Lactoferrin-procyanidine-carrageenan ternary gel as well as preparation method and application thereof

Abstract

The embodiment of the invention discloses lactoferrin-procyanidine-carrageenan ternary gel as well as a preparation method and application thereof. The method comprises the following steps: mixing a lactoferrin aqueous solution and a procyanidine aqueous solution, uniformly mixing the obtained mixed solution under a dark condition to obtain a compound solution of lactoferrin and procyanidine, and then adding carrageenan under a stirring condition to obtain the lactoferrin-procyanidine-carrageenan ternary gel. Ternary gel is formed in a self-assembly mode under the normal temperature condition, the gel has excellent oxidation resistance and membrane stability, contact between cheese and oxygen is reduced to a great extent, the fat oxidation process is effectively delayed, then the purpose of improving the nutritional quality of dairy products is achieved, and good application prospects are achieved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of food processing, and particularly to a lactoferrin-proanthocyanidin-carrageenan ternary gel, its preparation method and application. Background Art

[0002] Cheese is one of the popular dairy products, with the characteristics of high moisture and high fat content. The high moisture content makes cheese vulnerable to microbial contamination, while the high fat content causes it to easily undergo oxidative deterioration during storage and processing. The products generated by the fat oxidation reaction, on the one hand, will cause the flavor of cheese to become worse, the color to become dull, and the texture to become hard, seriously affecting the sensory quality and nutritional value of cheese; on the other hand, the lipid and protein oxidation products generated during the oxidation process may pose potential hazards to human health.

[0003] The existing technologies mainly focus on using edible films (such as chitosan-based) packaging or adding natural preservatives to inhibit the growth and reproduction of microorganisms in cheese. However, most of these technologies mainly control microbial spoilage and pay less attention to the oxidation index of cheese. Although there are currently various antioxidants that can achieve the purpose of food antioxidant, most of the highly efficient natural antioxidants (such as polyphenols, flavonoids, etc.) are water-soluble, and this characteristic limits their application in high-fat foods (such as cheese). Therefore, developing a suitable antioxidant carrier is crucial for ensuring the stability of antioxidants and their applicability in high-fat foods.

[0004] CN118872838A discloses a preparation method of a ternary composite gel, which uses soy protein isolate and tannic acid as raw materials to prepare a protein-polyphenol binary complex, heats it to 60 °C, and adds carrageenan powder to obtain a protein-polyphenol-carrageenan ternary composite gel. It is found that the antioxidant property and film stability of this ternary composite gel are poor, and this gel system needs to be formed under heating conditions, and the process is relatively complex. Summary of the Invention

[0005] Therefore, the embodiments of the present invention provide a lactoferrin-proanthocyanidin-carrageenan ternary gel, its preparation method and application. The present invention forms a ternary gel by self-assembly under normal temperature conditions. This gel system has excellent antioxidant property and film stability, greatly reduces the contact between cheese and oxygen, effectively delays the fat oxidation process, and thus achieves the purpose of improving the nutritional quality of dairy products.

[0006] To achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0007] According to the first aspect of the embodiments of the present invention, the present invention provides a preparation method of a lactoferrin-proanthocyanidin-carrageenan ternary gel, the method comprising:

[0008] Mix the lactoferrin aqueous solution with the proanthocyanidin aqueous solution, and mix the obtained mixture evenly under light-shielded conditions to obtain a composite solution of lactoferrin and proanthocyanidin. Then, add carrageenan under stirring conditions to obtain the lactoferrin-proanthocyanidin-carrageenan ternary gel.

[0009] Furthermore, the pH value of the lactoferrin aqueous solution is 7.0;

[0010] In the mixture, the concentration of lactoferrin is 0.18 - 0.22 w / v%, and the concentration of proanthocyanidin is 0.01 - 0.05 w / v%;

[0011] The mixing conditions are: 25 - 30 °C.

[0012] Furthermore, the addition amount of carrageenan is 0.8% - 1.4 w / v%;

[0013] The carrageenan is κ-carrageenan;

[0014] The temperature of the stirring is 25 - 30 °C.

