Vanillin-betaine co-crystal system, and preparation method and application thereof

Abstract

This invention provides a vanillin-betaine eutectic system. Using vanillin as a model flavor molecule and betaine as the eutectic form, a vanillin-betaine eutectic system is constructed. Its crystal structure and thermal behavior are analyzed using single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis systems. Its release performance in an aqueous system is evaluated using dissolution experiments. Based on this, GC-IMS and GC-MS techniques are used to systematically compare the volatilization behavior of eutectic, physical mixtures, and pure vanillin under simulated baking conditions, from two levels: overall volatile flavor fingerprint and quantitative analysis of key aroma components. Simultaneously, density functional theory calculations are used to elucidate the intrinsic driving forces of eutectic formation and its stability from electronic structure and thermodynamic perspectives. This invention establishes the correlation between the structural characteristics of vanillin eutectic and its volatilization behavior and flavor release, providing a new theoretical basis for the structural regulation and functional application of flavor molecules.

Description

Technical Field

[0001] This invention belongs to the field of crystal engineering technology, specifically relating to a vanillin-betaine eutectic system, its preparation method, and its application. Background Technology

[0002] Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one of the most widely used natural flavorings globally, extensively applied in baked goods, beverages, dairy products, and daily chemical products. Besides its typical vanilla flavor, vanillin also possesses certain antioxidant and bioactive properties. However, in actual processing and application, vanillin suffers from problems such as volatility, insufficient heat resistance, and difficulty in precisely controlling flavor release. This is particularly evident in high-temperature baking or complex matrix systems, where aroma loss and flavor imbalance are especially pronounced.

[0003] Therefore, how to effectively regulate the stabilization and volatility of vanillin without altering its chemical structure is a crucial issue that needs to be addressed in the fields of flavor science and food engineering. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a vanillin-betaine eutectic system, its preparation method and application. The vanillin-betaine eutectic system provided by the present invention can achieve effective control of its stabilization and volatility behavior without changing the chemical structure of the vanillin molecule itself.

[0005] This invention provides a vanillin-betaine eutectic system.

[0006] Preferably, one molecule of vanillin and one molecule of betaine constitute an asymmetric unit of the eutectic system;

[0007] The interaction between vanillin and betaine includes intermolecular hydrogen bonding and electrostatic interaction.

[0008] The vanillin-betaine eutectic system is a neutral eutectic.

[0009] Preferably, the vanillin-betaine eutectic system has a monoclinic crystal structure with space group P21 / c; cell parameters are a=6.6533(4)Å, b=32.501(2)Å, c=6.6943(4)Å, β=108.186(4)°, and cell volume is 1375.25(15)Å. 3 Z=4, calculated density is 1.301 g / cm³ 3 .

[0010] Preferably, the hydrophobic aromatic ring layer of vanillin and the hydrophilic amine layer of betaine are stacked alternately to form an alternating hydrophobic-hydrophilic layered structure; the interlayer interaction of the layered structure includes van der Waals interaction.

[0011] This invention also provides a method for preparing the above-mentioned vanillin-betaine eutectic system, comprising the following steps:

[0012] Vanillin, betaine, and anhydrous ethanol were mixed to obtain a mixed solution;

[0013] The mixed solution was concentrated to induce crystal precipitation, and the obtained crystals were dried to obtain a vanillin-betaine eutectic system.

[0014] Preferably, the molar ratio of vanillin to betaine is 1:1 to 3;

[0015] The total molar amount of vanillin and betaine to the volume ratio of anhydrous ethanol is 0.02~0.04 mol: 20 ml;

[0016] The concentration is selected from rotary evaporation concentration; preferably, ultrasonication is assisted during concentration, and the power of the ultrasonication is 90~180 W.

[0017] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in sustained-release flavorings.

[0018] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in food.

[0019] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in daily chemical products.

[0020] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in pharmaceutical excipients.

[0021] Compared with existing technologies, this invention provides a vanillin-betaine co-crystal system. Using vanillin as a model flavor molecule and betaine as the co-crystal form, this invention constructs a vanillin-betaine co-crystal system. Its crystal structure and thermal behavior are analyzed using single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis systems, and its release performance in an aqueous system is evaluated using dissolution experiments. Based on this, GC-IMS and GC-MS techniques are used to systematically compare the volatilization behavior of co-crystals, physical mixtures, and pure vanillin under simulated baking conditions from two levels: overall volatile flavor fingerprint and quantitative analysis of key aroma components. Simultaneously, density functional theory (DFT) calculations are used to elucidate the intrinsic driving forces of co-crystal formation and its stability from electronic structure and thermodynamic perspectives. This invention establishes the correlation between the structural characteristics of vanillin co-crystals and their volatilization behavior and flavor release, providing a new theoretical basis for the structural regulation and functional application of flavor molecules. Attached Figure Description

[0022] Figure 1 Structural characterization diagrams of vanillin, betaine, and vanillin-betaine eutectic samples;

[0023] Figure 2 This is a diagram of the vanillin-betaine eutectic molecular structure.

[0024] Figure 3 TG and DTG curves for pure vanillin, pure betaine, and vanillin-betaine eutectic;

[0025] Figure 4 Comparison of cumulative dissolution curves of pure vanillin and vanillin-betaine cocrystal in pure water at 37°C;

[0026] Figure 5 Quantitative analysis of vanillin content and evaluation of its thermal stability in each treatment group;

[0027] Figure 6 This is a schematic diagram of the DFT calculation results;

[0028] Figure 7 To characterize the overall features of the volatile composition of different samples using GC-IMS;

[0029] Figure 8 To classify volatile components and analyze differences in flavor characteristics among samples;

[0030] Figure 9 OPLS-DA discriminant analysis and key biomarker screening for volatile components;

[0031] Figure 10 Differential scanning calorimetry (DSC) analysis of vanillin-betaine systems with different molar ratios

[0032] Figure 11 Photograph of the vanillin-betaine eutectic prepared for Comparative Example 1;

[0033] Figure 12 Photographs of the entire process of ultrasonic and rotary evaporation crystallization for preparing vanillin-betaine eutectic;

[0034] Figure 13 To investigate the differences in thermal behavior and crystal morphology of samples under different ultrasonic power conditions. Detailed Implementation

[0035] This invention provides a vanillin-betaine eutectic system.

[0036] In this invention, in the vanillin-betaine eutectic system, one molecule of vanillin and one molecule of betaine constitute an asymmetric unit of the eutectic system.

[0037] Betaine (trimethylglycine) is a naturally occurring zwitterionic compound with good water solubility and GRAS (Generally Recognized As Safe and Reliable Foods). Its molecule contains both a positively charged quaternary ammonium group and a negatively charged carboxylate group, enabling it to form strong charge-assisted hydrogen bonds. Furthermore, betaine often exhibits significant steric hindrance and hydrophilic properties in its crystal structure, providing a structural basis for controlling the distribution of hydrophobic-hydrophilic microregions and the degrees of freedom of molecular motion in the eutectic.

