Metal-polyphenol network modified coconut protein composite particle as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of emulsion materials, and particularly relates to metal-polyphenol network modified coconut protein composite particles as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing a coconut protein-pectin compound by taking coconut protein and pectin as raw materials, adding a tannic acid solution into the coconut protein-pectin compound, mixing, adding a Fe < 3 + > solution, and mixing to obtain metal-polyphenol network modified coconut protein composite particles; according to the preparation method, tannic acid and the coconut protein-pectin compound are subjected to non-covalent interaction, Fe < 3 + > and phenolic hydroxyl groups on the tannic acid are subjected to coordination reaction, a metal-polyphenol network is formed through cross-linking of Fe-O coordination bonds, and a compact modification layer is constructed on the surface of the coconut protein-pectin compound, so that on one hand, waste coconut protein resources are utilized; on the other hand, the problem that composite particles prepared from pectin and coconut protein are prone to depolymerization is solved, the structural stability is improved, and meanwhile iron and polyphenol are supplemented.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of emulsion materials, and in particular relates to a metal-polyphenol network modified coconut protein composite particle and a preparation method and application thereof. BACKGROUND

[0002] Coconut protein is an important tropical and subtropical plant protein, is a new source of plant protein, has good nutritional value and balanced structure, has the effects of promoting health and preventing diseases, and will not cause food allergy and has the potential to inhibit obesity. As a new plant protein, coconut protein is obtained from coconut meal, a waste after extraction of coconut oil, and is widely used in the field of plant-based food due to its rich nutritional value and unique flavor and taste. Coconut protein contains a large amount of essential amino acids for the human body, especially rich in arginine and methionine. At present, due to the instability and easy delamination of coconut protein emulsion, great inconvenience is caused to production and transportation, so the research on the protein contained in coconut is relatively less.

[0003] In the prior art, pectin and coconut protein are used to prepare composite particles, but the composite particles formed by the electrostatic interaction of coconut protein and pectin are prone to depolymerization in a neutral or acidic environment, resulting in structure collapse. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a metal-polyphenol network modified coconut protein composite particle, a preparation method and application thereof. The application first uses coconut protein and pectin as raw materials to prepare a coconut protein-pectin complex, then adds a tannic acid solution to the coconut protein-pectin complex and mixes, and then adds a Fe 3+ solution and mixes to obtain a metal-polyphenol network modified coconut protein composite particle. The application constructs a new composite system containing coconut protein, pectin, polyphenol and metal ions. Non-covalent interaction occurs between tannic acid and the coconut protein-pectin complex, Fe 3+ and the phenolic hydroxyl group on the tannic acid undergoes coordination reaction, and a metal-polyphenol network is formed through Fe-O coordination bond crosslinking to construct a dense modified layer on the surface of the coconut protein-pectin complex. On the one hand, the waste coconut protein resource is fully utilized, and on the other hand, the problem of easy depolymerization of the composite particles prepared from pectin and coconut protein is overcome, the structural stability is improved, and iron elements and polyphenols are supplemented.

[0005] Based on the above technical purposes, the application adopts the following technical solutions: The application protects the preparation method of the metal-polyphenol network modified coconut protein composite particle, which comprises the following steps: The coconut protein and the pectin are dissolved in water respectively to obtain a pectin dispersion and a coconut protein dispersion, the pectin dispersion is added into the coconut protein dispersion, and the coconut protein and the pectin are combined through electrostatic interaction to obtain a coconut protein-pectin complex.

[0006] The tannic acid and the soluble iron salt are dissolved in water respectively to obtain a tannic acid solution and an iron salt solution, the tannic acid solution is mixed with the coconut protein-pectin complex first, non-covalent interaction occurs between the tannic acid and the coconut protein-pectin complex to form a complex particle-tannic acid pre-complex, then the iron salt solution is added and mixed, Fe 3+ in the iron salt solution coordinates with the phenolic hydroxyl groups on the complex particle-tannic acid pre-complex to form a metal-polyphenol network through Fe-O coordination bond crosslinking, and a dense modification layer is constructed on the surface of the coconut protein-pectin complex to obtain a metal-polyphenol network modified coconut protein complex particle.