[0015] Furthermore, in the composite solution, the concentration of lactoferrin is 0.2 w / v%, and the concentration of proanthocyanidin is 0.03 w / v%; the addition amount of carrageenan is 1 w / v%.

[0016] Furthermore, the preparation method of the lactoferrin aqueous solution is as follows:

[0017] Add lactoferrin powder to deionized water, stir at 300 - 500 rpm for 1.5 - 3 hours, then let it stand at 1 - 6 °C for 8 - 16 hours, restore to room temperature, and adjust the pH value of the system to 7.0 with NaOH.

[0018] According to the second aspect of the embodiments of the present invention, the present invention provides a lactoferrin-proanthocyanidin-carrageenan ternary gel, which is prepared by the method described in any one of the above.

[0019] According to the third aspect of the embodiments of the present invention, the present invention provides the application of the above-mentioned lactoferrin-proanthocyanidin-carrageenan ternary gel in the preparation of high-fat solid foods.

[0020] Furthermore, the high-fat solid food is cheese.

[0021] The embodiments of the present invention have the following advantages:

[0022] (1) The present invention uses lactoferrin, proanthocyanidin, and carrageenan as raw materials to form a ternary gel through self-assembly under normal temperature conditions. This ternary gel has excellent antioxidant properties and membrane stability.

[0023] (2) The ternary gel of the present invention acts on high-fat solid foods by means of coating. Among them, lactoferrin is adsorbed on the surface of fat globules in the emulsified food system as an emulsifier; proanthocyanidins are enriched at the oil-water interface as inclusions (embedded substances) and preferentially scavenge free radicals in lipid oxidation reactions; carrageenan forms a viscoelastic interfacial film to reduce oxygen penetration. The three act synergistically to improve the oxidative stability of the food.

[0024] (3) In order to maintain its excellent quality and nutritional value, and to ensure food safety, the present invention uses the method of gel coating to inhibit the fat oxidation in cheese. Lactoferrin molecules have good emulsifying properties and a certain binding ability with proanthocyanidins, so it can be used as a carrier of a good antioxidant. And carrageenan helps proteins and bioactive substances form a gel system, making it have spreadability and uniformity. Gel coating can form a protective film to reduce the contact between cheese and oxygen, thereby delaying the fat oxidation process.

[0025] (4) The coating composition of the present invention contains lactoferrin and proanthocyanidins, and can also achieve the purpose of enhancing the nutrition and functionality of cheese and improving the nutritional quality of dairy products.

[0026] (5) The present invention does not use any organic solvents, which reduces the production cost. The ingredients used are all food-grade, improving food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0028] Figure 1 Photographs of physical objects of the system provided by the present invention with different polysaccharides added. The polysaccharides added from left to right are pullulan, lactose, gum arabic, maltodextrin and carrageenan;

[0029] Figure 2 Results of the effect of κC concentration on the rheological properties of the ternary gel provided by the present invention, a: dynamic viscoelasticity; b: static rheology;

[0030] Figure 3 Results of the effect of PC concentration on the rheological properties of the ternary gel provided by the present invention, a: dynamic viscoelasticity; b: static rheology;

[0031] Figure 4 Results of the effect of pH on the rheological properties of the ternary gel provided by the present invention, a: dynamic viscoelasticity; b: static rheology;

[0032] Figure 5 This is a physical photo of the lactoferrin-procyanidin-carrageenan ternary gel provided by the present invention;

[0033] Figure 6 This is a scanning electron micrograph of the lactoferrin-procyanidin-carrageenan ternary gel provided by the present invention. a: 0.02% LF; b: 0.02% LF - 0.03% P; c: 1% κC; d: 0.02% LF - 0.01% PC - 1% κC; e: 0.02% LF - 0.03% PC - 1% κC; f: 0.02% LF - 0.05% PC - 1% κC;

[0034] Figure 7 This is the test result of the interaction force (Fourier transform infrared spectrum) between the components provided by the present invention;

[0035] Figure 8 This is the ultraviolet spectrum of the interaction between carrageenan and Fe 3+ in the present invention.

