A nervonic acid-rich xanthoceraside oil and a preparation method thereof

Abstract

This invention discloses a nervonic acid-rich *Xanthoceras sorbifolium* diester oil and its preparation method, belonging to the field of oleochemical technology. The invention first removes some long-chain monounsaturated free fatty acids from *Xanthoceras sorbifolium* oil through saponification and low-temperature settling. Then, porous organic polymer materials are used to further enrich nervonic acids with higher molecular weight and larger particle size. Glycerol is added to the free fatty acids, and esterification with lipase catalyzes the synthesis of diglycerides, thus obtaining a nervonic acid-rich *Xanthoceras sorbifolium* diester oil. The addition of a compound antioxidant effectively prevents oxidative rancidity of the diester oil. The *Xanthoceras sorbifolium* diester oil prepared by this invention has a rich nervonic acid content, a high diglyceride content, and excellent thermal stability, thus showing good application prospects and value in the field of oleochemicals.

Description

Technical Field

[0001] This invention belongs to the field of oleochemical technology, specifically relating to a nervonic acid-rich *Sapindus mukorossi* diester oil and its preparation method. Background Technology

[0002] Nervonic acid is not only an important component of nerve fibers, but also plays a vital role in physiological functions such as regulating nerve signal transmission, participating in cell signal transduction processes, inhibiting inflammatory responses, and promoting lipid metabolism regulation, thus attracting widespread attention. Diacylglycerol (DAG), as a structural lipid, has the function of reducing postprandial serum triacylglycerol, serum total cholesterol and low-density lipoprotein cholesterol, and the accumulation of body fat. However, the DAG content in natural oils is usually less than 10%, and it is easily oxidized and rancid, thus failing to effectively exert its functional properties.

[0003] Xanthoceras sorbifolium is one of China's top ten woody oil crops. Its oil contains over 90% unsaturated fatty acids, rich in oleic acid and linoleic acid, and also contains a long-chain monounsaturated fatty acid (nervonic acid). Therefore, the preparation of diglyceride oil rich in nervonic acid and possessing good antioxidant effects from Xanthoceras sorbifolium oil has significant application prospects and value. Summary of the Invention

[0004] This invention provides a method for preparing nervonic acid-rich Xanthoceras sorbifolium diester oil, comprising the following steps: (1) Saponification Add alkali solution to the *Sapindus mukorossi* oil and stir at 80-90℃ for 1-3 hours to carry out saponification and hydrolysis; then adjust the pH to acidic and continue stirring at 80-90℃ for 1-3 hours; after cooling to room temperature, adjust the pH to neutral, let stand, take the upper layer solution, filter it through a two-dimensional covalent triazine framework material to obtain concentrated free fatty acids of *Sapindus mukorossi* oil. (2) Esterification The concentrated free fatty acids of *Sapindus mukorossi* oil were mixed with glycerol, a catalytic enzyme was added, and a compound antioxidant was added. The mixture was then subjected to esterification at 60-90℃ for 1-5 hours. The catalytic enzyme, unreacted glycerol, and compound antioxidant were removed by centrifugation. The final product was obtained by molecular distillation.

[0005] In the above preparation method, the alkaline solution is a NaOH ethanol solution with a concentration of 0.5~2 mol / L; preferably 1 mol / L.

[0006] In the above preparation method, the mass ratio of the *Sapindus mukorossi* oil to the alkaline solution is 1:(5~10); preferably 1:6.

[0007] In the above preparation method, the pH is adjusted to acidic by adding sulfuric acid; and the pH is adjusted to neutral by adding distilled water.

[0008] In the above preparation method, the standing conditions are: standing at 10~15℃ for 1~2 hours.

[0009] In the above preparation method, the filtration conditions of the two-dimensional covalent triazine framework material are: temperature 20~25℃, flow rate 0.3-0.5 mL / min.