[0038] The interaction between vanillin and betaine includes intermolecular hydrogen bonding and electrostatic interactions. During eutectic formation, non-covalent interactions such as hydrogen bonding play a crucial role in constructing a stable crystal structure.

[0039] The vanillin-betaine eutectic system is a neutral eutectic.

[0040] In this invention, the vanillin-betaine eutectic system has a monoclinic crystal system with space group P21 / c; the cell parameters are a=6.6533(4)Å, b=32.501(2)Å, c=6.6943(4)Å, β=108.186(4)°, and the cell volume is 1375.25(15)Å. 3 Z=4, calculated density is 1.301 g / cm³ 3 .

[0041] The vanillin-betaine eutectic system provided by this invention exhibits excellent thermal stability and sustained-release properties of volatile substances. This suppression of volatility and improvement in thermal stability can be attributed to the strong hydrogen bond network formed in the eutectic lattice. Vanillin molecules are anchored within the supramolecular framework constructed by betaine, requiring higher energy to break the lattice potential and escape, thus effectively improving the thermal properties of vanillin. Therefore, the vanillin-betaine eutectic system provided by this invention has potential advantages in aroma retention during thermal processing. Furthermore, the release pattern of volatile components is regulated through the intermolecular hydrogen bond network and lattice interactions within the vanillin-betaine eutectic system.

[0042] In this invention, the hydrophobic aromatic ring layer of vanillin and the hydrophilic amine layer of betaine are alternately stacked, forming an alternating hydrophobic-hydrophilic layered structure; the interlayer interactions of this layered structure include van der Waals interactions. This structure may be more prone to interlayer dissociation under the action of solvents. The above structural features are in good agreement with the faster dissolution rate exhibited by the cocrystal in water, suggesting that cocrystallization alters the solid-liquid interaction behavior of vanillin to some extent, thereby promoting its release process. Therefore, the vanillin-betaine cocrystal system provided by this invention has superior water solubility compared to vanillin and may further improve its bioavailability.

[0043] Vanillin and betaine molecules form in-plane chain structures that extend laterally via hydrogen bonds. However, due to the differences in spatial volume and configuration between the aromatic ring plane of vanillin and the quaternary ammonium group of betaine, these molecular chains exhibit a wavy rather than linear extension pattern. Specifically, the hydrophobic aromatic ring layer of vanillin and the hydrophilic amine layer of betaine alternately stack, forming an alternating hydrophobic-hydrophilic layered structure; the van der Waals interactions between the layers further enhance the close packing and overall stability of the crystals.

[0044] This allows the system to exhibit a more balanced, lasting, and layered flavor profile during heat treatment.

[0045] This invention also provides a method for preparing the above-mentioned vanillin-betaine eutectic system, comprising the following steps:

[0046] Vanillin, betaine, and anhydrous ethanol were mixed to obtain a mixed solution;

[0047] The mixed solution was concentrated to induce crystal precipitation, and the obtained crystals were dried to obtain a vanillin-betaine eutectic system.

[0048] The present invention first mixes and dissolves vanillin and betaine with anhydrous ethanol, wherein the mixing and dissolution is preferably performed by ultrasonic dissolution.

[0049] The molar ratio of vanillin to betaine is 1:1 to 3, and can be any ratio between 1:1, 1:1.5, 1:2, 1:2.5, 1:3, or 1:1 to 3, preferably 1:1.

[0050] The total molar amount of vanillin and betaine to the volume ratio of anhydrous ethanol is 0.02~0.04 mol:20 ml, which can be 0.02 mol:20 ml, 0.03 mol:20 ml, 0.04 mol:20 ml, or any ratio between 0.02~0.04 mol:20 ml, preferably 0.02 mol:20 ml.

[0051] After obtaining the mixed solution, the mixed solution is concentrated to induce crystal precipitation. In this invention, the concentration is selected from rotary evaporation concentration. More preferably, ultrasonication is assisted during rotary evaporation, and the power of the ultrasonication is 90~180 W, which can be any value between 90, 120, 135, 150, 180, or 90~180 W.

[0052] After obtaining the crystals, collect them and dry them in a freeze dryer to obtain the vanillin-betaine eutectic system.

[0053] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in sustained-release flavorings.

[0054] This invention also provides an application of the above-mentioned vanillin-betaine eutectic system in food. In this invention, there are no special limitations on the food, which can be baked goods.

[0055] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in daily chemical products.

[0056] The present invention also provides an application of the above-mentioned vanillin-betaine eutectic system in pharmaceutical excipients.

[0057] This invention successfully prepared a vanillin-betaine 1:1 molar ratio eutectic (VAN–BTN) using the zwitterionic compound betaine as the eutectic form via an ultrasonic-assisted solvent evaporation method. Single-crystal X-ray diffraction results showed that the eutectic crystal belongs to the monoclinic crystal system with space group P21 / c. Strong charge-assisted hydrogen bonds (O–H⋯O) are formed between the vanillin phenolic hydroxyl group and the betaine carboxylate group, constructing a stable heterodimeric structural unit, and further forming a layered stacked structure with alternating hydrophobic aromatic layers and hydrophilic amine layers. Thermal analysis (DSC / TG) and powder X-ray diffraction (PXRD) confirmed the formation of the new crystalline phase and indicated that eutecticization significantly improved the thermal stability of vanillin. Aqueous phase dissolution experiments showed that, compared with pure vanillin, the eutectic sample exhibited a faster release rate and a higher cumulative dissolution level at 37°C. In the oil phase system, GC-MS quantitative analysis further revealed that the cocrystallized structure can delay the volatilization rate of vanillin, resulting in a higher retention level of vanillin under heating or solvent conditions compared to the pure vanillin group, demonstrating a significant sustained-release effect. Gas-phase GC-IMS volatile fingerprint analysis combined with PCA and OPLS-DA results showed that the cocrystallized group was significantly distinguishable from the pure vanillin and physically mixed groups in terms of overall volatile flavor profile, indicating that cocrystallization is not a simple physical superposition but rather reshapes the release pattern of volatile components. Density functional theory (DFT) calculations verified the electrostatic complementarity between molecules and the thermodynamic feasibility of cocrystallization at the electronic structure level. This study systematically reveals the synergistic effects of vanillin-betaine cocrystallization in terms of structure, thermal behavior, solubility, and flavor release regulation, providing a new research approach for the precise regulation of flavor molecule volatilization behavior through cocrystallization strategies.

[0058] To further understand the present invention, the vanillin-betaine eutectic system, its preparation method, and its application are described below with reference to embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0059] Example 1

[0060] 1. Raw materials

[0061] Vanillin (4-hydroxy-3-methoxybenzaldehyde, 99% purity, Shandong Keyuan Biochemical Co., Ltd.), betaine (trimethylglycine, anhydrous, 99% purity, Hangzhou Haiershi Livestock Co., Ltd.), soybean oil (Foshan Haitian Seasoning Food Co., Ltd.), anhydrous ethanol (analytical grade, Fuchen Tianjin Chemical Reagent Co., Ltd.), sucrose (Maclean's, 99% purity, Shandong Keyuan Biochemical Co., Ltd.).