[0007] Preferably, the mass ratio of the coconut protein to the pectin is 1.5-2.5:1. This range balances the functionality of the coconut protein, such as water holding capacity and nutritional carrier, and the colloidal properties of the pectin, such as thickening, gelling and stabilization, to avoid imbalance of the system caused by excessive single component; if the proportion of the coconut protein is too high, i.e. the coconut protein is excessive and the pectin is insufficient, the following defects exist: a, the stability of the system decreases: if the pectin is insufficient, the coconut protein is easy to aggregate due to electrostatic repulsion imbalance, leading to delamination and precipitation of the coconut protein-pectin complex, or loose texture and formation of a gel; b, the texture and mouthfeel become poor: when the coconut protein is excessive, the coconut protein-pectin complex lacks the buffering of the pectin and is easy to form hard and rough texture; c, the gelling function is invalid: insufficient pectin will lead to insufficient strength of the coconut protein-pectin complex, which cannot be shaped or is easy to collapse, losing the proper elasticity and hardness. If the proportion of the coconut protein is too low, i.e. the coconut protein is insufficient and the pectin is excessive, the following defects exist: a, the texture is sticky or too soft: when the pectin is excessive, its strong thickening property will make the system too viscous, even forming "over-strong gelation"; b, the flavor and nutrition are weakened: low proportion will lead to weak product flavor and decreased nutritional value.

[0008] Preferably, the concentration of tannic acid in the metal-polyphenol network modified coconut protein composite particles is 18 mmol / L to 30 mmol / L. This concentration is obtained by combining the coordination balance formed by the metal-polyphenol three-dimensional network structure and the protein modification requirements. The metal-polyphenol three-dimensional network structure is denoted as MPN. The following defects exist when the tannic acid concentration is too low: a) When the concentration is too low, there is insufficient tannic acid ligand, which prevents metal ions from fully participating in coordination. The resulting MPN network is loose and has high porosity, failing to effectively encapsulate the coconut protein-pectin complex, leading to a decrease in the structural stability of the metal-polyphenol network-modified coconut protein composite particles; b) When the concentration is too low, there are insufficient binding sites between tannic acid and iron ions, resulting in a decrease in the antioxidant capacity and emulsifying properties of the metal-polyphenol network-modified coconut protein composite particles. Furthermore, coconut protein is prone to aggregation or denaturation due to the lack of MPN protection; c) The "anchoring" effect of MPN on the coconut protein-pectin complex is insufficient. During the preparation process, coconut protein is prone to forming large particles due to its own aggregation tendency. This self-aggregation tendency, such as hydrophobic interactions, results in a wide particle size distribution and poor uniformity of the metal-polyphenol network-modified coconut protein composite particles, affecting subsequent applications. Excessive tannic acid concentration has the following drawbacks: First, it forms excessive coordination bonds with iron ions and excessively binds to coconut protein, leading to overly dense MPN (polyphenol network) and even causing "bridging" aggregation between metal-polyphenol network-modified coconut protein composite particles, forming large-particle precipitates and disrupting dispersibility. Second, the highly polar phenolic hydroxyl functional groups of high-concentration tannic acid can damage the secondary and tertiary structures of coconut protein, causing denaturation and loss of its original functions, such as water retention and bioactivity, thus affecting the core performance of the metal-polyphenol network-modified coconut protein composite particles. Third, high-concentration tannic acid can non-specifically bind to other components in the system, such as cations other than iron ions, interfering with the functionality of the metal-polyphenol network-modified coconut protein composite particles.

[0009] Preferably, in the metal-polyphenol network modified coconut protein composite particles, Fe 3+ The concentration is 9 mmol / L to 15 mmol / L, which is the concentration of bound Fe. 3+ The results were obtained from the coordination chemistry of tannic acid and the structural requirements of metal-polyphenol network-modified coconut protein complex particles. (Fe) 3+ Too low a concentration has the following drawbacks: a) At too low a concentration, there are insufficient cross-linking points, resulting in a loose and incomplete MPN structure, which cannot effectively encapsulate the coconut protein-pectin complex; b) Fe 3+ Insufficient concentration leads to a large amount of tannic acid not participating in coordination, and free tannic acid will excessively bind to the coconut protein-pectin complex, causing protein aggregation, resulting in turbidity and precipitation in the system; c. When the concentration is too low, the active sites of MPN decrease, reducing the antioxidant and antibacterial effects of the metal-polyphenol network modified coconut protein complex particles. 3+a. Excessive Fe 3+ will form excessive coordination bonds with tannins, leading to excessive densification of MPN, and even causing multi-point cross-linking, which makes multiple metal-polyphenol network modified coconut protein composite particles agglomerate through Fe 3+ bridges, forming large particle size precipitates, and destroying dispersibility and uniformity; b. The metallic taste of Fe 3+ affects the sensory of the product, and high concentration of Fe 3+ reacts with other components in the system, such as vitamins and organic acids, reducing the nutritional value or stability of the product.

