Astringent substance loaded emulsion as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of food processing, and particularly relates to an astringent substance loaded emulsion and a preparation method and application thereof.The astringent substance loaded emulsion takes a solution containing astringent substances, gels and a solvent (which can contain astringent fruit juice such as roxburgh rose juice) as an inner water phase and a mixture of liquid grease, polyglycerol ricinoleate and lecithin as an outer oil phase, the emulsion is prepared by a one-step emulsification method. By regulating and controlling the gel, a stable emulsion system with high encapsulation efficiency and high loading capacity is constructed, a lipid layer formed by an outer oil phase can mask astringent taste, and the acceptability of consumers is improved. The emulsion can delay lipid oxidation and prolong the shelf life, has good smearing performance, and can be used for developing nutritional smearing sauce products with low astringent taste and high stability.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to an emulsion loaded with astringent substances, its preparation method, and its application. Background Technology

[0002] Astringency is a common sensory characteristic in food. Essentially, it arises from the reduced lubrication of the oral mucosa after contact with certain substances, resulting in a dry, rough, and tight sensation. It is primarily caused by polyphenols such as tannins, gallic acid, flavonoids, catechins, epicatechin, and chlorogenic acid, with tannins having the most significant impact on astringency intensity. These astringent substances are widely found in natural foods and ingredients such as wine, green tea, beans, coffee, prickly pear, and sea buckthorn, exhibiting a dual nature: on the one hand, appropriate amounts of astringent substances can enrich the flavor profile of food and possess excellent biological activities such as anti-oxidation, anti-tumor, blood pressure reduction, and blood lipid reduction, making them important functional components in food; on the other hand, when the content of astringent substances is too high, it produces a strong astringent taste, severely damaging the sensory experience of the food, reducing consumer acceptance, and thus limiting the processing, utilization, and market promotion of these highly nutritious food ingredients.

[0003] To address the sensory defects caused by astringent substances, the food industry has developed various astringency control technologies, including additive methods, separation methods, enzyme treatment methods, protein-like reaction methods, and encapsulation methods. Among these, encapsulation methods have become a research hotspot due to their unique advantages: this method can form a physical barrier through carrier materials, preventing astringent substances from directly binding to astringent receptors in the oral cavity, thus masking unpleasant flavors at the source; at the same time, it can isolate astringent substances from contact with the external environment (such as oxygen, light, and temperature), reducing their oxidative degradation or structural changes, effectively preserving their biological activity, and providing a feasible path for the resource utilization of high-astringency, high-nutrition food raw materials.

[0004] High internal phase emulsions (also known as ultra-concentrated emulsions), as a novel carrier system, have a dispersed phase volume fraction greater than 74%. They possess tunable gel-like rheological properties, a large oil-water interface area, high encapsulation capacity, and excellent storage stability, showing broad application prospects in the field of food functional ingredient delivery. Among them, water-in-oil high internal phase emulsions, with a lipid continuous external phase, exhibit more outstanding encapsulation and protection effects on water-soluble active ingredients, and have gradually become a research focus in food carrier technology in recent years.

[0005] However, existing technologies still have significant limitations and cannot meet the specific needs of encapsulating astringent substances. For example, patent CN118515885B discloses a high internal phase emulsion stabilized by cellulose nanocrystals, tannic acid, and calcium chloride. Its core is to use tannic acid as an interface stabilizer in the emulsion construction, but it does not systematically study tannic acid or other polyphenols as astringent target substances to be encapsulated. Patent CN116919899B reports a high internal phase emulsion stabilized by spirulina isolate protein and tannic acid, mainly used for delivering curcumin. Patent CN118633675B discloses the application of protein-polyphenol composite nanoparticles in antioxidant Pickering emulsions. Both focus on the storage stability, antioxidant properties, and active ingredient loading capacity of the emulsion, but do not conduct systematic research on key issues such as the specific encapsulation requirements of water-soluble polyphenolic astringent substances, the regulation of oral release behavior, the restoration of oral lubrication, and the optimization of astringent sensory experience.