[0010] In the above preparation method, the mass ratio of the concentrated free fatty acids of the *Sapindus mukorossi* oil to glycerol is (5~10):1; preferably 8:1.

[0011] In the above preparation method, the catalytic enzyme is Novozym 435 lipase, and its addition amount is 2-6%; preferably 3%.

[0012] In the above preparation method, the centrifugation conditions are: centrifugation at 6000~10000 rpm for 5~20 min; preferably: centrifugation at 8500 rpm for 10 min.

[0013] In the above preparation method, the molecular distillation is a two-stage molecular distillation, and the distillation conditions are as follows: First-stage distillation: Evaporation temperature 160℃~190℃, condensation temperature 10℃, scraper rotation speed 130 rpm~150 rpm, feed rate 2 g / min~4 g / min, vacuum degree 0.01×10 -2 bar~1×10 -2 bar; Secondary distillation: Evaporation temperature 160℃~240℃, condensation temperature 10℃, scraper rotation speed 130 rpm~150 rpm, feed rate 1.5 g / min~3 g / min, vacuum degree 0.01×10 -2 bar~1×10 -2 bar.

[0014] In the above preparation method, the amount of the composite antioxidant added is 0.1~0.2%; preferably 0.15%.

[0015] In the above preparation method, the composite antioxidant is a g-C3N4 / TP-PA composite antioxidant, and its preparation method is as follows: (1) Preparation of g-C3N4 quantum dots Dissolve 3-10 parts of urea in 50-100 parts of water, sonicate until completely dissolved, stir to form a homogeneous solution, then transfer the solution to a reaction vessel and react at 150-250℃ for 10-20 h, then cool to room temperature; centrifuge the reaction solution, filter the supernatant, and vacuum dry to obtain g-C3N4 quantum dots; (2) Preparation of composite antioxidants Dissolve 3-10 parts of tea polyphenol palmitate in ethanol until completely dissolved, then add 1-5 parts of g-C3N4 quantum dots, sonicate, and then evaporate to remove the ethanol to obtain g-C3N4 / TP-PA composite antioxidant.

[0016] In the above preparation method, the two-dimensional covalent triazine framework material is prepared by the following method: 1,4-terephthalonitrile was mixed with zinc chloride and reacted at 200-300℃ for 1-5 h; then reacted at 400-550℃ for 10-50 h; after the reaction was completed, the mixture was naturally cooled to room temperature, the solid product was washed and dried to obtain a two-dimensional covalent triazine framework material.

[0017] In the above-mentioned method for preparing two-dimensional covalent triazine framework materials, the mass ratio of 1,4-terephthalonitrile to zinc chloride is 1:(5~20); preferably 1:10.

[0018] This invention provides a nervonic acid-rich saxifrage diester oil prepared by the above method.

[0019] The beneficial effects of this invention are as follows: This invention first removes some long-chain monounsaturated free fatty acids from *Xanthoceras sorbifolium* oil through saponification and low-temperature settling. Then, porous organic polymer materials are used to further enrich nervonic acid, which has a higher molecular weight and larger particle size. Glycerol is added to the free fatty acids, and esterification with lipase catalyzes the synthesis of diglycerides, thus obtaining a *Xanthoceras sorbifolium* diester oil rich in nervonic acid. The addition of a compound antioxidant effectively prevents oxidative rancidity of the diester oil. Characterization experiments demonstrate that the *Xanthoceras sorbifolium* diester oil prepared by this invention is rich in nervonic acid, has a high diglyceride content, and exhibits excellent thermal stability, thus showing good application prospects and value in the field of oleochemistry. Attached Figure Description

[0020] Figure 1 This study investigated the effect of single-factor experiments on diglyceride content.

[0021] Figure 2 For infrared spectrum analysis.

[0022] Figure 3 These are the results of the antioxidant test.

[0023] Figure 4 These are the results of thermal stability analysis.