[0010] Preferably, the amount of coconut protein in the metal-polyphenol network modified coconut protein composite particles is 7 mg / mL to 13 mg / mL, which is determined according to the binding efficiency of MPN and coconut protein-pectin complex, and the dispersibility and structural stability of the metal-polyphenol network modified coconut protein composite particles. a. Low concentration will result in a small amount of coconut protein available for reaction in a unit volume, resulting in a small number of metal-polyphenol network modified coconut protein composite particles; b. The amount of Fe 3+ and tannins in the system is relatively high, which is easy to form a large amount of free MPN that is not combined with coconut protein-pectin complex, i.e. without protein core, resulting in a decrease in the purity of metal-polyphenol network modified coconut protein composite particles, an increase in stray structures, and interference with its functionality, such as antioxidant and emulsifying properties; c. The MPN around a single coconut protein is insufficiently supported due to the small protein core, which is easy to collapse or dissociate in stirring and centrifugation operations, resulting in a decrease in the mechanical strength of the metal-polyphenol network modified coconut protein composite particles and poor dispersibility. a. At high concentration, the hydrophobic interaction and hydrogen bonding between coconut protein molecules are enhanced, which is easy to cause spontaneous aggregation, resulting in uneven coating of MPN on a single coconut protein-pectin complex, and finally forming metal-polyphenol network modified coconut protein composite particles with wide particle size distribution and poor uniformity; b. When there is excessive coconut protein, Fe 3+ and tannins are relatively insufficient to completely coat all coconut protein-pectin complexes, and part of the coconut protein-pectin complexes are exposed, which is easy to be affected by the environment, resulting in a decrease in the stability of the metal-polyphenol network modified coconut protein composite particles. mg / mL does not refer to the volume of coconut protein-pectin complex, but the concentration of coconut protein in the dispersion system when preparing metal-polyphenol network modified coconut protein composite particles, i.e. 7 mg to 13 mg of coconut protein per milliliter of liquid medium.

[0011] Preferably, the pH of the metal-polyphenol network modified coconut protein composite particles is adjusted to 3.5-4.5 by using 0.1 mol / L sodium hydroxide solution or hydrochloric acid solution, which is obtained by combining the coordination characteristics of MPN, the stability of coconut protein and the functional requirements of the metal-polyphenol network modified coconut protein composite particles. Acidic conditions can reduce the hydrolysis of Fe 3+ , ensure stable coordination with the phenolic hydroxyl groups of tannic acid, and maintain the integrity of the MPN structure; the pH range deviates from the isoelectric point of coconut protein, which can inhibit the self-aggregation of coconut protein through moderate electrostatic repulsion, ensuring the dispersibility of the metal-polyphenol network modified coconut protein composite particles. Over-acid will destroy the structure of the phenolic hydroxyl groups of tannic acid, and over-alkali will accelerate the hydrolysis of Fe 3+ and the aggregation of coconut protein, both of which will cause the structure collapse or functional failure of the metal-polyphenol network modified coconut protein composite particles.

[0012] The application also protects a metal-polyphenol network modified coconut protein composite particle prepared by the above preparation method.

[0013] The application also protects the application of the metal-polyphenol network modified coconut protein composite particle in preparing a high internal phase emulsion.

[0014] Preferably, the high internal phase emulsion is prepared by the following steps: taking medium-chain triglyceride as the oil phase, mixing the oil phase with the metal-polyphenol network modified coconut protein composite particle to obtain the high internal phase emulsion.

[0015] Preferably, the high internal phase emulsion is used for preparing a probiotic preparation or a nutrient preparation, and the high internal phase emulsion can also be used as a saturated fatty acid substitute, a hydrogenated oil substitute and a porous material.

[0016] Among them, the probiotic preparation is obtained by loading probiotics in the high internal phase emulsion, and the nutrient preparation is obtained by loading nutrients in the high internal phase emulsion.

[0017] Compared with the prior art, the application has the following beneficial effects: 1. In the application, coconut protein and pectin are used as raw materials, a coconut protein-pectin complex is prepared first, then tannic acid solution is added to the coconut protein-pectin complex, and then Fe 3+ solution is added, mixed to obtain metal-polyphenol network modified coconut protein composite particles. In this process, the changes are: the NH3 + positive charge on the surface of the coconut protein is combined with the COO -The negative charge is strongly combined by electrostatic attraction to form a protein-pectin complex structure; after the addition of tannic acid, the tannic acid first interacts with the coconut protein-pectin complex to form a complex particle-tannic acid pre-complex, and the interaction with the coconut protein specifically includes: the phenolic hydroxyl group of tannic acid forms a hydrogen bond with the amino group and the hydroxyl group of the coconut protein, and the aromatic ring of tannic acid interacts with the hydrophobic region of the coconut protein; the interaction with pectin specifically includes: the phenolic hydroxyl group of tannic acid forms a hydrogen bond with the hydroxyl group and the carboxyl group of pectin, and because pectin is a polysaccharide chain structure, tannic acid can be combined with the pectin chain through multiple hydrogen bonds to enhance the anchoring of the coconut protein-pectin complex, and then a polyphenol adsorption layer is formed on the surface of the coconut protein-pectin complex; after the addition of iron ions, specific coordination reactions occur with the phenolic hydroxyl group of tannic acid, and a stable metal-polyphenol three-dimensional network structure is formed through Fe-O coordination bonds, and finally a dense modification layer is constructed on the surface of the coconut protein-pectin complex.