[0036] Figure 9 This is a schematic diagram of the self-assembly principle of the lactoferrin-procyanidin-carrageenan ternary gel provided by the present invention;

[0037] Figure 10 This is the test result of the oxidative stability (peroxide value) of the cheese during storage provided by the present invention. Detailed implementation manners

[0038] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0039] Pullulan: Beijing Solarbio Science & Technology Co., Ltd.;

[0040] Lactose: Shanghai Macklin Biochemical Co., Ltd.;

[0041] Gum arabic: Beijing Solarbio Science & Technology Co., Ltd.;

[0042] Maltodextrin: Beijing Solarbio Science & Technology Co., Ltd.;

[0043] κ-carrageenan: Beijing Solarbio Science & Technology Co., Ltd.;

[0044] Lactoferrin: Shanghai Macklin Biochemical Co., Ltd.;

[0045] Procyanidins: purity 95%, Nanjing Herb Origin Biotechnology Co., Ltd.

[0046] Example 1

[0047] Preparation method of lactoferrin-procyanidin-carrageenan ternary gel

[0048] Step 1. Preparation of lactoferrin (LF) stock solution

[0049] Accurately weigh 0.25 g of lactoferrin powder and moisten it with an appropriate amount of deionized water, then make up the volume of lactoferrin powder to 25 mL with deionized water, stir with a magnetic stirrer (400 rpm) for 2 hours to fully dissolve it, and place the stirred solution in a refrigerator at 4 °C for 12 hours to promote its full hydration. After taking it out and restoring it to room temperature, adjust the pH of the system to 5 - 9 with HCl or NaOH to obtain a 1% (w / v) LF stock solution for standby.

[0050] Step 2. Preparation of procyanidin (PC) stock solution

[0051] Make up the volume of 0.02 g of procyanidin powder to 20 mL with deionized water, stir with a magnetic stirrer (400 rpm) for 2 hours to fully dissolve it, and obtain a 0.1% (w / v) PC stock solution for standby.

[0052] Step 3. Preparation of lactoferrin-procyanidin complex solution (LF-PC)

[0053] Mix the lactoferrin stock solution prepared in Step 1 with the procyanidin stock solution prepared in Step 2, and stir it in the dark at 25 °C for 30 min to fully mix it, obtaining a series of lactoferrin-procyanidin complex solutions, in which the concentration of lactoferrin is 0.2% (w / v), and the concentrations of procyanidin are 0.01% (w / v), 0.02% (w / v), 0.03% (w / v), 0.04% (w / v), 0.05% (w / v) respectively. The above complex solution is denoted as 0.2% LF-(0.01 - 0.05)% PC.

[0054] Step 4. Preparation of lactoferrin-procyanidin-carrageenan ternary gel (LF-PC-κC)

[0055] The composite solution of lactoferrin and procyanidins prepared in Step 3 was placed on a magnetic stirrer (400 rpm), and κ-carrageenan powder (κC) was added during the stirring process (25 °C) to obtain a ternary gel of lactoferrin-procyanidin-carrageenan. Among them, the concentrations of κC were 0.6% (w / v), 0.8% (w / v), 1% (w / v), 1.2% (w / v), and 1.4% (w / v), respectively. The above ternary gel was denoted as 0.2% LF-(0.01 - 0.05)% PC-(0.6 - 1.4)% κC.

[0056] Test Example 1

[0057] 1. Influence of different polysaccharides on gel formation

[0058] The composite solution 0.2% LF - 0.03% PC prepared in Step 3 of Example 1 was placed on a magnetic stirrer (400 rpm). During the stirring process (25 °C), pullulan, lactose, gum arabic, maltodextrin, and κ-carrageenan were added respectively, and the polysaccharide concentration in the final system was controlled to be 1.0 w / v%. Figure 1 It was shown that pullulan, lactose, gum arabic, and maltodextrin could not form a solid-like gel and were not suitable for the coating treatment of solid foods. Therefore, carrageenan was selected as the polysaccharide in the present invention.

