A method for preparing medium-long chain fatty acid triglycerides

Abstract

The application discloses a preparation method of medium and long chain fatty acid triglyceride, and belongs to the technical field of oil deep processing. Firstly, plant oil and medium chain fatty acid triglyceride are used as substrates, a low eutectic solvent is used as a reaction medium, and an ester exchange reaction is carried out under the catalysis of immobilized lipase; after the reaction is completed, centrifugal treatment is carried out, and the low eutectic solvent, the immobilized lipase and the reaction product are recovered respectively; the recovered low eutectic solvent and the immobilized lipase are used for the next batch of reaction, and the recovered upper oil phase is the reaction product. The application uses immobilized lipase to catalyze ester exchange to prepare medium and long chain fatty acid triglyceride in a low eutectic system, the substrate conversion rate and the product generation amount are high, the product separation is easy, further separation and purification are not needed, the low eutectic solvent is green, environment-friendly and reusable, and the method has good ecological, economic benefits and industrialization application prospects.

Description

Technical Field

[0001] This invention belongs to the field of deep processing technology of oils and fats, and specifically relates to a method for preparing medium- and long-chain fatty acid triglycerides. Background Technology

[0002] Edible oils are essential nutrients providing energy, essential fatty acids, and fat-soluble nutrients. With extensive research into lipid nutrition, increasing evidence suggests that the intramolecular structure and fatty acid composition of triglycerides are crucial factors influencing the nutritional characteristics of specific oils. Medium- and long-chain triglycerides are novel structural esters containing both medium- and long-chain fatty acids in their triglyceride backbone. Medium- and long-chain triglycerides not only possess the advantages of both medium- and long-chain triglycerides in terms of metabolism and nutrition but also overcome their shortcomings, such as increasing the smoke point and significantly reducing foaming during use. Some preclinical studies have shown that medium- and long-chain triglycerides have effects such as inhibiting obesity, lowering blood lipids, reducing cholesterol levels, and improving insulin resistance. Given that medium- and long-chain triglycerides not only provide nutrition and immediate energy but also possess various physiological benefits, they have attracted widespread attention from scientists and consumers in recent years.

[0003] Typically, chemical transesterification and enzymatic esterification, acid hydrolysis, or transesterification are used to prepare medium- and long-chain fatty acid triglycerides. Chemical catalysis not only suffers from harsh reaction conditions, complex products, high energy consumption, and severe environmental pollution, but also suffers from catalyst deactivation during the chemical catalysis process, making it difficult to reuse and even producing byproducts that are difficult to remove. Most significantly, chemically catalyzed transesterification reactions cannot catalyze fatty acids at specific positions, resulting in low added value products that fail to meet the requirements for the production and health functions of medium- and long-chain fatty acid triglycerides. Compared to traditional chemical methods, selectivity is the most important advantage of enzymes in lipid synthesis and modification. Enzymes, as biocatalysts, also offer many potential benefits, including mild reaction conditions, high catalytic efficiency, the production of specific biomolecular products, and control over the composition and structure of products.

[0004] CN 114875080A discloses a method for preparing medium- and long-chain fatty acid glycerides. Using medium-chain fatty acids, glycerol, oils, and antioxidants as substrates, and sodium methoxide or lipase as catalysts, a transesterification reaction is catalyzed to prepare medium- and long-chain fatty acid glycerides. After refining, the reaction product yields a structured ester product. The final product contains 62.54%–76.71% medium- and long-chain fatty acid triglycerides and 12.97%–34.45% long-chain fatty acid triglycerides. Zou Xiaoqiang et al. prepared medium- and long-chain fatty acid triglycerides by transesterification of medium-chain triglycerides with walnut oil under the catalysis of lipase. Byproduct fatty acids were generated during the reaction. Under optimized reaction conditions, molecular distillation was used to remove the byproduct fatty acids, resulting in a product containing 76.2% medium- and long-chain fatty acid triglycerides, 14.3% medium-chain fatty acid triglycerides, and 9.5% long-chain fatty acid triglycerides (Zou Xiaoqiang et al., 2022, 47(4): 58-63). Yang et al. used rapeseed oil and medium-chain triglycerides as substrates and immobilized lipase Lipozyme TLIM as a catalyst to catalyze the transesterification of medium- and long-chain triglycerides. After the reaction was carried out under optimized reaction conditions, the crude product was purified by molecular distillation. The final product contained 87.42% medium- and long-chain triglycerides and 11.05% long-chain triglycerides (China Oils and Fats, Optimization of the Synthesis of Medium- and Long-Chain Triglycerides Catalyzed by Lipozyme TLIM Enzyme, 2022, doi:10.19902 / j.cnki.zgyz.1003-7969.210599).

