NL2026589B1

NL2026589B1 - Method for preparing mixed ester rich in OPO-structured fat

Info

Publication number: NL2026589B1
Application number: NL2026589A
Authority: NL
Inventors: Bi Yanlan; Cheng Yapeng; Sun Shangde; Zong Lei; Yang Guolong
Original assignee: Univ Henan Technology
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2022-06-01

Abstract

The present invention provides a method for preparing a mixed ester rich in l,3—dioleoyl—2—palmitoyl triglyceride (OPO)— 5 structured fat, and belongs to the technical field of organic synthesis. The preparation method provided in the present invention adopts peanut oil with high oleic acid content as a raw material, where, the peanut oil is subjected to alcoholysis and medium—pressure hydrolysis to give fatty acid 10 ethyl esters (FAEEs) or fatty acids, and the FAEEs or fatty acids directly react with palm stearin under the catalysis of an enzyme to give a mixed ester rich in OPO—structured fat, which reduces the purification step for oleic acid, shortens the process flow, and improves the safety of the product. The 15 data of examples show that, in the mixed ester rich in OPO— structured fat prepared using FAEEs/fatty acids and palm stearin according to the present invention, the OPO content (based on the C52 triglyceride (TG) content according to the national standard), the percentage of 2—position palmitic 20 acids in total palmitic acids, and the content of the remaining palmitoyl triglycerides are 46.35%/44.l7%, 60.73%/57.60%, and 5.67%/4.07%, respectively, and all indexes for the product meet the requirements in GB 30604—2015.

Description

Method for preparing mixed ester rich in OPO-structured fat

TECHNICAL FIELD The present invention relates to the technical field of organic synthesis, and in particular to a method for preparing a mixed ester rich in 1,3-dioleoyl-2-palmitoyl triglyceride (OPO) -structured fat.

BACKGROUND Breast milk is the optimal food source for infants, which provides comprehensive and balanced nutrition for infants and promotes the growth and development of infants. Breast milk includes about 4% of fat, with triglyceride (TG) accounting for more than 98%, which is one of the main nutrients in breast milk and provides a certain amount of energy for infants. As there are cases where it is lack of conditions for breastfeeding in some areas, infants who cannot get breastfeeding mainly take infant formula as a substitute. However, fatty acids in traditional infant formulas have structures quite different {from that of fat in breast milk, which is not conducive to the healthy growth of infants. Therefore, it is extremely important to choose a suitable infant formula. 1,3-dioleoyl-2-palmitoyl triglyceride {(OPO- structured fat) is a new substitute for fat in breast milk, and the addition of OPO-structured fat to an infant formula can allow the infant formula to exhibit an effect closest to breast milk. The OPO-structured fat is synthesized by rearranging the positions of fatty acids on a glycerol molecule via enzymatic interesterification (EIE), which has a fatty acid composition and structure closer to that of fat in breast milk. Compared with traditional infant formulas, palmitic acids in an OPO infant formula are mainly concentrated on the Sn-2 position (the content of 2-position palmitic acid is higher than 40%), which can promote the absorption of fatty acids by the human body, ensure the proper energy supply, effectively reduce the possibility to produce calcium soap, alleviate the constipation of infants, improve the absorption and utilization of energy and minerals by infants, mitigate the

— 2 _ lack of calcium ions, magnesium ions and other nutrients in infants, and promote the natural growth of the physique and skeletons of infants. Therefore, the addition of OPO- structured fat to an infant formula can make the infant formula exhibit an effect close to breast milk. At present, someone uses camellia oil and olive oil to provide oleic acid to synthesize OPO-structured fat, which has disadvantages, such as high cost and few sources for oil raw materials. Commercial oleic acid is made of a mixed oil, the source cannot be traced, and the fatty acids prepared by hydrolyzing the oil under medium pressure need to be subjected to high-temperature distillation to give purified oleic acid, which increases the production procedures.