[0059] 2. Rheological properties

[0060] Dynamic viscoelasticity test method: After equilibrating the sample at room temperature for 30 min, it was placed on the stage of the rheometer. A parallel plate with a diameter of 50 mm was selected, and the parameters were set as follows: oscillation - frequency, slit 1 mm, temperature 25 °C, stress 1%. The storage modulus and loss modulus of the sample were measured in the range of angular frequency from 0.1 - 100 rad / s.

[0061] Static rheology test method: After equilibrating the sample at room temperature for 30 min, it was placed on the stage of the rheometer. A parallel plate with a diameter of 50 mm was selected, and the parameters were set as: slit 1 mm, shear rate from 0 - 1000 s -1 .

[0062] Under the conditions that the LF concentration in the composite solution LF - PC was 0.2%, the PC concentration was 0.03%, and the pH of the lactoferrin stock solution was 7, the influence of the κC concentration on the dynamic viscoelasticity and static rheology of the ternary gel was investigated. The results are shown in Figure 2 .

[0063] Under the conditions that the LF concentration in the ternary gel was 0.2%, the κC concentration was 1%, and the pH of the lactoferrin stock solution was 7, the influence of the PC concentration on the dynamic viscoelasticity and static rheology of the ternary gel was investigated. The results are shown in Figure 3 .

[0064] Under the conditions that the concentration of LF is 0.2%, the concentration of PC is 0.03%, and the concentration of κC is 1% in the ternary gel, the effects of the pH of the lactoferrin stock solution on the dynamic viscoelasticity and static rheology of the ternary gel were investigated. The results are shown in Figure 4 .

[0065] The results showed that when the concentration of κC in the system was above 1%, G’ was always greater than G”, indicating that a structure similar to a solid gel appeared in LF-PC-κC.

[0066] The apparent viscosity of the ternary gel decreased with the increase of the shear rate, indicating shear thinning. The viscosity increased with the increase of the κC concentration and the PC concentration, indicating that the intermolecular interaction gradually enhanced.

[0067] With the increase of pH, the viscosity first increased and then decreased. This may be because when the pH was 9, lactoferrin was close to the isoelectric point and its binding ability to carrageenan became weak. When the pH was 7, the rheology of the gel reached the peak. Therefore, pH 7 was selected as the optimal pH condition for gel formation.

[0068] Under the conditions that the concentration of LF was 0.2% and the concentration of PC was 0.03% in the composite liquid LF-PC, and the pH of the lactoferrin stock solution was 7, the appearance photos of the ternary gels prepared with κC concentrations of 0.6%, 0.8%, 1.0%, 1.2%, and 1.4% are shown in Figure 5 . The results showed that when the κC concentration was greater than 0.8%, a quasi-solid gel could basically be formed, thus meeting the coating requirements of solid foods. Preferably, the κC concentration was greater than 1%.

[0069] 3. Scanning electron microscopy test (SEM)

[0070] Scanning electron microscopy tests were carried out on 0.02% LF, 0.02% LF-0.03% PC, 1% κC, 0.02% LF-0.01% PC-1% κC, 0.02% LF-0.03% PC-1% κC, and 0.02% LF-0.05% PC-1% κC. The results are shown in Figure 6 . The results showed that single lactoferrin (LF) and 0.02% LF-0.03% PC could not form a porous structure ( Figure 6 a, 6b); although single carrageenan could form a network structure, it was relatively loose and had a large pore size ( Figure 6 c). After combining LF, PC, and κC, the pore distribution area decreased; compared with single κC, LF-PC-κC formed a ternary gel with a dense network and stable interconnectivity, enhancing the stability of the system. Among them, under the condition that the contents of LF and κC were the same, 0.02% LF-0.03% PC-1% κC had the highest density ( Figure 6d, 6e, 6f). Therefore, the present invention selects 0.03% as the optimal addition concentration of PC.

