Freeze-drying processing method of tea oil chocolate

Abstract

The invention belongs to the technical field of food processing, and particularly relates to a tea oil chocolate freeze-drying processing method. The method comprises the following steps: embedding the tea oil into nano microcapsules by using a polylactic acid-glycolic acid copolymer; hyperbranched polyglycerol ester is introduced into the chocolate matrix; the two components are compounded and homogenized through high-pressure microjet to form a structured emulsion; complete vitrification is realized through directional crystallization and programmed freezing; and finally carrying out low-temperature steady-state sublimation drying and annealing treatment. According to the method, two-phase performance matching is realized through rigid support of the nano-microcapsules, interface coupling of the hyperbranched polymer and cooperation of a precise process, so that the product has high crispness, fine and smooth melt taste and excellent stability.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, and specifically relates to a method for freeze-drying tea oil chocolate. Background Technology

[0002] As a popular solid food, the taste, flavor, and texture of chocolate are key factors determining consumer acceptance. With the growing popularity of healthy food concepts, introducing functional oils (such as tea oil rich in unsaturated fatty acids) into the chocolate base to develop products with added nutritional value has become an important research direction in this field. However, the combination of liquid oils with solid chocolate systems consistently faces significant challenges in achieving both stability and flavor harmony.

[0003] Freeze-drying technology, capable of removing moisture at low temperatures while preserving heat-sensitive components (such as active substances in tea oil) to the greatest extent and imparting a unique crisp and porous structure to the product, is considered a potential method for preparing high-end functional solid foods. While attempts have been made to freeze-dry oil-containing slurries, their application to chocolate systems typically reveals the following common problems: the glassy structure formed during freeze-drying of components such as sugars and cocoa solids in the chocolate matrix lacks sufficient strength and is prone to collapse due to stress from water sublimation or subsequent moisture absorption, resulting in a loss of crispness and a tough or sticky texture. During the freezing and sublimation stages of freeze-drying, liquid oils are prone to phase separation and migration. Because ice crystal growth displaces oil components, and the pressure gradient at the sublimation front can drive oil movement, the dried oils are unevenly distributed at the microscale, with localized enrichment areas prone to oxidative rancidity and resulting in greasy spots on the palate. Physically mixed oils and the chocolate matrix fail to achieve effective flavor fusion within the porous structure formed during freeze-drying, easily leading to a flavor separation sensation during consumption.

[0004] To address the aforementioned issues, existing technologies typically employ the following conventional approaches: adding maltodextrin, colloids, etc., to increase solids content and emulsion stability, attempting to form a more robust skeletal structure during drying; controlling the freezing rate and temperature and pressure parameters during the sublimation stage to obtain a more uniform ice crystal structure and gentler drying stress; and using methods such as spray drying to pre-encapsulate the oils, reducing their direct interaction with the matrix and the risk of oxidation through physical isolation.

[0005] However, these conventional methods have obvious limitations. The introduction of additives may alter the inherent flavor and texture of chocolate; optimizing process parameters has limited effectiveness in addressing issues such as oil migration and interfacial stress concentration at the microscale; and traditional microencapsulation processes (such as spray drying) often involve high-temperature steps, which may damage heat-sensitive nutrients in tea oil, and the capsule wall material may have poor compatibility with the chocolate matrix, resulting in a foreign body sensation in the final product.

[0006] More importantly, existing technologies typically focus on macroscopic structural integrity, drying efficiency, or oxidative stability, neglecting a fundamental issue lurking at the microscopic scale that affects the final texture and taste experience of the product: during the freeze-sublimation phase transition of a complex system composed of multiphase components (liquid oils, solid chocolate matrix, ice crystals), the differences in their thermophysical properties (such as coefficients of thermal expansion, glass transition temperatures, and moduli) cause persistent microscopic internal stresses at their phase interfaces. These stresses gradually lead to numerous nano- to micrometer-scale microcracks within the product after drying and during storage. These microcracks not only directly weaken the product's mechanical strength, making it more fragile during packaging and transportation, but also cause uneven disintegration and abrupt oil release during chewing, severely compromising the smoothness and integrity of the taste. Currently, no technical solution in this field has been found that can systematically identify and effectively solve the problem of microscopic cracks caused by the mismatch of multiphase dynamic mechanical properties in freeze-dried tea oil chocolate products.

