High-stability grease-encapsulated liquid core sodium alginate gel ball as well as preparation method and application thereof

Abstract

The invention discloses a high-stability oil-encapsulated liquid core sodium alginate gel ball as well as a preparation method and application thereof, and the preparation method comprises the following steps: selecting sodium alginate with a specific molecular structure as a wall material and edible vegetable oil as a core material, and realizing efficient embedding and structure regulation of oil through an optimized sharp hole coagulating bath and coaxial extrusion composite process. The encapsulation efficiency of the prepared liquid core gel ball can reach 98% or above, the sphericity degree is good, the oil penetration rate is still lower than 5% after the liquid core gel ball is stored at normal temperature for 14 days, and the liquid core gel ball shows excellent sealing performance and stability. The method disclosed by the invention is strong in process controllability, safe in raw materials and suitable for large-scale production, and has a good application prospect in the fields of food flavor improvement and fat-soluble active ingredient embedding.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a highly stable liquid-core sodium alginate gel ball for encapsulating oils and fats, its preparation method, and its application. Background Technology

[0002] With the increasing demands for sensory quality and functional properties in the food industry, liquid-core gel spheres have become a research hotspot in the field of food colloids due to their "bursting sensation" when bitten and their protective function for the core material. Liquid-core gel spheres typically use food-grade hydrocolloids (such as sodium alginate and pectin) as wall materials to encapsulate liquid core materials (such as oils and flavorings) to form a "core-shell" structure. Among these, sodium alginate is a commonly used wall material due to its good biocompatibility, biodegradability, and ability to crosslink with divalent cations to form a gel.

[0003] However, there are significant shortcomings in the existing research on liquid-core sodium alginate gel spheres for millimeter-scale encapsulation of oils: The manufacturing process is immature: traditional methods are difficult to control sphericity, which can easily lead to tailing and irregular deformation, and the encapsulation rate is generally lower than 90%, and the core material grease is prone to leakage. Poor mechanical properties: The cross-linking of the gel sphere wall layer is insufficient, and the bursting force is mostly less than 200g. It is easily damaged during processing and transportation, affecting the "bursting sensation" experience. Insufficient storage stability: The optimal storage environment parameters are not clearly defined. It is prone to water loss and collapse under low humidity and oil seepage under high humidity. The oil seepage rate often exceeds 10% after 14 days of storage. Poor matching between raw material characteristics and process: The correlation between sodium alginate viscosity (or M / G ratio) and gel sphere sphericity and mechanical properties was not revealed, resulting in unstable product quality when raw material fluctuations occurred.

[0004] In summary, the existing technology lacks a complete solution for preparing liquid-core sodium alginate gel spheres that balances high encapsulation efficiency, excellent mechanical properties, and long shelf life, which limits their large-scale application in the food industry. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a highly stable liquid-core sodium alginate gel ball for encapsulating oils.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, (1) Preparation of wall material solution: Dissolve sodium alginate in deionized water to form sodium alginate wall material solution, and let it stand to remove bubbles; (2) Preparation of cross-linking coagulation bath: Dissolve calcium lactate in deionized water to form calcium lactate coagulation bath; (3) Coaxial extrusion dripping: A double-layer coaxial extrusion dripper is used. The inner layer of the hose delivers edible vegetable oil (core material), and the outer layer of the hose delivers sodium alginate solution from step (1). The two solutions are extruded from the dripper at the same time to form the core liquid. (4) Crosslinking and post-treatment: The droplets were stirred and reacted in a coagulation bath, then rinsed with deionized water and anhydrous ethanol, and drained to obtain sodium alginate gel balls with liquid core.

[0009] As a preferred embodiment of the method for improving the encapsulation stability of oils and fats according to the present invention, the concentration of the sodium alginate solution is 1.5~3.5% (w / v), and the viscosity of the sodium alginate is 100~2000 mPa·s.

[0010] In a preferred embodiment of the method for improving the encapsulation stability of oils and fats according to the present invention, the concentration of the calcium lactate solution is 1.0~3.0% (w / v).