[0062] 2. Instruments

[0063] Bruker D8 VENTURE dual-wavelength (Mo / Cu) single-crystal X-ray diffractometer, PANalytical EMPYREAN X-ray diffractometer (Malvern Panalytical, Netherlands), METTLER TOLEDO-DSC 3+ (Switzerland), HITACHISTA200 thermogravimetric analyzer (Japan), IRTracer-100 infrared spectrometer (SHIMADZU, Japan), dual-beam UV-Vis spectrophotometer (UV-Vis, ULP 2405004A, Shanghai Meipuda Instrument Co., Ltd.), electric oven (NB-HM3810, Xiamen Jiansong Electric Co., Ltd.), gas chromatography-ion mobility spectrometry (GC-IMS, FlavorSpec 25, 5H4, GAS Gesellschaft fur analytische) Sensorsysteme) and gas chromatography-mass spectrometry (GC-MS, GC-2030AM, 230V, SHIMADZU), ultrasonic cell disruptor (JY92-IIDN, Ningbo Xinzhi Biotechnology Co., Ltd.), rotary evaporator (RE-6000A, Shanghai Yarong Biochemical Instrument Factory), freeze dryer (freeze-Dryer, Econi-60, Nanjing Jinshi), etc.

[0064] 3. Preparation of eutectic

[0065] Accurately weigh 1.522 g (0.01 mol) of vanillin and 1.172 g (0.01 mol) of betaine, add 20 mL of anhydrous ethanol to a 100 mL round-bottom flask, and sonicate at room temperature for 30 min until completely dissolved. Then transfer to a rotary evaporator to concentrate the solvent to induce crystal precipitation. Collect the obtained crystals and dry them in a freeze dryer for 72 h to obtain the VAN–BTN eutectic sample.

[0066] 4. Characterization of eutectic

[0067] 4.1 SC-XRD

[0068] Single crystals of VAN–BTN were obtained by dissolving the monomer in anhydrous ethanol and then crystallizing by solvent evaporation. A single crystal with a complete morphology and no cracks was selected and data was acquired using a Bruker D8 VENTURE dual-wavelength (Mo / Cu) single-crystal diffractometer. The crystal was maintained at 193.00 K during the measurements. Structure analysis was performed using Olex2, with the structure solved using the SHELXT program based on intrinsic phase, and refined using the SHELXL program based on full-matrix least squares. All non-hydrogen atoms were refined using anisotropic parameters, while hydrogen atoms were treated according to ideal geometric positions using a riding model.

[0069] 4.2 PXRD

[0070] Powder X-ray diffraction data were obtained using a PANalytical EMPYREAN X-ray diffractometer (Malvern Panalytical, Netherlands). The samples were analyzed using Cu Kα rays (λ = 1.5406 Å, tube voltage 40 kV, tube current 40 mA). The scanning range was 2θ = 5°–40°, with a step size of 0.0167° and a scanning rate of 2 ° / min. Powder diffraction patterns of pure vanillin, pure betaine, and eutectic samples were measured to verify the phase purity and phase composition of the eutectic samples.

[0071] 4.3 DSC

[0072] The tests were performed on a METTLER-TOLEDO DSC instrument. Approximately 3–5 mg of sample was weighed into a sealed aluminum crucible (an empty crucible served as a blank reference), and heated from 30 °C to 350 °C at a heating rate of 5 °C / min under a nitrogen atmosphere. The melting and phase transition thermal characteristics of the sample were recorded.

[0073] 4.4 TGA

[0074] The samples were analyzed using a HITACHI STA200 thermogravimetric analyzer. The experiment was conducted under a nitrogen atmosphere, with a heating rate of 5 °C / min, from room temperature to 350 °C. The mass change of the samples was recorded to determine the decomposition temperature.

[0075] 4.5 FT-IR

[0076] Fourier transform infrared spectroscopy was performed using an IRTracer-100 infrared spectrometer (SHIMADZU, Japan). Samples were prepared using the KBr pellet method, and measurements were taken at 4000–400 cm⁻¹. -1 Scan within the range, with a resolution of 4 cm. -1A total of 32 scans were performed to analyze the vibrational characteristics of functional groups in the samples and to explore possible intermolecular interactions.

[0077] 4.6 Dissolution performance test

[0078] Equal amounts of pure vanillin and VAN–BTN eutectic samples were placed in pure water at 37℃ (ensuring that the mass of vanillin in the two groups of samples was equal). 1 mL of sample was taken at 0, 1, 3, 5, 7, 10, 12, 15, 20, 30, 45, and 60 min, and the solution was replenished in time. The vanillin concentration was measured at a wavelength of 312 nm using a UV-Vis spectrophotometer, and the cumulative dissolution rate was plotted as a function of time.

[0079] 5. Volatile Flavor Analysis

[0080] A basic sugar-oil-water matrix (total mass 100g) was prepared by mixing sucrose, soybean oil, and water in a mass ratio of 15:8:77. Five groups of samples were prepared: a blank group (matrix only), a pure betaine group, a pure vanillin group, a physical mixture of vanillin and betaine (1:1), and a VAN–BTN eutectic group. In the pure vanillin group, 0.1 g of vanillin was added; in the VAN–BTN eutectic group, 0.178 g of eutectic sample was added to ensure consistent vanillin content across all groups; in the physical mixture group, 0.1 g of vanillin was added in an equimolar amount with betaine; and in the pure betaine group, the amount of betaine added was equal to the amount in the eutectic system. All samples were baked at 180℃ for 15 min to simulate the baking process. After baking, the samples were cooled and aliquoted. GC-IMS was used for qualitative fingerprint analysis of volatile flavor compounds, and principal component analysis (PCA) and hierarchical clustering heatmap analysis were employed to compare the differences in volatile component distribution among the samples. Furthermore, GC-MS was used to quantitatively determine the vanillin content in the samples.

[0081] 6. Theoretical Calculations

[0082] Based on the molecular pairing patterns observed in the single-crystal structure, density functional theory (DFT) calculations were performed using Gaussian 16 software. The B3LYP / 6-311G(d) basis set was used for geometry optimization and vibrational power analysis of the vanillin-betaine molecular complex. The calculations included the distribution of the molecular electrostatic potential (ESP), frontier molecular orbitals (HOMO, LUMO), intermolecular binding energy ΔE, and binding Gibbs free energy ΔG, to explore the electronic structure characteristics and thermodynamic feasibility of the eutectic formation.

[0083] 7 Test Results

[0084] (1) Characterization of eutectic structure

[0085] To verify whether vanillin and betaine form a new solid phase, the pure components and their 1:1 eutectic samples were characterized by PXRD, DSC and FT-IR.