[0007] Therefore, there is an urgent need to develop a novel freeze-drying processing method for tea oil chocolate. This method must not only ensure the integrity of the macroscopic structure and the stability of the oil, but also achieve precise control over the interfacial structure and mechanical behavior of multiphase components at the nano and micro scales through material selection and process design, so as to obtain innovative products with excellent nutrient retention, superior taste and texture, and long-term stability. Summary of the Invention

[0008] The technical problem to be solved by this invention is to develop a novel freeze-drying processing method for tea oil chocolate. This method not only needs to ensure the integrity of the macroscopic structure and the stability of the oil, but also needs to achieve precise control over the interface structure and mechanical behavior of multiphase components at the nano and micro scales from the aspects of material selection and process design, so as to obtain an innovative product with excellent nutrient retention, superior taste and texture and long-term stability.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: The freeze-drying process for tea oil chocolate includes the following steps: S1: Using polylactic acid-glycolic acid copolymer (PLGA) as the wall material, nanocapsules encapsulating tea oil were prepared by emulsification-solvent evaporation method, wherein the average particle size of the nanocapsules was 150-400 nm. S2: Melt the dark chocolate, add hyperbranched polyglycerol (HPG) and isomaltitol, and stir until smooth; S3: The nano-microcapsule powder obtained in S1 is redispersed in refined tea oil to form a suspension, which is then added to the chocolate matrix in S2 and homogenized by high-pressure microfluidic jet to form a nano-composite structured emulsion. S4: The emulsion obtained in S3 is subjected to programmed cooling and freezing, including isothermal cooling at the chocolate fat crystallization temperature to promote crystallization, followed by rapid cooling to complete vitrification; S5: Low-temperature steady-state sublimation drying: Under vacuum, the shelf temperature is controlled to carry out sublimation drying and desorption drying, so that the moisture content of the final product is ≤2%; S6: After drying, let the product stand for 24-48 hours in a low-humidity environment at 25-30℃.

[0010] Furthermore, in the above-mentioned freeze-drying processing method for tea oil chocolate, in S1, the molecular weight Mw of the polylactic acid-glycolic acid copolymer is 10,000-30,000, the molar ratio of lactic acid to glycolic acid is 75:25, and the mass ratio of tea oil to polylactic acid-glycolic acid copolymer is 100:(5-15).

[0011] Furthermore, in the above-mentioned freeze-drying processing method for tea oil chocolate, in S2, the hyperbranched polyglycerol has a generation number of 3-5, and its addition amount is 0.5%-3% of the total mass of the chocolate matrix; the addition amount of isomaltitol is 3%-8% of the total mass of the chocolate matrix.

[0012] Furthermore, in the above-mentioned freeze-drying processing method for tea oil chocolate, in S3, the ratio of the total mass of tea oil to the total mass of chocolate matrix is ​​1:(5-8); the pressure of the high-pressure micro-jet homogenization is 15000-25000 psi, and the number of cycles is 3-5.

[0013] Furthermore, in the above-mentioned freeze-drying processing method for tea oil chocolate, S4 specifically includes: the first stage of cooling to 29-31℃ at 1.5-2℃ / min and maintaining the temperature for 20-30 minutes; the second stage of cooling to -10℃ at 0.5-1℃ / min; and the third stage of rapidly cooling to below -50℃ at 2-3℃ / min and maintaining the temperature.

[0014] Furthermore, in the above-mentioned freeze-drying processing method for tea oil chocolate, in step S5, the pressure in the chamber is controlled at 8-12 Pa during the sublimation drying stage, and the shelf temperature is slowly and linearly increased from -40℃ to -15℃ for 15-20 hours.

[0015] The beneficial effects of this invention are as follows: By constructing a gradient modulus nano-buffered interface, the product showed almost no new microcracks after accelerated stability testing (temperature cycling, vibration), solving the core problem of identification in the background technology.

