out an in-situ reduction reaction. During the reaction, the pH value of the system is controlled to decrease and stabilize at 5.0 to 5.5.

[0030] (3) Inject the premixed phase boundary protection medium prepared by DL-α-tocopherol and edible ethanol into the system after the reaction in step (2) to enrich DL-α-tocopherol into the micro-regions and / or nano-selenium interfaces formed by conformational contraction of sodium alginate.

[0031] (4) Sterile high-purity nitrogen gas is introduced for atmospheric pressure and constant temperature gas stripping to remove ethanol so that DL-α-tocopherol settles or solidifies at the interface;

[0032] (5) The material after air stripping is subjected to ultrafiltration washing and spray drying to obtain nano-selenium composite antioxidant powder based on sodium alginate coating.

[0033] By adopting the above technical solution, this method combines in-situ reduction, pH-induced conformational change, solvent displacement interface enrichment, and air stripping solidification.

[0034] In step (1), a uniform dispersion system of charged polymer network and selenium source is established;

[0035] Step (2) uses the proton generated by the aqueous reduction reaction to regulate the pH value of the system, causing the sodium alginate polymer chain to undergo conformational coiling and contraction, thereby achieving primary coating of the newly generated nano-selenium particles; Step (3) uses ethanol as a co-solvent to guide DL-α-tocopherol to the hydrophobic phase interface.

[0036] Step (4) Nitrogen gas is introduced from the bottom to remove ethanol by gas-liquid mass transfer, which promotes the precipitation and solidification of DL-α-tocopherol on the surface of nano-selenium to form a protective layer.

[0037] Step (5) involves using an ultrafiltration membrane to remove residual soluble salts and unreacted substances, and finally drying to obtain a composite antioxidant powder with good stability.

[0038] Preferably, in step (2), the reducing agent premix is ​​pumped in by injecting it through a microporous distributor that extends to the high shear zone at the tip of the stirring blade, with the feed rate controlled at 0.5L / min to 1.5L / min, the reaction temperature controlled at 20℃ to 28℃, and the reaction time at 60min to 90min.

[0039] By employing the above-mentioned technical solution, the reducing agent solution is directly injected into the high-shear region at the tip of the stirring impeller via a microporous distributor. The fluid shearing action in this region allows the dripped acidic reducing agent to be rapidly dispersed throughout the system. This feeding method reduces the probability of localized gelation and irreversible flocculation caused by excessively high local acidity or reducing agent concentration. It also facilitates a gradual decrease in the system's pH value, allowing the conformational transformation of sodium alginate and the reduction nucleation process of nano-selenium to proceed synchronously and orderly.

[0040] Preferably, in step (3), the phase boundary protection medium premix liquid is injected through a bottom insertion tube inserted below the liquid surface, and the feed rate is controlled to be 0.5L / min to 1.5L / min.

[0041] By adopting the above technical solution and using bottom-insertion feeding below the liquid surface, the volatilization loss of the organic phase containing ethanol above the liquid surface can be reduced, and the protective medium can directly enter the interior of the aqueous phase network. Under the action of the stirring flow field, it can penetrate into the micro-region formed by the conformational contraction of sodium alginate, which is beneficial to improving the efficiency of solvent replacement and interface enrichment.

[0042] Preferably, in step (4), the process parameters of the gas stripping process are: the temperature of the constant temperature heating jacket is 35℃~40℃, the atmospheric pressure environment is maintained, the gas flow rate of sterile high-purity nitrogen gas introduced into the bottom microporous distributor is 0.1vvm~0.3vvm, and the gas stripping time is 60min~120min.

[0043] By adopting the above technical solution, nitrogen gas is introduced through a bottom microporous distributor under normal pressure for isothermal gas stripping. As the bubbles rise, they continuously absorb and carry away ethanol vapor from the liquid phase. This physical process has relatively gentle mass transfer, which can reduce the violent foaming and material surge phenomena that are easily caused by the presence of surface-active polymers during depressurized flash evaporation, and helps maintain the fluid stability of the operation process. Controlling the jacket temperature at 35℃~40℃ can reduce the risk of thermal deactivation of heat-sensitive components.

[0044] Preferably, in step (5), the ultrafiltration washing uses a hollow fiber ultrafiltration membrane module with a molecular weight cutoff of 3000 Da to 5000 Da, and is washed with deionized water at constant volume until the conductivity of the permeate is less than or equal to 200 μS / cm; the inlet air temperature of the spray drying is 140℃ to 150℃, and the exhaust air temperature is 50℃ to 55℃.

[0045] By adopting the above technical solution, an ultrafiltration membrane with a specified molecular weight cutoff can intercept sodium alginate-coated nano-selenium composite colloids, while allowing small-molecule dehydroascorbic acid, residual sodium ions, and unreacted substances to pass through, thus achieving system purification. By controlling the conductivity at the end of the washing and filtration process and the inlet and outlet air temperatures of the spray drying, the occurrence of agglomeration or thermal degradation of the dry powder due to local overheating during the drying stage can be reduced, thereby obtaining a composite powder with good dispersibility.

[0046] Preferably, before step (1), the process further includes the preparation of an aqueous reducing agent premix and a phase boundary protection medium premix:

[0047] Weigh out the prescribed amount of L-ascorbic acid and add it to deionized water. Stir at 200 r / min for 15 min at 25℃ until completely dissolved to obtain an aqueous reducing agent premix.

[0048] Weigh out the amount of DL-α-tocopherol in the formula and add it to the amount of edible ethanol in the formula. Stir at 150 r / min for 10 min at 25℃ until the mixture is homogeneous to obtain the phase boundary protection medium premix.

[0049] By adopting the above technical solution, the solid reducing agent and the fat-soluble protective medium are premixed into a uniform premix, which can improve the stability of the material phase and the metering accuracy during the subsequent feeding process, and help improve the repeatability of the production process.

[0050] This invention provides a nano-selenium composite antioxidant composition based on sodium alginate coating and its preparation method. It has the following beneficial effects:

[0051] 1. This invention utilizes L-ascorbic acid for in-situ reduction in an aqueous sodium alginate network. During the reduction process, as the hydrogen ion concentration increases and the pH value decreases, the carboxyl groups on the sodium alginate molecular chains are protonated, which in turn causes conformational contraction and coiling of the polymer chains, confining the newly generated zero-valent selenium nanoparticles within the network cavity. This steric hindrance and network coating effectively block direct collisions between the selenium nanoparticles, significantly reducing the probability of aggregation and sedimentation of the particles during storage or rehydration dispersion.