[0086] See Figure 1 , Figure 1 The images show the structural characterization of vanillin, betaine, and vanillin-betaine eutectic samples. Figure 1 (A) Schematic diagram of functional groups of vanillin and betaine molecules, indicating sites that may participate in hydrogen bonding; (B) DSC curves of pure vanillin, pure betaine, eutectic and 1:1 physical mixture; (C) Comparison of PXRD spectra of pure vanillin, pure betaine and eutectic samples; (D) Comparison of experimental PXRD spectra and PXRD spectra calculated and simulated based on single crystal structure; (E) Comparison of FT-IR spectra of pure vanillin and eutectic samples.

[0087] like Figure 1 As shown in (A), the phenolic hydroxyl group in the vanillin molecule can act as a hydrogen bond donor, while the carboxylate group in the betaine molecule has good acceptor ability, providing a structural basis for the formation of stable intermolecular interactions between the two. It is worth noting that this schematic diagram is only used to mark potential molecular recognition sites and does not reflect all the actual interaction networks in the crystal.

[0088] DSC test results are as follows Figure 1 As shown in (B), pure vanillin exhibits a distinct endothermic melting peak at approximately 82.1 °C, while pure betaine displays an endothermic decomposition peak at approximately 303.2 °C. In contrast, no melting peak of any monomer was detected in the DSC curve of the VAN–BTN eutectic sample; instead, a new melting peak appeared at approximately 135.7 °C, whose thermal behavior is significantly different from that of any single component. This indicates that the system forms a new thermally independent solid phase, rather than a simple physical mixture.

[0089] Further PXRD analysis results are as follows Figure 1 As shown in (C): pure vanillin and pure betaine each exhibit clear and representative diffraction peaks, but the diffraction pattern of the VAN–BTN eutectic sample is significantly different from that of the raw material. The characteristic diffraction peaks of the raw material are significantly weakened or disappear, while a series of new diffraction peaks appear, indicating that a new crystal phase has formed in the sample.

[0090] To further verify the rationality of this new crystal phase, we compared the experimentally obtained PXRD pattern with the diffraction pattern obtained from calculations and simulations based on the single crystal structure. Figure 1 (D) The results show that the two have good consistency in peak position and relative intensity, further proving that the VAN–BTN sample is a well-defined eutectic phase.

[0091] FT-IR spectral analysis results are as follows Figure 1 As shown in (E), compared with pure vanillin, the O–H stretching vibration peak (approximately 3200–3500 cm⁻¹) in the VAN–BTN eutectic sample is significantly higher. -1 The peak broadened and shifted significantly, indicating that the phenolic hydroxyl group of vanillin participated in hydrogen bonding. Meanwhile, the characteristic vibrational peak of betaine carboxylate (approximately 1611 cm⁻¹) was also observed. -1 The changes also occurred in the eutectic, and the C=O stretching vibration peak in the vanillin molecule (approximately 1661 cm⁻¹) was observed. -1 The spectroscopic features show subtle shifts. These spectroscopic features indicate that non-covalent interactions such as hydrogen bonds play an important role in building a stable crystal structure during eutectic formation.

[0092] In summary, the results of DSC, PXRD, and FT-IR corroborate each other, clearly demonstrating that vanillin and betaine successfully formed a new eutectic phase under a 1:1 molar ratio, laying the foundation for subsequent crystal structure analysis and property studies.

[0093] To further reveal the molecular arrangement and interaction mode of the vanillin-betaine eutectic, single-crystal X-ray diffraction analysis was performed. The single-crystal X-ray diffraction results showed that the vanillin-betaine eutectic (VAN–BTN) belongs to the monoclinic crystal system with space group P21 / c. The cell parameters are a = 6.6533(4) Å, b = 32.501(2) Å, c = 6.6943(4) Å, β = 108.186(4)°, and the cell volume is 1375.25(15) Å. 3 Z=4, calculated density is 1.301 g / cm³ 3 This reflects the density of the structure. Data refinement shows R1 = 0.0779 (I>=2σ), indicating the reliability of the structural analysis results (see Table 1). The asymmetric unit contains one molecule of vanillin and one molecule of betaine, coexisting in a 1:1 stoichiometric ratio. This result is consistent with the formation of new crystalline phases revealed in the aforementioned PXRD and DSC analyses.

[0094] Table 1. Crystal data and structural refinement parameters of vanillin-betaine eutectic samples

[0095] See Figure 2 , Figure 2 This is a molecular structure diagram of vanillin-betaine eutectic. Figure 2(A) Schematic diagram of the asymmetric unit cell of the VAN-BTN eutectic, where vanillin and betaine molecules are connected by hydrogen bonds (hydrogen bond geometry parameters are labeled); (B) Schematic diagram of the superposition of vanillin molecules (gray) in the pure vanillin unit cell and vanillin molecules (red) in the eutectic along the main packing direction; (C) Schematic diagram of the molecular layered stacking structure of the eutectic along the b-axis of the crystal, where vanillin and betaine molecules are alternately stacked (hydrogen bonds are represented by blue dashed lines).

[0096] In the asymmetric unit cell of the crystal, one molecule of vanillin and one molecule of betaine are linked by a distinct O–H•••O hydrogen bond (see...). Figure 2 (A) Specifically, the geometric parameters of this hydrogen bond (O3–H3•••O4) are D–H distance = 0.840 Å, H•••A distance = 1.694 Å, and D•••A distance = 2.530 Å, with a bond angle of approximately 172.9° (see Table 2), indicating that the intermolecular interaction has high directionality and stability. This structural feature suggests that the interaction between vanillin and betaine mainly exists in the form of intermolecular hydrogen bonds, and its overall structure is more consistent with the typical characteristics of neutral eutectic.

[0097] Table 2. Hydrogen bond geometry parameters (Å, °) of vanillin–betaine eutectic.

[0098] Comparing the crystal structure of pure vanillin with the packing pattern of vanillin in the eutectic, it can be seen that the two are highly consistent in the main packing direction. Figure 2 (B)). In the figure, vanillin molecules within the pure vanillin unit cell are shown in gray, while those in the co-crystal are shown in red. Both are well-aligned along the main packing direction. This indicates that the original packing pattern of vanillin molecules was not significantly altered during co-crystal formation; the addition of betaine primarily constructs the supramolecular framework of the co-crystal, rather than rearranging the packing sequence of the vanillin molecules themselves. At the three-dimensional crystal packing level, the co-crystal exhibits a significant layered structure. Figure 2 (C) Vanillin and betaine molecules form a chain-like structure in the plane and extend laterally through the aforementioned hydrogen bonds (blue dashed lines in the figure). However, due to the difference in spatial volume and configuration between the aromatic ring plane of vanillin and the quaternary ammonium group of betaine, these molecular chains exhibit a wavy rather than linear extension pattern. Specifically, the hydrophobic aromatic ring layer of vanillin and the hydrophilic amine layer of betaine are stacked alternately, forming an alternating hydrophobic-hydrophilic layered structure; the van der Waals interactions between the layers further enhance the close packing and overall stability of the crystal.