[0006] Current technologies have failed to achieve synergistic optimization in the efficient encapsulation, precise masking of astringency, and enhancement of functional stability of water-soluble polyphenolic astringent substances, lacking an emulsion carrier system specifically designed for the characteristics of astringent substances. Therefore, developing an emulsion preparation technology that can efficiently load astringent substances, significantly mask astringency, improve storage stability, and meet the needs of food processing is of great significance for expanding the application scenarios of high-astringency, high-nutrient food raw materials and improving the sensory quality and market value of food products. Summary of the Invention

[0007] The purpose of this invention is to provide an emulsion loaded with astringent substances, its preparation method and application, which encapsulates astringent substances in the internal aqueous phase of a water-in-oil emulsion to reduce the perception of astringency, improve its storage stability and sensory acceptance, and enhance its application value in food systems.

[0008] The objective of this invention is achieved through the following technical solution: This invention provides a water-in-oil emulsion with a high internal phase loading of astringent substances, the raw materials of which include an aqueous phase and an oil phase. The aqueous phase includes the astringent substances, a gelling agent and a solvent; the oil phase includes liquid oil, polyglycerol ricinoleate and lecithin.

[0009] Furthermore, the mass concentration of the astringent substance in the aqueous phase is 0-2%; the gelling agent includes one or more of carrageenan, guar gum, gellan gum, and konjac gum.

[0010] Furthermore, the mass concentration of the gelling agent in the aqueous phase is 0-5%.

[0011] Furthermore, the mass concentration of the polyglycerol ricinoleate in the oil phase is 1% to 10%; the mass concentration of the lecithin in the oil phase is 1% to 8%; and the mass ratio of the polyglycerol ricinoleate to the lecithin is 10:1 to 2:3.

[0012] Furthermore, the oil phase has a mass fraction of 20-90%.

[0013] Furthermore, the astringent substance includes at least one of tannic acid, gallic acid, flavonoids, catechins, epicatechin, and chlorogenic acid; the solvent includes at least one of distilled water, PBS buffer at a concentration of 5-500 mM, citrate buffer at a concentration of 5-500 mM, and fruit juice containing the astringent substance; the liquid oil includes at least one of rapeseed oil, corn oil, olive oil, medium-chain triglycerides, flaxseed oil, castor oil, walnut oil, peony seed oil, peanut oil, camellia oil, soybean oil, perilla seed oil, and sunflower seed oil.

[0014] This invention also provides a method for preparing a water-in-oil emulsion with high internal phase content containing the aforementioned astringent substance, comprising the following steps: (1) Dissolve the astringent substance and gelling agent in a solvent to obtain an aqueous phase; (2) The liquid oil, polyglycerol ricinoleate and lecithin are heated and mixed to obtain the oil phase; (3) The aqueous phase is added to the heated oil phase for homogeneous dispersion to obtain a water-in-oil emulsion with high internal phase loading of astringent substances.

[0015] Furthermore, in step (2), the temperature for heating and mixing is 35–85°C.

[0016] Furthermore, in step (3), the shear mixing speed for homogeneous dispersion is 6000~12000 rpm, and the shear mixing time is 4~10 min.

[0017] The present invention also provides the application of the water-in-oil emulsion with high internal phase of the loaded astringent substance in the preparation of a low-astringency, high-stability nutritional spread sauce.