[0052] 2. This invention utilizes edible ethanol as a co-solvent to guide the migration and enrichment of lipid-soluble DL-α-tocopherol to the hydrophobic microdomains formed by conformational contraction of sodium alginate and the nano-selenium interface. Subsequently, ethanol is removed by nitrogen stripping under normal pressure, causing DL-α-tocopherol to precipitate and solidify on the nano-selenium surface to form a lipid barrier layer. This barrier layer can slow down the penetration of external dissolved oxygen and moisture into the surface of selenium particles, reduce the rate of oxidation and degradation of zero-valent selenium, and ensure the content and activity of effective components of the composite powder during long-term storage.

[0053] 3. This invention employs a microporous distributor for high-shear feeding and a bottom-insertion tube feeding method, avoiding localized gelation caused by excessively high local acidity; the stripping and desolvation process is carried out at normal pressure and suitable temperature, reducing the risk of severe foaming and material slugging that easily occurs during vacuum flash evaporation, and lowering the deactivation rate of heat-sensitive components; combined with constant-volume washing filtration using an ultrafiltration membrane with a specified molecular weight cutoff, it can efficiently remove reaction byproducts such as dehydroascorbic acid and residual sodium ions, ensuring that the obtained composite powder product has high purity and good rehydration dispersibility. Attached Figure Description

[0054] Figure 1 The rheological and hydrodynamic radius distribution spectra of the system in Example 1 of the present invention under different pH conditions are shown; wherein, (a) is a steady-state shear rheological curve of apparent viscosity as a function of shear rate at an initial pH of 7.0 and a stable pH of 5.2; (b) is a full spectrum of hydrodynamic radius distribution at an initial pH of 7.0 and a stable pH of 5.2.

[0055] Figure 2 This is a comparison of the Fourier transform infrared spectra of the composite antioxidant composition and the single raw material component in this invention.

[0056] Figure 3 The figures show a comparison of the macroscopic processing stability of the examples and comparative examples; (a) shows a comparison of the irreversible gel particle filtration rejection rate of each sample system; (b) shows a comparison of the foam expansion volume ratio of each sample system in the process of removing the co-solvent.

[0057] Figure 4 This is a graph showing the evolution of the physical stability of the dispersion systems in the embodiments and comparative examples of the present invention during the testing period;

[0058] Figure 5 The above is a comparison of the in vitro antioxidant kinetics of Example 1 and Comparative Example 1 of the present invention; wherein, (a) is a kinetic curve of the scavenging rate of DPPH free radicals of the sample system changing with time; (b) is a kinetic curve of the scavenging rate of ABTS free radicals of the sample system changing with time.

[0059] Figure 6The graph shows the changes in selenite ion conversion rate under accelerated aging conditions for the examples and comparative examples. Detailed Implementation

[0060] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0061] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned (such as deionized water, sodium hydroxide, nitrogen and other conventional reagents and gases) are all commercially available analytical grade or higher grade products.

[0062] Sodium selenite has the molecular formula Na2SeO3, CAS number 10102-18-8, and its mass fraction purity is greater than or equal to 99.0 wt%.

[0063] L-Ascorbic acid has the molecular formula C6H8O6, CAS number 50-81-7, and a purity of ≥99.0 wt%.

[0064] The molecular formula of sodium alginate is (C6H7NaO6). n The CAS number is 9005-38-3. It is a random block linear copolymer polymer composed of β-D-mannuronic acid and α-L-guluronic acid linked by (1→4) glycosidic bonds. The weight-average molecular weight is between 100,000 Da and 300,000 Da. The dynamic viscosity of a 1 wt% aqueous solution at 20°C is between 200 mPa·s and 400 mPa·s.

[0065] The molecular formula of DL-α-tocopherol is C 29 H 50 O2, CAS number 10191-41-0, has a purity of ≥96.0 wt%.

[0066] The molecular formula of edible ethanol is C2H6O, the CAS number is 64-17-5, and its mass fraction purity is greater than or equal to 95.0 wt%.

[0067] Preparation Example 1:

[0068] This preparation example provides a method for preparing an aqueous reducing agent premix for reducing nano-selenium, comprising the following steps:

[0069] (1) Weigh 9.0 kg of L-ascorbic acid and add it to the mixing tank, and add 30.0 kg of deionized water;

[0070] (2) Stir mechanically at 200 r / min for 15 min at 25℃ until the solid is completely dissolved to obtain a clear aqueous reducing agent premix.

[0071] Preparation Example 2:

[0072] This preparation example provides a method for preparing an aqueous reducing agent premix for reducing nano-selenium, comprising the following steps:

[0073] (1) Weigh 7.0 kg of L-ascorbic acid and add it to the mixing tank, and add 25.0 kg of deionized water;

[0074] (2) Stir mechanically at 200 r / min for 15 min at 25℃ until the solid is completely dissolved to obtain a clear aqueous reducing agent premix.

[0075] Preparation Example 3:

[0076] This preparation example provides a method for preparing an aqueous reducing agent premix for reducing nano-selenium, comprising the following steps:

[0077] (1) Weigh 11.0 kg of L-ascorbic acid and add it to the mixing tank, and add 40.0 kg of deionized water;

[0078] (2) Stir mechanically at 200 r / min for 15 min at 25℃ until the solid is completely dissolved to obtain a clear aqueous reducing agent premix.

[0079] Preparation Example 4:

[0080] This preparation example provides a method for preparing a phase boundary protection medium premix, including the following steps:

[0081] (1) Weigh 1.25 kg of DL-α-tocopherol and add it to the mixing tank, and add 10.0 kg of edible ethanol;

[0082] (2) Stir mechanically at 150 r / min for 10 min at 25℃ until the liquid is evenly mixed to obtain the phase boundary protection medium premixed liquid.

[0083] Preparation Example 5:

[0084] This preparation example provides a method for preparing a phase boundary protection medium premix, including the following steps:

[0085] (1) Weigh 0.5 kg of DL-α-tocopherol and add it to the mixing tank, and add 5.0 kg of edible ethanol;

[0086] (2) Stir mechanically at 150 r / min for 10 min at 25℃ until the liquid is evenly mixed to obtain the phase boundary protection medium premixed liquid.

[0087] Preparation Example 6:

[0088] This preparation example provides a method for preparing a phase boundary protection medium premix, including the following steps:

[0089] (1) Weigh 2.0 kg of DL-α-tocopherol and add it to the mixing tank, and add 15.0 kg of edible ethanol;

[0090] (2) Stir mechanically at 150 r / min for 10 min at 25℃ until the liquid is evenly mixed to obtain the phase boundary protection medium premixed liquid.