[0005] As can be seen from the existing technologies described above, regardless of whether chemical or enzymatic methods are used to prepare medium- and long-chain fatty acid triglycerides, the product not only contains less than 77% medium- and long-chain fatty acid triglycerides, but also retains a certain amount of unreacted medium- and long-chain fatty acid triglycerides. Therefore, further molecular distillation purification is needed to increase the content of medium- and long-chain fatty acid triglycerides in the product. Thus, improving the substrate conversion rate in the enzymatic transesterification process for preparing medium- and long-chain fatty acid triglycerides, thereby increasing the content of medium- and long-chain fatty acid triglycerides in the product, is the key technical problem to be solved in the enzymatic transesterification process for preparing medium- and long-chain fatty acid triglycerides. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a method for preparing medium- and long-chain fatty acid triglycerides, which significantly increases the content of medium- and long-chain fatty acid triglycerides in the product and significantly reduces the content of both medium-chain and long-chain fatty acid triglycerides in the product; furthermore, it effectively suppresses hydrolysis side reactions during the reaction process. The final product has a high content of medium- and long-chain fatty acid triglycerides and a low content of both medium-chain and long-chain fatty acid triglycerides, and the product does not require further separation and purification.

[0007] This invention is achieved through the following technical solution:

[0008] A method for preparing medium- and long-chain fatty acid triglycerides includes the following steps:

[0009] Step 1: Using vegetable oil and medium-chain fatty acid triglycerides as substrates and a eutectic solvent as the reaction medium, transesterification reaction was carried out under the catalysis of immobilized lipase.

[0010] Step 2: After the reaction is completed, centrifugation is performed to recover the eutectic solvent, immobilized lipase and reaction product respectively; the recovered eutectic solvent and immobilized lipase are used for the next batch of reaction, and the recovered upper oil phase is the reaction product.

[0011] Preferably, in step 1, the vegetable oil is walnut oil, red walnut oil, purple walnut oil, flaxseed oil, olive oil, tea oil, peony seed oil, rapeseed oil, soybean oil, peanut oil, or corn oil.

[0012] Preferably, in step 1, the medium-chain fatty acid triglyceride is rich in one or more of caprylic acid, capric acid and lauric acid.

[0013] Preferably, in step 1, the eutectic solvent is choline chloride-urea, betaine-urea-water, betaine-lactic acid, or betaine-glucose-water.

[0014] More preferably, when the eutectic solvent is choline chloride-urea, the molar ratio of choline chloride to urea is 1:2; when the eutectic solvent is betaine-urea-water, the molar ratio of betaine, urea, and water is 1:2:1; when the eutectic solvent is betaine-lactic acid, the molar ratio of betaine to lactic acid is 1:2; and when the eutectic solvent is betaine-glucose-water, the molar ratio of betaine, glucose, and water is 5:2:10.

[0015] Preferably, in step 1, the amount of eutectic solvent added is 10% to 50% of the total mass of vegetable oil and medium-chain fatty acid triglycerides.

[0016] Preferably, in step 1, the immobilized lipase is Lipozyme 435 or Novozyme 435.

[0017] Preferably, in step 1, the conditions for the transesterification reaction are: the molar ratio of vegetable oil to medium-chain fatty acid triglycerides is 1:1 to 2, the reaction temperature is 40 to 80°C, the amount of immobilized lipase added is 3% to 8% of the total substrate mass, and the reaction time is 6 to 12 hours.

[0018] Preferably, in step 2, the centrifugation speed is 10,000 to 12,000 rpm and the time is 2 to 3 minutes.