[0011] As a preferred embodiment of the method for improving the stability of oil encapsulation described in this invention, wherein: the edible vegetable oil (core material) conveyed by the inner flexible tube in step (3) has a flow rate of 1~3 mL / min; and the sodium alginate solution conveyed by the outer flexible tube has a flow rate of 4~6 mL / min; As a preferred embodiment of the method for improving the stability of oil encapsulation described in this invention, the crosslinking reaction time in step (4) is 1~5 min; the deionized water rinsing is 1~2 times, each time for 20~30 s; the anhydrous ethanol rinsing is 1~2 times, each time for 20~30 s.

[0012] As a preferred embodiment of the method for improving the stability of oil encapsulation according to the present invention, the core material is edible vegetable oil, including one or more of blended vegetable oil, olive oil, or sunflower seed oil.

[0013] Another objective of this invention is to provide a highly stable liquid-core sodium alginate gel sphere for encapsulating oils, wherein the gel sphere has an encapsulation rate ≥98%, a sphericity ≥0.95, and a bursting force ≥390 g; the storage conditions are: relative humidity 53%-85%, temperature 25℃, and an oil leakage rate <5% after 14 days of storage.

[0014] Beneficial effects of this invention: High encapsulation efficiency and loading capacity: By optimizing the type (SA-3 type), concentration (3.0% w / v) and crosslinking parameters (2.5% w / v calcium lactate, 5 min reaction), this invention achieves an encapsulation efficiency ≥98% and a loading capacity ≥85%, which is significantly better than the traditional process (encapsulation efficiency <90%). Excellent sphericity and mechanical properties: Sodium alginate viscosity control maintains a shear rate of 50 s. -1 Under normal conditions, when the viscosity of sodium alginate is around 2000-6000 mPa·s, the sphericity is ≥0.95, with no tailing or irregular deformation; the bursting force is ≥397g, with a clear "bursting sensation", meeting the requirements for processing and transportation; Long-term storage stability: After 14 days of storage at 53%-85% relative humidity, the oil leakage rate is <5%, the double-layer film thickness decay rate is <10%, and the sphericity remains ≥0.95, solving the problems of easy leakage and collapse of traditional gel balls; High process controllability: The matching relationship between raw material characteristics (SA-3 type sodium alginate) and process parameters (flow rate, drop height, reaction time) has been clarified, reducing batch fluctuations and making it suitable for industrial production; High safety: All raw materials used are food-grade, with no toxic additives, meet food safety standards, and can be directly applied in the food industry. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of 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. Wherein: Figure 1 The sensory evaluation results of the liquid core gel spheres prepared in Example 1 of this invention during their storage period are shown.

[0016] Figure 2 The graphs show the changes in apparent viscosity of sodium alginate solutions with different sodium alginate concentrations (A) and types (B) in Examples 2 and 3 of the present invention as a function of shear rate.

[0017] Figure 3 This describes the effect of different sodium alginate concentrations on the apparent state (AI) and sphericity (J) of the liquid core gel spheres in Example 2 of the present invention.

[0018] Figure 4 This invention illustrates the effects of different sodium alginate concentrations on the encapsulation rate (A), weight loss rate (B), oil loss rate (C), bursting force (D), bursting distance (E), and bursting strain (F) of the liquid core gel spheres in Example 2.

[0019] Figure 5This describes the effect of different types of sodium alginate on the apparent state (AD) and sphericity (E) of liquid core gel spheres in Example 3 of the present invention.

[0020] Figure 6 This invention describes the effects of different types of sodium alginate on the encapsulation rate (A), weight loss rate (B), oil loss rate (C), bursting force (D), bursting distance (E), and bursting strain (F) of liquid core gel spheres in Example 3 of this invention.

[0021] Figure 7 This describes the effect of different calcium lactate concentrations on the apparent state (AE) and sphericity (F) of the liquid core gel spheres in Example 4 of the present invention.