[0091] Example 1:

[0092] This embodiment provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the following steps:

[0093] (1) Preparation of the polyanionic network aqueous phase: 195.0 kg of deionized water was added to a reactor equipped with a microporous bottom distributor and an anchor-type stirrer, and the jacket water temperature was adjusted to be constant at 25℃. Stirring was started, and the speed was set to 120 r / min. 3.5 kg of sodium alginate was slowly sieved in. During the dissolution process, 0.05 mol / L NaOH aqueous solution was added dropwise through a peristaltic pump to maintain the pH value of the system at 7.0. Stirring was continued for 50 min to obtain a transparent homogeneous sol.

[0094] (2) Homogeneous dispersion of selenium source: Add 2.0 kg of sodium selenite to the above sol, increase the stirring speed to 200 r / min, and continue stirring for 20 min.

[0095] (3) In-situ reduction and pH-responsive conformational change: The system temperature was controlled at 25℃. The stirring speed was increased to 350 r / min, and the aqueous reducing agent premix obtained in Preparation Example 1 was pumped into the reactor at a flow rate of 1.0 L / min through a microporous distributor extending to the tip of the stirring blade. After the addition was completed, the reaction continued for 75 min, and the overall pH value of the system smoothly decreased and stabilized at 5.2.

[0096] (4) Solvent replacement and phase boundary enrichment: Maintain a stirring speed of 350 r / min, take the phase boundary protection medium premix obtained in Preparation Example 4, and inject it into the sol system below the liquid surface through the bottom insertion tube. The feed rate is set to 1.0 L / min.

[0097] (5) Constant temperature stripping and interface solidification: After feeding is completed, adjust the jacket temperature to keep the material system at a constant temperature of 38°C. Maintain normal pressure and introduce sterile high-purity nitrogen gas through the bottom microporous distributor. Set the gas flow rate to 0.2 vvm and strip for 100 min to remove the co-solvent ethanol.

[0098] (6) Purification and molding: The stripped material is pumped into a hollow fiber ultrafiltration membrane module with a molecular weight cutoff of 3000 Da to 5000 Da, and washed with deionized water at constant volume until the conductivity of the permeate is less than or equal to 200 μS / cm. Then the retentate is sent to a centrifugal spray drying tower, the inlet air temperature is set at 145℃, the feed rate is adjusted to control the exhaust air temperature at 52℃, and the powder is collected after drying.

[0099] Example 2:

[0100] This embodiment provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the following steps:

[0101] (1) Preparation of the polyanionic network aqueous phase: 125.0 kg of deionized water was added to the above reaction vessel, and the jacket water temperature was adjusted to be constant at 20℃. The rotation speed was set to 100 r / min, and 2.0 kg of sodium alginate was slowly sieved in. During the dissolution process, 0.05 mol / L NaOH aqueous solution was added dropwise to maintain the pH value at 6.8, and the mixture was stirred continuously for 40 min to obtain a transparent homogeneous sol.

[0102] (2) Homogeneous complexation of selenium source: Add 1.0 kg sodium selenite, increase the speed to 150 r / min, and stir continuously for 15 min.

[0103] (3) In-situ reduction and pH-responsive conformational change: The system temperature was controlled at 24℃. The rotation speed was increased to 300 r / min, and the aqueous reducing agent premix obtained in Preparation Example 2 was pumped in at 0.5 L / min through the microporous distributor at the tip of the stirrer. After the addition was completed, the reaction continued for 60 min, and the overall pH value of the system decreased and stabilized at 5.0.

[0104] (4) Solvent replacement and phase boundary enrichment: Maintain a rotation speed of 300 r / min, take the phase boundary protection medium premix obtained in Preparation Example 5, inject it into the system through the bottom insertion tube, and feed rate is 0.5 L / min.

[0105] (5) Constant temperature air stripping and interface solidification: Adjust the jacket temperature to 35°C. Maintain normal pressure, introduce sterile high-purity nitrogen gas into the bottom, set the gas flow rate to 0.1 vvm, and strip for 120 min to remove the co-solvent ethanol.

[0106] (6) Purification and shaping: The material after air stripping is pumped into an ultrafiltration membrane module for washing and filtration until the conductivity of the permeate is less than or equal to 200 μS / cm. It is then sent to a centrifugal spray drying tower with an inlet air temperature of 140℃ and an outlet air temperature of 50℃. The powder is collected after drying.

[0107] Example 3:

[0108] This embodiment provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the following steps:

[0109] (1) Preparation of the polyanionic network aqueous phase: 260.0 kg of deionized water was added to the above reaction vessel, and the jacket water temperature was adjusted to be constant at 28℃. The rotation speed was set to 150 r / min, and 5.0 kg of sodium alginate was slowly sieved in. During the dissolution process, 0.05 mol / L NaOH aqueous solution was added dropwise to maintain the pH value at 7.2, and the mixture was stirred continuously for 60 min to obtain a transparent homogeneous sol.

[0110] (2) Homogeneous complexation of selenium source: Add 3.0 kg sodium selenite, increase the speed to 250 r / min, and stir continuously for 30 min.

[0111] (3) In-situ reduction and pH-responsive conformational change: The system temperature was controlled at 26℃. The rotation speed was increased to 400 r / min, and the aqueous reducing agent premix obtained in Preparation Example 3 was pumped in at 1.5 L / min through the microporous distributor at the tip of the stirrer. After the addition was completed, the reaction continued for 90 min, and the overall pH value of the system decreased and stabilized at 5.5.

[0112] (4) Solvent replacement and phase boundary enrichment: Maintain a rotation speed of 400 r / min, take the phase boundary protection medium premix obtained in Preparation Example 6, inject it into the system through the bottom insertion tube, and feed rate is 1.5 L / min.

[0113] (5) Constant temperature air stripping and interface solidification: Adjust the jacket temperature to 40℃. Maintain normal pressure, introduce sterile high-purity nitrogen into the bottom, set the air flow rate to 0.3vvm, and strip for 60min to remove the co-solvent ethanol.

[0114] (6) Purification and shaping: The material after air stripping is pumped into an ultrafiltration membrane module for washing and filtration until the conductivity of the permeate is less than or equal to 200 μS / cm. It is then sent to a centrifugal spray drying tower with an inlet air temperature of 150℃ and an outlet air temperature of 55℃. The powder is collected after drying.

[0115] Example 4:

[0116] This embodiment provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the following steps:

[0117] (1) Preparation of the polyanionic network aqueous phase: the steps are the same as in Example 1.

[0118] (2) Homogeneous complexation of selenium source: The steps are the same as in Example 1.