[0018] The present application defines that tannic acid solution is first added to the coconut protein-pectin complex, and then Fe 3+ solution is added. 3+ If Fe 3+ solution is first added, and then tannic acid solution is added, MPN modification will fail, and the specific reasons are as follows: a, Fe 3+ will preferentially bind to the coconut protein-pectin complex, Fe 3+ is a strong coordination ion, and MPN cannot directionally modify Fe 3+ in the iron salt, Fe 3+ will preferentially bind to the carboxyl group of pectin and the amino group of coconut protein to form a "Fe 3+ -pectin" complex or a "Fe 3+ -protein" complex, resulting in the subsequent addition of tannic acid lacking binding sites, which can only coordinate with free Fe 3+ in the solution to form free MPN small aggregates, and cannot effectively modify the surface of the coconut protein-pectin complex.

[0019] The present application defines that tannic acid solution is first added to the coconut protein-pectin complex, and then Fe 3+ solution is added. 3+ If Fe 3+ solution and tannic acid are added to the coconut protein-pectin complex at the same time, MPN will self-aggregate in the solution, and the modification layer will be uneven, and the specific reasons are as follows: the coordination reaction rate of tannic acid and Fe 3+The coordination constant of the metal ions is much higher than the non-covalent interaction between the coconut protein / pectin, and if they are added at the same time, the two will preferentially react in the solution to form a large number of free MPN nanoparticles, rather than being directionally combined on the surface of the coconut protein-pectin complex; these free MPN nanoparticles will be randomly adsorbed on the surface of the coconut protein-pectin complex, resulting in uneven thickness of the modified layer, and some coconut protein-pectin complexes being excessively wrapped, and some being completely exposed; in addition, the negative charge of the pectin will adsorb the free MPN nanoparticles through electrostatic interaction, further intensifying the local aggregation, and destroying the uniformity of the metal-polyphenol network modified coconut protein composite particles.

[0020] 2、In the metal-polyphenol network modified coconut protein composite particles of the present application, the coconut protein and the pectin form a stable composite inner core, which is the structural basis of the metal-polyphenol network modified coconut protein composite particles, the composite inner core forms a polyphenol adsorption layer with tannic acid, the tannic acid is combined with the composite inner core through non-covalent interaction, providing a reaction platform for the subsequent formation of MPN, and the metal ions are combined with the tannic acid through coordination bonds to form MPN, which is wrapped outside the composite inner core.

[0021] The pectin is combined with the coconut protein through electrostatic and hydrogen bonds, optimizing the dispersibility and hydrophilicity of the coconut protein, providing a rigid core for the metal-polyphenol network modified coconut protein composite particles, the tannic acid is anchored on the surface of the rigid core through non-covalent interaction, providing reaction sites for MPN, and the metal ions crosslink the tannic acid into a protective shell through coordination bonds.

[0022] 3、Compared with the composite particles prepared by the prior art using pectin and coconut protein, the core advantage of the metal-polyphenol network modified coconut protein composite particles of the present application lies in that the structural stability is significantly improved, the anti-aggregation ability is stronger, the performance in extreme environments is optimized, and the functionality is more diverse and rich.

[0023] 4、The present application constructs a metal-polyphenol three-dimensional network structure, polyphenols have excellent biological activity and chemical reactivity, metal-phenol networks are a kind of multipurpose supramolecular materials self-assembled by metal ions and phenolic ligands through coordination bonds, and the metal-phenol network has various properties and functions, such as photothermal effect, adhesion, pore size control, pH responsiveness, thermal stability, anti-inflammatory, antioxidant, and antibacterial beneficial properties; in the present application, the ortho-phenolic groups of tannic acid form dynamic coordination bonds with Fe 3+ to construct a three-dimensional network structure on the surface of the coconut protein-pectin complex, inhibit the dissociation of the coconut protein-pectin interface, and the pH-sensitive properties of MPN can maintain the integrity of the particles in the acidic environment of the gastrointestinal tract, avoiding premature release of drugs or functional ingredients; the core advantage lies in naturalness, multifunctionality, environmental adaptability, and processing compatibility, which can accurately solve the problems of instability of natural ingredients, easy inactivation of functional factors, and poor processing adaptability in the current food industry.