[0024] Figure 5 The results are from the thermodynamic property analysis. Detailed Implementation

[0025] In this invention, the two-dimensional covalent triazine frameworks (CTFs) material is prepared by the following method: 5 g of 1,4-terephthalonitrile and 50 g of anhydrous zinc chloride catalyst were placed in a quartz ampoule and sealed. The sealed ampoule was placed in a muffle furnace, and the temperature was first increased to 250 °C at a rate of 2 °C / min and held for 3 h to complete the prepolymerization. Then, the temperature was increased to 450 °C at a rate of 1 °C / min and held for 30 h to complete the framework polymerization. After the reaction was completed, the mixture was naturally cooled to room temperature. The resulting solid product was washed three times each with 0.1 mol / L hydrochloric acid solution, deionized water, and anhydrous ethanol to remove residual zinc chloride and unreacted monomers. Then, it was vacuum dried at 80 °C for 12 h to obtain a light yellow powder, which is the two-dimensional covalent triazine framework material.

[0026] In this invention, the composite antioxidant used is a g-C3N4 / TP-PA composite antioxidant, and its preparation method is as follows: (1) Preparation of g-C3N4 quantum dots 5 g of urea was dissolved in 80 mL of deionized water and sonicated for 20 min until completely dissolved. The mixture was then magnetically stirred for 30 min to form a homogeneous solution. The solution was then transferred to a reaction vessel and reacted at 200 °C for 12 h. After natural cooling to room temperature, the reaction solution was centrifuged, and the supernatant was filtered through a 0.22 μm filter membrane and vacuum dried for 12 h to obtain g-C3N4 quantum dots.

[0027] (2) Preparation of composite antioxidants 5g of tea polyphenol palmitate (TP-PA) was dissolved in a small amount of warm anhydrous ethanol (40℃, concentration 50 mg / mL) until completely dissolved. Then, 1g of g-C3N4 quantum dots were added, and the mixture was sonicated for 30 min. The ethanol was then removed by rotary evaporation of the composite solution to obtain the g-C3N4 / TP-PA composite antioxidant.

[0028] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way. Example 1

[0029] The steps for preparing Xanthoceras sorbifolium diester oil are as follows: (1) Saponification Add NaOH ethanol solution (1 mol / L) to *Xanthoceras sorbifolium* oil at a mass ratio of 1:6. Maintain the oil bath temperature at 85℃ and stir for 2 h to carry out saponification and hydrolysis. Then, adjust the pH to 2.0 with sulfuric acid (10%) and continue stirring at 85℃ for 2 h. Cool to room temperature, adjust the pH to neutral by adding distilled water, and let stand at 15℃ for 1 h. Take the supernatant solution (free fatty acids of *Xanthoceras sorbifolium* oil) and filter it through a two-dimensional covalent triazine framework material at 20℃ and a flow rate of 0.3 mL / min to obtain concentrated free fatty acids of *Xanthoceras sorbifolium* oil.

[0030] (2) Esterification The concentrated free fatty acids of *Xanthoceras sorbifolium* oil were mixed with glycerol in a 6:1 (mass ratio). 2% Novozym 435 lipase was added based on the total substrate mass, followed by 0.15% of a compound antioxidant. The mixture was reacted at 80°C for 3 h under a vacuum of 0.1 Pa to obtain crude *Xanthoceras sorbifolium* diester oil. The crude product was centrifuged at 8500 rpm for 10 min to remove lipase, unreacted glycerol, and the compound antioxidant. The final product was obtained by molecular distillation.

[0031] The molecular distillation process is as follows: Two-stage molecular distillation was used to separate the crude *Sapindus mukorossi* diester oil, removing free fatty acids and monoglycerides. The molecular distillation conditions were as follows: First-stage distillation: evaporation temperature 180℃, condensation temperature 10℃, scraper rotation speed 130 rpm, feed rate 2 g / min, vacuum degree 0.01×10 -2 bar.