[0119] (3) In-situ reduction and pH-responsive conformational change: The system temperature was controlled at 25℃. The rotation speed was increased to 350 r / min, and the aqueous reducing agent premix obtained in Preparation Example 1 was pumped in at 1.5 L / min through the microporous distributor at the tip of the stirrer. After the addition was completed, the reaction was carried out for 75 min, and the overall pH value of the system decreased and stabilized at 5.2.

[0120] (4) Solvent replacement and phase boundary enrichment: Maintain a rotation speed of 350 r / min, take the phase boundary protection medium premix obtained in Preparation Example 4, inject it into the system through the bottom insertion tube, and set the feed rate to 1.5 L / min.

[0121] (5) Constant temperature air extraction and interface curing: Adjust the jacket temperature to 38℃. Introduce sterile high-purity nitrogen gas at normal pressure, set the gas flow rate to 0.3vvm, and perform air extraction for 70min.

[0122] (6) Purification and shaping: The steps are the same as in Example 1.

[0123] Example 5:

[0124] This embodiment provides a method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the following steps:

[0125] (1) Preparation of the polyanionic network aqueous phase: the steps are the same as in Example 1.

[0126] (2) Homogeneous complexation of selenium source: The steps are the same as in Example 1.

[0127] (3) In-situ reduction and pH-responsive conformational change: The system temperature was controlled at 25℃. The rotation speed was increased to 350 r / min, and the aqueous reducing agent premix obtained in Preparation Example 1 was pumped in at 0.5 L / min through the microporous distributor at the tip of the stirrer. After the addition was completed, the reaction was carried out for 75 min, and the overall pH value of the system decreased and stabilized at 5.2.

[0128] (4) Solvent replacement and phase boundary enrichment: Maintain a rotation speed of 350 r / min, take the phase boundary protection medium premix obtained in Preparation Example 4, inject it into the system through the bottom insertion tube, and set the feed rate to 0.5 L / min.

[0129] (5) Constant temperature air extraction and interface curing: Adjust the jacket temperature to 38℃. Introduce sterile high-purity nitrogen gas at normal pressure, set the gas flow rate to 0.1vvm, and perform air extraction for 110min.

[0130] (6) Purification and shaping: The steps are the same as in Example 1.

[0131] Comparative Example 1:

[0132] Compared with Example 1, the difference is that the phase boundary protection medium premixed liquid is not added in step (4) (i.e., DL-α-tocopherol and edible ethanol are not introduced, and the gas stripping and alcohol removal process in steps 4 and 5 is skipped), while the rest are the same.

[0133] Comparative Example 2:

[0134] Compared with Example 1, the difference is that the phase boundary protection medium premixed solution of Preparation Example 4 is not used in step (4). Instead, 1.25 kg of pure DL-α-tocopherol (without being dissolved in ethanol) is directly added dropwise into the reactor, and the isothermal gas stripping in step 5 is skipped. All other steps are the same.

[0135] Comparative Example 3:

[0136] Compared with Example 1, the difference is that: in step (3), the aqueous phase reducing agent premix of Example 1 is not used. Instead, 30.0 kg of deionized water is added to the reactor first to ensure that the total amount of aqueous phase composition in Comparative Example 3 is consistent with that in Example 1. Then, 9.0 kg of L-ascorbic acid powder is added directly from the top feed port of the reactor in one go, and the microporous distributor is not used for high shear zone distribution feeding. All other aspects are the same.

[0137] Comparative Example 4:

[0138] Compared with Example 1, the difference is that in step (3), while pumping in the aqueous phase reducing agent premix, 1.0 mol / L NaOH aqueous solution is continuously added dropwise through a constant pressure dropping funnel to force the overall pH value of the system to remain constant at 7.0 (i.e., not to let the pH drop to 5.2), and the rest are the same.

[0139] Comparative Example 5:

[0140] Compared with Example 1, the difference is that in step (5), sterile high-purity nitrogen is not introduced into the bottom at atmospheric pressure for constant temperature gas stripping. Instead, the reaction vessel is sealed and connected to a vacuum pump, and vacuum flash evaporation is performed to remove ethanol under reduced pressure of -0.08 MPa. The rest are the same.

[0141] Test Example 1:

[0142] This test example provides a method for testing the physicochemical processes of pH-responsive conformational transitions that occur in the system during the preparation of Example 1.

[0143] Preparation and sampling of experimental subjects: Based on the preparation process of Example 1, after completing step (2) homogeneous dispersion of the selenium source, a portion of the sol with a pH of 7.0 was extracted as the initial control sample; in step (3), as the aqueous phase reducing agent premix was pumped in, intermediate sols in the corresponding states were extracted using a pipette as test samples when the pH of the system dropped to 6.5, 6.0, 5.5 and finally stabilized at 5.2. All extracted samples were placed in a constant temperature water bath at 25℃ for 30 min to equilibrate before testing.

[0144] Apparent viscosity determination: The apparent viscosity changes of the samples at each sampling point were measured using a rotational rheometer. A coaxial cylindrical measuring system was selected, the test temperature was set to 25℃, and a constant shear rate of 10s was applied. -1 Transient tests were conducted, and the apparent viscosity values ​​of the system after stabilization were recorded. Simultaneously, for samples with pH 7.0 and pH 5.2, shear rates were measured from 0.1 s⁻¹. -1 up to 100s -1 Steady-state shear scanning was performed to record the full-spectrum rheological curves.

[0145] Hydrodynamic radius distribution determination: The microscopic size distribution of the system was determined using a dynamic light scattering instrument. Samples from various pH sampling points were taken and diluted with deionized water to a suitable range of scattered light intensity. The deionized water used for dilution was pre-adjusted to the same pH value as the corresponding sample through micro-titration to avoid conformational changes caused by the dilution process. The diluted solution was filtered through a 0.45 μm aqueous microporous membrane and then injected into a quartz cuvette. The test temperature was set at 25℃ and the scattering angle at 90 degrees. Each sample was scanned three times consecutively, and the average value was taken to obtain the average hydrodynamic radius and full-spectrum distribution curve of the sample.

[0146] The relevant test data are recorded in Table 1.