[0024] 5、The application takes coconut protein as raw material, which is cheap and easy to obtain, and expands the application range and application way of coconut protein.

[0025] 6、The coconut protein, pectin, tannic acid and iron element used in the application are edible and beneficial to human body, and the prepared metal-polyphenol network modified coconut protein composite particles are safe and non-toxic.

[0026] 7、The application also uses the metal-polyphenol network modified coconut protein composite particles to prepare high internal phase emulsion, and the preparation method is simple, and the stability of the high internal phase emulsion is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Fig. 1 is the appearance diagram, particle size diagram and potential diagram of the coconut protein dispersion liquid of Comparative Example 1, the coconut protein-pectin composite of Comparative Example 2 and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4; wherein, a diagram is the appearance diagram, b diagram is the particle size diagram, and c diagram is the potential diagram.

[0028] Figure 2 Fig. 2 is the appearance diagram, centrifugal stability diagram and oil holding capacity diagram of the high internal phase emulsion prepared by using the coconut protein dispersion liquid of Comparative Example 1, the coconut protein-pectin composite of Comparative Example 2 and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4 respectively; wherein, a diagram is the appearance diagram, b diagram is the centrifugal stability diagram, and c diagram is the oil holding capacity diagram.

[0029] Figure 3 Fig. 3 is the transmission curve diagram of the high internal phase emulsion prepared by using the coconut protein dispersion liquid of Comparative Example 1, the coconut protein-pectin composite of Comparative Example 2 and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4 respectively.

[0030] Figure 4 Fig. 4 is the stability diagram of the high internal phase emulsion prepared by using the coconut protein dispersion liquid of Comparative Example 1, the coconut protein-pectin composite of Comparative Example 2 and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4 respectively, wherein, a diagram is the integral transmittance evolution diagram with time, and b diagram is the instability index diagram.

[0031] Figure 5 Fig. 5 is the microstructure diagram and emulsion particle size diagram of the high internal phase emulsion prepared by using the coconut protein dispersion liquid of Comparative Example 1, the coconut protein-pectin composite of Comparative Example 2 and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4 respectively, wherein, a diagram is the microstructure diagram, and b diagram is the emulsion particle size diagram.

[0032] Figure 6Rheological diagrams of high internal phase emulsions prepared by using the coconut protein dispersion of Comparative Example 1, the coconut protein-pectin complex of Comparative Example 2, and the metal-polyphenol network modified coconut protein composite particles of Example 1 to Example 4, respectively, wherein a diagram is a viscosity diagram, and b diagram is a frequency scanning diagram. DETAILED DESCRIPTION

[0033] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application. The experimental methods described in the embodiments of the present application are conventional methods unless otherwise specified.

[0034] Example 1 The preparation method of the metal-polyphenol network modified coconut protein composite particle comprises the following steps: According to the mass ratio of coconut protein to pectin powder of 2:1, the coconut protein and the pectin powder are weighed and dissolved in deionized water to obtain a pectin dispersion and a coconut protein dispersion. The pectin dispersion is added to the coconut protein dispersion, and magnetic stirring is performed for 15 min to obtain a coconut protein-pectin complex. Tannic acid and FeCl3·6H2O are dissolved in deionized water to obtain a 24 mmol / L tannic acid solution and a 12 mmol / L FeCl3·6H2O solution. 0.25 mL of the tannic acid solution is first added to the coconut protein-pectin complex and stirred, and then 0.25 mL of the FeCl3·6H2O solution is added. The mixture is stirred for 15 min under dark conditions to obtain a metal-polyphenol network modified coconut protein composite particle. In the metal-polyphenol network modified coconut protein composite particle, the coconut protein is 10 mg / mL. The pH of the metal-polyphenol network modified coconut protein composite particle is adjusted to 4.0.

[0035] Example 2 The preparation method of the metal-polyphenol network modified coconut protein composite particle is the same as that of Example 1, except that in step S3, 0.5 mL of the tannic acid solution is first added to the coconut protein-pectin complex, and then 0.5 mL of the FeCl3·6H2O solution is added.

[0036] Example 3 The preparation method of the metal-polyphenol network modified coconut protein composite particle is the same as that of Example 1, except that in step S3, 0.75 mL of the tannic acid solution is first added to the coconut protein-pectin complex, and then 0.75 mL of the FeCl3·6H2O solution is added.