SUMMARY In view of this, the present invention is intended to provide a method for preparing a mixed ester rich in OPO-structured fat. The preparation method provided in the present invention adopts peanut oil with high oleic acid content as a raw material, which reduces the purification step for oleic acid, shortens the process flow, and improves the safety of the product to meet the national standard. The present invention provides a method for preparing a mixed ester rich in OPO-structured fat, including the following steps: 1) subjecting peanut oil with high oleic acid content to alcoholysis or medium-pressure hydrolysis to give reaction products, where, the peanut oil with high oleic acid content has an oleic acid content 2 70%, the reaction products of the alcoholysis are fatty acid ethyl esters (FAEEs), and the reaction products of the medium-pressure hydrolysis are fatty acids; and 2) mixing the reaction products obtained in step 1), palm stearin and Sn-1,3-specific lipase, and then subjecting the resulting mixture to interesterification to give a mixed ester rich in OPO-structured fat. Preferably, the alcoholysis in step 1) is conducted at 60°C to 80°C for 1 h to 3 h. Preferably, the medium-pressure hydrolysis in step 1) is

— 3 — conducted at 240°C to 260°C for 8 h to 10 h. Preferably, the medium-pressure hydrolysis in step 1) is conducted under a pressure of 24 kg/cm? to 28 kg/cm. Preferably, the interesterification in step 2) is conducted at 50°C to 90°C for 1 h to 6 h. Preferably, in step 2), the reaction products and palm stearin are mixed at a mole ratio of 2:1 to 6:1. Preferably, the Sn-1,3-specific lipase in step 2) is Novozyme immobilized lipase 40086, Novozyme immobilized lipase TL IM, immobilized Candida sp. 99-125 lipase, or immobilized porcine pancreatic lipase. Preferably, in step 2), the mass of the Sn-1,3-specific lipase is 2% to 10% of the total mass of the reaction products and palm stearin. Beneficial technical effects: The present invention provides a method for preparing a mixed ester rich in OPO-structured fat. The preparation method provided in the present invention adopts peanut oil with high oleic acid content as a raw material, where, the peanut oil is subjected to alcoholysis or medium pressure hydrolysis to give reaction products, and the reaction products directly react with palm stearin under the catalysis of Sn-1,3-specific lipase to give a mixed ester rich in OPO-structured fat, which omits the purification step for oleic acid, shortens the process flow, and improves the safety of the product. The data of examples show that, in the mixed ester rich in OPO-structured fat prepared using FAEEs/fatty acids and palm stearin according to the present invention, the OPO content (based on the C52 TG content according to the national standard), the percentage of 2-position palmitic acids in total palmitic acids, and the content of the remaining palmitoyl triglycerides are 46.35%/44.17%,

60.73%/57.60%, and 5.67%/4.07%, respectively, and all indexes for the product meet the requirements in GB 30604-2015.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a flowchart illustrating the method for preparing 1,3-dioleoyl-2-palmitoyl triglyceride according to the present invention; FIG. 2 is a gas chromatogram for the fatty acid composition

- 4 — of FAEEs obtained in Example 1; FIG. 3 shows the influence of the mole ratio of FAEEs to palm stearin on the synthesis effect in Example 1;4 FIG. 4 shows the influence of the interesterification time on the synthesis effect in Example 2; FIG. 5 shows the influence of the content of enzyme on the synthesis effect in Example 3; FIG. 6 shows the influence of the interesterification temperature on the synthesis effect in Example 4; FIG. 7 is a thin-layer chromatogram for the target product obtained in Example 5; FIG. 8 is a gas chromatogram for the target product obtained in Example 5; FIG. 9 is a gas chromatogram for the TG composition of the target product obtained in Example 5; FIG. 10 is a gas chromatogram for the fatty acid composition of all TGs in the target product obtained in Example 2; FIG. 11 is a gas chromatogram for the Sn-2 fatty acid composition of TGs in the target product obtained in Example 5; FIG. 12 is a curve illustrating the SFC in the target product obtained in Example 5 that varies with temperature; FIG. 13 is a gas chromatogram for the TG composition of the target product obtained in Example 6; FIG. 14 is a gas chromatogram for the fatty acid composition of all TGs in the target product obtained in Example 6; and FIG. 15 is a gas chromatogram for the Sn-2 fatty acid composition of TGs in the target product obtained in Example 6.