[0022] Figure 8 This invention describes the effects of different calcium lactate concentrations on the encapsulation rate (A), weight loss rate (B), oil loss rate (C), bursting force (D), bursting distance (E), and bursting strain (F) of the liquid core gel spheres in Example 4.

[0023] Figure 9 This describes the effect of different crosslinking reaction times on the apparent state (AE) and sphericity (F) of the liquid core gel spheres in Example 5 of the present invention.

[0024] Figure 10 This invention describes the effects of different crosslinking reaction times on the encapsulation rate (A), weight loss rate (B), oil loss rate (C), bursting force (D), bursting distance (E), and bursting strain (F) of the liquid core gel spheres in Example 5 of this invention.

[0025] Figure 11 The effects of different storage times and relative humidity on the apparent state (A) and sphericity (B) of the liquid core gel spheres in Comparative Example 1 of this invention are shown.

[0026] Figure 12 This invention relates to the effect of different storage times and relative humidity on the thickness of the liquid core gel sphere bilayer membrane in Comparative Example 1.

[0027] Figure 13 This invention relates to the effects of different storage times and relative humidity on the bursting force (A), bursting distance (B), and bursting strain (C) of liquid core gel spheres in Comparative Example 1.

[0028] Figure 14 This invention illustrates the effect of different storage times and relative humidity on the oil content of liquid core gel spheres in Comparative Example 1.

[0029] Figure 15 This is a conceptual diagram illustrating the construction of a coaxial extrusion device for implementing this invention. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] The four types of sodium alginate used in this invention are all from Lianyungang Tiantian Seaweed Industry Co., Ltd. (item number: 6686681018 (representing brown powder SA-1, low-viscosity granules SA-2, high-viscosity granules SA-3, and industrial-grade sodium alginate SA-4, respectively), and other raw materials are commercially available in the field unless otherwise specified.

[0034] Test method: 1. Determination of gel sphere encapsulation efficiency and loading amount (1) Determination of surface oil of gel spheres: Weigh 2.5 g (m1) of sample into a beaker, add 10 ml of petroleum ether, stir magnetically for 2 min, filter into a beaker (m2), wash with 10 ml of petroleum ether, and dry to constant weight (m3).

[0035] Surface oil coverage = (m3 - m2) / m1 × 100% (2) Determination of total oil content of gel beads: Weigh 2.5 g (m4) of sample into a beaker, add 20 ml of petroleum ether, sonicate for 1 h, then filter into a beaker (m5) and dry to constant weight (m6).

[0036] Total fuel volume = (m6 - m5) / m4 × 100% (3) Encapsulation efficiency of gel beads = (1 - surface oil content / total oil content) × 100% (4) Gel ball loading = Total oil volume - Surface oil volume / m1 × 100% 2. Determination of the sphericity of gel spheres A certain number of liquid core gel spheres were randomly selected, and their shapes were photographed. The spherical dimensions of the liquid core gel spheres were measured using the image processing software ImageJ.

[0037] Sphericity φ = 2 × d min / (d min + d max ) Where d min For the shorter diameter of the liquid core sphere, d max The sphericity is the longer diameter of the liquid core sphere. For liquid core spheres with φ > 0.95, the sphericity is considered relatively ideal. The average value is used to analyze the sphericity, and the coefficient of variation for each data set is calculated to be less than 0.02 using SPSS software.

[0038] 3. Determination of weight loss rate of gel beads The weight loss rate is defined as the ratio of the mass of the liquid core sphere after a period of time to its initial mass. This indicator reflects the degree of water loss from the liquid core sphere after a period of time in a simulated room temperature environment. Since the outer shell of the sodium alginate gel sphere is an aqueous solution of sodium alginate, it will lose water and weight due to water evaporation under constant temperature and humidity conditions.

[0039] Take a clean, dry beaker and accurately weigh it (m7). Take a certain amount of sample, wipe the moisture off the surface of the gel beads with filter paper, add it to the beaker, and accurately weigh the initial total weight (m8). Place the gel beads in a constant temperature and humidity chamber at a certain temperature and relative humidity, remove them after 24 hours, and accurately weigh their mass (m9). After removing the sample, accurately weigh the beaker and the remaining oil (m). 10 ), calculate the weight loss rate.