[0099] In summary, the single-crystal X-ray diffraction results clearly revealed the hydrogen-bonded intermolecular interaction mode and its ordered stacking characteristics in the vanillin-betaine eutectic, providing a reliable structural basis for subsequent discussions on the changes in the physicochemical properties of the eutectic.

[0100] (2) Analysis of thermal behavior, dissolution and release characteristics

[0101] See Figure 3 , Figure 3 TG and DTG curves of pure vanillin, pure betaine, and vanillin-betaine eutectic: (A) TG curve, (B) DTG curve.

[0102] Figure 3 Thermogravimetric analysis (TG) and derivative thermogravimetric (DTG) curves of vanillin, betaine and their eutectic are shown to evaluate the thermal stability characteristics of crystalline materials.

[0103] As can be observed from Figures A and B, pure vanillin exhibits poor thermal stability, with a low onset temperature for mass loss and undergoing a rapid and complete weight loss process (100% weight loss rate) between 100°C and 200°C. This is mainly attributed to the sublimation or volatilization characteristics of vanillin molecules at high temperatures. In contrast, pure betaine exhibits higher thermal stability, with no significant decomposition observed before 300°C. Comparing the slopes of the TG curves, the VAN–BTN eutectic shows superior thermal stability compared to pure vanillin. Although the eutectic sample begins to show mass loss around 150°C, its weight loss rate is significantly slower than that of pure vanillin. More importantly, the DTG curves show that the decomposition process of the eutectic exhibits multi-stage characteristics, and the peak temperature of the maximum decomposition rate shifts significantly to the right (towards higher temperatures) compared to pure vanillin. This suppression of volatility and improvement in thermal stability can be attributed to the strong hydrogen bond network formed in the eutectic lattice (as described in the crystal structure section above). Vanillin molecules are anchored in the supramolecular framework constructed by betaine, requiring higher energy to break the lattice potential energy and escape, thus effectively improving the thermal properties of vanillin.

[0104] To simply evaluate the effect of eutectic on improving the solubility of poorly soluble drugs, a dissolution experiment was conducted in water at 37°C.

[0105] See Figure 4 , Figure 4 Comparison of cumulative dissolution curves of pure vanillin and vanillin-betaine eutectic in pure water at 37°C. Figure 4Dissolution curves of pure vanillin and the cocrystal over time were compared. Experimental results showed that the cocrystal achieved rapid drug release in the initial dissolution phase. Specifically, within the first 10 minutes, the cumulative dissolution rate of the cocrystal sample rapidly increased to approximately 80%, while the dissolution rate of pure vanillin under the same conditions was only about 60%. Throughout the test period, the cocrystal consistently maintained a higher dissolution level than the pure component, eventually reaching a higher equilibrium concentration. Based on the previous analysis, the improved dissolution behavior may be related to the hydrophilic properties of betaine in the cocrystal and its crystal stacking pattern. As a highly water-soluble zwitterionic compound, betaine molecules introduce charged functional groups into the cocrystal structure. These structural features facilitate strong interactions between the cocrystal surface and water molecules, thereby increasing the wettability of water relative to the crystal surface. Simultaneously, single-crystal structure analysis revealed that the VAN–BTN cocrystal exhibits a layered stacking characteristic with alternating hydrophobic aromatic layers and hydrophilic amine layers. This structure may be more prone to interlayer dissociation under solvent conditions. The above structural features are in good agreement with the faster dissolution rate of the cocrystallized material in water, suggesting that cocrystallization alters the solid-liquid interaction behavior of vanillin to some extent, thereby promoting its release process.

[0106] To further clarify the effects of co-crystallization and different treatment methods on vanillin, GC-MS was used to quantitatively analyze vanillin.

[0107] See Figure 5 , Figure 5 Quantitative analysis of vanillin content and evaluation of its thermal stability in each treatment group. (Bar chart: Vanillin concentration (μg / mL) of each group after heat treatment; Line graph: Negative logarithmic function value based on vanillin residual rate -lg(remaining fraction); *** in the figure represents extremely significant difference (P<0.001), ns represents no statistically significant difference)

[0108] Figure 5The differences in vanillin concentration among the treatment groups after heat treatment are shown. GC-MS results indicate that the vanillin concentration in the eutectic group (VAN–BTN) was significantly higher than that in the pure vanillin group (VAN) and the physical mixture group (PM) (P<0.001). No significant difference (ns) was observed between the PM and VAN groups, indicating that simple physical mixing did not effectively change the vanillin retention level at high temperatures. The -lg (remaining fraction) line plot corresponding to the right axis further reveals the differences in system stability. The corresponding value of the VAN–BTN group was significantly lower than that of the control group, indicating that its vanillin residue ratio was relatively high after heat treatment. After logarithmic transformation of the remaining fraction, the differences between the systems are presented more intuitively, which helps to compare the heat loss trends of different samples. The vanillin residue in the VAN–BTN group was significantly higher than in other groups, demonstrating that the cocrystallized system has a stronger sustained-release effect on vanillin. This phenomenon is consistent with the results of thermogravimetric analysis and dissolution tests. In the cocrystallized sample, the establishment of intermolecular interactions, such as hydrogen bonds or ionic interactions, may have altered the microenvironment of vanillin to some extent, thereby enhancing its thermal stability and sustained-release capacity. Notably, no significant difference was observed between the PM group and the VAN group, indicating that the simple coexistence of betaine is insufficient to change the behavior of vanillin under high-temperature conditions.

[0109] Therefore, GC-MS analysis revealed that the eutectic group (VAN–BTN) exhibited stronger vanillin retention and sustained-release effects during heat treatment. This phenomenon may be related to the hydrogen bond network formed between vanillin and betaine in the eutectic lattice. This mechanism effectively improves the thermal stability of vanillin and enhances its aroma retention potential in heat-processing systems through sustained release. This result is consistent with the conclusions of the previous thermogravimetric and dissolution behavior analyses, indicating that cocrystallization not only improves the thermal stability of vanillin but also makes its volatility more stable during heat processing by altering its release pattern, revealing that the cocrystallization process may regulate the thermal stability behavior of key flavor compounds. From an application perspective, the eutectic system exhibited higher vanillin retention under the conditions of this study, suggesting its potential aroma retention advantage in heat-processing systems.

[0110] (3) DFT intermolecular interaction analysis

[0111] To further understand the driving force behind the formation of vanillin-betaine eutectics from a theoretical perspective, density functional theory (DFT) calculations were performed on the vanillin-betaine eutectics. The computational model was constructed based on the molecular pairing patterns observed in experiments to analyze the electronic structure characteristics of intermolecular interactions and their thermodynamic feasibility.

[0112] See results Figure 6 , Figure 6 Schematic diagram of DFT calculation results: (A) Electrostatic potential (ESP) distribution of vanillin, betaine, and their complexes (red indicates negative ESP regions, blue indicates positive ESP regions). (B) Schematic diagram of optimized geometry and major intermolecular interactions of vanillin-betaine cocrystal. (C) Frontier molecular orbital (HOMO and LUMO) distribution and corresponding energy level diagram of vanillin and vanillin-betaine cocrystal.