[0018] The beneficial effects of this invention are as follows: The water-in-oil emulsion with high internal phase, loaded with astringent substances, provided by this invention, exhibits significant technical advantages through scientific and rational raw material formulation and structural design. This emulsion uses a solution formed by the astringent substance, gelling agent, and solvent as the inner aqueous phase, and a mixture of liquid oil, polyglycerol ricinoleate, and lecithin as the outer oil phase. By controlling the type and amount of gelling agent, the gelation characteristics and viscosity of the inner aqueous phase can be effectively improved, laying the foundation for constructing a stable high internal phase emulsion system. Due to its high internal phase volume fraction, the internal aqueous phase exhibits a close-packed structure. The gel network of the aqueous phase itself and the spatial structure formed by the close packing of droplets synergistically enhance the stability of the emulsion. Centrifugation tests verified that the emulsion transmittance remained almost unchanged during 4 hours of centrifugation, the instability index was below 0.01, and it maintained a uniform milky white creamy appearance after 4 weeks of storage at room temperature, without obvious stratification or deterioration. Meanwhile, this structural design achieves high encapsulation efficiency and high loading of astringent substances. The lipid layer formed by the outer oil phase can effectively block the binding of internal astringent molecules to astringent receptors in the oral cavity, significantly masking the unpleasant flavor of astringent substances. Sensory evaluation results show that the astringency scores of all samples are below 4 points, reaching a low or slight astringency level, which greatly improves the consumer acceptability of the product and expands the application path of hydrophilic nutrients in oil-based foods.

[0019] The technical solution of this invention also possesses outstanding advantages such as simple preparation, diverse functions, and broad application prospects. Its preparation process employs a one-step emulsification method, requiring only heating and mixing of the aqueous and oil phases followed by homogenization and dispersion. The operation is simple and easy to control, requiring no complex equipment and suitable for industrial production. In terms of formulation design, by adding lecithin to partially replace polyglycerol ricinoleate (PGPR) to stabilize the emulsion, the amount of synthetic small-molecule emulsifier added is effectively reduced, better meeting the health requirements of food processing. When the inner phase of the emulsion is loaded with polyphenolic astringent substances, these substances can also exert antioxidant effects, effectively slowing down the lipid oxidation process of the outer oil phase, significantly extending the product's shelf life. Testing showed that after 4 weeks of storage, the tannin retention rate was still above 90%. In addition, the prepared emulsion has good rheological properties and spreadability, exhibiting the characteristics of a shear-thinning pseudoplastic fluid. When spread on carriers such as bread, it is delicate and smooth without any grainy feel. The texture and spreadability scores are both higher than 7 points. It is especially suitable for encapsulating natural raw materials rich in astringent substances, such as prickly pear juice. It can mask the astringency while retaining the nutritional components and characteristic flavor of the raw materials. It provides an ideal technical solution for developing low-astringency, high-stability nutritional spreads and other foods, and has important practical application value. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 These are macroscopic morphology images of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 of this invention; Figure 2 These are laser confocal microstructure diagrams of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 of this invention. Figure 3 These are centrifugation stability test results of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 of this invention; Figure 4 The strain scanning curves are of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 of this invention. Figure 5 The shear viscosity scan curves of the water-in-oil high internal phase emulsions prepared in Examples 1-5 of this invention are shown. Figure 6 The above are tribological curves of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 of this invention. Figure 7 These are images of the freshly prepared emulsions and the emulsions stored at room temperature for 4 weeks, as shown in Examples 1-5 of this invention. Figure 8 The graph shows the retention rate of tannic acid in the water-in-oil emulsions with high internal phase prepared in Examples 2-5 of this invention. Figure 9 Sensory evaluation radar images of the water-in-oil emulsions with high internal phase obtained in Examples 1-5 and Application Examples 1-2 of this invention; Figure 10 The images show the appearance of the water-in-oil emulsions with high internal phase prepared in Examples 1-5 and Application Examples 1-2 of this invention when applied to bread slices. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings: Unless otherwise specified, room temperature is expressed as 25±2℃.