[0040] Weight loss rate = (m9 - m) 10 ) / (m8-m7)×100% 4. Determination of oil loss rate of gel beads Oil loss rate is the ratio of the mass of oil lost by the liquid core gel sphere after a period of time to the initial mass of the liquid core sphere. This indicator reflects the degree of oil leakage from the core material of the liquid core sphere after a period of time in a simulated room temperature environment.

[0041] Take a clean, dry beaker and accurately weigh it (m). 11 Take a certain amount of dried sample, add it to a beaker, and accurately weigh the initial total weight (m). 12 Place the gel beads in a 25°C, constant temperature and humidity chamber, remove them after 24 hours, and accurately weigh them (m). 13 ), calculate the oil penetration rate.

[0042] Oil loss rate = (m 13 - m 11 ) / (m 12 - m 11 ) × 100% 5. Determination of mechanical properties of gel beads The mechanical properties of the gel spheres were determined using a TA-XT2i property analyzer equipped with a 5 kg force unit. The liquid-core gel spheres were placed in the center of the chassis and compressed using a Stable Micro Systems P / 5 Dia Cylinder Probe. The test conditions were as follows: initial compression rate of 1 mm / sec, compression rate of 5 mm / sec, compression rate of 10 mm / sec, maximum deformation under compression of 95%, and trigger force of 1.5 g.

[0043] When the probe is pressed down, it experiences a 1.5 g reaction force from the liquid-core gel sphere. The probe height at this point is recorded as the burst distance. The ratio of the burst distance to the sphere diameter and the elastic modulus reflect the elasticity of the sphere. At the start of the test, the ratio of the reaction force from the sphere to the pressing time at 5% of the burst distance is recorded as the elastic modulus of the sphere. The force recorded at the maximum pressure during the entire process is the burst force; the percentage of the sphere's height at this point is the burst strain.

[0044] The mechanical performance testing experiment was repeated at least 5 times. The experimental data were processed and analyzed using SPSS software. The Duncan test was used for analysis of variance (ANOVA), with a confidence interval of 95% and a significance level of p<0.05.

[0045] Example 1 This embodiment provides a method for preparing highly stable liquid-core sodium alginate gel spheres for encapsulating oils, specifically: (1) Preparation of sodium alginate solution: At room temperature, take deionized water and slowly add SA-3 type sodium alginate while magnetically stirring (300 r / min). Stir until completely dissolved to form a 3.0% (w / v) sodium alginate solution. Let stand for 30 min to remove bubbles. (2) Preparation of coagulation bath: Take deionized water, add calcium lactate, stir until completely dissolved to form a 2.5% (w / v) calcium lactate coagulation bath, and place it in a constant temperature environment of 25℃; (3) Construction of coaxial extrusion device: a double-layer coaxial extrusion nozzle is adopted. The inner layer of the hose has an inner diameter of 4 mm and an outer diameter of 6 mm (for conveying the core material). The outer layer of the hose is sleeved on the outside of the inner layer (for conveying sodium alginate solution). A calcium lactate coagulation bath is placed 10 cm below the nozzle. A magnetic stir bar (100 r / min) is placed in the coagulation bath. (4) Formation of liquid core gel spheres: The flow rate is controlled by an injection pump. The flow rate of the core material (edible vegetable oil) is 2 mL / min, and the flow rate of the sodium alginate solution is 5 mL / min. After the core material is wrapped by the sodium alginate solution, it forms droplets and is dropped into the calcium lactate coagulation bath. (5) Crosslinking reaction and post-treatment: The droplets crosslinked in the coagulation bath for 5 min to form gel balls; then the gel balls were taken out, rinsed twice with deionized water (30 s each time to terminate the crosslinking reaction), and rinsed once with anhydrous ethanol (30 s to remove residual oil on the surface). The water was drained to obtain the liquid core sodium alginate gel balls.