[0016] Before entering the mouth, the product exhibits extremely high crispness (high glassy strength). After entering the mouth, under the action of saliva and body temperature, the HPG-PLGA buffer layer allows heat and moisture to be evenly transferred. The tea oil nanocapsules and chocolate matrix melt and release in a synergistic and gradual manner, bringing an unprecedented "delicate, silky, and integrated luxurious taste" without any abrupt oily or grainy feeling.

[0017] The PLGA shell provides excellent physical insulation and antioxidant protection for tea oil, and the introduction of HPG did not promote oxidation. Under accelerated oxidation conditions (60℃), the peroxide value of the product increased significantly slower than that of the control group, and the shelf life is predicted to be extended by more than 50%.

[0018] This method allows for greater flexibility in adjusting the amount of tea oil added without worrying about cracking or deterioration in taste, opening up a new path for developing functional chocolate products with high tea oil content. Detailed Implementation

[0019] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0020] This invention relates to a freeze-drying processing method for tea oil chocolate, comprising the following steps: S1: Refined tea oil is mixed with a certain amount of medium-low molecular weight polylactic acid-glycolic acid copolymer (PLGA, LA:GA=75:25, molecular weight Mw 10,000-30,000) at a mass ratio of 100:(5-15), and an appropriate amount of dichloromethane is added as a co-solvent to form a homogeneous oil phase. Simultaneously, a polyvinyl alcohol (PVA, degree of hydrolysis 87-89%) solution (concentration 2-5%) is used as the aqueous phase. Under ice-water bath and high-speed shearing (15,000-20,000 rpm), the oil phase is slowly injected into the aqueous phase for pre-emulsification for 2-5 minutes. The pre-emulsion is then transferred to a probe-type ultrasonic cell disruptor and ultrasonically treated (2 seconds working, 3 seconds rest) for a total of 5-10 minutes under ice bath and power of 400-600W to form an O / W promulgated emulsion. The colostrum was subjected to magnetic stirring and solvent evaporation at room temperature for 12-24 hours. After centrifugation, washing, and freeze-drying, tea oil-PLGA nanocapsule powder was obtained. The average particle size of these microcapsules was 150-400 nm, with an encapsulation efficiency >92%. The core of this step is the transformation of liquid tea oil into solid nanoparticles with a clearly defined polymer shell. The Tg of these nanoparticles is determined by the PLGA shell (approximately 45-50℃), which is much higher than the Tg of pure tea oil (approximately -80℃), thus fundamentally altering the dynamic mechanical properties of the oil phase.

[0021] S2: Melt dark chocolate (cocoa content ≥60%) at 45-48℃. While stirring, add 0.5%-3% of hyperbranched polyglycerol ester (HPG, generation 3-5) and 3%-8% of isomaltitol, based on the total mass of the chocolate matrix (chocolate + additives). Continue stirring until completely dissolved and evenly dispersed. HPG, as a highly branched polymer with numerous terminal hydroxyl groups, possesses excellent interfacial activity and reactive sites, but it has never been used in chocolate or freeze-dried food systems before. Its role is not traditional emulsification, but rather physical entanglement and hydrogen bonding with the PLGA shell in subsequent steps, forming a strong "interfacial coupling layer." Isomaltitol acts as a low-hygroscopic, high-Tg filler, helping to improve the glassy strength of the matrix.

[0022] S3: The tea oil-PLGA nanocapsule powder obtained in S1 is redispersed in a small amount (approximately 2-3 times the powder mass) of refined tea oil preheated to 35-40℃. A "nanocapsule-enhanced tea oil suspension" is formed using gentle ultrasound (100W power, 1 minute). This suspension is then added to the warm chocolate matrix from S2 under slow stirring. The total mass ratio of tea oil (including the microcapsules and suspension medium) to the total mass of the chocolate matrix is ​​1:(5-8). Homogenization is performed for 3-5 cycles using a high-pressure microfluidic homogenizer at 30-40℃ and 15000-25000 psi, ultimately forming a "nanocomposite structured emulsion" with uniformly dispersed nanocapsules coupled to the matrix interface via HPG. The key to this process is temperature control, ensuring that the chocolate matrix is ​​not fully crystallized and that the HPG has good fluidity to achieve effective interfacial coupling.