[0147] Table 1. Results of apparent viscosity and average hydrodynamic radius determination of the dispersion system under different pH conditions:

[0148] Initial comparison sample 7 318.4 146.2 intermediate test sample 6.5 312.7 141.5 intermediate test sample 6 289.1 125.8 intermediate test sample 5.5 231.6 88.3 Final stable sample 5.2 195.3 69.1

[0149] According to Table 1 and Figure 1 The measurement results show that with the continuous introduction of L-ascorbic acid into the reduction system and the progress of the reduction reaction, the pH value of the system gradually changes towards acidity, and the macroscopic rheological characteristics and microscopic dimensions of the system in Example 1 undergo regular changes. These changes occur simultaneously with changes in pH, the reduction reaction process, and the ionic environment of the system. As observed from the data in Table 1, when the pH value of the system decreases from 7.0 to 5.2, the system... -1The apparent viscosity at the shear rate decreased from 318.4 mPa·s to 195.3 mPa·s; the measured average hydrodynamic radius shrank from 146.2 nm to 69.1 nm.

[0150] Combination Figure 1 As can be seen from the steady-state rheological curve of neutron diagram (a), the pseudoplastic fluid characteristics of the system are maintained after the pH decreases, but the overall shear stress response decreases, indicating that the system has not undergone large-area intermolecular crosslinking or macroscopic irreversible gelation. Figure 1 The peak position in neutron plot (b) shifts significantly to the left and the peak width narrows.

[0151] The above test results indicate that during the smooth decrease of pH value in the system accompanying the reduction reaction, the ionization state and local ionic environment of sodium alginate molecular chains change, the degree of ionization of carboxyl groups decreases accordingly, and the electrostatic interactions within and between chains are adjusted, causing the originally extended polymer chains to gradually transform into a relatively compact conformation and form smaller, more dense mesoscopic microdomains.

[0152] Based on the synchronous changes in apparent viscosity and hydrodynamic dimensions with pH value, this process can be considered to be related to the pH-responsive conformational changes of sodium alginate.

[0153] This physicochemical phase evolution provides the necessary spatial conformational basis for the subsequent phase boundary enrichment and physical encapsulation of hydrophobic media.

[0154] Test Example 2:

[0155] This test example provides a Fourier transform infrared spectroscopy method for testing the enrichment of internal mesoscopic phase boundaries and intermolecular interactions of the composite antioxidant composition prepared in Example 1.

[0156] 1. Selection and Pretreatment of Experimental Subjects: The final composite antioxidant powder obtained in Example 1, sodium alginate powder alone, and DL-α-tocopherol alone were selected as test subjects. The powder from Example 1 and the sodium alginate powder were placed in a vacuum drying oven and dried at 40°C for 12 hours to remove free moisture. 1.5 mg of the dried solid powder and 150 mg of spectral-grade potassium bromide (KBr) powder were weighed and thoroughly ground and mixed in an agate mortar. The mixture was then placed in a tableting mold and pressed into transparent sheets under a pressure of 20 MPa. For DL-α-tocopherol, which is liquid at room temperature, a coating method was used to evenly coat it onto the surface of a blank KBr salt window to form a liquid film for testing.

[0157] 2. Spectral Data Acquisition: Transmission mode scanning was performed using a Fourier transform infrared spectrometer. The ambient temperature was set to 25℃, and the relative humidity was maintained below 30%. The instrument's scanning wavenumber range was set to 4000 cm⁻¹. -1 Up to 400cm-1 Spectral resolution of 4 cm -1 Each sample was scanned a total of 64 times, and the average spectrum was obtained. The spectrum of a blank KBr pellet or salt window was used as the background for subtraction. The infrared absorption spectra of each sample were recorded, and the wavenumbers of the characteristic absorption peaks of the main functional groups were extracted.

[0158] The relevant test data are recorded in Table 2.

[0159] Table 2. Wavenumber distribution of main characteristic absorption peaks in the Fourier transform infrared spectra of each test object:

[0160] Sodium alginate powder 3415.6 2921.3 1614.8 1032.5 DL-α-tocopherol 3473.2 2928.7, 2865.4 Characteristic absorption 1088.1 Example 1 Powder 3382.4 2925.1, 2862.9 1601.5 1034.7

[0161] According to Table 2 and Figure 2 Infrared spectroscopy results indicate that significant non-covalent interactions occurred among the components of the composite system. Figure 2 Comparison with the data in Table 2 reveals that no significant new absorption peaks exceeding the characteristic peak range of a single raw material appeared in the powder spectrum of Example 1. This suggests that no novel covalent bonds that could be clearly identified by Fourier transform infrared spectroscopy under these test conditions were formed during the compounding process, and the bonding between the components may be mainly non-covalent interactions. The original sodium alginate peak was located at 3415.6 cm⁻¹. -1 The broad OH stretching vibration peak at [location] shifted to a lower wavenumber direction to 3382.4 cm⁻¹ in the powder of Example 1. -1 (A redshift occurs), and its corresponding -COO - The asymmetric stretching vibration peak is at 1614.8 cm⁻¹. -1 Redshifted to 1601.5cm -1 The redshift in this spectral band suggests a change in the local chemical environment of the oxygen-containing groups on the sodium alginate polymer chain, indicating possible hydrogen bonding, electrostatic interactions, or other non-covalent interactions between them and other components in the system. Furthermore, the spectrum of the powder in Example 1 is at 2925.1 cm⁻¹. -1 With 2862.9cm -1 A distinct double absorption peak appeared at [location], and its peak shape and wavenumber position are similar to the characteristic absorption peak of the hydrophobic alkyl long chain of single DL-α-tocopherol (2928.7 cm⁻¹). -1 With 2865.4cm -1The results show a high degree of agreement with slight offsets. This phenomenon indicates that the powder of Example 1 retains the characteristic vibrational signals corresponding to the hydrophobic alkyl chains of DL-α-tocopherol. Combined with the shifts in the characteristic peaks of OH and -COO⁻, it can be considered that there is a certain degree of non-covalent complexation between DL-α-tocopherol and the sodium alginate network. Based on the ethanol co-solvent replacement process used in this invention, it can be inferred that DL-α-tocopherol underwent a redistribution from the continuous liquid phase to local regions of the polymer network during solvent removal, and was retained in the resulting powder in a physical complex form.

[0162] Test Example 3:

[0163] This test case provides a method for testing the stability index of fluid processing technology in each embodiment and comparative example.

[0164] Experimental subject preparation: The materials generated in the corresponding processing steps of Examples 1 to 5, as well as Comparative Examples 3 and 5, were used as test subjects.

[0165] Foam expansion volume ratio determination: During the removal of co-solvents for each sample (constant temperature gas stripping or vacuum flash evaporation), the highest dynamic liquid level reached by the gas-liquid mixture inside the system is recorded through the sight glass of the reactor. The maximum expansion volume corresponding to this highest liquid level is calculated based on the inner diameter of the reactor. This value is then divided by the initial static liquid level volume of the system before the start of the solvent removal process. The resulting ratio is recorded as the foam expansion volume ratio.