[0113] Molecular electrostatic potential (ESP) distribution as follows Figure 5 As shown in (A), a distinct negative potential region exists around the phenolic hydroxyl oxygen atom in the vanillin molecule, while a relatively high positive potential region exists around the carboxylate oxygen atom in the betaine molecule. This spatial complementarity of positive and negative potentials provides favorable conditions for the interaction between the two molecules, consistent with the hydrogen bond positions observed in the single-crystal structure. ESP analysis results indicate that electrostatic interactions play a crucial role in the molecular recognition and binding of vanillin and betaine. Further frontier molecular orbital analysis results are shown below. Figure 5 As shown in (B), frontier molecular orbital analysis reveals that the highest occupied molecular orbitals (HOMOs) of vanillin are mainly distributed in the aromatic ring and phenolic hydroxyl regions, while the lowest unoccupied molecular orbitals (LUMOs) of betaine are mainly localized in the quaternary ammonium and carboxylic acid structural units. In the complex model, the frontier orbitals of the two molecules exhibit a relatively close spatial distribution, reflecting a good spatial configuration match between the molecules. It should be noted that this orbital analysis is mainly used to describe the electron distribution characteristics and does not directly indicate the specific charge transfer process, but its results are consistent with the stable hydrogen bonding and overall structural stability observed in experiments. At the energy level, the binding energy of the vanillin-betaine eutectic is calculated to be ΔE = -82.39 kJ / mol, and the binding Gibbs free energy is ΔG = -30.70 kJ / mol. Both the binding energy and the free energy are negative, indicating that under the calculated conditions, the formation of a complex between vanillin and betaine is thermodynamically favorable. This result theoretically supports the possibility of spontaneous assembly of the two molecules through non-covalent interactions.

[0114] Based on the combined results of ESP analysis, frontier molecular orbital distribution, and binding energy calculations, it can be seen that the interaction between vanillin and betaine is mainly driven by electrostatic interaction and hydrogen bonding, providing a reasonable explanation for the stable existence of the eutectic structure from the perspectives of electronic structure and thermodynamics.

[0115] (4) Effect of eutectic on vanillin volatility characteristics

[0116] ①GC-IMS volatile fingerprint analysis

[0117] To investigate the effects of cocrystallization on the volatile composition and release behavior of the vanillin system, volatile fingerprint analysis was performed on the blank group (Blank), pure betaine group (BTN), pure vanillin group (VAN), physical mixture group (PM), and cocrystallized group (VAN–BTN) samples using GC-IMS.

[0118] See results Figure 7 , Figure 7 The overall characteristics of the volatile composition of different samples were characterized by GC-IMS: (A) GC-IMS volatile fingerprints of different samples; (B) Correlation heatmap of volatile components; (C) GC-IMS difference comparison chart with the blank group as a reference. (Blank: blank group; BTN: pure betaine group; VAN: pure vanillin group; PM: physical mixture group; VAN–BTN: eutectic group.)

[0119] Based on the structural characterization results above, it is known that vanillin and betaine form a stable, ordered crystal structure in the eutectic through hydrogen bonding. This intermolecular interaction may alter the volatilization behavior and flavor release pattern of vanillin during thermal processing. Figure 7 As shown in the fingerprint spectrum of (A), the volatile components of each group of samples exhibit significant characteristic differences. The blank group and the BTN group have low signal intensities and sparse characteristic peaks, indicating that betaine itself does not contribute significantly to volatility. The fingerprint distributions of the VAN group and the PM group are highly similar, indicating that simple physical mixing has failed to fundamentally change the volatility characteristics of vanillin. In contrast, the cocrystallized group (VAN–BTN) exhibits unique fingerprint spectrum characteristics, not only retaining some of the original characteristic signals of vanillin, but also showing signal enhancement or new signal peaks in multiple regions. This change in characteristic distribution confirms that cocrystallization is not a simple physical superposition, but rather regulates the release pattern of volatile components through intermolecular hydrogen bond networks and lattice interactions, thereby significantly enhancing the richness and complexity of the flavor.

[0120] Furthermore, this study constructed a heatmap of correlations of volatile components based on the Pearson correlation coefficient. Figure 7(B) reveals the intrinsic relationships among the volatile components in the vanillin system. The horizontal and vertical axes in the figure represent the detected volatile compounds, and the color of the blocks and the significance markers (* or **) reflect the degree of linear correlation between components. The results show that most esters, aldehydes, and heterocyclic compounds (such as ethyl butyrate and 2,5-dimethylpyrazine) in the system exhibit significant positive correlations (P<0.05), forming several significant positively correlated clusters in the heatmap. This synchronized release phenomenon may reflect the synergistic regulatory effect of intermolecular interactions in the eutectic structure on the volatile components, thus differing from the random release pattern of components in the physical mixture group. This will help maintain the relative stability and balance of the flavor profile of the vanillin system.

[0121] Using the blank group as a reference, the differences between the treatment groups are further visually presented through two-dimensional topographic plots. Figure 7 (C)). In the figure, red indicates that the concentration of the component is higher than the reference, and blue indicates that it is lower than the reference. The results show that the signal intensity and distribution range of the PM group are not substantially expanded compared to the VAN group. On the contrary, the density and response intensity of the characteristic signal points of the cocrystal group (VAN–BTN) are significantly better than other groups throughout the migration time range. Especially in the high retention time region, the cocrystal group exhibits a large area and dark red response region, which to some extent reflects the moderating effect of cocrystal technology on the release mode of volatile components. This differential distribution indicates that the hydrogen bond network formed between the vanillin hydroxyl group and the betaine carboxylic acid group in the cocrystal structure may change the molecular microenvironment of the system, thereby affecting the release path and behavior of volatile components during heating. This process not only promotes the sustained release effect of volatile components, but also makes the flavor performance of the cocrystal system significantly different from that of the physical mixture group.

[0122] ②PCA and heatmap analysis

[0123] To further evaluate the regulatory effect of eutectic treatment on the flavor evolution of the vanillin system, GC-IMS was used to perform qualitative and quantitative analysis of the volatile components of five simulated baking samples.

[0124] See results Figure 8 , Figure 8 For the classification of volatile components and analysis of differences in flavor characteristics among samples: (A) Pie chart of the proportion of volatile compounds. (B) PCA score chart of samples in each treatment group. (C) Heatmap of relative content of volatile components.

[0125] like Figure 8As shown in A, a total of 31 volatile components were identified (see Table 3 for specific values), covering 9 categories of chemical substances including esters (25.8%), alcohols (22.6%), and ketones (19.4%). Among them, esters, alcohols, and ketones constituted the main framework of the system's flavor, accounting for more than 67% in total.