[0019] Preferably, in step 2, the reaction product contains: medium- and long-chain fatty acid triglycerides ≥94%, medium-chain fatty acid triglycerides ≤2%, long-chain fatty acid triglycerides ≤3%, and free fatty acid content ≤1%.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention discloses a method for preparing medium- and long-chain fatty acid triglycerides, using vegetable oil and medium-chain fatty acid triglycerides as substrates and a eutectic solvent as the reaction medium, under the catalysis of immobilized lipase. Due to the interaction between the eutectic solvent and the catalytic active site of the immobilized lipase under these reaction conditions, the positional specificity of the immobilized lipase for the glycerol ester backbone is reduced, thereby increasing the transesterification activity of the immobilized lipase by more than two times. Furthermore, the regulatory effect of the eutectic solvent on the water activity in the reaction system significantly reduces the occurrence of side reactions during the enzymatic transesterification reaction. Therefore, when preparing medium- and long-chain fatty acid triglycerides in this system, the conversion rate of medium- and long-chain fatty acid triglycerides (vegetable oil) is greatly improved due to the significant enhancement of the transesterification activity of the immobilized lipase and the inhibition of side reactions. This results in a significant increase in the content of medium- and long-chain fatty acid triglycerides in the product, while the content of both medium- and long-chain fatty acid triglycerides (vegetable oil) is significantly reduced. The final medium- and long-chain fatty acid triglycerides prepared contain: medium- and long-chain fatty acid triglyceride content ≥94%, medium-chain fatty acid triglyceride content ≤2%, long-chain fatty acid triglyceride content ≤3%, and free fatty acid content ≤1%. Furthermore, the product mixture can be separated from the eutectic solvent by centrifugation, making product separation simple. More importantly, no further separation and purification is required after product separation. Moreover, the eutectic solvent and immobilized lipase obtained from centrifugation can be recovered and reused multiple times. In summary, this invention utilizes immobilized lipase to catalyze transesterification in a eutectic system to prepare medium- and long-chain fatty acid triglycerides. The substrate conversion rate and product yield are high, the product is easy to separate without further purification, and the eutectic solvent is environmentally friendly and reusable, demonstrating good ecological and economic benefits and promising prospects for industrial application.

[0022] Furthermore, the eutectic solvent is one of choline chloride-urea, betaine-urea-water, betaine-lactic acid, and betaine-glucose-water, which can effectively regulate the position specificity of the immobilized lipase for the glycerol ester skeleton, improve the transesterification activity of the immobilized enzyme, and inhibit the occurrence of side reactions, ensuring high substrate conversion rate and product yield.

[0023] Furthermore, the molar ratio of choline chloride to urea in the eutectic solvent used is 1:2, the molar ratio of betaine to urea and water is 1:2:1, the molar ratio of betaine to lactic acid is 1:2, and the molar ratio of betaine to glucose and water is 5:2:10. This not only effectively controls the transesterification activity of the immobilized enzyme used, but also ensures that the eutectic solvent used has a low viscosity, ensuring good mass transfer in the transesterification reaction.

[0024] Furthermore, the amount of eutectic solvent added is 10% to 50% of the total mass of vegetable oil and medium-chain fatty acid triglycerides, which can effectively promote mass transfer during the reaction process and the separation of the reaction products from the eutectic solvent.

[0025] Furthermore, immobilizing the lipase as Lipozyme 435 or Novozyme 435 ensures that medium-chain fatty acid triglycerides and long-chain fatty acid triglycerides can be rapidly and completely converted into medium- and long-chain fatty acid triglycerides in the eutectic system used.

[0026] Furthermore, the conditions for the transesterification reaction can ensure that when medium-chain fatty acid triglycerides and long-chain fatty acid triglycerides are transesterified to prepare medium- and long-chain fatty acid triglycerides, the substrate conversion rate is high, the product yield is high, and the amount of by-product free fatty acids generated is low.

[0027] Furthermore, centrifugation can effectively separate eutectic solvents, immobilized lipases, and reaction products. Attached Figure Description

[0028] Figure 1 This is a product separation image after the reaction in Example 1 of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for illustrative purposes only and not for limiting the scope of the invention. Unless otherwise stated, all percentages are by weight.

[0030] Example 1

[0031] Add 500g of a mixture of walnut oil and medium-chain triglycerides (rich in caprylic and capric acids, with caprylic acid content of 52.46% and capric acid content of 47.54%) to a 2.5L reaction flask (the molar ratio of walnut oil to medium-chain triglycerides is 1:1). Heat the reaction mixture to 40°C, then add 50g of a eutectic solvent consisting of choline chloride and urea (molar ratio of 1:2). Stir and mix thoroughly at 500rpm. After the temperature reaches 40°C, add 15g of Novozym 435, and start timing the reaction. After reacting for 12 hours, centrifuge at 10,000rpm for 3 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is a mixture of the eutectic solvent and immobilized lipase Novozym 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 94.42% medium- and long-chain triglycerides, 1.97% medium-chain triglycerides, 2.67% long-chain triglycerides, and 0.94% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Novozym 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition. Figure 1 This is a product separation image after the reaction in Example 1. As can be seen from the image, after centrifugation, the product separated into three layers: the upper layer is medium- and long-chain fatty acid triglycerides, the middle layer is immobilized lipase Novozym 435, and the lower layer is a eutectic solvent composed of choline chloride and urea.