[0071] 4. Interaction among ternary gel components (Fourier transform infrared spectroscopy)

[0072] Freeze-dry 0.2% LF, 0.03% PC, 0.2% LF - 0.03% PC, 0.2% LF - 0.01% PC - 1% κC, 0.2% LF - 0.03% PC - 1% κC, 0.2% LF - 0.05% PC - 1% κC into powders, mix them with KBr at a volume ratio of 1:100 to make thin slices. Scan the sample thin slices with a Fourier transform infrared spectrometer in the range of 4000 cm -1 -400 cm -1 Set the number of scans: 64, resolution: 4 cm -1 .

[0073] The infrared spectroscopy detection results of LF, PC and LF-PC are shown in Figure 7 a. The results show that PC presents three characteristic peaks at 3374 cm -1 , 1614 cm -1 , 1519 cm -1 . However, the above three characteristic peaks are not seen in LF-PC. This may be due to the interaction between procyanidin (PC) and lactoferrin (LF), resulting in the merging or overlapping of absorption bands. This result proves the formation of the complex. Further analysis finds that compared with LF alone, no absorption bands related to the vibration of new chemical bonds appear in the complex LF-PC. The above results indicate that the interaction between LF and PC is achieved through non-covalent bonds.

[0074] The infrared spectroscopy detection results of LF-PC-κC are shown in Figure 7 b. The results show that in the amide I band (1600 cm -1 -1700 cm -1 ) and amide II band (1500 cm -1 -1600 cm -1 ), the ternary complex presents characteristic peaks similar to those of LF-PC. Moreover, the spectral characteristics of the ternary complex are highly similar to those of κC, indicating that there is no new chemical bond between κC and LF-PC, and the two are combined through non-covalent interactions. The above content shows that both LF and PC, and κC and LF-PC interact with each other in the form of non-covalent bonds.

[0075] 5. Interaction between carrageenan and Fe 3+ Interaction

[0076] During the self-assembly process to form a gel, it is speculated that there is a chelation effect between the iron ions in lactoferrin and carrageenan. This chelation effect may promote the binding of lactoferrin and carrageenan, thereby forming a more stable structure. To verify this hypothesis, an aqueous solution of carrageenan with a concentration of 0.1% (w / v) was mixed with an aqueous solution of FeCl3 with a concentration of 50 mM in equal volumes, and ultraviolet spectral scanning was carried out. From Figure 8 it can be seen that no absorption peak appears for pure κC within the detection range, and there are two absorption peaks for pure Fe 3+ in the wavelength range of 300 - 500 nm. However, the ultraviolet spectrum of κC-Fe shows an obvious blue shift, which is because the hydroxyl groups in the carrageenan molecule coordinate with Fe 3+ . The above results indicate that carrageenan can chelate with Fe 3+ , thereby enhancing the stability of the gel.

[0077] The schematic diagram of the self-assembly principle of the lactoferrin-procyanidin-carrageenan ternary gel of the present invention is shown in Figure 9 . Lactoferrin and procyanidin bind through hydrophobic interaction and hydrogen bonds. Lactoferrin and carrageenan spontaneously bind through electrostatic adsorption (system pH = 7. Under this condition, lactoferrin is positively charged and carrageenan contains a large amount of sulfate ester groups and is negatively charged). In addition, there are iron ions in lactoferrin, so carrageenan can chelate with iron ions and participate in metal ion bridging, enhancing the stability of the complex.

[0078] 6. Antioxidant property detection

[0079] The antioxidant property detection was carried out by the DPPH free radical scavenging and ABTS free radical scavenging rate methods. The specific content is as follows:

[0080] DPPH method: A DPPH solution with a concentration of 0.2 mM was prepared with absolute ethanol. 1 mL of the sample solution was fully mixed with 1 mL of the DPPH solution and reacted in the dark for 30 min. Subsequently, the absorbance of the mixture at 517 nm was measured using a microplate reader.

[0081] DPPH free radical scavenging rate (%) = [1 - (A1 - A2) / A0] × 100%

[0082] In the formula, A1 is the absorbance of DPPH and the sample, A2 is the absorbance of ethanol and the sample, and A0 is the absorbance of DPPH and water.