[0126] To assess the flavor differences among samples from an overall perspective, principal component analysis (PCA) was performed on the relative contents of each component. Figure 8 B). The results show that the cumulative variance contribution rate of the first two principal components (PC1=81.6%, PC2=12.2%) reached 93.8%, which can effectively represent the original information of the samples. In the score plot, the blank group, pure betaine group (BTN), pure vanillin group (VAN), and physical mixture group (PM) are relatively concentrated in the negative half-axis region of PC1, reflecting that these samples have a certain similarity in the composition of volatile components. In stark contrast, the eutectic group (VAN–BTN) has shifted significantly along the positive direction of PC1 axis, and is independently distributed in the quadrant region of other groups of samples, showing that the overall volatility profile has changed significantly. Combined with the hierarchical clustering heatmap ( Figure 8 C) Observations revealed that the eutectic group showed significantly higher response intensities to various characteristic flavor compounds (such as acetic acid and some ketones) than other groups, and its independent high-abundance band distribution and PCA score were also observed. Figure 1 This further validated the regulatory effect of cocrystallization on the release of flavor components. This change in the overall volatile profile may be related to the intermolecular interactions formed in the cocrystallized lattice. The single-crystal structure analysis previously showed that vanillin and betaine form a stable crystal structure through hydrogen bonds. This lattice constraint not only limits the rapid release of volatile components but may also slow down the release rate of some components, thus achieving a similar sustained-release effect. The results indicate that cocrystallization can coordinate the release rhythm of various volatile components, enabling the system to exhibit a more balanced, persistent, and layered flavor profile during heat treatment.

[0127] Table 3. Volatile flavor compounds and their composition analysis

[0128] ③ OPLS-DA differential volatile matter screening

[0129] To further clarify the essential differences between cocrystallization and simple physical mixing in the regulation of volatile flavors, orthogonal partial least squares discriminant analysis (OPLS-DA) was performed on the cocrystallization group, the physical mixing group, and the pure vanillin group.

[0130] Figure 9OPLS-DA discriminant analysis and key biomarker screening for volatile components. AC: Comparative analysis of the eutectic group (VAN–BTN) and the physical mixture group (PM). (A) OPLS-DA score plot; (B) 200-times substitution test plot; (C) VIP weight distribution plot of key differentially expressed components (red bars represent VIP>1). DF: Comparative analysis of the eutectic group (VAN–BTN) and the pure vanillin group (VAN). (D) OPLS-DA score plot; (E) 200-times substitution test plot; (F) VIP weight distribution plot of key differentially expressed components (red bars represent VIP>1).

[0131] The results showed that the eutectic group exhibited a significantly different distribution pattern of volatile components compared to the two control groups. Figure 9 A, D). Verified through 200 displacement tests ( Figure 9 B, E), Q 2 The intercepts were all negative, confirming that the model has good stability and no overfitting.

[0132] The main components that differentiated the eutectic group and the physical mixture group based on VIP>1 screening included acetic acid, thiophene derivatives, and ethyl formate, etc. Figure 9 (C) The enhancement of acetic acid and pyrazines may be related to their volatility and polarity. Acetic acid is a short-chain volatile organic acid with a strong sour taste and is easily volatilized during heating. The hydrogen bond network and intermolecular interactions in the eutectic structure limit its volatility, making the release of acetic acid slower and more sustained, thus improving aroma persistence, avoiding an instantaneous peak in sourness, and reducing flavor imbalance caused by excessively rapid volatility. Pyrazines, such as 2-methylpyrazine, are usually associated with nutty and roasted aromas. They are highly volatile, but the release of pyrazine compounds is regulated by the eutectic structure, allowing them to be released over a longer period, forming a layered flavor profile. The enhanced response of these components in the eutectic group indicates that eutecticization not only affects the types of volatile components but may also regulate their release patterns. Compared to the simple superposition of physical mixtures, the eutectic system achieves a slow and uniform release of volatile components through its unique hydrogen bond network and intermolecular interactions. This sustained-release effect may be due to the molecular interaction between vanillin and betaine in the cocrystal, which makes the diffusion process of volatile components more stable, thereby changing the volatility characteristics of vanillin and improving the persistence and stability of flavor.

[0133] Comparison between the eutectic group and the pure vanillin group ( Figure 9In F), key differentiating components include acetic acid, 2-methylpyrazine, and 3-pentanone. The significant variations in these components within the cocrystallized group likely stem from changes in the behavior of vanillin molecules within the cocrystallized structure. The cocrystallization process, through intermolecular hydrogen bonds and lattice constraints, slows the diffusion rate of vanillin molecules, resulting in a more structured volatile release pattern compared to pure vanillin alone. Specifically, vanillin molecules are fixed within a supramolecular framework formed with betaine, reducing the likelihood of rapid volatilization during heat treatment, thus making the release of volatile components more orderly and stable.

[0134] In summary, the VIP analysis results of both groups indicate that cocrystallization not only modulates the release pattern of volatile components but also alters the volatility behavior of vanillin itself to some extent. Hydrogen bonds and ionic interactions in the cocrystallized structure are likely the key mechanisms behind these changes, suggesting that cocrystallization can improve the overall flavor stability and persistence by controlling the release rate of volatile components. This further verifies the sustained-release effect observed in "(2) Thermal Behavior, Dissolution and Release Characteristics Analysis," thus providing a scientific basis for the stabilization and controlled release of vanillin in food systems. From a flavor application perspective, cocrystallization, by regulating the overall volatile flavor profile and the release behavior of key flavor substances, is expected to impart a more mellow, stable, and lasting aroma to products. This flavor regulation method differs from simple physical mixing and provides an effective strategy for the stable application and controlled release of vanillin in food systems, demonstrating good practical application potential.

[0135] 8. Conclusion

[0136] This study constructed a vanillin-betaine cocrystal system and systematically compared its physicochemical properties and volatility behavior with those of the single-component and physically mixed systems. Single-crystal structure analysis and theoretical calculations showed that the two molecules formed a stable structure through hydrogen bonding, and this interaction altered the molecular environment of vanillin within the crystal. Thermal analysis and dissolution results indicated that cocrystalization modulated the thermal response and dissolution characteristics of vanillin to some extent, and GC-MS data further demonstrated a slow-release effect of vanillin. This suggests that the cocrystal structure, through hydrogen bonding networks and intermolecular interactions, not only improved the thermal response and dissolution characteristics of vanillin but also delayed the rapid release of volatile substances. GC-IMS fingerprint analysis and multivariate statistical results revealed significant differences in the distribution of volatile components in the cocrystal system compared to the pure component and physically mixed systems, indicating a reconstruction of the overall volatility behavior. In summary, this study established a framework relating crystal structure, physicochemical properties, and volatility behavior, demonstrating that eutectic engineering is an effective strategy for regulating the physicochemical properties and volatility characteristics of small-molecule flavor compounds, providing theoretical support for the stabilization of flavor-active molecules such as vanillin in food systems. While this study was conducted based on a model system and has not yet addressed systematic validation at the complex food formulation or sensory level, its results can provide important references for subsequent functional evaluation in actual food systems.