[0037] Example 4 The preparation method of the metal-polyphenol network modified coconut protein composite particles is the same as the preparation steps in Example 1, except that in step S3, 1 mL of tannic acid solution is first added to the coconut protein-pectin complex, followed by 1 mL of FeCl3·6H2O solution.

[0038] Example 5 The preparation method of metal-polyphenol network modified coconut protein composite particles includes the following steps: Weigh coconut protein and pectin powder at a mass ratio of 1.5:1. Dissolve the coconut protein and pectin powder separately in deionized water to obtain pectin dispersion and coconut protein dispersion, respectively. Add the pectin dispersion to the coconut protein dispersion and stir magnetically for 15 min to obtain a coconut protein-pectin complex. Dissolve tannic acid and FeCl3·6H2O separately in deionized water to obtain an 18 mmol / L tannic acid solution and a 9 mmol / L FeCl3·6H2O solution. First, add 0.25 mL of tannic acid solution to the coconut protein-pectin complex and stir, then add 0.25 mL of FeCl3·6H2O solution and stir for 15 min under light-protected conditions to obtain metal-polyphenol network modified coconut protein composite particles. The coconut protein content in the metal-polyphenol network modified coconut protein composite particles is 7 mg / mL. Adjust the pH of the metal-polyphenol network modified coconut protein composite particles to 3.5.

[0039] Example 6 The preparation method of metal-polyphenol network modified coconut protein composite particles includes the following steps: Weigh coconut protein and pectin powder at a mass ratio of 2.5:1. Dissolve the coconut protein and pectin powder separately in deionized water to obtain pectin dispersion and coconut protein dispersion, respectively. Add the pectin dispersion to the coconut protein dispersion and stir magnetically for 15 min to obtain a coconut protein-pectin complex. Dissolve tannic acid and FeCl3·6H2O separately in deionized water to obtain a 30 mmol / L tannic acid solution and a 15 mmol / L FeCl3·6H2O solution. First, add 0.25 mL of tannic acid solution to the coconut protein-pectin complex and stir, then add 0.25 mL of FeCl3·6H2O solution and stir for 15 min under light-protected conditions to obtain metal-polyphenol network modified coconut protein composite particles. The coconut protein content in the metal-polyphenol network modified coconut protein composite particles is 13 mg / mL. Adjust the pH of the metal-polyphenol network modified coconut protein composite particles to 4.5.

[0040] Comparative Example 1 The preparation method of coconut protein dispersion includes the following steps: Dissolve 1g of coconut protein in deionized water and stir magnetically for 4 hours to obtain a 10mg / mL coconut protein dispersion, which is then stored in a refrigerator at 4°C.

[0041] Comparative Example 2 The method for preparing coconut protein-pectin complex includes the following steps: Coconut protein and pectin powder were dissolved separately in deionized water to obtain pectin dispersion and coconut protein dispersion. The pectin dispersion was added to the coconut protein dispersion and magnetically stirred to obtain a coconut protein-pectin complex. The mass ratio of coconut protein to pectin powder was 2:1, and the coconut protein in the coconut protein-pectin complex was 10 mg / mL.

[0042] The following comparative study uses the metal-polyphenol network modified coconut protein composite particles of Examples 1-4 as examples, with the coconut protein dispersion of Comparative Example 1 and the coconut protein-pectin complex of Comparative Example 2 as controls. The specific research methods and results are as follows: 0. Determination of the structure of metal-polyphenol network modified coconut protein composite particles: (1) Appearance: Coconut protein dispersion, coconut protein-pectin complex, and products containing different concentrations of tannic acid and Fe were prepared under pH 4 conditions. 3+ Appearance of the metal-polyphenol network modified coconut protein complex particles.

[0043] (2) Particle size and potential diagram: The metal-polyphenol network modified coconut protein composite particles of Examples 1 to 4, the coconut protein dispersion of Comparative Example 1 and the coconut protein-pectin complex of Comparative Example 2 were measured using a nanoparticle size analyzer.

[0044] 1. Determination of stability of emulsions with high internal phase: (1) Appearance of high internal phase emulsion: Coconut protein dispersion, coconut protein-pectin complex and four metal-polyphenol network modified coconut protein composite particles were prepared under pH 4. Taking the above samples as examples, 7.5 mL of medium-chain triglycerides was added to 2.5 mL of different samples as the oil phase, and then homogenized at 12000 rpm for 1 min using a high-speed shearing device. The gel formation was evaluated using the inverted tube method.