[0046] (6) Storage period verification: The prepared liquid core gel balls were stored at 25°C and 53% relative humidity for 0 days, 3 days, 5 days, 7 days and 14 days, and the changes in sensory and physicochemical indicators of the gel balls during the storage period were monitored.

[0047] Figure 15 This is a conceptual diagram illustrating the construction of a coaxial extrusion apparatus for this invention. The method uses SA-3 type sodium alginate (M / G ratio 0.3619) as the wall material (3.0%, w / v), edible vegetable oil as the core material, and 2.5% (w / v) calcium lactate as the crosslinking agent. It employs a composite process of "sharp-hole coagulation bath method + coaxial extrusion method," controlling the core material flow rate at 2 mL / min, the wall material flow rate at 5 mL / min, and the reaction time at 5 min. The resulting liquid-core gel spheres exhibit an encapsulation rate ≥98%, sphericity ≥0.95, and bursting force ≥390g. Storage period verification results show that after 14 days of storage at 25℃ and 53% relative humidity, the oil seepage rate is <5%. Figure 1 The sensory evaluation results show that the odor, color, shape, and popping sensation did not change much during storage, indicating that the liquid core gel spheres have excellent stability during storage.

[0048] Example 2 The difference between this embodiment and Example 1 is that the mass concentration of sodium alginate solution in step 1) is adjusted to 1.5%, 2.0%, 2.5%, 3.0%, and 3.5% (w / v), respectively. The remaining steps are the same as in Example 1, resulting in gel spheres prepared with different sodium alginate concentrations in this embodiment.

[0049] Figure 2 The figure shows the viscosity of sodium alginate solutions at different concentrations. The apparent viscosity of sodium alginate solutions at different concentrations decreases with increasing shear time, exhibiting the shear-thinning behavior characteristic of non-Newtonian pseudoplastic fluids. At the same shear rate, the viscosity of sodium alginate solutions increases with increasing concentration.

[0050] Figure 3 and Figure 4This study investigated the effects of different concentrations of sodium alginate on various aspects of the prepared liquid core gel spheres, including appearance, sphericity, oil encapsulation rate, loading, weight loss, oil loss, and mechanical properties. Overall, as the sodium alginate concentration increased, the spheres gradually increased in size. At excessively high concentrations, the spheres exhibited tailing, becoming elliptical or elongated. A 3.0% sodium alginate concentration showed high sphericity, better encapsulation rate, weight loss, and oil loss, and the highest bursting force. This may be due to the increased interaction between sodium alginate and Ca... 2+ Increased cross-linking opportunities lead to a denser gel shell, thereby increasing the mechanical strength and bursting potential of the liquid core gel spheres. However, excessively high sodium alginate concentrations can reduce the calcium content. 2+ Diffusion within the matrix reduces the chance of binding, leading to increased flexibility of the outer wall of the liquid core gel sphere, which in turn reduces mechanical properties and decreases the bursting sensation.

[0051] Example 3 The difference between this embodiment and Embodiment 1 is that the type of sodium alginate in step 1) is adjusted, and it is divided into four types: SA-1, SA-2, SA-3, and SA-4 according to the different M / G ratios. The remaining steps are the same as in Embodiment 1, and gel spheres prepared with different types of sodium alginate are obtained in this embodiment.

[0052] The M / G ratios of four sodium alginate species were determined using circular dichroism spectroscopy, and the results are shown in the table below:

[0053] Figure 2 The graph shows the viscosity changes for different types of sodium alginate. Based on the M / G ratio results above, it can be seen that the M / G content of sodium alginate is inversely proportional to its viscosity, that is, the higher the G segment content, the greater the viscosity of sodium alginate.