[0083] ABTS method: Mix a 7 mM ABTS solution and a 2.45 mM potassium persulfate solution in a volume ratio of 1:1, and react for 12 h in a dark environment to obtain the ABTS stock solution. Dilute the ABTS stock solution with PBS (pH = 7.4) until its absorbance at 734 nm is 0.70 ± 0.02 to obtain the ABTS working solution. Take 1 mL of the sample solution and mix it with 1 mL of the ABTS working solution, and react in the dark for 6 min. Then, use a microplate reader to measure the absorbance of the mixture at 734 nm.

[0084] ABTS radical scavenging rate (%) = [(A0 - A) / A0] × 100%

[0085] In the formula, A0 is the absorbance of ABTS and water, and A is the absorbance of ABTS and the sample.

[0086] The antioxidant test results of 0.2% LF, 0.2% LF - 1% κC, 0.03% PC - 1% κC, 0.2% LF - 0.03% PC - 1% κC, and the soy protein isolate - tannic acid - carrageenan composite gel (SPI - TA - 1% κC) prepared in Example 3 of CN118872838A are shown in Table 1 below.

[0087] Table 1 Antioxidant properties of gels with different ratios

[0088]

[0089] Note: Completely different lowercase letters in the same column indicate significant differences between samples, p < 0.05.

[0090] The results show that both the DPPH radical scavenging rate and the ABTS radical scavenging rate of the ternary gel formed by the combination of LF, PC, and κC are higher than those of LF - κC and PC - κC, and are also significantly higher than those of SPI - TA - 1% κC. Therefore, the ternary gel provided by the present invention has excellent antioxidant properties.

[0091] 7. Zeta potential detection

[0092] Zeta potential detection method: Dilute the freeze - dried sample powder with water to 1 mg / mL, and use a particle size analyzer to measure the Zeta potential of the sample.

[0093] Test the Zeta potential of 0.2% LF, 0.2% LF - 1% κC, 0.03% PC - 1% κC, 0.2% LF - 0.03% PC - 1% κC, and the soy protein isolate - tannic acid - carrageenan composite gel (SPI - TA - 1% κC) prepared in Example 3 of CN118872838A. The results are shown in Table 2 below.

[0094] Zeta potential of gels with different ratios for antioxidant property

[0095]

[0096]

[0097] Note: Completely different lowercase letters in the same column indicate significant differences between samples, p < 0.05.

[0098] Zeta potential is an important indicator to characterize the stability of a system. The higher the absolute value of Zeta potential, the greater the electrostatic repulsion between particles, and the lower the degree of aggregation between particles. When the absolute value of Zeta potential is greater than 30 mV, the system can be considered to be in a stable state.

[0099] The results show that the absolute value of the Zeta potential of the ternary gel formed by the combination of LF, PC and κC is significantly higher than that of LF-PC and PC-κC, and also higher than that of SPI-TA-1% κC. The above content indicates that the ternary gel LF-PC-κC provided by the present invention has excellent stability.

[0100] 8. Peroxide value of cheese during storage

[0101] Cheese coating: The purchased Inner Mongolia cooked cheese (containing about 37% protein, 46% fat, 30% moisture, 0% sucrose, 1% sodium, 70% calcium) was cut into small pieces of 1 cm × 1 cm × 1 cm in a sterilized ultra-clean bench. The cheese pieces were immersed in the coating solution (0.2% LF, 0.2% LF-1% κC, 0.2% LF-0.03% PC-1% κC) for 30 s to allow the gel to fully coat the cheese, and then dried by blowing in the ultra-clean bench for 1 h. The cheese was stored in a 4°C refrigerator, and the peroxide value index was measured at 14 days and 21 days respectively. At the same time, a control was made with uncoated cheese.