[0028] Example 1 This embodiment provides a water-in-oil emulsion loaded with tannic acid, and its preparation method is as follows: (1) Dissolve 6g of κ-carrageenan powder in 294g of distilled water to obtain 300g of aqueous phase (tannic acid mass concentration 0%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0029] Example 2 This embodiment provides a water-in-oil emulsion loaded with tannic acid, and its preparation method is as follows: (1) Dissolve 0.3g of tannic acid powder and 6g of κ-carrageenan powder in 293.7g of distilled water to obtain 300g of aqueous phase (tannic acid mass concentration 0.1%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0030] Example 3 This embodiment provides a water-in-oil emulsion loaded with tannic acid, and its preparation method is as follows: (1) Dissolve 0.6g of tannic acid powder and 6g of κ-carrageenan powder in 293.4g of distilled water to obtain 300g of aqueous phase (tannic acid mass concentration 0.2%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0031] Example 4 This embodiment provides a water-in-oil emulsion loaded with tannic acid, and its preparation method is as follows: (1) Dissolve 0.9g of tannic acid powder and 6g of κ-carrageenan powder in 293.1g of distilled water to obtain 300g of aqueous phase (tannic acid mass concentration 0.3%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0032] Example 5 This embodiment provides a water-in-oil emulsion loaded with tannic acid, and its preparation method is as follows: (1) Dissolve 1.2g of tannic acid powder and 6g of κ-carrageenan powder in 292.8g of distilled water to obtain 300g of aqueous phase (tannic acid mass concentration 0.4%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0033] Application Example 1 This application example provides a water-in-oil emulsion with high internal phase loading of prickly pear juice, and its preparation method is as follows: (1) Dissolve 18g of prickly pear juice, 0.3g of vitamin C and 6g of κ-carrageenan powder in 275.7g of distilled water to obtain 300g of aqueous phase (prickly pear juice mass concentration 6%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0034] Application Example 2 This application example provides a water-in-oil emulsion with high internal phase loading of prickly pear juice, and its preparation method is as follows: (1) Dissolve 36g of prickly pear juice, 0.3g of vitamin C and 6g of κ-carrageenan powder in 257.7g of distilled water to obtain 300g of aqueous phase (prickly pear juice mass concentration 12%). (2) 95g rapeseed oil, 2g soybean lecithin and 3g polyglycerol ricinoleate were heated and mixed evenly at 70°C to obtain 100g oil phase; (3) The heated oil phase obtained in step (2) is transferred into a beaker and placed in a high-speed shearing machine. During the process of adding the water phase into the oil phase, the rotation speed is sheared at a rate of 11,000 rpm for 6 minutes to obtain a water-in-oil emulsion with high internal phase.

[0035] Macroscopic morphology analysis of the emulsions obtained in Examples 1-5 of Experiment 1 After the emulsions in Examples 1-5 were prepared, images of the emulsion appearance were taken.

[0036] Results Analysis: The appearance of the water-in-oil emulsions with high internal phase emulsions obtained in Examples 1-5 is as follows: Figure 1As shown, all the emulsions are milky white and creamy, with a uniform, smooth, and delicate texture.

[0037] Laser confocal microstructure diagrams of the emulsions obtained in Examples 1-5 of Experiment 2 The microstructure of the high internal phase emulsions obtained in Examples 1–5 was observed using a Zeiss LSM780 inverted laser confocal microscope. The oil phase was stained with Nile Red (1 mg / mL, dissolved in ethanol, stored at 4°C). During observation, a 40x oil immersion microscope was used, with an Ar lamp as the excitation source. The excitation wavelength was set to 488 nm, and the absorption wavelength was 500–755 nm. Based on the microstructure images, the average droplet size of the high internal phase emulsion was measured using Image J (v1.8.0), and 100 randomly selected droplets were statistically analyzed for their size.