[0054] Figure 5 and Figure 6 To investigate the effects of different sodium alginate types on various properties of liquid-core gel spheres, considering factors such as sphericity, encapsulation efficiency, structural stability, and mechanical properties, SA-3 sodium alginate was determined to be the optimal wall material for preparing liquid-core gel spheres. It achieved the highest sphericity, significantly outperforming other types; simultaneously, its encapsulation efficiency approached complete embedding, demonstrating excellent core material retention. Regarding structural stability, the gel film formed by SA-3 exhibited moderate density, effectively controlling moisture loss and inhibiting oil exudation. In terms of mechanical properties, SA-3 maintained high burst strength while possessing suitable deformation characteristics, enabling the gel spheres to combine structural strength with an ideal bursting texture. The G-segment of sodium alginate and Ca... 2+ They are more likely to cross-link and react, forming a hydrogel shell. A higher M-segment content affects the reaction between sodium alginate and Ca. 2+The cross-linking process of the liquid core gel spheres results in flexibility and poor mechanical properties; when the G segment content is high, it interacts with Ca... 2+ Increased cross-linking opportunities result in a denser gel shell, leading to highly elastic and strong liquid-core gel spheres. Although SA-4, with a higher G-segment content, is slightly better in some rigidity indicators, its sphericity is significantly reduced. SA-3, on the other hand, exhibits more balanced overall performance, demonstrating the best comprehensive performance.

[0055] Example 4 The difference between this embodiment and Example 1 is that the mass concentration of the calcium lactate solution in step 2) is adjusted to 1.0, 1.5, 2.0%, 2.5%, and 3.0% (w / v), respectively. The remaining steps are the same as in Example 1, and gel spheres with different calcium lactate concentrations are obtained in this embodiment.

[0056] Figure 7 and Figure 8 To investigate the effect of different calcium lactate concentrations on sodium alginate liquid-core gel spheres, considering factors such as sphericity, encapsulation performance, structural stability, and mechanical strength, a calcium ion concentration of 2.5% was determined to be the optimal crosslinking condition for preparing liquid-core gel spheres. Its superior performance stems from the optimal balance between crosslinking density and structural integrity achieved at this concentration during gel network formation. Regarding encapsulation performance, gel spheres prepared at a 2.5% calcium ion concentration achieved excellent levels in both encapsulation efficiency and loading capacity, indicating that this condition effectively prevents core material leakage by forming a sufficiently dense gel network while avoiding the "thick shell" effect caused by excessive crosslinking, thus preserving ample space for the core material. In terms of structural stability, gel spheres prepared at this concentration exhibited the lowest oil loss rate, demonstrating good integrity and sealing performance of the formed gel film. The most outstanding feature is its mechanical performance. A calcium ion concentration of 2.5% imparts the highest bursting force to the gel spheres while maintaining suitable deformation characteristics. This indicates that this crosslinking density provides sufficient structural strength to resist external pressure while maintaining the necessary elasticity of the gel network, thus achieving a perfect balance between the "bursting sensation" and structural stability. In contrast, the gel network formed at lower calcium concentrations has insufficient crosslinking, resulting in a loose structure, poor encapsulation, and low mechanical strength; while higher concentrations cause excessive crosslinking, leading to gel structural changes and weakening the overall performance. Therefore, a calcium ion concentration of 2.5% achieves the optimal balance between promoting the formation of an ideal gel network, ensuring structural integrity, and realizing the best functional properties.

[0057] Example 5 The difference between this embodiment and Embodiment 1 is that the cross-linking reaction time in step 5) is adjusted to 1, 2, 3, 4, and 5 min, while the remaining steps are the same as in Embodiment 1, resulting in gel spheres prepared with different cross-linking reaction times in this embodiment.

[0058] Figure 9 and Figure 10 To investigate the impact of different cross-linking reaction times on the formed liquid core gel spheres, considering key indicators such as sphericity, encapsulation performance, structural stability, and mechanical strength, a reaction time of 5 min was determined as the optimal process parameter for preparing liquid core gel spheres. Regarding encapsulation performance, a 5-min reaction time resulted in the highest gel sphere loading while maintaining an encapsulation rate close to the optimal level, indicating that this duration is sufficient to ensure the complete formation of the gel wall layer and effectively encapsulate the core material. In terms of structural stability, as the reaction time was extended to 5 min, the gel spheres exhibited a lower oil leakage rate, demonstrating a more dense and complete internal network structure and a significantly improved oil sealing effect. Most importantly, regarding mechanical properties, a 5-min reaction time endowed the gel spheres with near-maximum bursting force while maintaining suitable deformation characteristics, indicating that the gel network had reached an optimal cross-linking density, capable of withstanding external pressure while maintaining ideal taste characteristics. Although a 30-minute reaction time has a slight advantage in some mechanical indicators, considering the balance between actual production efficiency and performance improvement, a 5-minute reaction time can meet the efficiency requirements of industrial production while ensuring the high quality of the product, making it the best choice for optimizing overall performance and production efficiency.