DETAILED DESCRIPTION The present invention provides a method for preparing a mixed ester rich in OPO-structured fat, and the method includes the following steps: 1) peanut oil with high oleic acid content is subjected to alcoholysis or medium-pressure hydrolysis to give reaction products, where, the peanut oil with high oleic

— 5 — acid content has an oleic acid content 2 70%, the reaction products of the alcoholysis are FAEEs, and the reaction products of the medium-pressure hydrolysis are fatty acids; and 2) the reaction products obtained in step 1), palm stearin and Sn-1,3-specific lipase are mixed, and then the resulting mixture is subjected to interesterification to give a mixed ester rich in OPO-structured fat. The present invention subjects peanut oil with high oleic acid content to alcoholysis or medium-pressure hydrolysis to give reaction products; the peanut oil with high oleic acid content has an oleic acid content 2 703; the reaction products of the alcoholysis are FAEEs; and the reaction products of the medium pressure hydrolysis are fatty acids.

In the present invention, the alcoholysis is conducted preferably at 60°C to 80°C, and more preferably at 65°C to 75°C; and the alcoholysis is conducted preferably for 1 h to 3 h, and more preferably for 1.5 h to 2.5 h.

In the present invention, the alcoholysis is conducted preferably under stirring. The present invention has no special limitation on the method for stirring, and a stirring method well known to those skilled in the art may be adopted. In the present invention, the alcoholysis is conducted preferably by mixing peanut oil with high oleic acid content, ethanol and sodium hydroxide and then subjecting the resulting mixture to alcoholysis to give FAEEs.

In the present invention, the peanut oil with high oleic acid content, ethanol and sodium hydroxide are mixed at a mass ratio preferably of 200:{60-100):1, and more preferably of 200: (75-85):1.

The present invention preferably further includes subjecting the reaction solution resulting from alcoholysis to vacuum distillaticn, separating, water-washing and dewatering in sequence to give FAEEs.

In the present invention, the vacuum distillation is conducted preferably at 40°C to 60°C, and more preferably at 45°C to 55°C; the vacuum distillation is conducted preferably for 0 min to 60 min, and more preferably for 40 min to 50 min; and the vacuum distillation is conducted under a pressure

— 6 — preferably of 0.03 kg/cm® to 0.05 kg/cm®, and more preferably of 0.035 kg/cm? to 0.045 kg/cm’. In the present invention, excessive ethanol is removed by vacuum distillation.

In the present invention, the separating is conducted preferably by placing the solution obtained from the distillation into a separatory funnel to stand for separating and reserving the upper layer of liquid. In the present invention, the standing {for separating is conducted to separate the lower layer with sodium hydroxide, glycerol and soap.

In the present invention, the water-washing preferably refers to washing the upper layer of liquid with water.

In the present invention, the water-washing preferably refers to washing with distilled water at 50°C. The present invention has no special limitation on the water-washing times, provided that the liquid is washed to neutral.

In the present invention, the dewatering preferably refers to dewatering the upper layer of liquid washed with water by rotary evaporation.

In the present invention, the rotary evaporation is conducted preferably at 70°C to 90°C, and more preferably at 75°C to 85°C; the rotary evaporation is conducted preferably for 80 min to 100 min, and more preferably for 85 min to 95 min; and the rotary evaporation is conducted under a pressure preferably of

0.03 kg/cm? to 0.05 kg/cm?, and more preferably of 0.035 kg/cm? to 0.045 kg/cm.

In the present invention, the medium-pressure hydrolysis is conducted preferably at 240°C to 260°C, and more preferably at 240°C to 255°C; the medium-pressure hydrolysis is conducted preferably for 8 h to 10 h, and more preferably for 8 h to 9 h; and the medium-pressure hydrolysis is conducted under a pressure preferably of 24 kg/cm? to 28 kg/cm? and more preferably of 24 kg/cm? to 27 kg/cm.

In the present invention, the medium-pressure hydrolysis is conducted preferably by mixing peanut oil with high oleic acid content with water and then subjecting the resulting mixture to medium-pressure hydrolysis to give fatty acids.

In the present invention, the peanut oil with high oleic acid content and water are mixed at a volume ratio preferably of

— 7 — 1:1.

In the present invention, the medium-pressure hydrolysis is conducted preferably at 240°C to 255°C; the medium-pressure hydrolysis is conducted under a pressure preferably of 24 kg/cm? to 27 kg/cm’; and the medium-pressure hydrolysis is conducted preferably for 8 h to 9 h.

The peanut oil with high oleic acid content used in the present invention has an oleic acid content preferably 2 70%, and more preferably of 75% to 80%.