[0038] Results analysis: such as Figure 2 As shown, in the absence of tannic acid, the droplets are relatively large spheres; as the tannic acid content increases, the droplet size decreases. From Example 1 to Example 3, the particle size shows a significant decreasing trend (p<0.05). From Example 3 to Example 5, there is no significant difference in the change of droplet size. The presence of tannic acid leads to a decrease in droplet size, which may be related to the interaction between carrageenan and tannic acid. Tannic acid molecules contain abundant hydroxyl and phenolic hydroxyl groups, which can form hydrogen bonds with the hydroxyl groups in carrageenan molecules. This hydrogen bonding can enhance the binding ability between the two, thereby affecting the formation and stability of the emulsion.

[0039] Centrifugal stability analysis of emulsions obtained in Examples 1-5 (Experimental Example 3) The stability of the emulsions was determined using a LUmisizer full-function stability analyzer. In the tests, the high internal phase emulsions obtained in Examples 1–5 were centrifuged at 25°C and 4000 rpm, and scanned using near-infrared light (880 nm). The transmittance characteristic line of the sample was recorded every 10 s, for a total of 720 records. The instrument recorded the intensity of transmitted light in the sample tube during centrifugation, and the stability of the emulsion was studied by the rate of change of the overall transmittance (%) over time.

[0040] Results analysis: such as Figure 3As shown, changes in transmittance can reflect the stability of the emulsion system. The results show that the overall transmittance of the high internal phase emulsions obtained in Examples 1-5 was low, showing almost no change during 4 h of centrifugation, and the instability index was very low (<0.01), indicating that the droplets inside the emulsion were uniformly distributed and aggregation was limited, resulting in good stability. In general, HIPEs exhibit good centrifugal stability, which may be attributed to the following three reasons: (i) the three-dimensional gel structure formed by KC in the aqueous phase significantly enhances the viscoelasticity of the system, inhibiting droplet aggregation. (ii) the small droplet size distribution of the emulsion supports its high stability. (iii) due to the high aqueous phase content, the droplets in the emulsion are tightly packed together. The tight packing of droplets in HIPEs can lead to high viscosity and strong resistance to gravity separation.

[0041] Strain scanning of the emulsions obtained in Examples 1-5 of Experiment 4 The rheological properties of high internal phase emulsions were studied using a HAAKE rheometer (MARS IQ AIR) with a parallel plate clamp (diameter = 35 mm) and a gap of 1 mm. High internal phase emulsion samples obtained in Examples 1–5 were spread on the test stage. A strain mode was selected, with a strain range of 0.01% to 1000% and an oscillation frequency of 1 Hz. Ten data points were collected within each order of magnitude, and the storage modulus (G') and loss modulus (G'') were recorded. The tests were conducted at 25°C.

[0042] Results analysis: Strain scanning test was used to detect the linear viscoelastic region of the sample. Figure 4 When the strain is below 0.1%, the G' and G'' values ​​of the high internal phase emulsions obtained in Examples 1-5 remain almost stable, indicating the existence of a linear viscoelastic region (LVR). Within the LVR, the G' value is always greater than the G'' value, indicating that the high internal phase emulsions obtained in Examples 1-5 exhibit predominantly elastic behavior. This is due to the elastic behavior of the internal phase hydrogel itself, and the high stacking and compression of droplets in the high internal phase emulsion, forming a viscoelastic gel-like soft solid structure. As the strain continues to increase, the G' and G'' curves intersect, after which the G' value of the sample rapidly decreases, and G'' becomes greater than G', indicating that the system evolves from an elastically dominated structure to a viscoelastically dominated structure. This is because higher stress irreversibly destroys the internal structure of the emulsion, including droplet coalescence, interfacial film rupture, and three-dimensional network disintegration, leading to the collapse of the emulsion system.

[0043] Shear viscosity scans of the emulsions obtained in Examples 1-5 (Experimental Example 5) The high internal phase emulsion samples obtained in Examples 1-5 were spread on the test stage, and the shear viscosity scan mode was selected, ranging from 0.01 to 1000 s. -1 Steady-state shear tests were conducted at a shear rate of 25°C to obtain the viscosity change curve of the emulsion.