[0045] (2) Determination of centrifugal stability and oil holding capacity: The high internal phase emulsion sample was placed in a 50 mL centrifuge tube and centrifuged at 4 °C for 30 min under a centrifugal force of 10000 g. The centrifuge tube was then removed and the data was recorded. Its binding capacity with oil was analyzed. Specifically, the mass of the sample before centrifugation was weighed, the upper layer of oil of the sample after centrifugation was removed, and the sample was weighed again.

[0046] (3) Determination of centrifugal stability: The centrifugal stability of the high internal phase emulsion was measured using a centrifugal stability analyzer. The experimental conditions were: 25℃, 4000rpm, 870nm transmission wavelength, and 50min centrifugation time.

[0047] (4) Microstructure and particle size determination of high internal phase emulsion: Take 10 μL of sample and place it on a glass slide, then cover it with a coverslip. Observe the microstructure of the sample using an optical microscope at a magnification of 10x. Calculate the particle size using Nano Measurer software.

[0048] (5) Rheological determination: The rheological properties of the high internal phase emulsion were evaluated using a multifunctional rheometer at 0.1 s⁻¹. -1 ~100s -1 Viscosity tests were performed within the shear rate range, frequency scanning was conducted within the range of 0.1 Hz to 10 Hz, and strain was maintained at a fixed frequency of 1 Hz at 0.5%.

[0049] Data Analysis: Figure 1 The images show the appearance, particle size distribution, and potential diagrams of the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. In Comparative Example 2, the particle size significantly decreased compared to the coconut protein dispersion of Comparative Example 1 after the addition of pectin. This is because the net charge increased after adding pectin, generating electrostatic repulsion between polymers, preventing coconut protein molecules from aggregating, thus resulting in smaller coconut protein-pectin complex particles. Furthermore, Examples 1-4 revealed that in the coconut protein-pectin complex, when tannic acid and Fe... 3+ With increasing concentration, the average particle size of the metal-polyphenol network modified coconut protein composite particles in Examples 1-4 all increased, possibly due to different amounts of tannic acid and Fe. 3+ Coordination bonds exist between them, resulting in the larger size of the metal-polyphenol network-modified coconut protein complex particles compared to the coconut protein-pectin complex. This is due to the presence of tannic acid and Fe... 3+ With increasing concentration, the potential of the metal-polyphenol network-modified coconut protein composite particles in Examples 1-3 all increased. This is because the negative charge of tannic acid caused a slight increase in the absolute value of the potential. However, the potential of the metal-polyphenol network-modified coconut protein composite particles in Example 4 decreased, indicating that excessive Fe... 3+ It binds to the negatively charged coconut protein-pectin complex through electrostatic interactions.

[0050] Figure 2The images show the appearance of high internal phase emulsions prepared using the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. The high internal phase emulsions were prepared according to the following steps: 7.5 mL of medium-chain triglycerides was added as the oil phase to 2.5 mL of each sample, and then homogenized at 12000 rpm for 1 min using a high-speed shearing device to obtain the high internal phase emulsion. The formation of the high internal phase emulsion was then evaluated using the inverted tube method. It is clearly seen from the images that the coconut protein dispersion of Comparative Example 1 and the coconut protein-pectin complex of Comparative Example 2 flowed after inversion and were unstable. In Examples 1-4, the metal-polyphenol network modified coconut protein composite particles could stably form high internal phase emulsions. Centrifugal stability was evaluated for the high internal phase emulsions prepared using the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. All samples separated into three layers: an oil phase, a cream layer, and an aqueous phase, with the oil phase at the top, the cream layer in the middle, and the aqueous phase at the bottom. Comparative Examples 1 and 2 appeared to have a larger oil phase. In Examples 1-4, tannic acid and Fe... 3+ After modifying the coconut protein-pectin complex, with the addition of tannins and Fe... 3+ With increasing concentration, the oil phase after centrifugation decreased significantly, and the oil holding capacity increased accordingly. This indicates that the use of tannic acid-Fe 3+ Modifying the coconut protein-pectin complex helps to form a robust high-internal-phase emulsion.

[0051] Figure 3 and Figure 4 The figures show the centrifugal stability evaluation of the high internal phase emulsions prepared using the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. The results indicate that the coconut protein dispersion of Comparative Example 1 and the coconut protein-pectin complex of Comparative Example 2 exhibited high transport curves and instability indices after centrifugation, indicating significant instability. In the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, with the increase of tannic acid and Fe... 3+ The increase in concentration, coupled with a lower transport curve and instability index, indicates increasing stability.