[0023] S4: Inject the nanocomposite emulsion obtained in S3 into the mold and perform precise temperature-controlled cooling. First stage: Cool to 29-31℃ (the typical crystallization temperature range of chocolate butter) at a rate of 1.5-2℃ / min, and maintain this temperature for 20-30 minutes to promote the formation of a stable β-V crystal form in chocolate butter. At this time, the interfacial coupling network between HPG and PLGA is initially formed and anchored by the growing butter crystals.

[0024] The second stage involves reducing the temperature from 31°C to -10°C at a rate of 0.5-1°C / min. During this stage, water is separated into ice crystals, and hydrophilic components such as isomaltitol are concentrated.

[0025] The third stage involves rapidly cooling the system to below -50°C at a rate of 2-3°C / min and maintaining this temperature for 2 hours, allowing the entire system (aqueous phase, oil phase, and polymer phase) to fully vitrify. At this point, the PLGA microcapsules (high Tg), HPG coupling layer, chocolate ester crystal network, and glassy aqueous matrix together constitute a multiphase composite glass with a gradient transition in dynamic mechanical properties.

[0026] S5: Place the sample in a freeze dryer. A near-Tg drying strategy is employed: the shelf temperature during the sublimation stage is controlled to remain at least 10°C below the glass transition temperature (Tg') of the chocolate matrix-water blend system, but above the Tg of the PLGA microcapsule shell (approximately 45°C) to ensure its rigidity. Specific parameters: chamber pressure 8-12 Pa, shelf temperature slowly and linearly increased from -40°C to -15°C (over 15-20 hours). During this stage, the ice crystals sublimate slowly. Due to the rigid support of the PLGA microcapsules and the stress buffering effect of the HPG coupling layer, the drying stress is evenly distributed, avoiding concentration at fragile interfaces.

[0027] Then, analytical drying is carried out: the shelf temperature is gradually increased to 25°C, the chamber pressure is reduced to below 5 Pa, and this process is continued for 5-8 hours, with the final product having a moisture content of ≤2%.

[0028] S6: Place the dried product in a sealed environment with a temperature controlled at 25-30℃ (above room temperature but far below the PLGA Tg and chocolate matrix Tg) and a relative humidity of <10% for 24-48 hours. This step aims to allow the product to release residual internal stress through the minimal relaxation of the molecular chains under no external stress conditions, thereby achieving a more thermodynamically stable state at the nanoscale coupling interface.

[0029] In the above embodiments, PLGA encapsulates low-Tg liquid tea oil into high-Tg rigid nanoparticles, fundamentally improving the mechanical properties of the oil phase. HPG acts as a "molecular bridge," with one end tightly bound to the PLGA shell through physical interaction, and the other end interacting with the chocolate matrix (especially sugars and proteins). The combination of these two forms an "elastic buffer interface layer" with a gradient modulus between the oil phase and the matrix phase, rather than a traditional sharp interface. This interface layer effectively absorbs and disperses micro-stress caused by differences in the thermal expansion coefficients of the two phases or external stress, preventing crack initiation.

[0030] High-pressure microfluidic homogenization ensured uniform dispersion and interfacial bonding of the nanocapsules and HPG. The subsequent directional crystallization process not only enabled the chocolate butter to form a stable crystal form, but more importantly, it allowed the HPG-PLGA coupling network to be orderly integrated into the entire solid network structure during the growth of the lipid crystals, achieving multi-level reinforcement of "points" (microcapsules), "lines" (HPG couplings), and "surfaces" (lipid crystal network).

[0031] The rigidity of the PLGA microcapsules provides an "internal skeleton" support during the sublimation drying stage, preventing structural collapse. The near-Tg drying strategy avoids viscous flow and structural reorganization caused by the glass transition of the matrix. While maintaining overall structural rigidity, the HPG-PLGA buffer interface absorbs and dissipates drying stress.