[0044] Results Analysis: Figure 5 It can be seen that the apparent viscosity of the high internal phase emulsions obtained in Examples 1-5 all decreases with increasing shear rate, exhibiting typical pseudoplastic fluid characteristics of shear-thinning. This is due to the destruction of the hydrogel structure at high shear rates. The droplets in the high internal phase emulsion are tightly packed, and the thin continuous phase between the droplets hinders droplet flow, enhancing inter-droplet interactions and leading to higher viscosity. At lower shear rates (<0.1 s⁻¹), the viscosity decreases further. 1 At this point, the emulsion exhibits higher viscosity because the network within the continuous phase is intact and provides higher shear resistance. However, when the shear rate exceeds 0.1 s⁻¹, the viscosity decreases. 1 At this point, the viscosity gradually decreases to its minimum value. In fact, the emulsion structure has already been disrupted and phase separation has occurred.

[0045] Tribological testing of the emulsions obtained in Examples 1-5, Experimental Example 6 The high internal phase emulsions obtained in Examples 1–5 were tribologically characterized using a HAAKE MARS iQ AIR rotational rheometer. The rheometer was equipped with a ball-to-plate tribometer unit with polydimethylsiloxane (PDMS) plates. The tribological properties of the samples were evaluated by measuring the coefficient of friction of the ball between the three plates. The PDMS plates and the ball were used to simulate the contact between the tongue surface and the palate, respectively. The test temperature was set at 37°C, the contact normal force was 1 N, and the changes in the coefficient of friction were recorded at entrainment velocities ranging from 0.01 to 100 mm / s.

[0046] Results analysis: Figure 6 In the examples 1-5, the high internal phase emulsions all followed the classic Stribeck curve. At lower sliding speeds (<0.15 mm / s), the friction coefficient of the samples gradually increased under boundary lubrication conditions. At this stage, the friction behavior was mainly determined by surface roughness and the interfacial film. Example 5 exhibited a higher friction coefficient, possibly due to its higher viscosity. As the sliding speed increased (0.15-10 mm / s), the friction coefficient of all samples showed a decreasing trend, reaching a mixed state. In this state, more emulsion and oil were absorbed into the region between the sliding surfaces, resulting in a decrease in μ. As the sliding speed further increased to above 10 mm / s, the original emulsion entered the hydrodynamic region, and friction increased significantly. This was because more emulsion was carried into the friction surfaces, and the lubrication effect was determined by the overall rheology of the sample. Simultaneously, the emulsion gel structure was largely disrupted, hydrogel diffused, and a lubricating film containing released hydrogel was formed, leading to a rapid increase in friction.

[0047] Storage stability analysis of emulsions obtained in Examples 1-5 (Experimental Example 7) After the emulsions in Examples 1-5 were prepared, they were stored at room temperature for 4 weeks, and the appearance of the emulsions was photographed.

[0048] Results analysis: Figure 7 The changes in appearance of emulsions with different tannic acid contents before and after storage are shown. All emulsions maintained a relatively uniform milky white, creamy appearance and showed almost no significant changes after 4 weeks of storage, indicating that the emulsions have good storage stability. The close packing of droplets in the emulsion system, the high viscosity of the system, and the hydrogelation of the internal phase work together to form a physical barrier to effectively resist gravity-induced sedimentation and droplet migration.

[0049] Evaluation of tannic acid retention rate of emulsions obtained in Examples 2-5 (Experimental Example 8) After the emulsions in Examples 2-5 were prepared, the tannic acid content was determined by spectrophotometry.