In the present invention, according to specifications in GB 30604-2015, OPO is prepared from oleic acids derived from edible vegetable oil under the catalysis of an enzyme. The reaction products obtained from the hydrolysis of peanut oil with high oleic acid content have an oleic acid content of more than 75%, and therefore, the reaction products can be mixed with palm stearin and Sn-1,3-specific lipase for interesterification to give a mixed ester rich in OPO- structured fat.

In the present invention, the obtained reaction products are preferably mixed with palm stearin and Sn-1,3-specific lipase for interesterification to give a mixed ester rich in OPO- structured fat.

In the present invention, the interesterification is conducted preferably at 50°C to 90°C, more preferably at 55°C to 70°C, and most preferably at 60°C; and the interesterification is conducted preferably for 1 h to 6 h, more preferably for 1 h to 3 h, and most preferably for 1 h.

In the present invention, the reaction products and palm stearin are mixed at a mole ratio preferably of 2:1 to 6:1, more preferably of 3:1 to 5:1, and most preferably of 5:1.

In the present invention, the Sn-1,3-specific lipase is preferably Novozyme immobilized lipase 40086, Novozyme immobilized lipase TL IM, immobilized Candida sp. 99-125 lipase, or imobilized porcine pancreatic lipase.

In the present invention, the mass of the Sn-1,3-specific lipase is preferably 2% to 10%, more preferably 5% to 8%, and most preferably 6% of the total mass of the reaction products and palm stearin.

In the present invention, after the interesterification, the

— 8 — method preferably further includes molecular distillation.

In the present invention, the molecular distillation is conducted preferably at 150°C to 210°C, and more preferably at 160°C to 200°C; and the molecular distillation is conducted preferably for 30 min to 90 min, and more preferably for 50 min to 80 min.

In the present invention, the fatty acids or FAEEs are removed by molecular distillation.

FIG. 1 is a flowchart illustrating the method for preparing a mixed ester with OPO-structured fat according to the present invention.

In order to better understand the present invention, content of the present invention is further illustrated below with reference to examples.

However, the content of the present invention is not limited to the following examples.

Example 1 1) 2.16 g of NaOH was weighed and added to a 1,000 mL three- necked flask, then 160 g of absolute ethanol and 432 g of peanut oil with high oleic acid content were added, and the resulting mixture was magnetically stirred for 1.5 h in an oil bath at 75°C under nitrogen atmosphere.

After the reaction was completed, the reaction solution was cooled to room temperature, then subjected to rotary evaporation to remove excessive ethanol, then poured into a separatory funnel, and stood for separating; the lower layer with sodium hydroxide, glycerol and soap was separated; the upper layer of liquid was washed with distilled water at 50°C to neutral, and dewatered by rotary evaporation to give FAEEs; and the reaction products were put into a 500 mL sample bottle, and the bottle was filled with nitrogen for protection, and then stored in a refrigerator for later use. 2) The FAEEs obtained in step 1) and palm stearin were weighed at mole ratios of 2:1, 3:1, 4:1, 5:1 and 6:1, separately, and the palm stearin was 20 g and 0.0225 mol.

The weighed FAEEs and palm stearin were added to a 250 mL three-necked flask, and magnetically stirred (at 400 r/min) in an oil bath until they were completely miscible; then Novozyme 40086 (lipase) was added at a mass 8% of the total mass of FAEEs and palm

— 9 — stearin; and the resulting mixture reacted at 70°C for 4 h.

Distillation was conducted to give the target product. 50 mg of the FAEEs was dissolved in 1 mL of n-hexane, and the resulting solution was pipetted and spotted on a 20 cm x 20 cm thin-layer chromatographic plate using a spotting needle.

The plate was put into a developing solvent (n-hexane : diethyl ether : glacial acetic acid = 80:20:2, v/v/v) for developing, and then taken out and dried after the developing was completed. 2',7"'-dichlorofluorescein was added for color development, then simple methyl esterification was conducted with a FAEE strip, and the sample was used for gas chromatography.

The relative content of each fatty acid in the FAEEs was analyzed by the area normalization method, and calculated according to formula (1): The peak area corresponding to The relative content ofa — the methyl ester of the fatty acid _4 44 fatty acid/% The peak area corresponding to methyl esters of all fatty acids formula (1) FIG. 2 is a gas chromatogram for the fatty acid composition of FAEEs obtained in Example 1. Table 1 shows the fatty acid composition of FAEEs obtained in Example 1 and the relative content of each component.