[0032] Secondary distillation: Evaporation temperature 200℃, condensation temperature 10℃, scraper rotation speed 130 rpm, feed rate 1.5 g / min, vacuum degree 0.01×10 -2 bar.

[0033] High-performance liquid chromatography (HPLC) analysis revealed that the content of diglycerides (DAG) in the *Sapindus mukorossi* diester oil was 92.46%, and the content of nervonic acid was 11.94%.

[0034] I. Effects of different esterification conditions on diglyceride content Based on Example 1, the esterification conditions were adjusted to study the effect of different esterification conditions on the content of diglyceride (DAG).

[0035] The experimental design is shown in Table 1: Table 1 Experimental Condition Design The test results are as follows Figure 1 As shown: Through single-factor experiments, the optimal preparation process for diglycerides was determined to be: reaction temperature 80℃, time 3 h, mass ratio 8:1, enzyme addition 3%, and antioxidant addition 0.15%. Testing showed that under this optimal process, the diglyceride (DAG) content in the *Sapindus mukorossi* diglyceride oil was 97.32%.

[0036] The *Sapindus mukorossi* diester oil used in the following experiments was prepared under the above-mentioned optimal process conditions.

[0037] II. Infrared Spectroscopy Analysis Fourier transform near-infrared spectroscopy: Fourier transform infrared spectra of *Xanthoceras sorbifolium* oil, free fatty acids from *Xanthoceras sorbifolium* oil, and *Xanthoceras sorbifolium* diester oil were obtained using an infrared spectrometer. Measurements were performed at room temperature, with a wavenumber range of 500 to 4000 cm⁻¹. -1 The spectral resolution was set to 4 cm. -1 .

[0038] Test results are as follows Figure 2 As shown: FTIR analysis provides information on the molecular structure and chemical bonds of molecules of any size. (2900 / 2800 cm⁻¹) -1 The absorption in the vicinity corresponds to the antisymmetric / symmetric stretching vibrations of alkyl groups (-CH2, -CH3), a common characteristic of all lipids. 1735 cm⁻¹ -1 Corresponding to the C=O stretching vibration of the ester group (-COO-), 1100-1200 cm⁻¹ -1 The COC stretching vibration of the ester group in the vicinity is a characteristic peak of ester substances. The presence of this peak in the diglyceride oil of *Crassula ovata* in the figure indicates that the esterification reaction has occurred, verifying the successful preparation of diglyceride.

[0039] III. Antioxidant properties The antioxidant activity of Xanthoceras sorbifolium oil and Xanthoceras sorbifolium diester oil was tested.

[0040] DPPH removal rate: The sample (200 mg) was dispersed in water by sonication (400 W, 1 min) and centrifuged (1611 × g, 10 min). Aliquots of the supernatant (2 mL) were mixed with 2 mL of DPPH solution (1 mmol / L) or water (control) and incubated in the dark for 30 min. The absorbance was recorded at 517 nm using an ethanol blank. Vitamin C was used as a positive control. Scavenging activity (SA) was measured. DPPH The calculation formula is as follows: SA DPPH (%) = 1 - (sample - blank) / control × 100%.

[0041] Hydroxyl radical scavenging rate: Three reaction systems were established: test sample (2 mL sample + 2 mL H2O), sample blank (2 mL sample + 2 mL H2O), and reagent control (4 mL H2O). First, 2 mL FeSO4 (6 mmol / L) and 2 mL H2O2 (6 mmol / L) were added to each system, vortexed, and incubated for 10 min to generate hydroxyl radicals. Subsequently, 2 mL salicylic acid (6 mmol / L) was added to the test and control groups, and 2 mL H2O was added to the sample blank group. After incubation for 30 min, absorbance (Ai, Aj, and A0) was measured at 510 nm. Scavenging activity (SA) was assessed. OH Calculate SA using the following formula: OH (%)=[1-(Ai-Aj) / A0]×100%.