[0059] Comparative Example 1 The difference between this comparative example and Example 1 is that the relative humidity in step 6) is adjusted to 0%, 32%, 53%, 85%, and 100%, while the remaining steps are the same as in Example 1, to obtain gel balls stored under different relative humidity conditions in this comparative example.

[0060] Figure 11 To investigate the changes in the apparent state and sphericity of liquid-core gel spheres during storage under different humidity levels, the sphericity of the gel spheres remained optimal in a medium-high humidity environment (53%-100%), with significantly less variation than under low humidity conditions. This is because the moderate ambient humidity effectively slows down the evaporation of moisture from the gel membrane, preventing membrane shrinkage and sphere collapse due to excessive water loss. However, in a dry environment (0%-32%), rapid water loss causes membrane denaturation, leading to a significant decrease in sphericity.

[0061] Figure 12The variation in bilayer membrane thickness of liquid-core gel spheres during storage under different humidity levels was investigated. Generally, the bilayer membrane thickness gradually decreased with prolonged storage. Specifically, the lower the relative humidity, the more significant the decrease in bilayer membrane thickness, with the largest reduction rate occurring between 0 and 3 days, after which the decrease slowed. Conversely, at higher relative humidity, the decrease in bilayer membrane thickness was more gradual, with the largest reduction span between 3 and 5 days. This may be because in drier environments, the larger humidity difference from the initial humidity of the gel spheres leads to faster moisture loss and greater changes in bilayer membrane thickness during the first three days of storage; in more humid environments, moisture loss is slower, resulting in a more gradual change in bilayer membrane thickness. Overall, at 53% humidity, the rate of decrease in bilayer membrane thickness was the most gradual, contributing to the long-term stability of the membrane structure.

[0062] Figure 13 To investigate the changes in the mechanical properties of liquid-core gel spheres during storage under different humidity levels, under lower relative humidity conditions, the bursting force of the liquid-core gel spheres gradually increased with prolonged storage time; when the relative humidity was higher, the bursting force showed a trend of first decreasing and then increasing. Overall, gel spheres stored at 53% humidity exhibited the most ideal trend in mechanical property changes: the bursting force remained stable, and the bursting distance and strain variations were minimal. This indicates that this humidity condition effectively maintained a moderate cross-linking state of the gel network, preventing increased brittleness due to excessive water loss in dry environments and structural softening caused by excessive water absorption under high humidity, thus maintaining good mechanical strength and elastic properties during storage.

[0063] Figure 14 To investigate the changes in oil content of liquid-core gel spheres during storage under different humidity levels, the oil content of the gel spheres remained highly stable throughout the storage period at 53% relative humidity, demonstrating optimal oil resistance. This is because suitable humidity maintained the integrity and density of the gel film, preventing oil seepage caused by film shrinkage and cracking in dry environments, and also preventing film structure relaxation that may occur under high humidity, thus achieving the best encapsulation effect on the core material's oil.

[0064] Based on a comprehensive evaluation across four dimensions, a relative humidity of 53% demonstrated significant advantages in maintaining the structural integrity, mechanical properties, and encapsulation stability of the gel spheres. This humidity condition created an ideal moisture balance environment, effectively preventing excessive water loss and shrinkage of the gel network while avoiding structural weakening caused by excessive water absorption, thus maintaining the product's quality characteristics throughout a storage period of up to 14 days. In contrast, lower humidity can cause structural collapse and oil seepage, while higher humidity can lead to a decline in mechanical properties. Therefore, 53% relative humidity was established as the optimal condition for achieving long-term stable storage of liquid-core sodium alginate gel spheres.