[0032] Example 2

[0033] Add 500g of a mixture of linseed oil and medium-chain triglycerides (octanoic acid content 99.24%) to a 2.5L reaction flask (molar ratio of linseed oil to medium-chain triglycerides 1:2). Heat the reaction mixture to 80°C, then add 250g of a eutectic solvent consisting of betaine, urea, and water (molar ratio 1:2:1). Stir at 500rpm until homogeneous. After heating to 80°C, add 40g of Lipozyme 435 and start timing the reaction. After 6 hours of reaction, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is the mixture of the eutectic solvent and immobilized lipase Lipozyme 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 95.63% medium- and long-chain triglycerides, 1.55% medium-chain triglycerides, 2.38% long-chain triglycerides, and 0.44% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Lipozyme 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0034] Example 3

[0035] Add 500g of olive oil and a mixture of medium-chain triglycerides (octanoic acid, capric acid, and lauric acid content: 42.57%, capric acid content: 36.36%, lauric acid content: 21.07%) to a 2.5L reaction flask (molar ratio of olive oil to medium-chain triglycerides: 1:1.5). Heat the reaction mixture to 60°C, then add 125g of a eutectic solvent composed of betaine and lactic acid (molar ratio: 1:2). Stir and mix thoroughly at 500rpm. After heating to 60°C, add 25g of Lipozyme 435 and start timing the reaction. After reacting for 10 hours, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium-chain triglycerides, and the lower layer is a mixture of the eutectic solvent and immobilized lipase Lipozyme 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 95.14% medium- and long-chain triglycerides, 1.87% medium-chain triglycerides, 2.69% long-chain triglycerides, and 0.30% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Lipozyme 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0036] Example 4

[0037] Add 500g of a mixture of tea oil and medium-chain triglycerides (decanoic acid content 99.63%) to a 2.5L reaction flask (molar ratio of tea oil to medium-chain triglycerides is 1:2). Heat the reaction mixture to 50°C, then add 150g of a eutectic solvent consisting of betaine-glucose-water (molar ratio 5:2:10). Stir and mix thoroughly at 500rpm. After the temperature reaches 50°C, add 30g of Novozym 435 and start timing the reaction. After 8 hours of reaction, centrifuge at 10000rpm for 3 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is the mixture of the eutectic solvent and immobilized lipase Novozym 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 96.21% medium- and long-chain triglycerides, 1.22% medium-chain triglycerides, 1.98% long-chain triglycerides, and 0.59% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Novozym 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0038] Example 5

[0039] Add 500g of a mixture of peony seed oil and medium-chain triglycerides (rich in caprylic and capric acids, with caprylic acid content of 52.46% and capric acid content of 47.54%) to a 2.5L reaction flask (molar ratio of peony seed oil to medium-chain triglycerides is 1:2). Heat the reaction mixture to 55°C, then add 200g of a eutectic solvent composed of choline chloride and urea (molar ratio of 1:2). Stir and mix thoroughly at 500rpm. After the temperature reaches 55°C, add 40g of Lipozyme 435, and start timing the reaction. After 6 hours of reaction, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium-chain triglycerides, and the lower layer is the mixture of the eutectic solvent and immobilized lipase Lipozyme 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 96.65% medium- and long-chain triglycerides, 1.09% medium-chain triglycerides, 1.93% long-chain triglycerides, and 0.33% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Lipozyme 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0040] Example 6

[0041] Add 500g of a mixture of red walnut oil and medium-chain triglycerides (caprylic acid content 99.24%) to a 2.5L reaction flask (molar ratio of red walnut oil to medium-chain triglycerides 1:1.5). Heat the reaction mixture to 65°C, then add 175g of a eutectic solvent consisting of betaine, urea, and water (molar ratio 1:2:1). Stir at 500rpm until homogeneous. After heating to 65°C, add 35g of Novozym 435 and start timing the reaction. After 7 hours of reaction, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is the mixture of the eutectic solvent and immobilized lipase Novozym 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 95.84% medium- and long-chain triglycerides, 1.70% medium-chain triglycerides, 2.01% long-chain triglycerides, and 0.45% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Novozym 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0042] Example 7