[0042] Lipid hydroperoxide clearance rate: Lecithin liposome suspensions (LLS) were prepared by dispersing 300 mg of lecithin in 30 mL of PBS (pH 7.4). The oxidation system consisted of 1 mL LLS, 1 mL ferric chloride (0.4 mmol / L), 1 mL ascorbic acid (0.4 mmol / L), and 1 mL of sample solution (test) or water (blank). The mixture was incubated at 37 °C in the dark for 60 min to induce oxidation. The reaction was terminated by adding 2 mL of TCA-TBA-HCl reagent (15 g TCA, 0.375 g TBA, and 2.1 mL HCl dissolved in 100 mL water). The mixture was heated at 95 °C for 15 min, rapidly cooled, and then centrifuged at 4000 × g for 10 min. The absorbance of the supernatant was measured at 532 nm (test: A; blank: A0). The inhibition efficiency was calculated using the following formula: Lipid peroxidation inhibition rate (%) = (1 - A / A0) × 100%.

[0043] The antioxidant activity of *Sapindus mukorossi* oil and *Sapindus mukorossi* diester oil was evaluated using DPPH radical, hydroxyl radical, and lipid hydroperoxide scavenging assays. The results are as follows: Figure 3 As shown, the antioxidant capacity of Xanthoceras sorbifolium diester oil is significantly higher than that of Xanthoceras sorbifolium oil. Its three free radical scavenging abilities are increased by 20%, 19% and 27% respectively compared to Xanthoceras sorbifolium oil. After adding the compound antioxidant, it can effectively prevent the oil from becoming rancid and deteriorating, and extend the shelf life of the oil.

[0044] IV. Physicochemical Properties Analysis of Xanthoceras sorbifolium Oil Before and After Processing (1) Fatty acid determination The methyl esterification process was carried out in accordance with GB 5009.168-2016 "Determination of Fatty Acids in Food". The fatty acid composition of the *Sapindus mukorossi* oil before and after processing was further determined by gas chromatography-mass spectrometry (GC-MS).

[0045] Chromatographic conditions: HP-5MS quartz flexible capillary column (30 m × 250 μm); carrier gas: ultrapure helium; total flow rate: 40 mL / min; column flow rate: 1.0 mL / min; injection port temperature: 280℃; injection volume: 1 μL; split ratio: 10:1. Temperature program: initial temperature 50℃, hold for 2 min; increase to 200℃ at 30℃ / min, hold for 3 min; then increase to 220℃ at 10℃ / min and hold for 3 min; finally increase to 280℃ at 10℃ / min and hold for 10 min.

[0046] Mass spectrometry conditions: electron impact energy 70 eV, ion source temperature 230℃, scan range 35~550 m / z. Qualitative analysis was performed using the NIST14 standard library search, with a retention match >85%. Quantitative analysis was performed using peak area normalization; the percentage of each substance's peak area to the total peak area represents the relative content of the corresponding substance.

[0047] The measurement results are shown in Table 2: Table 2. Changes in fatty acid composition of *Sapindus mukorossi* oil and *Sapindus mukorossi* diester oil As shown in Table 2, the fatty acids mainly consist of two saturated fatty acids, palmitic acid and stearic acid; four monounsaturated fatty acids, oleic acid, eicosenoic acid, docosahexaenoic acid, and docosahexaenoic acid (nervonic acid); and one polyunsaturated fatty acid, linoleic acid. After preparing diester oil through saponification and filtration with CTFs materials, the fatty acid composition changed. The covalent triazine framework possesses a unique triazine structure, abundant porosity, high conjugation properties, and excellent chemical and thermal stability. By enriching long-chain monounsaturated fatty acids from the mixed fatty acids and separating short-chain monounsaturated fatty acids, the C24:1 ratio of docosahexaenoic acid (nervonic acid) increased more than threefold. Antioxidants only affect oxidative stability and do not affect the types and proportions of fatty acids themselves; therefore, the fatty acid composition did not change significantly before and after the addition of antioxidants.