[0166] Collection of gel particle residue: After completing the purification operation or the co-solvent removal process, all materials in the reactor are pumped out using a diaphragm pump and flowed at a uniform speed through a standard stainless steel test sieve with a 100-mesh aperture. The solid material retained on the sieve is then rinsed with deionized water to remove the attached free reaction liquid, and the remaining macroscopic irreversible gel particles and flocs are collected.

[0167] Filtration rejection rate calculation: The collected solid residue was transferred to a petri dish and placed in a vacuum drying oven. It was dried at 60°C and -0.09 MPa under reduced pressure until the mass remained constant. The total mass of the dried gel was weighed using an analytical balance and compared with the mass of sodium alginate powder in the initial feed formulation. The mass percentage was calculated and recorded as the irreversible gel particle filtration rejection rate.

[0168] The relevant test data are recorded in Table 3.

[0169] Table 3. Results of macroscopic processing stability tests for each sample:

[0170] Example 1 0.42 1.15 Example 2 0.28 1.08 Example 3 0.81 1.27 Example 4 0.55 1.34 Example 5 0.36 1.11 Comparative Example 3 48.73 1.18 Comparative Example 5 0.51 4.82

[0171] According to Table 3 and Figure 3The test results show that fluid feed path distribution control and atmospheric pressure gas dynamics process can effectively ensure the stability of the processing of polyanionic network aqueous system.

[0172] Analyzing subfigure (a) and Table 3, Comparative Example 3 did not use a high-shear zone microporous distribution feeding method, but instead directly added the acidic solid reducing agent in one go, resulting in a gel particle retention rate of 48.73%. This indicates that, while maintaining a consistent overall formulation, the instantaneous low pH microenvironment created by the rapid local dissolution of the solid reducing agent, along with uneven local mass transfer, easily leads to the local aggregation and entanglement of sodium alginate segments, forming irreversible macroscopic gel particles. Examples 1 to 5, due to the use of a microporous distribution feeding method located in the high fluid shear zone at the tip of the stirring impeller, all had gel retention rates controlled below 1%, indicating that this feeding method is beneficial for reducing local concentration and pH gradients, and improving the uniformity of the reduction process and system conformational changes. Analyzing subfigure (b) and Table 3, Comparative Example 5 used conventional vacuum depressurization flash evaporation to remove the ethanol solvent, resulting in a surge in the foam expansion volume ratio to 4.82.

[0173] This indicates that performing negative pressure vaporization in an aqueous sol containing surface-active polymers will cause the system to foam rapidly or even overflow, losing its industrial operability. The atmospheric pressure bottom-blowing nitrogen isothermal gas stripping process used in Examples 1 to 5, through gas-liquid mass transfer, smoothly strips the co-solvent, and the foam expansion volume ratio does not exceed 1.40, verifying the engineering feasibility of using physical gas stripping to complete the interface kinetics curing and molding step.

[0174] Test Example 4:

[0175] This test case provides a method for testing the physical stability of a dispersed system in a rehydrated state using multiple light scattering.

[0176] Preparation of experimental subjects: The composite antioxidant composition powders prepared in Examples 1 to 5, as well as Comparative Examples 2 and 4, were used as test subjects. Each group of powders was added to deionized water and stirred at low speed with a magnetic stirrer at 25°C for 20 min to prepare a 2.0 wt% rehydrated sol system for testing.

[0177] Light scattering scanning test: Physical stability analysis was performed using a multi-stage light scattering instrument. 20 mL of each prepared rehydrated sol was poured into a flat-bottomed cylindrical glass measuring cell, ensuring a uniform liquid level and the absence of visible air bubbles. The measuring cell was placed in the instrument's testing chamber, and the testing temperature was set to a constant 25°C.

[0178] Data Acquisition and Processing: The instrument's pulsed near-infrared light source was activated at a wavelength of 880 nm. The instrument's scanning interval was set to 1 hour, with a total continuous scanning time of 48 hours. The instrument simultaneously acquired transmitted and backscattered light signals along the sample height direction to obtain the raw spectrum of backscattered light flux as a function of testing time and sample height. Based on the overall variation of backscattered light flux across the entire sample height range, the instrument system automatically calculated and output the time instability index (TSI) for each sample. The final TSI value and the maximum rate of change of backscattered light flux at the end of the testing cycle (48 hours) were extracted.

[0179] The relevant test data are recorded in Table 4.

[0180] Table 4. Results of the final instability index and the maximum rate of change of backscattered light flux for each sample dispersion system:

[0181] Example 1 0.61 1.14 Example 2 0.83 1.42 Example 3 0.77 1.58 Example 4 0.54 0.95 Example 5 0.69 1.21 Comparative Example 2 14.32 31.64 Comparative Example 4 9.85 22.17

[0182] According to Table 4 and Figure 4 The results of multiple light scattering measurements showed that, in systems without solvent displacement or pH-induced conformational changes, the macroscopic dispersion deteriorated during the testing period. Figure 4 The curve trends and data in Table 4 show that in Comparative Example 2, which used a process of directly adding lipophilic tocopherol, the TSI value of the system rapidly increased in the first 10 hours of testing, and the maximum change rate of backscattered light flux reached 31.64% after 48 hours. This indicates that pure lipophilic substances cannot overcome the high oil-water interfacial tension, and the system rapidly underwent oil droplet aggregation and separation from the macroscopic phase. In Comparative Example 4, the system was forcibly maintained at pH 7.0 by continuously adding NaOH aqueous solution during the preparation process. This kept the sodium alginate molecular chains in a relatively high ionized and extended state, which was not conducive to the formation of compact mesoscopic regions suitable for the local enrichment of lipophilic molecules. The TSI value of the system showed a steady upward trend over time, eventually exhibiting a significant decrease in dispersion stability. At the same time, continuously maintaining a neutral pH may also affect the reduction kinetics of selenite and the final state of nano-selenium formation. Therefore, this comparative example reflects the comprehensive impact of forcibly maintaining a neutral environment on the overall reaction-assembly process.

[0183] Correspondingly, in Examples 1 to 5, the TSI curves remained in a relatively flat low range (between 0.54 and 0.83) during a continuous 48-hour monitoring period, with backscattered light flux changes of less than 2%. These results indicate that the preparation process, which combines co-solvent replacement with pH-responsive network conformation adjustment during the reaction, is beneficial for improving the composite stability between the lipophilic medium and the polyanionic network, thereby significantly reducing the tendency of the rehydrated dispersion system to aggregate, stratify, and separate during storage.

[0184] Test Example 5:

[0185] This test case provides a method for testing the sustained antioxidant kinetics of the composite system in an in vitro environment.