Table 1 The fatty acid composition of FAEEs obtained in Example 1 and the relative content of each component Fatty acid CI60 CI80 C181 CI82 C00 C201 C2290 C22:1 C240 Content/% 5.58 1.99 78.08 6.28 1.05 2.37 2.56 0.29 1.80 C16:0 represents palmitic acid; C18:0 represents stearic acid; C18:1 represents oleic acid; C18:2 represents linoleic acid; C20:0 represents arachidic acid; C20:1 represents eicosenoic acid; C22:0 represents behenic acid; C22:1 represents erucic acid; and C24:0 represents lignoceric acid.

It can be seen from FIG. 2, Table 1 and formula (1) that FAEEs obtained from the peanut oil with high oleic acid content have an oleic acid content as high as 78.08%, and thus can be used as an ideal raw material for the synthesis of OPO.

Table 2 shows the physical and chemical indexes for the FAEEs obtained in Example 1.

— 1 0 — Table 2 Physical and chemical indexes for the FAEEs obtained in Example 1 Acid value Peroxide value (PV) Moisture and volatile (AV) (mg/g) (mmol/kg) matter (%o) FAEEs obtained in Example

0.61 + 0.08 0.015 % 0.030 0.13 £0.02 1 It can be seen from Table 2 that the FAEEs obtained in Example 1 have prominent physical and chemical indexes, and thus can be used as an ideal raw material for the synthesis of OPO. FIG. 3 shows the influence of the mole ratio of FAEEs to palm stearin on the synthesis effect in Example 1. It can be seen from FIG. 3 that, during the process where the mole ratio for substrates is increasing from 2:1 to 6:1, the OPO content and the percentage of 2-position palmitic acids in total palmitic acids are first increased and then stabilized, and the content of palmitoyl triglycerides is first decreased and then stabilized; during the process where the mole ratio for substrates is increasing from 2:1 to 5:1, the OPO content increases significantly, because the increase of the ethyl oleate concentration promotes the reaction to proceed in the direction of positive reaction; and during the process where the mole ratio for substrates is further increasing to 6:1, the OPO content does not change significantly and is stabilized at about 41.14%, the percentage of 2-position palmitic acids in total palmitic acids is stabilized at 48%, and the content of palmitoyl triglycerides is stabilized at about 4.7%. Too much ethyl oleate is not conducive to the separation of the product, and increases the production cost, so the optimal mole ratio for substrates is 5:1. Example 2 The mole ratio of FAEEs to palm stearin was 5:1, and the interesterification was conducted for 30 min, 1 h, 2 h, 4 h, and 6 h, separately. The other reaction conditions were the same as in Example 1. The target product was obtained. FIG. 4 shows the influence of the interesterification time on the synthesis effect in Example 2. It can be seen from FIG. 4 that during the process where the reaction time is increasing from 30 min to 6 h, the OPO

- 11 - content and the percentage of 2-position palmitic acids in total palmitic acids first increase and then decrease, and the content of palmitoyl triglycerides is first decreased and then stabilized. During the process where the reaction time is increasing from 30 min to 1 h, the reaction proceeds in the direction of positive reaction; the reaction is more complete; the content of the target product increases significantly; and the reaction reaches equilibrium at 1 h, and at this point, the OPO content and the percentage of 2-position palmitic acids in total palmitic acids both have the maximum value,

44.07% and 56.29%, respectively, and the content of palmitoyl triglycerides is 6.07%. During the process where the reaction time is increasing from 1 h to 4 h, as the reaction time increases, OPO undergoes acyl transfer during the reaction; the content of by-products increases; the percentage of 2- position palmitic acids in total palmitic acids significantly deceases; and the content of palmitoyl triglycerides does not change significantly. During the process where the reaction time is increasing from 4 h to 6 h, the OPO content and the percentage of 2-position palmitic acids in total palmitic acids both significantly decrease, because the by-products generated from acyl transfer react with palm stearin under the catalysis of Sn-1,3-specific lipase. The present invention requires short reaction time, which leads to high economic benefit, and can better save power and energy while ensuring the product yield. Considering the product yield and power- saving, the optimal reaction time is 1 h. Example 3 The FAEEs obtained in step 1) of Example 1 were mixed with palm stearin at a mole ratio of 5:1, then Novozyme 40086 (lipase) was added at a mass 2%, 4%, 6%, 8% and 10% of the total mass of FAEEs and palm stearin separately, and interesterification was conducted at 70°C for 1 h. The other reaction conditions were the same as in Example 1. The target product was obtained. FIG. 5 shows the influence of the content of enzyme on the synthesis effect in Example 3. It can be seen from FIG. 5 that, during the process where the amount of enzyme is