[0137] Example 2

[0138] Different molar ratios of vanillin to betaine were used, namely 1:1, 1:1.5, 1:2, and 1:3, with a 1:1 molar ratio as the starting point for the experiments. The molecular weight of vanillin was 152.15 g / mol; the molecular weight of betaine was 117.15 g / mol. 1.522 g of VAN and 1.172 g of BTN were weighed and mixed to obtain a 1:1 molar mixture; other ratios were calculated in the same manner.

[0139] Vanillin-betaine cocrystals with different molar ratios were prepared according to the method of "Preparation of 3-Cocrystal" in Example 1.

[0140] See Figure 10 , Figure 10Differential scanning calorimetry (DSC) analysis was performed on vanillin-betaine systems with different molar ratios. At a 1:1 molar ratio, the system exhibited a sharp and strongest endothermic melting peak at approximately 130 °C, while showing no significant endothermic signal near 300 °C (pure vanillin showed a significant endothermic melting peak at approximately 82.1 °C, while pure betaine showed a decomposition endothermic peak at approximately 303.2 °C). This indicates that the system formed a new thermally independent solid phase, rather than a simple physical mixture, and that vanillin and betaine formed a homogeneous eutectic with no free betaine residue, indicating optimal phase purity. When the betaine ratio was excessive (1:1.5, 1:2, 1:3), the low-temperature melting peak gradually broadened and weakened in intensity, while a characteristic endothermic peak of betaine appeared at 280–310 °C. This high-temperature peak corresponds to free betaine that did not participate in the eutectic formation, proving that excessive betaine would destroy the eutectic integrity of the original complex. Therefore, 1:1 was selected as the optimal molar ratio.

[0141] Comparative Example 1

[0142] Vanillin and betaine were dissolved in a 1:1 molar ratio and allowed to crystallize naturally upon cooling without any auxiliary measures. The results showed that the crystallization process was relatively slow, typically requiring about 4–5 days to form visible crystals. However, during prolonged exposure, the solution was affected by environmental factors, leading to impurities adhering to the crystal surface, color changes, and the development of off-odors (such as…). Figure 11 As shown in the figure, it is not conducive to obtaining high-purity products.

[0143] Example 3

[0144] Based on Comparative Example 1, an optimized method combining ultrasound-assisted rotary evaporation concentration was introduced. Rotary evaporation accelerates ethanol evaporation, while ultrasound enhances intermolecular contact and nucleation processes. Experimental results show that this method significantly shortens crystallization time, allowing crystals to precipitate in a shorter time. The resulting crystals are uniform in appearance, have high transparency, and show a significant reduction in impurities. Figure 12 The entire process of preparing vanillin-betaine eutectic by ultrasonication and rotary evaporation takes approximately 40 minutes.

[0145] After determining the crystallization method, the effect of different ultrasonic powers on eutectic formation was further investigated using the vanillin-betaine (1:1 molar ratio) system as the research object.

[0146] Differential scanning calorimetry results showed that pure vanillin and pure betaine exhibited characteristic endothermic peaks at approximately 82.1℃ and 303.2℃, respectively, while the eutectic sample showed a new melting peak at approximately 135.7℃, indicating the formation of a new solid phase.

[0147] See Figure 13 , Figure 13To investigate the differences in thermal behavior and crystal morphology of samples under different ultrasonic power conditions. Figure 13 It can be known that:

[0148] 20% ultrasonic power (180 W): The sample exhibited a single, sharp melting endothermic peak, and no other obvious thermal events were observed; the crystal morphology was regular and the size distribution was uniform under the microscope. This indicates that the eutectic formation was relatively complete under these conditions, and the phase purity was high.

[0149] 15% ultrasonic power (135 W): The melting peak in the DSC curve broadened to some extent, and the peak intensity decreased; the micrograph showed uneven crystal size distribution and the presence of some irregular grains. This indicates that there may be components in the system that did not fully participate in the eutectic process.

[0150] 10% ultrasonic power (90 W): In addition to the main melting peak, secondary thermal events occur above 250℃, which may contain unreacted betaine; multiple morphologies are observed in the micrograph, and the crystal dispersion is poor. This indicates that the nucleation and growth process is insufficient under low-frequency conditions, and the system is relatively complex.

[0151] Based on the combined results of thermal analysis and microstructure analysis, it can be inferred that higher ultrasonic power helps enhance the degree of micro-mixing and intermolecular interactions in the system, promoting more uniform crystal nucleation and thus forming a more stable eutectic phase. Conversely, at lower power, the cavitation effect is insufficient, leading to local supersaturation and uneven nucleation, which can easily result in multiphase coexistence. Therefore, 20% ultrasonic power was selected as the optimal condition for subsequent eutectic preparation experiments.

[0152] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A vanillin-betaine eutectic system.

2. The vanillin-betaine co-crystal system of claim 1, wherein, One molecule of vanillin and one molecule of betaine constitute an asymmetric unit of the eutectic system; The interaction between vanillin and betaine includes intermolecular hydrogen bonding and electrostatic interaction. The vanillin-betaine eutectic system is a neutral eutectic.

3. The vanillin-betaine co-crystal system of claim 1, wherein, The crystal structure of the vanillin-betaine co-crystal system belongs to a monoclinic system, a space group is P21 / c; a cell parameter is a = 6.6533(4) A, b = 32.501(2) A, c = 6.6943(4) A, β = 108.186(4) °, a cell volume is 1375.25(15) A 3 3, Z = 4, and a calculated density is 1.301 g / cm 3 .

4. The vanillin-betaine eutectic system according to claim 1, characterized in that, The alternating stacking of the hydrophobic aromatic ring layer of vanillin and the hydrophilic amine layer of betaine forms an alternating hydrophobic-hydrophilic layered structure; the interlayer interactions of the layered structure include van der Waals interactions.

5. A method for preparing the vanillin-betaine eutectic system as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Vanillin, betaine, and anhydrous ethanol were mixed to obtain a mixed solution; The mixed solution was concentrated to induce crystal precipitation, and the obtained crystals were dried to obtain a vanillin-betaine eutectic system.

6. The preparation method according to claim 5, characterized in that, The molar ratio of vanillin to betaine is 1:1 to 3; The total molar amount of vanillin and betaine to the volume ratio of anhydrous ethanol is 0.02~0.04 mol: 20 ml; The concentration is selected from rotary evaporation concentration; preferably, ultrasonication is assisted during concentration, and the power of the ultrasonication is 90~180 W.

7. The application of the vanillin-betaine eutectic system as described in any one of claims 1 to 4 in sustained-release flavorings.

8. The application of the vanillin-betaine eutectic system as described in any one of claims 1 to 4 in food.

9. The application of the vanillin-betaine eutectic system as described in any one of claims 1 to 4 in daily chemical products.

10. The application of the vanillin-betaine eutectic system as described in any one of claims 1 to 4 in pharmaceutical excipients.

Images