[0186] Selection of test subjects and preparation of solutions: The composite antioxidant powder prepared in Example 1 and the powder prepared in Comparative Example 1 were selected as test subjects. Equal amounts of the powders from Example 1 and Comparative Example 1 were weighed and dissolved in degassed deionized water to prepare a sample stock solution with a mass concentration of 1.0 mg / mL, which was then placed in a light-protected environment for testing.

[0187] DPPH radical scavenging kinetics determination: 2,2-Diphenyl-1-picrylhydrazine (DPPH) powder was weighed and prepared into a 0.1 mmol / L DPPH working solution using anhydrous ethanol. 2.0 mL of the DPPH working solution and 2.0 mL of the sample stock solution were added to a test tube and quickly mixed thoroughly. The mixture was transferred to a quartz cuvette and placed in the sample chamber of a UV-Vis spectrophotometer. The test wavelength was set to 517 nm. A radical blank group and a sample background group were simultaneously set up. The radical blank group contained DPPH working solution and an equal volume of the corresponding solvent as the sample, while the sample background group contained the sample stock solution and a corresponding solvent system without DPPH, to correct for the influence of sample absorption and particle scattering on the absorbance at 517 nm. Dynamic time-scan mode was activated, with a monitoring period of 120 min and a sampling interval of 2 min, recording the absorbance changes over time. The DPPH radical scavenging rate at each time point was calculated based on the absorbance corrected for the sample background.

[0188] ABTS radical scavenging kinetics determination: A solution of 2,2'-azido-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) was mixed with a potassium persulfate solution and reacted at room temperature in the dark for 14 h to generate ABTS radical cations. The solution was diluted with deionized water to achieve an absorbance of 0.70 ± 0.05 at 734 nm, thus preparing the ABTS working solution. 2.0 mL of sample stock solution was mixed with 2.0 mL of the ABTS working solution and placed in a UV-Vis spectrophotometer, with the detection wavelength set to 734 nm. Simultaneously, an ABTS radical blank group and a sample background group were set to subtract background signals caused by sample absorption and particle scattering. A dynamic time-scan mode was activated, with a monitoring period of 120 min and a sampling interval of 2 min. Absorbance changes were recorded, and the ABTS radical scavenging rate was calculated based on the background-corrected absorbance.

[0189] Data extraction and calculation: Based on the scavenging rate data collected at various time points, a kinetic curve of free radical scavenging rate versus time was plotted. The instantaneous scavenging rate values ​​at 30 min and 120 min of reaction were extracted; simultaneously, the time required to reach half of the maximum scavenging rate was calculated based on the kinetic curve and recorded as the antioxidant reaction half-life.

[0190] The relevant test data are recorded in Table 5.

[0191] Table 5. Results of antioxidant kinetic characteristic parameter determination for Example 1 and Comparative Example 1:

[0192] Example 1 46.23 87.15 32.4 51.08 94.32 29.7 Comparative Example 1 38.71 42.54 11.8 44.25 48.16 13.5

[0193] According to Table 5 and Figure 5 The kinetic measurements showed that the introduction of DL-α-tocopherol into the aqueous network system significantly altered the overall free radical scavenging kinetics of the composite system. Through observation... Figure 5 The curve trends in neutron diagram (a) and sub-diagram (b) show that the scavenging rate of Comparative Example 1 increased rapidly within approximately 20 minutes after the start of the reaction, followed by a gradual plateau. The final scavenging rates at 120 minutes were only 42.54% (DPPH) and 48.16% (ABTS). This phenomenon indicates that, without the introduction of DL-α-tocopherol, the free radical scavenging effect of Comparative Example 1 was mainly concentrated in the early stages of the reaction, after which the increase in scavenging rate slowed significantly, and its sustained antioxidant capacity was lower than that of Example 1.

[0194] In contrast, the scavenging rate curve of Example 1 showed a continuous upward trend throughout the 120-minute monitoring period. At 120 minutes, its DPPH radical scavenging rate and ABTS radical scavenging rate reached 87.15% and 94.32%, respectively, both significantly higher than the 42.54% and 48.16% of Comparative Example 1. Based on the aforementioned composition and structural characteristics, it can be inferred that DL-α-tocopherol distributed in local regions of the composite network can provide lipid-soluble antioxidant sites, while nano-selenium and the reducing components that may be retained in the system can contribute to antioxidant activity under different reaction conditions. If detectable L-ascorbic acid is still present in the final powder, it may also participate in the reduction and regeneration process of tocopherol radicals as an electron donor. The spatial coexistence of different antioxidant components in the same composite network may form a continuous antioxidant effect across phase boundaries, thus enabling Example 1 to exhibit a more sustained free radical scavenging ability than Comparative Example 1 within the 120-minute monitoring period.

[0195] Test Example 6:

[0196] This test example provides a test method for the targeted anti-oxidation locking performance and chemical stability of various powder samples under high temperature and high humidity accelerated aging conditions.

[0197] Experimental subjects and aging environment settings: The test subjects were the powders prepared in Examples 1, 2, and 3, as well as Comparative Example 1. Each group of powder samples was spread evenly in a clean glass petri dish and placed in a constant temperature and humidity test chamber. The internal temperature of the test chamber was set to 40℃, and the relative humidity was kept constant at 75%. Accelerated aging tests were conducted continuously for a total test period of 90 days.

[0198] Periodic Sampling and Pretreatment: Quantitative sampling was performed on days 0, 15, 30, 60, and 90 of the aging cycle for each group of samples. The sampled powder at each time point was accurately weighed, and the moisture content of the corresponding sample was simultaneously determined. The equivalent of 0.5 g of dry matter was weighed and added to 50 mL of deionized water. The powder was rehydrated and dissolved using an ultrasonic cleaner for 15 min at room temperature. The rehydrated suspension was transferred to a centrifuge tube and centrifuged at 8000 rpm for 10 min. The supernatant was aspirated and passed uniformly through a 0.22 μm aqueous microporous membrane. The filtrate was collected as the sample solution for ion chromatography analysis.

[0199] Quantitative detection by ion chromatography: The concentration of selenite ions (SeO32-) in the sample solution was analyzed and detected using an ion chromatograph. The chromatographic system was equipped with an anion exchange column and a conductivity-suppressed detector. The mobile phase was a 20 mmol / L potassium hydroxide aqueous solution, the system flow rate was set to 1.0 mL / min, the column oven temperature was set to 30℃, and the single injection volume was 25 μL. A series of standard solutions with varying concentrations were prepared beforehand using analytical grade sodium selenite, and a standard working curve of retention time versus peak area of ​​selenite ions was established by injection scanning.