[0032] The aforementioned steps constructed a highly non-equilibrium glassy composite system. Mild annealing allows for minute relaxation at the nanoscale while maintaining macroscopic solidity and a crisp texture, promoting a more balanced conformation of the HPG-PLGA coupling interface, thereby maximizing its buffering capacity and achieving long-term stability.

[0033] Example 1 S1: Dissolve 100g of tea oil and 10g of PLGA (Mw=15,000, LA:GA=75:25) in 50mL of dichloromethane. Dissolve 5g of PVA in 200mL of deionized water as the aqueous phase. Under ice bath conditions, pour the oil phase into the aqueous phase and pre-emulsify by high-speed shearing at 18,000 rpm for 3 minutes. Transfer to an ultrasonic disruptor (500W, ice bath) and sonicate for 8 minutes in a pulse mode with a 2-second working time and a 3-second intermittent time. Then, magnetically stir for 24 hours to evaporate the solvent, centrifuge at 8,000 rpm for 15 minutes to collect the precipitate, wash twice with deionized water, and freeze-dry to obtain a pale yellow powder. The average particle size of the nanocapsules was measured to be 220 nm, with an encapsulation efficiency of 94.5%.

[0034] S2: Melt 500g of dark chocolate (70% cocoa content) at 47℃. Add 5g of hyperbranched polyglycerol (4th generation, HPG-4) and 30g of isomaltitol, and stir until completely homogeneous.

[0035] S3: Take 10g of the nano-microcapsule powder obtained in S1 and mix it with 20g of refined tea oil preheated to 38℃. Disperse the mixture by gentle sonication (100W, 1 minute). Add this suspension to the S2 chocolate matrix while stirring. The total mass of tea oil is 30g (10g from the microcapsules + 20g from the suspension medium), and the mass ratio of tea oil to chocolate matrix is ​​approximately 1:16.7. Homogenize for 4 cycles using a high-pressure microfluidic homogenizer at 35℃ and 20,000 psi.

[0036] S4: Inject into the mold. Programmed cooling: ① 2℃ / min to 30℃, hold for 25 minutes; ② 0.8℃ / min to -10℃; ③ 2.5℃ / min rapid cooling to -55℃, hold for 2 hours.

[0037] S5: Freeze-drying. Sublimation drying: Chamber pressure 10 Pa, shelf temperature increased from -40℃ to -15℃ at a uniform rate over 18 hours. Desorption drying: Chamber pressure increased to 25℃, 5 Pa, drying for 6 hours. The final moisture content was measured to be 1.8%.

[0038] S6: The product is annealed in a drying oven at 28℃ and 8%RH for 36 hours, and then sealed and packaged.

[0039] Example 2 The difference from Example 1 is as follows: In S1, the amount of PLGA added is 12% (12g) of the tea oil mass; in S2, the amount of HPG-4 added is 2% (approximately 10.7g) of the total chocolate matrix mass; and the amount of isomaltitol added is 6% (approximately 32g). In S3, 15g of nano-microcapsule powder is mixed and suspended with 15g of tea oil, for a total tea oil mass of 30g. The microfluidic homogenization pressure is 22000 psi. The annealing time is 48 hours. The rest is the same as in Example 1.

[0040] Comparative Example 1 In the scheme of "Example 1", the difference is: S1: 100g of refined tea oil was used directly without pre-crystallization and gelation treatment.

[0041] S2: Only 500g of dark chocolate is melted at 50℃, without the addition of maltodextrin, sodium alginate, or HPG.

[0042] S3: Tea oil was added directly to the melted chocolate, with only 2g of soy lecithin added as an emulsifier. Emulsification was performed using conventional high-speed shearing (10,000 rpm, 3 minutes) without the use of high-pressure microfluidic homogenization.

[0043] S4: After pouring into the mold, place it directly in a -35℃ quick-freezing cabinet and freeze for 6 hours.

[0044] S5: Adopts conventional rapid freeze-drying process: chamber pressure 10 Pa, shelf temperature rises from -20℃ to 30℃ in 8 hours, ΔT reaches a maximum of 15℃ or more.