[0043] Add 500g of corn oil and a mixture of medium-chain triglycerides (rich in caprylic and capric acids, with caprylic acid content of 52.46% and capric acid content of 47.54%) to a 2.5L reaction flask (molar ratio of corn oil to medium-chain triglycerides is 1:1.5). Heat the reaction mixture to 50°C, then add 150g of a eutectic solvent consisting of choline chloride and urea (molar ratio of 1:2). Stir and mix thoroughly at 500rpm. After the temperature reaches 50°C, add 25g of Novozym 435 and start timing the reaction. After reacting for 10 hours, centrifuge at 10000rpm for 3 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is a mixture of the eutectic solvent and immobilized lipase Novozym 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 94.89% medium- and long-chain triglycerides, 1.66% medium-chain triglycerides, 2.58% long-chain triglycerides, and 0.87% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Novozym 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0044] Example 8

[0045] Add 500g of peanut oil and a mixture of medium-chain triglycerides (octanoic acid, capric acid, and lauric acid content: 42.57%, capric acid content: 36.36%, lauric acid content: 21.07%) to a 2.5L reaction flask (molar ratio of peanut oil to medium-chain triglycerides: 1:1). Heat the reaction mixture to 70°C, then add 225g of a eutectic solvent composed of betaine and lactic acid (molar ratio: 1:2). Stir and mix thoroughly at 500rpm. After the temperature reaches 70°C, add 35g of Lipozyme 435, and start timing the reaction. After 7 hours of reaction, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium-chain triglycerides, and the lower layer is a mixture of the eutectic solvent and immobilized lipase Lipozyme 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 95.37% medium- and long-chain triglycerides, 1.57% medium-chain triglycerides, 2.49% long-chain triglycerides, and 0.57% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Lipozyme 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0046] Example 9

[0047] Add 500g of a mixture of rapeseed oil and medium-chain triglycerides (decanoic acid content 99.63%) to a 2.5L reaction flask (molar ratio of rapeseed oil to medium-chain triglycerides is 1:1.8). Heat the reaction mixture to 55°C, then add 250g of a eutectic solvent consisting of betaine-glucose-water (molar ratio 5:2:10). Stir at 500rpm until homogeneous. After the temperature reaches 55°C, add 40g of Novozym 435 and start timing the reaction. After 6 hours of reaction, centrifuge at 12000rpm for 2 minutes. The upper oil phase obtained is the medium- and long-chain triglycerides, and the lower layer is the mixture of the eutectic solvent and immobilized lipase Novozym 435, which can be recycled for reuse in the next batch of reaction. Analysis of the upper oil phase product revealed the following composition: 95.99% medium- and long-chain triglycerides, 1.35% medium-chain triglycerides, 2.11% long-chain triglycerides, and 0.55% free fatty acids. The reaction was repeated with new substrate added to the recovered eutectic solvent and immobilized lipase Novozym 435. After 20 batches of this reaction, the product composition remained essentially consistent with the initial product composition.

[0048] Comparative Example 1

[0049] 500g of walnut oil and a mixture of medium-chain triglycerides (rich in caprylic and capric acids, with caprylic acid content of 52.46% and capric acid content of 47.54%) were added to a 2.5L reaction flask (the molar ratio of walnut oil to medium-chain triglycerides was 1:1). The reaction mixture was heated to 40°C, and 15g of Novozym 435 was added. The reaction time was started. After reacting for 12 hours, the mixture was centrifuged at 10,000 rpm for 3 minutes. The upper oil phase obtained was the medium- and long-chain triglycerides. Analysis of the upper oil phase product showed that the content of medium- and long-chain triglycerides was 72.52%, medium-chain triglycerides was 12.78%, long-chain triglycerides was 8.44%, and free fatty acids were 6.26%. Compared to Example 1, Comparative Example 1, conducted in a solvent-free system, showed a significantly lower content of medium- and long-chain fatty acid triglycerides (72.52%) in the product compared to Example 1 (94.42%). Furthermore, the product still contained a large amount of unreacted medium- and long-chain fatty acid triglycerides (12.78%) and long-chain fatty acid triglycerides (8.44%), and a significant amount of free fatty acids (6.26%) were generated. In conclusion, compared to a solvent-free system, the transesterification reaction for preparing medium- and long-chain fatty acid triglycerides in a eutectic system resulted in higher substrate conversion and product yield, with less byproduct formation.