- 12 — increasing from 2% to 103, the OPO content and the percentage of 2-position palmitic acids in total palmitic acids are first increased and then stabilized, and the content of palmitoyl triglycerides is first decreased and then stabilized; during the process where the amount of enzyme is increasing from 2% to 6%, the contact area between the enzyme and the substrates increases, the positive reaction is accelerated, the reaction is more complete, and the content of the target product increases significantly; and during the process where the amount of enzyme is further increasing to 10%, the OPO content does not change significantly and is stabilized at about

44.11%, the percentage of 2-position palmitic acids in total palmitic acids is stabilized at about 56.37%, and the content of palmitoyl triglycerides is stabilized at about 5.96%. This is because when the amount of enzyme increases to a certain degree, the reaction enters a steady state, and at this point, excessive lipase will increase the rate of reverse reaction. The appropriate amount of lipase can reduce the generation of by-products and lower the production cost under the premise of ensuring the reaction rate. Considering comprehensively, the optimal amount of enzyme for the reaction is 6%. Example 4 The FAEEs obtained in step 1) of Example 1 were mixed with palm stearin at a mole ratio of 5:1, then Novozyme 40086 (lipase) was added at a mass 6% of the total mass of FAEEs and palm stearin, and reaction was conducted at 50°C, 60°C, 70°C, 80°C and 90°C for 1 h, separately. The other reaction conditions were the same as in Example 1. The target product was obtained. FIG. 6 shows the influence of the interesterification temperature on the synthesis effect in Example 4. It can be seen from FIG. 6 that during the process where the temperature is increasing from 50°C to 90°C, the OPO content first increases and then decreases, the percentage of 2-position palmitic acids in total palmitic acids is first stabilized and then decreased, and the content of palmitoyl triglycerides first decreases and then increases. As the temperature increases {from 50°C to 60°C, palm stearin is completely

— 13 — dissolved and has increased miscibility with ethyl oleate; the enzyme 1s fully mixed with the reaction substrates; the rate of positive reaction increases; the OPO content significantly increases to (46.32%0.03)%; and the content of palmitoyl triglycerides significantly decreases.

As the temperature increases from 60°C to 80°C, the OPO content is about 43.64%; the percentage of 2-position palmitic acids in total palmitic acids is about 56.58%; and the content of palmitoyl triglycerides is about 6.25%. As the temperature further increases, the stability of some enzymes is destroyed, and the acyl transfer in the lipase-catalyzed reaction is enhanced, so the OPO content and the percentage of 2-position palmitic acids in total palmitic acids significantly decrease, and the content of palmitoyl triglycerides significantly increases.

According to the operating requirements of Novozyme 40086, 60°C is selected as the optimal reaction temperature.

Example 5 The FAEEs obtained in step 1) of Example 1 were mixed with palm stearin at a mole ratio of 5:1 (where the palm stearin was 20 g and 0.0225 mol), then Novozyme 40086 (lipase) was added at a mass 8% of the total mass of FAEEs and palm stearin, and reaction was conducted at 70°C for 2 h.

The other reaction conditions were the same as in Example 1. The target product was obtained.

Thin-layer chromatography was conducted for the target product obtained in Example 5. The results are shown in FIG. 7. The right side shows the standard sample for the mixture of glyceride and ethyl oleate, and the left side shows the target product obtained in Example 5. FIG. 8 is a gas chromatogram for the target product obtained in Example 5. Table 3 shows the composition of the target product obtained in Example 5 and the relative content of each component.

Table 3 The composition of the target product obtained in Example 5 and the relative content of each component Component FAEEs Diglyceride (DG) TG It can be seen from FIG. 7, FIG. 8 and Table 3 that the target

— 14 — product obtained in Example 5 has an extremely-low content of FAEEs, and the main components are DG and TG. FIG. 9 is a gas chromatogram for the TG composition of the target product obtained in Example 5.

Table 4 shows the TG composition of the target product obtained in Example 5 and the relative content of each component.