[0048] (2) Determination of acid value and peroxide value Peroxide value is an indicator of the content of peroxides or hydroperoxides in the initial stage of oil oxidation. Refer to GB5009.227-2023 "Determination of Peroxide Value in Food" and GB 5009.229-2025 "Determination of Acid Value in Food".

[0049] The measurement results are shown in Table 3: Table 3. Determination of Acid Value and Peroxide Value Table 3 shows that the peroxide value of *Xanthoceras sorbifolium* oil is higher than that of *Xanthoceras sorbifolium* diester oil. This is because the free hydroxyl groups give *Xanthoceras sorbifolium* diester oil its oxidative stability, and the DAG molecules can form a crystalline barrier, reducing the contact between oxygen and unsaturated fatty acyl groups. Therefore, DAG gives the oil higher oxidative stability. The acid values ​​of the two oils are 1.07 mg / g and 0.63 mg / g, respectively, both of which do not exceed the national standard (≤3 mg / g).

[0050] V. Thermal Stability Analysis Thermal stability analysis: To verify thermal stability, TGA analysis was performed on *Xanthoceras sorbifolium* oil, free fatty acids, and *Xanthoceras sorbifolium* diester oil. Samples were weighed in 150 μL sealed alumina crucibles, and their thermal behavior was analyzed within the temperature range of 25–600 °C. Scans were performed under nitrogen atmosphere at a ramp rate of 10 °C / min.

[0051] Test results are as follows Figure 4 As shown: Xanthoceras sorbifolium oil exhibits the best thermal stability, only beginning to show significant weight loss at 350-400℃, and completely losing its mass at approximately 500℃. Xanthoceras sorbifolium diester oil, on the other hand, begins to show significant weight loss at approximately 300-350℃, and its mass is essentially lost by 450℃. The superior thermal stability of Xanthoceras sorbifolium oil compared to its diester oil is determined by their molecular structures. The former is a triglyceride with three fatty acid chains linked to its glycerol backbone, while the latter is a diglyceride with only two fatty acid chains. The increased number of ester bonds and intermolecular forces makes the triglyceride molecule more compact, requiring greater energy to break down. However, compared to free fatty acids, Xanthoceras sorbifolium diester oil can withstand higher temperatures. Although its thermal stability does not surpass that of natural triglycerides, it has reached or exceeded the levels of most modified oils, capable of withstanding typical processing temperatures such as frying and baking, thus meeting practical application requirements in food processing.

[0052] VI. Analysis of Thermodynamic Properties Thermodynamic properties of the samples were analyzed using differential scanning calorimetry (DSC). 10 mg of sample was weighed into an aluminum crucible, sealed, and placed inside the instrument for analysis. The determination method was as follows: Under a constant nitrogen flow rate of 50 mL / min, the initial temperature was 25 °C, then increased to 80 °C at a rate of 40 °C / min and held for 10 min. The temperature was then decreased to -80 °C at the same rate and held for 10 min. Finally, the temperature was increased to 80 °C at a rate of 10 °C / min. Crystallization and melting curves of the samples were obtained through this heating and cooling program.

[0053] Test results are as follows Figure 5 As shown In the crystallization curve, the crystallization peak of *Sapindus mukorossi* oil appears at -64.1℃, while the crystallization peak of *Sapindus mukorossi* diglyceride oil is -26.4℃. This peak represents the lowest crystallization point. As the content of diglycerides increases, the low-temperature crystallization peak shifts to the right. The temperature at the beginning of crystallization increases because the content of unsaturated fatty acids exceeds 80%.

[0054] In the melting curve, the melting peak of *Sapindus mukorossi* oil is at a lower temperature, the content of diglycerides increases, the melting peak shifts to the right, and the high melting point components of the fat are increased.