[0050] Comparative Example 2

[0051] A mixture of 500g linseed oil and medium-chain triglycerides (octanoic acid content 99.24%) was added to a 2.5L reaction flask (molar ratio of linseed oil to medium-chain triglycerides 1:2). The reaction mixture was heated to 80℃, and 40g Lipozyme 435 was added. The reaction time was started. After 6 hours of reaction, the mixture was centrifuged at 12000rpm for 2 minutes. The upper oil phase obtained was the medium- and long-chain triglycerides. Analysis of the upper oil phase product showed that the content of medium- and long-chain triglycerides was 76.78%, medium-chain triglycerides 10.23%, long-chain triglycerides 8.02%, and free fatty acids 4.97%. Compared to Example 2, Comparative Example 2 was carried out in a solvent-free system. The content of medium- and long-chain fatty acid triglycerides in the product (76.78%) was significantly lower than that in Example 1 (95.63%). Furthermore, the product still contained a large amount of unreacted medium- and long-chain fatty acid triglycerides (10.23%) and long-chain fatty acid triglycerides (8.02%), and a large amount of free fatty acids (4.97%) were generated. In summary, compared to the solvent-free system, the transesterification reaction for preparing medium- and long-chain fatty acid triglycerides in a eutectic system resulted in higher substrate conversion and product yield, with less byproduct formation.

[0052] The table below compares the reaction systems and product compositions of Examples 1-9 and Comparative Examples 1 and 2:

[0053]

[0054] The above description is only a part of the embodiments of the present invention. Although some terms are used in the present invention, the possibility of using other terms is not excluded. The use of these terms is merely for the convenience of describing and explaining the essence of the present invention, and interpreting them as any kind of additional limitation would contradict the spirit of the present invention. The above description is only to further illustrate the content of the present invention through embodiments to facilitate easier understanding, but it does not mean that the embodiments of the present invention are limited to this. Any technical extension or re-creation based on the present invention is protected by the present invention.

Claims

1. A method for preparing medium- and long-chain fatty acid triglycerides, characterized in that, Includes the following steps: Step 1: Using vegetable oil and medium-chain triglycerides as substrates and a eutectic solvent as the reaction medium, a transesterification reaction is carried out under the catalysis of an immobilized lipase. The eutectic solvent is choline chloride-urea, betaine-urea-water, betaine-lactic acid, or betaine-glucose-water. The immobilized lipase is Lipozyme 435 or Novozyme 435. The vegetable oil is walnut oil, flaxseed oil, olive oil, tea oil, peony seed oil, rapeseed oil, soybean oil, peanut oil, or corn oil. The medium-chain triglycerides are rich in one or more of caprylic acid, capric acid, and lauric acid. Step 2: After the reaction is completed, centrifugation is performed to recover the eutectic solvent, immobilized lipase and reaction product respectively; the recovered eutectic solvent and immobilized lipase are used for the next batch of reaction, and the recovered upper oil phase is the reaction product.

2. The method for preparing medium- and long-chain fatty acid triglycerides according to claim 1, characterized in that, When the eutectic solvent is choline chloride-urea, the molar ratio of choline chloride to urea is 1:2; when the eutectic solvent is betaine-urea-water, the molar ratio of betaine, urea, and water is 1:2:1; when the eutectic solvent is betaine-lactic acid, the molar ratio of betaine to lactic acid is 1:2; when the eutectic solvent is betaine-glucose-water, the molar ratio of betaine, glucose, and water is 5:2:

10.

3. The method for preparing medium- and long-chain fatty acid triglycerides according to claim 1, characterized in that, In step 1, the amount of eutectic solvent added is 10% to 50% of the total mass of vegetable oil and medium-chain fatty acid triglycerides.

4. The method for preparing medium- and long-chain fatty acid triglycerides according to claim 1, characterized in that, In step 1, the transesterification reaction conditions are as follows: the molar ratio of vegetable oil to medium-chain fatty acid triglycerides is 1:1~2, the reaction temperature is 40~80℃, the amount of immobilized lipase added is 3%~8% of the total substrate mass, and the reaction time is 6~12 h.

5. The method for preparing medium- and long-chain fatty acid triglycerides according to claim 1, characterized in that, In step 2, the centrifugation speed is 10,000~12,000 rpm and the time is 2~3 min.

6. The method for preparing medium- and long-chain fatty acid triglycerides according to claim 1, characterized in that, In step 2, the reaction products contain: medium- and long-chain fatty acid triglycerides ≥94%, medium-chain fatty acid triglycerides ≤2%, long-chain fatty acid triglycerides ≤3%, and free fatty acid content ≤1%.

Images