[0050] Tannic acid retention rate = (tannic acid content after storage ÷ initial tannic acid content) × 100% Results analysis: Figure 8 The results show that the high internal phase emulsions obtained in Examples 2-5 all exhibited good protective effects on tannic acid, retaining more than 90% of the tannic acid even after 4 weeks of storage. The KC hydrogel network effectively protected the tannic acid, reducing its migration and the probability of contact with free radicals. Furthermore, the higher viscosity of HIPEs also contributed to reducing free radical migration. Water and tannic acid were immobilized within the hydrogel network structure, inhibiting the flow and aggregation of liquid water. Due to the support and protection of the semi-solid hydrogel structure, the internal tannic acid was less susceptible to contact with adverse factors in the external environment, and the three-dimensional network structure in the emulsion system was beneficial for protecting bioactive substances. Simultaneously, the continuous external oil phase also provided some protection for the internal tannic acid. In addition, the interfacial layer formed by PGPR and lecithin enhanced the barrier effect, effectively isolating light and heat, and providing even better protection for the internal tannic acid.

[0051] Sensory evaluation of the emulsions obtained in Experimental Examples 9, Examples 1-5, and Application Examples 1-2 Sixteen professionally trained volunteers (8 males and 8 females) conducted sensory evaluations of the samples, scoring them according to Tables 1 and 2 on a scale of 0 to 10. Samples were added to disposable transparent plastic cups and randomly numbered. Each sample was required to remain in the mouth for at least 30 seconds. Evaluators were instructed to rinse their mouths with water between tasting and scoring each sample to maintain oral hygiene. The entire evaluation process was conducted independently by members of the sensory evaluation team.

[0052] Table 1. Tannic acid solution concentration and astringency standard

[0053] Table 2 Sensory Evaluation Table of Samples

[0054] Results Analysis: Sensory evaluation was performed on the water-in-oil emulsions with high internal phase content prepared in Examples 1-5 and Application Examples 1-2. The results are as follows: Figure 9 As shown. The visual smoothness scores of the emulsions were all above 8 points, indicating that the samples were very smooth, without any graininess, and had good gloss. The visual viscosity score increased with increasing tannin content. The visual viscosity score of the samples encapsulated with prickly pear juice was around 5 points, indicating moderate viscosity and good flowability and adhesion. The odor scores of the samples were not high, because the external continuous phase of W / O-HIPEs is an oil phase, and the samples had a noticeable oily odor. The astringency scores of all samples were below 4 points, indicating low to slight astringency. This shows that W / O-HIPEs have a good astringency masking effect. The lubrication perception scores of the samples were all high, indicating good lubricity and a good taste. The overall acceptability score of the samples was around 6 points, indicating that the volunteers were relatively satisfied with the samples, with slight shortcomings, but not affecting the overall experience. The addition of prickly pear juice improved the overall acceptability of the samples; volunteers reported that the addition of prickly pear juice increased the prickly pear fruit aroma. The study shows that the oil phase can provide a physical barrier, limiting the ability of flavor molecules to interact with taste buds on the tongue, thereby reducing their perceived intensity. Therefore, astringency can be reduced by encapsulating astringent substances in the aqueous phase of W / O-HIPEs, as these substances are protected by the surrounding oil phase and kept away from receptors on the tongue. Overall, emulsions have good masking properties for astringency and show promising application potential in the preparation of nutritious spreads rich in prickly pear juice.

[0055] Test Example 10: Spreadability test of the emulsions obtained from Examples 1-5 and Application Examples 1-2 Sixteen professionally trained volunteers (8 boys and 8 girls) conducted a spreadability test on the samples. The samples were spread on bread slices, observed, and their spreadability was evaluated using sensory methods, with scores assigned according to Table 3.