[0055] In summary, both the crystallization point and melting point increased with increasing diglyceride content. These results indicate that, compared to *Xanthoceras sorbifolium* oil, diglyceride oil exhibits greater plasticity over a wider temperature range, thus expanding the application scope of *Xanthoceras sorbifolium* oil.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a nervonic acid-rich *Sapindus mukorossi* diester oil, characterized in that, Includes the following steps: (1) Saponification Add alkali solution to the *Sapindus mukorossi* oil and stir at 80-90℃ for 1-3 hours to carry out saponification and hydrolysis; then adjust the pH to acidic and continue stirring at 80-90℃ for 1-3 hours; after cooling to room temperature, adjust the pH to neutral, let stand, take the upper layer solution, filter it through a two-dimensional covalent triazine framework material to obtain concentrated free fatty acids of *Sapindus mukorossi* oil. (2) Esterification The concentrated free fatty acids of *Sapindus mukorossi* oil were mixed with glycerol, a catalytic enzyme was added, and a compound antioxidant was added. The mixture was then subjected to esterification at 60-90℃ for 1-5 hours. The catalytic enzyme, unreacted glycerol, and compound antioxidant were removed by centrifugation. The final product was obtained by molecular distillation.

2. The preparation method according to claim 1, characterized in that, The mass ratio of *Sapindus mukorossi* oil to alkaline solution is 1:(5~10); the alkaline solution is a NaOH ethanol solution with a concentration of 0.5~2 mol / L.

3. The preparation method according to claim 1, characterized in that, The conditions for standing are: standing at 10~15℃ for 1~2 hours.

4. The preparation method according to claim 1, characterized in that, The filtration conditions for the two-dimensional covalent triazine framework material are: temperature 20~25℃, flow rate 0.3-0.5 mL / min.

5. The preparation method according to claim 1, characterized in that, The mass ratio of free fatty acids to glycerol in the concentrated *Sapindus mukorossi* oil is (5~10):

1.

6. The preparation method according to claim 1, characterized in that, The catalytic enzyme is Novozym 435 lipase, and its addition amount is 2-6%.

7. The preparation method according to claim 1, characterized in that, The molecular distillation is a two-stage molecular distillation, and the distillation conditions are as follows: First-stage distillation: Evaporation temperature 160℃~190℃, condensation temperature 10℃, scraper rotation speed 130 rpm~150 rpm, feed rate 2 g / min~4 g / min, vacuum degree 0.01×10 -2 bar~1×10 -2 bar; Secondary distillation: Evaporation temperature 160℃~240℃, condensation temperature 10℃, scraper rotation speed 130 rpm~150 rpm, feed rate 1.5 g / min~3 g / min, vacuum degree 0.01×10 -2 bar~1×10 -2 bar.

8. The preparation method according to claim 1, characterized in that, The amount of the composite antioxidant added is 0.1~0.2%.

9. The preparation method according to claim 1, characterized in that, The composite antioxidant is a g-C3N4 / TP-PA composite antioxidant, and its preparation method is as follows: (1) Preparation of g-C3N4 quantum dots Dissolve 3-10 parts of urea in 50-100 parts of water, sonicate until completely dissolved, stir to form a homogeneous solution, then transfer the solution to a reaction vessel and react at 150-250℃ for 10-20 h, then cool to room temperature; centrifuge the reaction solution, filter the supernatant, and vacuum dry to obtain g-C3N4 quantum dots; (2) Preparation of composite antioxidants Dissolve 3-10 parts of tea polyphenol palmitate in ethanol until completely dissolved, then add 1-5 parts of g-C3N4 quantum dots, sonicate, and then evaporate to remove the ethanol to obtain g-C3N4 / TP-PA composite antioxidant.

10. The nervonic acid-rich Xanthoceras sorbifolium diester oil prepared by the method according to any one of claims 1 to 9.

Images