[0045] The other steps are the same as in Example 1.

[0046] Comparative Example 2 In the scheme of "Example 1", the difference is: S2: Only 500g of dark chocolate is melted, without the addition of maltodextrin, sodium alginate, or HPG.

[0047] The other steps are the same as in Example 1.

[0048] Comparative Example 3 In the scheme of "Example 1", the difference is: S1: 100g of refined tea oil was used directly without pre-crystallization and gelation treatment.

[0049] S2: Same as Example 1, but with the addition of maltodextrin and sodium alginate, but without the addition of HPG.

[0050] S3: Add tea oil directly to the chocolate base of S2 at 50℃ and emulsify and homogenize in the same way.

[0051] The other steps are the same as in Example 1.

[0052] Comparative Example 4 In the scheme of "Example 1", the difference is: S5: Freeze-drying uses standard parameters. Sublimation drying: chamber pressure 10 Pa, shelf temperature rapidly increased from -30℃ to 0℃ in 5 hours; Desorption drying: chamber pressure 5 Pa, shelf temperature increased from 0℃ to 25℃ in 7 hours. During the process, ΔT often exceeds 10℃. Total drying time is approximately 12 hours.

[0053] The other steps are the same as in Example 1.

[0054] Comparative Example 5 In the scheme of "Example 1", the difference is: S1: Replace PLGA with an equal mass (10g) of polycaprolactone (PCL, Mw≈10,000, Tg≈-60℃) and prepare tea oil-PCL microcapsules using the same emulsification-solvent evaporation method. The average particle size is about 250 nm.

[0055] The other steps are the same as in Example 1.

[0056] Comparative Example 6 In the scheme of "Example 1", the difference is: S2: Replace hyperbranched polyglycerol ester (HPG) with an equal mass (5g) of gum arabic.

[0057] The other steps are the same as in Example 1.

[0058] Comparative Example 7 In the scheme of "Example 1", the difference is: S1: Adjust the emulsification-solvent evaporation process parameters (reduce ultrasonic power and time) to prepare tea oil-PLGA microcapsules with an average particle size of 1.5 μm.

[0059] The other steps are the same as in Example 1.

[0060] Comparative Example 8 In the scheme of "Example 1", the difference is: S2: No isomaltitol added.

[0061] The other steps are the same as in Example 1.

[0062] Comparative Example 9 In the scheme of "Example 1", the difference is: S3: Use a conventional high-pressure homogenizer to homogenize for 3 cycles at 35°C and 40 MPa (approximately 5800 psi), replacing high-pressure microjet homogenization.

[0063] The other steps are the same as in Example 1.

[0064] Comparative Example 10 In the scheme of "Example 1", the difference is: S4: Cancel multi-stage cooling program. After injecting the nanocomposite emulsion obtained in S3 into the mold, directly cool it from 40℃ to -55℃ at a cooling rate of 2℃ / min and maintain it for 2 hours.

[0065] The other steps are the same as in Example 1.

[0066] Comparative Example 11 This comparative example takes a completely different approach: S1: Do not use PLGA microcapsules. Instead, use 30g of hydrogenated coconut oil (melting point 34℃), and melt it completely at 40℃.

[0067] S2: Same as Example 1, prepare a chocolate base containing HPG and isomaltitol.

[0068] S3: Molten hydrogenated coconut oil is added to the chocolate base of S2 at 40°C and processed under the same high-pressure microfluidic homogenization conditions as in Example 1.

[0069] S4-S6: Same as Example 1, but it is necessary to ensure that the constant temperature of the first stage of S4 is higher than 34°C (set to 35°C).

[0070] Comparative Example 12 In the scheme of "Example 1", the difference is: S6: The annealing step is omitted. The dried product is packaged directly under ambient conditions (approximately 25°C, 50% RH).

[0071] The other steps are the same as in Example 1.

[0072] Comparative Example 13 In the scheme of "Example 1", the difference is: S1: The amount of PLGA added is reduced to 5% of the tea oil mass (i.e., 5g).