[0056] Table 3 Evaluation Table of Sample Spreadability Test

[0057] Results analysis: such as Figure 10As shown, the water-in-oil emulsions with high internal phase prepared in Examples 1-5 and Application Examples 1-2 are creamy white with a glossy surface and exhibit certain viscosity and fluidity. When the emulsion is evenly spread on the bread surface, it is smooth, delicate, and does not easily break, with no grainy texture, indicating that the prepared emulsion samples have good spreadability. In the subsequent sensory evaluation of spreadability, the morphology scores of the samples were all above 7, indicating good fluidity and a uniform and fine texture. The morphology score of the sample with added prickly pear juice was between 7.8 and 7.9, slightly lower than the sample without added prickly pear juice. The spreadability scores of the samples were all above 7, indicating smooth spreadability, a smooth coating, and uniform thickness. As the tannin concentration increased, the spreadability score decreased from 7.8 to 7.1, which may be due to the higher viscosity of Example 5, consistent with the shear viscosity rheology test results. After adding prickly pear juice, the taste and flavor scores were between 7.4 and 7.6, higher than the samples without added prickly pear juice. This is because the spread with added prickly pear juice has a more refreshing prickly pear flavor, thus improving the taste and flavor score. The above results indicate that the prepared emulsion sample has good spreadability and can be used to prepare a nutritious spread sauce rich in prickly pear juice.

[0058] Table 4 Sensory evaluation results of the spreadability of the samples

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A water-in-oil emulsion with a high internal phase content and loaded with astringent substances, characterized in that, Its raw materials include an aqueous phase and an oil phase. The aqueous phase includes astringent substances, gelling agents, and solvents; the oil phase includes liquid oils, polyglycerol ricinoleate, and lecithin.

2. The water-in-oil emulsion with high internal phase concentration carrying astringent substances according to claim 1, characterized in that, The astringent substance has a mass concentration of 0-2% in the aqueous phase; the gelling agent includes one or more of carrageenan, guar gum, gellan gum, and konjac gum.

3. The water-in-oil emulsion with high internal phase concentration carrying astringent substances according to claim 2, characterized in that, The mass concentration of the gelling agent in the aqueous phase is 0-5%.

4. The water-in-oil emulsion with high internal phase concentration carrying astringent substances according to claim 1, characterized in that, The mass concentration of the polyglycerol ricinoleate in the oil phase is 1% to 10%; the mass concentration of the lecithin in the oil phase is 1% to 8%; and the mass ratio of the polyglycerol ricinoleate to the lecithin is 10:1 to 2:

3.

5. The water-in-oil emulsion with high internal phase content carrying astringent substances according to claim 1, characterized in that, The oil phase has a mass fraction of 20-90%.

6. The water-in-oil emulsion with high internal phase concentration carrying astringent substances according to claim 1, characterized in that, The astringent substance includes at least one of tannic acid, gallic acid, flavonoids, catechins, epicatechin, and chlorogenic acid; the solvent includes at least one of distilled water, PBS buffer at a concentration of 5-500 mM, citrate buffer at a concentration of 5-500 mM, and fruit juice containing the astringent substance; the liquid oil includes at least one of rapeseed oil, corn oil, olive oil, medium-chain triglycerides, flaxseed oil, castor oil, walnut oil, peony seed oil, peanut oil, camellia oil, soybean oil, perilla seed oil, and sunflower seed oil.

7. A method for preparing a water-in-oil emulsion with a high internal phase content and loaded with astringent substances as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Dissolve the astringent substance and gelling agent in a solvent to obtain an aqueous phase; (2) The liquid oil, polyglycerol ricinoleate and lecithin are heated and mixed to obtain the oil phase; (3) The aqueous phase is added to the heated oil phase for homogeneous dispersion to obtain a water-in-oil emulsion with high internal phase loading of astringent substances.

8. The preparation method according to claim 7, characterized in that, In step (2), the temperature for heating and mixing is 35-85℃.

9. The preparation method according to claim 7, characterized in that, In step (3), the shear mixing speed for homogeneous dispersion is 6000~12000 rpm, and the shear mixing time is 4~10 min.

10. The use of a water-in-oil emulsion with high internal phase emulsion loading astringent substances as described in any one of claims 1 to 6 in the preparation of a low-astringency, high-stability nutritional spread sauce.

Images