[0052] Figure 5These are optical micrographs of high internal phase emulsions prepared using the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. In Comparative Example 1, the emulsion droplets formed by the coconut protein exhibit collapse and obvious aggregation; in Comparative Example 2, the droplets formed by the coconut protein-pectin complex are larger; in Examples 1-4, with the increase of tannic acid-Fe... 3+ With increasing concentration, the high internal phase emulsion structure becomes more complete. The particle size distribution diagram of the high internal phase emulsion shows that the droplets are more uniform, smaller in size, and without obvious aggregation, indicating that tannic acid-Fe 3+ The addition of [a specific ingredient] can significantly improve the stability of high internal phase emulsions. This is because the phenolic groups in tannic acid react with Fe [a specific ingredient]. 3+ This is caused by non-covalent interactions between them.

[0053] Figure 6 This is an evaluation graph showing the viscosity and frequency sweep of high internal phase emulsions prepared using the metal-polyphenol network modified coconut protein composite particles of Examples 1-4, the coconut protein dispersion of Comparative Example 1, and the coconut protein-pectin complex of Comparative Example 2. Compared with Comparative Example 1 and Comparative Example 2, the tannic acid-Fe... 3+ After modification of the coconut protein-pectin complex, the stable high internal phase emulsion viscosity, G' and G" are both higher, and with the increase of tannic acid-Fe 3+ The viscosity increases with increasing concentration because the droplet size of the high internal phase emulsion stabilized by the metal-polyphenol network modified coconut protein composite particles is smaller; the metal-polyphenol network modified coconut protein composite particles form coordination crosslinks at the oil-water interface, which increases the viscosity.

[0054] The preparation of the metal-polyphenol network modified coconut protein composite particles of the present invention has broad application prospects in improving the processing stability of coconut protein.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing metal-polyphenol network modified coconut protein composite particles, characterized in that, Includes the following steps: Coconut protein and pectin are dissolved separately in water, and then the two are mixed. The coconut protein and pectin combine through electrostatic interaction to obtain a coconut protein-pectin complex. Tannic acid and soluble iron salts were dissolved in water separately to obtain tannic acid solution and iron salt solution, respectively. First, the tannic acid solution was mixed with a coconut protein-pectin complex. The tannic acid and the coconut protein-pectin complex underwent non-covalent interactions to form a composite particle-tannic acid pre-complex. Then, the iron salt solution was added and mixed. The Fe in the iron salt solution... 3+ The phenolic hydroxyl groups on the composite particles-tannic acid precomplex undergo a coordination reaction, crosslinking through Fe-O coordination bonds to form a metal-polyphenol network, and a modification layer is constructed on the surface of the coconut protein-pectin complex to obtain metal-polyphenol network modified coconut protein composite particles.

2. The method for preparing metal-polyphenol network modified coconut protein composite particles according to claim 1, characterized in that, The mass ratio of coconut protein to pectin is 1.5~2.5:

1.

3. The method for preparing metal-polyphenol network modified coconut protein composite particles according to claim 1, characterized in that, In the metal-polyphenol network modified coconut protein composite particles, the concentration of tannic acid was 18 mmol / L to 30 mmol / L.

4. The method for preparing metal-polyphenol network modified coconut protein composite particles according to claim 1, characterized in that, In metal-polyphenol network modified coconut protein complex particles, Fe 3+ The concentration ranges from 9 mmol / L to 15 mmol / L.

5. The method for preparing metal-polyphenol network modified coconut protein composite particles according to claim 1, characterized in that, In the metal-polyphenol network modified coconut protein composite particles, the amount of coconut protein is 7 mg / mL to 13 mg / mL.

6. The method for preparing metal-polyphenol network modified coconut protein composite particles according to claim 1, characterized in that, Adjust the pH of the metal-polyphenol network-modified coconut protein complex particles to 3.5-4.

5.

7. A metal-polyphenol network modified coconut protein composite particle, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the metal-polyphenol network modified coconut protein composite particles according to claim 7 in the preparation of high internal phase emulsions.

9. The application according to claim 8, characterized in that, High internal phase emulsions are prepared according to the following steps: Using medium-chain triglycerides as the oil phase, the oil phase was mixed with coconut protein composite particles modified by a metal-polyphenol network to obtain a high internal phase emulsion.

10. The application according to claim 8, characterized in that, High internal phase emulsions are used to prepare probiotic preparations or nutrient preparations, and they can also be used as substitutes for saturated fatty acids, hydrogenated oils, and porous materials. Among them, the probiotic preparation is a preparation obtained by loading probiotics into a high internal phase emulsion, and the nutrient preparation is a preparation obtained by loading nutrients into a high internal phase emulsion.

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