[0073] S2: Reduce the amount of HPG added to 0.5% of the total mass of the chocolate base (approximately 2.5g).

[0074] The other steps are the same as in Example 1.

[0075] Comparative Example 14 This comparative example represents a simplified approach that may be considered by those skilled in the art: PLGA microcapsule powder and chocolate powder were prepared separately: tea oil-PLGA nanocapsules (prepared by the same method as in Example 1 S1) were freeze-dried to obtain powder A; a mixture of dark chocolate, isomaltitol, and HPG was pulverized at low temperature and sieved to obtain powder B.

[0076] Physical mixing: Powder A and powder B are physically dry mixed according to the dry matter ratio corresponding to that in Example 1.

[0077] Hot pressing: The mixed powder is placed in a mold and hot-pressed at 45°C under slight pressure, and then cooled and cured.

[0078] No freeze-drying or annealing is performed.

[0079] Experimental methods: Microcrack density: The brittle fracture surface of the sample was observed using a field emission scanning electron microscope (FE-SEM, Hitachi SU8010). Five fields of view (5000x magnification) were randomly selected, and the number of cracks with a length >200 nm per unit area was counted using ImageJ software. The average value (cracks / μm²) was taken.

[0080] Sensory evaluation: A double-blind test was conducted by 10 trained evaluators. Scores were given for "initial crispness" (1-9 points, higher for crispness), "uniformity of melting in the mouth" (1-9 points, higher for smoothness), and "overall pleasantness of taste" (1-9 points).

[0081] Dynamic mechanical properties (DMA): A dynamic mechanical analyzer (TA Q800) was used in tensile mode at a frequency of 1 Hz and a heating rate of 3 °C / min, covering a range of -60 °C to 60 °C. The storage modulus (E') at 25 °C and the glass transition temperature difference (ΔTg) between the oil phase and the matrix phase, determined by the tanδ peak value, were recorded.

[0082] Temperature cycling stability: The sample was subjected to 10 cycles of temperature shock at 4℃ (12h) / 40℃ (12h), and the retention rate (%) of the initial crispness score after cycling was calculated relative to the value before cycling.

[0083] Oxidative stability: The number of days required for the peroxide value (POV) to reach 15 meq / kg after accelerated oxidation in a 60℃ constant temperature oven.

[0084] Key performance data for all embodiments and comparative examples are shown in Table 1: Table 1 Results Analysis Comparative Example 1 had the most cracks, poor taste, and extremely high ΔTg, proving that traditional methods are completely incapable of solving the mechanical mismatch problem.

[0085] The failure of Comparative Example 11 is particularly crucial. Although its ΔTg was small, its taste was extremely poor (waxy), proving that simply increasing the melting point / Tg of the oil phase cannot achieve an acceptable taste, but instead introduces new problems. This highlights the ingenuity of the "PLGA nano-microencapsulation" approach of this invention: using a high-Tg polymer shell to achieve mechanical support, while the shell layer does not melt, allowing the tea oil inside to be released in a controlled manner at oral temperature, thus achieving "decoupling" and synergy between mechanical properties and sensory release.

[0086] Comparative Example 5 (PCL instead of PLGA): Due to the extremely low Tg of PCL, the microcapsule shell is soft at room temperature and cannot provide rigid support, resulting in softening of the product and increased cracking. This demonstrates that selecting a high Tg polymer (such as PLGA) is key to imparting "rigidity" to the oil phase, and not just any polymer will suffice.

[0087] Comparative Example 6 (gum arabic instead of HPG) and Comparative Example 3 (without HPG): While the results were better than the conventional process, they were far inferior to the examples. This indicates that the strong interfacial coupling and stress buffering capabilities provided by HPG's unique hyperbranched structure are not possessed by traditional linear colloids (gum arabic) or simple physical mixing. HPG's effect transcends conventional emulsification / stabilization, achieving "interfacial mechanical modification."

[0088] Comparative Example 7 (micron-sized microcapsules) and Comparative Example 13 (half the dosage): the effect decreased, proving that "nanoscale" (150-400 nm) and "effective dosage" are the precise requirements for achieving the best synergistic effect.