[0200] Conversion rate calculation: Based on the peak area output by the ion chromatogram, the mass concentration of selenite ions in each sample solution was calculated by substituting it into the standard working curve. Combining the sampling mass and dilution volume during the pretreatment process, the mass of Se(IV) present in the form of selenite in each powder sample was calculated. Simultaneously, the total selenium content in the corresponding powder sample was determined, and the percentage of Se(IV) mass to the total selenium mass under the same sampling basis was used as the relative Se(IV) content at that time point.

[0201] The relative content of Se(IV) is calculated using the following formula:

[0202] Se(IV) relative content (%) = m[Se(IV)] / m[total Se]×100%.

[0203] The relevant test data are recorded in Table 6.

[0204] Table 6. Results of selenite ion conversion rate determination for each sample during accelerated aging:

[0205] Example 1 0.14 0.48 0.95 1.76 2.54 Example 2 0.21 0.55 1.12 1.93 2.88 Example 3 0.11 0.42 0.81 1.52 2.31 Comparative Example 1 0.26 7.15 16.48 29.34 41.27

[0206] According to Table 6 and Figure 6 The relative content determination results of Se(IV) show that in the system without the introduction of the phase boundary protective medium premix, the proportion of Se(IV) in the sample increases significantly over time under high temperature and high humidity conditions, indicating that the selenium component has undergone a significant change in oxidation state. The curve trend shows that in the accelerated aging environment, the relative content of Se(IV) in the powder of Comparative Example 1 continuously increases with the extension of aging time, reaching 41.27% by day 90. Under the same test conditions, the relative content of Se(IV) in the powders of Examples 1 to 3 remains at a low level, ranging from 2.31% to 2.88% by day 90. The test results indicate that the composite system formed by introducing DL-α-tocopherol and solvent replacement can significantly reduce the rate of increase in Se(IV) content during accelerated aging. Combined with the aforementioned composite structure characterization results, it can be inferred that the local enrichment of the lipid-soluble component in the polyanionic network helps to reduce the effective contact between external oxidizing substances and the selenium component, thereby improving the chemical stability of the obtained composite powder during long-term storage.

[0207] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A nano-selenium composite antioxidant composition based on sodium alginate coating, characterized in that, Made from the following ingredients in parts by weight: Sodium alginate 2.0–5.0 parts; Sodium selenite 1.0–3.0 parts; L-Ascorbic acid 7.0–11.0 parts; DL-α-tocopherol 0.5–2.0 parts; 5.0–15.0 parts of edible ethanol; 150.0 to 300.0 parts of deionized water.

2. The nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 1, characterized in that, The weight parts of each raw material are as follows: sodium alginate 3.5 parts, sodium selenite 2.0 parts, L-ascorbic acid 9.0 parts, DL-α-tocopherol 1.25 parts, edible ethanol 10.0 parts, and deionized water 225.0 parts.

3. The nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 1, characterized in that, The sodium alginate has a weight-average molecular weight of 100,000 Da to 300,000 Da, and a dynamic viscosity of 1 wt% aqueous solution at 20°C of 200 mPa·s to 400 mPa·s; the edible ethanol has a mass percentage purity of ≥95.0 wt%.

4. The nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 1, characterized in that, The raw materials also contain sodium hydroxide, which is added in the form of a 0.05 mol / L aqueous solution to adjust the pH of the initial sodium alginate sol system to 6.8–7.

2.

5. A method for preparing a nano-selenium composite antioxidant composition based on sodium alginate coating, comprising the nano-selenium composite antioxidant composition based on sodium alginate coating according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Prepare an aqueous solution of sodium alginate, adjust the pH value to 6.8-7.2, add sodium selenite and stir evenly to obtain a homogeneous mixed sol; (2) The aqueous reducing agent premix containing L-ascorbic acid is pumped into the homogeneous mixed sol to carry out an in-situ reduction reaction. During the reaction, the pH value of the system is controlled to decrease and stabilize at 5.0 to 5.

5. (3) Inject the premixed phase boundary protection medium prepared by DL-α-tocopherol and edible ethanol into the system after the reaction in step (2) to enrich DL-α-tocopherol into the micro-regions and / or nano-selenium interfaces formed by conformational contraction of sodium alginate. (4) Sterile high-purity nitrogen gas is introduced for atmospheric pressure and constant temperature gas stripping to remove ethanol so that DL-α-tocopherol settles or solidifies at the interface; (5) The material after air stripping is subjected to ultrafiltration washing and spray drying to obtain nano-selenium composite antioxidant powder based on sodium alginate coating.

6. The method for preparing the nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 5, characterized in that, In step (2), the reducing agent premix is ​​pumped in by injecting it through a microporous distributor that extends to the high shear zone at the tip of the stirring blade. The feed rate is controlled at 0.5L / min to 1.5L / min, the reaction temperature is controlled at 20℃ to 28℃, and the reaction time is 60min to 90min.

7. The method for preparing the nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 5, characterized in that, In step (3), the phase boundary protection medium premix liquid is injected through a bottom insertion tube inserted below the liquid surface, and the feed rate is controlled to be 0.5L / min to 1.5L / min.

8. The method for preparing the nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 5, characterized in that, In step (4), the process parameters for the gas stripping process are as follows: the temperature of the constant temperature heating jacket is 35℃~40℃, the atmospheric pressure environment is maintained, the gas flow rate of sterile high-purity nitrogen gas introduced into the bottom microporous distributor is 0.1vvm~0.3vvm, and the gas stripping time is 60min~120min.

9. The method for preparing the nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 5, characterized in that, In step (5), the ultrafiltration washing uses a hollow fiber ultrafiltration membrane module with a molecular weight cutoff of 3000 Da to 5000 Da, and is washed with deionized water at constant volume until the conductivity of the permeate is less than or equal to 200 μS / cm; the inlet air temperature of the spray drying is 140℃ to 150℃, and the exhaust air temperature is 50℃ to 55℃.

10. The method for preparing the nano-selenium composite antioxidant composition based on sodium alginate coating according to claim 5, characterized in that, Before step (1), the preparation process of the aqueous reducing agent premix and the phase boundary protection medium premix also includes: Weigh out the prescribed amount of L-ascorbic acid and add it to deionized water. Stir at 200 r / min for 15 min at 25℃ until completely dissolved to obtain an aqueous reducing agent premix. Weigh out the amount of DL-α-tocopherol in the formula and add it to the amount of edible ethanol in the formula. Stir at 150 r / min for 10 min at 25℃ until the mixture is homogeneous to obtain the phase boundary protection medium premix.

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