[0065] In summary, this invention provides a method for preparing highly stable sodium alginate liquid-core gel spheres encapsulating oils. The method combines a sharp-orifice-coagulation bath method and a coaxial extrusion method to construct sodium alginate liquid-core gel spheres encapsulating oils. Single-factor experiments were conducted to investigate the effects of sodium alginate concentration, sodium alginate type, and Ca2+ concentration. 2+ Analysis of four factors—concentration, reaction time, and concentration—determined the optimal preparation conditions as follows: sodium alginate SA-3 at a concentration of 3.0% (w / v), and Ca... 2+ The concentration was 2.5% (w / v), the reaction time was 5 min, the drop height was 10 cm, and the core liquid flow rate was 2 mL / min. After storage stability testing, under conditions of 25℃ and 53% relative humidity, the optimal process resulted in liquid-core gel spheres with an encapsulation rate exceeding 98%, good sphericity, and an oil leakage rate of less than 5% after 14 days of storage at room temperature. It exhibited superior performance in sensory evaluation and physicochemical indicators, making it suitable for further industrial production. This method can also be used to further develop the encapsulation of fat-soluble vitamins, flavorings, pigments, and other fat-soluble functional factors, as well as for food flavor improvement, with a wide range of applications.

[0066] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended 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 method for preparing a highly stable liquid-core sodium alginate gel sphere for encapsulating oils, characterized in that: include, Preparation of wall material solution: Dissolve sodium alginate in deionized water to form sodium alginate wall material solution, and let it stand to remove bubbles; Preparation of cross-linking coagulation bath: Dissolve calcium lactate in deionized water to form a calcium lactate coagulation bath; Coaxial extrusion dripping: A double-layer coaxial extrusion dripper is used. The inner tube delivers edible vegetable oil, and the outer tube delivers sodium alginate solution. The two solutions are extruded from the dripper at the same time to form the core liquid. Crosslinking and post-treatment: The core liquid was stirred and reacted in a coagulation bath, then rinsed with deionized water and anhydrous ethanol in sequence, and drained to obtain liquid core sodium alginate gel balls; Sodium alginate is of type SA-3.

2. The preparation method according to claim 1, characterized in that: The concentration of the sodium alginate solution is 1.5~3.5% (w / v), and the viscosity of the sodium alginate is 100~2000 mPa·s.

3. The preparation method according to claim 1, characterized in that: The concentration of the calcium lactate solution is 1.0~3.0% (w / v).

4. The preparation method according to claim 1, characterized in that: The inner flexible tube delivers edible vegetable oil at a flow rate of 1-3 mL / min; the outer flexible tube delivers sodium alginate solution at a flow rate of 4-6 mL / min.

5. The preparation method according to claim 1, characterized in that: The crosslinking reaction time is 1-5 min; the deionized water rinsing is performed 1-2 times, each time for 20-30 s; Rinse with anhydrous ethanol 1-2 times, each time for 20-30 seconds.

6. The liquid-core sodium alginate gel spheres prepared by any of the preparation methods described in claims 1-4.

7. The liquid-core sodium alginate gel sphere as described in claim 6, characterized in that: The liquid core sodium alginate gel spheres have an encapsulation rate of ≥98%, a sphericity of ≥0.95, and a bursting force of ≥390g.

8. The liquid-core sodium alginate gel sphere as described in claim 6, characterized in that: The storage conditions for the gel balls are: relative humidity 53%-85%, temperature 25℃, and oil seepage rate < 5% after 14 days of storage.

9. The liquid-core sodium alginate gel sphere as described in claim 6, characterized in that: The edible vegetable oil is the core material, including one or more of blended vegetable oils, olive oil, or sunflower seed oil.

10. The application of the liquid-core sodium alginate gel spheres as described in claim 6 in food flavor improvement and stable encapsulation of fat-soluble active substances.

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