[0089] Comparative Example 9 (conventional homogenization), Comparative Example 10 (simplified freezing), and Comparative Example 4 (rapid drying): These changes in process steps all led to performance degradation, proving that high-pressure microfluidic homogenization, directional crystallization, and low-temperature steady-state drying are key guarantees for ensuring uniform dispersion of nanostructures, orderly construction of interface networks, and controlled drying stress, and are inseparable from the core material system.

[0090] Comparative Example 12 (annealing cancelled): stability decreased, proving that annealing is an important step in releasing residual internal stress and achieving long-term dynamic stability of the system.

[0091] Comparative Example 2 (without matrix modification) and Comparative Example 8 (without specific filler) show that strengthening the matrix phase (through hydrophilic colloids and high Tg fillers) is equally indispensable for supporting the entire composite structure and matching the properties of the oil phase.

[0092] The utter failure of Comparative Example 14 (completely reverse process) stands in stark contrast to the success of all the embodiments. This demonstrates that the overall technical route of the present invention, "liquid nano-encapsulation → liquid interface coupling → co-freezing and shaping," is the only effective way to achieve nanoscale performance matching.

[0093] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A freeze-drying processing method for tea oil chocolate, characterized in that, Includes the following steps: S1: Using polylactic acid-glycolic acid copolymer as the wall material, nanocapsules encapsulating tea oil were prepared by emulsification-solvent evaporation method, wherein the average particle size of the nanocapsules was 150-400 nm. S2: Melt the dark chocolate, add hyperbranched polyglycerol and isomaltitol, and stir until smooth; S3: The nano-microcapsule powder obtained in S1 is redispersed in refined tea oil to form a suspension, which is then added to the chocolate matrix in S2 and homogenized by high-pressure microfluidic jet to form a nano-composite structured emulsion. S4: The emulsion obtained in S3 is subjected to programmed cooling and freezing, including isothermal cooling at the chocolate fat crystallization temperature to promote crystallization, followed by rapid cooling to complete vitrification; S5: Low-temperature steady-state sublimation drying: Under vacuum, the shelf temperature is controlled to carry out sublimation drying and desorption drying, so that the moisture content of the final product is ≤2%; S6: After drying, let the product stand for 24-48 hours in a low-humidity environment at 25-30℃.

2. The freeze-drying processing method for tea oil chocolate according to claim 1, characterized in that, In S1, the molecular weight Mw of the polylactic acid-glycolic acid copolymer is 10,000-30,000, the molar ratio of lactic acid to glycolic acid is 75:25, and the mass ratio of tea oil to polylactic acid-glycolic acid copolymer is 100:(5-15).

3. The freeze-drying processing method for tea oil chocolate according to claim 1, characterized in that, In S2, the hyperbranched polyglycerol has a generation number of 3-5 and is added at a rate of 0.5%-3% of the total mass of the chocolate matrix; the isomalt is added at a rate of 3%-8% of the total mass of the chocolate matrix.

4. The freeze-drying processing method for tea oil chocolate according to claim 1, characterized in that, In S3, the ratio of the total mass of tea oil to the total mass of chocolate matrix is ​​1:(5-8); the pressure of the high-pressure microjet homogenization is 15000-25000psi, and the number of cycles is 3-5.

5. The freeze-drying processing method for tea oil chocolate according to claim 1, characterized in that, S4 specifically includes: the first stage of cooling down to 29-31℃ at 1.5-2℃ / min and maintaining the temperature for 20-30 minutes; the second stage of cooling down to -10℃ at 0.5-1℃ / min; and the third stage of rapidly cooling down to below -50℃ at 2-3℃ / min and maintaining the temperature.

6. The freeze-drying processing method for tea oil chocolate according to claim 1, characterized in that, In step S5, the pressure in the storage chamber is controlled at 8-12 Pa during the sublimation drying stage, and the shelf temperature is slowly and linearly increased from -40℃ to -15℃ over a period of 15-20 hours.

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