[0102] The peroxide value is an index to evaluate the degree of oxidation of oil, and it is an important index to measure the degree of oxidation of oil in the initial stage of oil oxidation. Detection method of peroxide value: The cheese sample was crushed in a mortar and then placed in a 250 mL conical flask. Petroleum ether (boiling range: 30 - 60°C) with 2 - 3 times the sample volume was added, shaken well, and left to soak for 12 h. After filtration through a funnel filled with anhydrous sodium sulfate, the filtrate was taken, and the petroleum ether was evaporated to dryness using a rotary evaporator (not higher than 40°C) to obtain the test sample. Weigh 2 g of the test sample and place it in an iodine flask, add 30 mL of chloroform - glacial acetic acid solution, shake until completely dissolved. Add 1 mL of saturated potassium iodide solution, shake for 0.5 min, place in the dark for 3 min, take out, add 100 mL of water, shake well, and immediately titrate with a standard sodium thiosulfate solution until it turns light yellow, then add 1 mL of starch indicator and continue titrating until the blue color of the solution disappears.

[0103] X = [(V - V0×c×0.1269) / m]×100

[0104] Wherein, X is the peroxide value, g / 100g;

[0105] V is the volume of the sodium thiosulfate standard solution consumed by the sample, (mL);

[0106] V0 is the volume of the sodium thiosulfate standard solution consumed by the blank sample, (mL);

[0107] c is the concentration of the sodium thiosulfate standard solution, (mol / L);

[0108] m is the mass of the sample, (g).

[0109] The test results of the peroxide values of the cheese treated with different coating solutions for 14 days and 21 days are as Figure 10 (Completely different lowercase letters in the figure indicate significant differences between samples, p < 0.05). The results show that the effect of coating with LF alone has little difference from that of the control group (uncoated). The LF-κC coating group can effectively block gas exchange and prevent oxygen from contacting lipids, thus significantly inhibiting the oxidation reaction. Further, the peroxide value of the cheese coated with LF-PC-κC is significantly lower than that of all treatment groups, and is reduced by about 66% compared with the uncoated group, indicating that the coating formed after adding PC can more effectively inhibit the oxidation of cheese. Especially with the increase of the storage days, the inhibitory effect of LF-PC-κC on oxidation is more significant.

[0110] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A preparation method of a lactoferrin-procyanidin-carrageenan ternary gel, characterized in that, The method includes: Mix an aqueous lactoferrin solution with an aqueous proanthocyanidin solution, and uniformly mix the obtained mixture under light-shielded conditions to obtain a composite solution of lactoferrin and proanthocyanidin. Then, add carrageenan under stirring conditions to obtain the lactoferrin-proanthocyanidin-carrageenan ternary gel.

2. The method for preparing the lactoferrin-proanthocyanidin-carrageenan ternary gel according to claim 1, wherein the pH value of the aqueous lactoferrin solution is 7.0; in the composite solution, the concentration of lactoferrin is 0.18 - 0.22 w / v%, and the concentration of proanthocyanidin is 0.01 - 0.05 w / v%; the uniform mixing conditions are: 25 - 30 °C.

3. The method for preparing the lactoferrin-proanthocyanidin-carrageenan ternary gel according to claim 1, wherein the addition amount of carrageenan is 0.8% - 1.4 w / v%; the carrageenan is κ-carrageenan; the temperature of the stirring is 25 - 30 °C.

4. The method for preparing the lactoferrin-proanthocyanidin-carrageenan ternary gel according to any one of claims 1 - 3, wherein in the composite solution, the concentration of lactoferrin is 0.2 w / v%, and the concentration of proanthocyanidin is 0.03 w / v%; the addition amount of carrageenan is 1 w / v%.

5. The preparation method of the lactoferrin-procyanidin-carrageenan ternary gel according to claim 1, characterized in that, The method for preparing the aqueous lactoferrin solution is as follows: Add lactoferrin powder to deionized water, stir at 300 - 500 rpm for 1.5 - 3 hours, then let it stand at 1 - 6 °C for 8 - 16 hours, restore to room temperature, and adjust the pH value of the system to 7.0 with NaOH.

6. A lactoferrin-proanthocyanidin-carrageenan ternary gel, characterized in that, It is prepared by the method according to any one of claims 1 - 5.

7. Use of the lactoferrin-proanthocyanidin-carrageenan ternary gel according to claim 6 in the preparation of high-fat solid foods.

8. The application according to claim 7, wherein, The high-fat solid food is cheese.

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