Table 4 The TG composition of the target product obtained in Example 5 and the relative content of each component TG C48 C50 C52 C54 Retention time/min 12.206 13.123 14.271 15.681 Content 6.43 29.77 44.95 18.85 It can be seen from FIG. 9 and Table 4 that, by comparing the relative content of C52 obtained from the TG composition analysis by gas chromatograph with the national standard (C52 2 40%) and the results of the research by some scholars (C52: around 40%), the target product obtained in Example 5 has a relatively-high content of OPO-structured fat, and a relatively-low content of the remaining palmitoyl triglycerides, which meets the requirements in the national standard.

FIG. 10 is a gas chromatogram for the fatty acid composition of all TGs in the target product obtained in Example 5.

Table 5 shows the fatty acid composition of all TGs in the target product obtained in Example 5 and the relative content of each component.

Table 5 The fatty acid composition of all TGs in the target product obtained in Example 5 and the content of each component Fatty acid C160 C180 CI8:1 C18:2 C200 C20:1 C22:0 C24:0 Retention time/min 8.795 11.679 12.402 13.617 15.361 16.231 19.609 24.745 Content/% 35.45 3.20 49.89 4.38 0.77 1.43 1.85 1.26 FIG. 11 is a gas chromatogram for the Sn-2 fatty acid composition of TGs in the target product obtained in Example

5.

Table 6 shows the Sn-2 fatty acid composition of TGs in the target product obtained in Example 5 and the content of each component.

Table 6 The Sn-2 fatty acid composition of TGs in the target product obtained in Example 5 and the content of each component

— 1 5 — Fatty acid C160 C18:0 C18:1 CI8:2 C20:1 Retention time/min 8.787 11.67 12.387 13.604 16.777 Content 59.29 6.98 26.62 4.09 3.02 It can be seen from FIG. 10, Table 5, FIG. 11 and Table 6 that, in the target product obtained at the reaction temperature of 60°C in Example 5, the content of Sn-2 position palmitic acids reaches 58.3%, the total content of oleic acids is 52.2%, and the insertion ratio of oleic acids is relatively high. FIG. 12 is a curve illustrating the SFC in the target product obtained in Example 5 that varies with temperature. It can be seen from FIG. 12 that the SFC of the target product drops sharply at 10°C to 30°C, and the SFC of OPO drops from

30.968% to 2.874%, indicating that the melting point of the TGs constituting OPO is at 10°C to 30°C, which is consistent with the melting point of the 1-saturated-2-unsaturated TG (1°C to 23°C). As the target product still includes a small amount of palm stearin with a higher melting point, there is a small amount of solid fat at 30°C to 45°C, with a content of about 0.203%.

In summary, the physical and chemical indexes for the target product obtained in Example 5 are shown in Table 7. Table 7 Physical and chemical indexes for the target product obtained in Example 5 Index GB 30604 2015 Target product OPO content. w/% > 40 46.53 + 0.03 Percentage of 2-position palmitic acids in total palmitic acids/{%) > 352 60.7+023 Content of palmitoyl triglycerides, w/% < 10 5.67 +£0.30 AV/(mg/g) <30 0.46 + 0.01 PV/(mmolkg) <20 0.12+ 0.01 It can be seen from Table 7 that the target product obtained in Example 5 is a mixed ester rich in OPO-structured fat, which conforms to the national standard.

The above descriptions are merely preferred implementations of the present invention. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present invention, but such improvements and modifications should be deemed as falling within the protection scope of the present invention.

— 16 — Example 6 The free fatty acids obtained from peanut oil with high oleic acid content by medium-pressure hydrolysis and palm stearin were weighed at a mole ratio of 6:1, where the palm stearin was 20 g and 0.0225 mol. The weighed free fatty acids and palm stearin were added to a 250 mL three-necked flask, and magnetically stirred {at 400 r/min) in an oil bath until they were completely miscible; then Novozyme 40086 (lipase) was added at a mass 10% of the total mass of free fatty acids and palm stearin; and the resulting mixture reacted at 70°C for 4 h. Distillation was conducted to give the target product. FIG. 13 is a gas chromatogram for the TG composition of the target product obtained in Example 6. Table 8 shows the TG composition of the target product obtained in Example 6 and the relative content of each component. Table 8 The TG composition of the target product obtained in Example 6 and the relative content of each component TG C48 C50 C32 C54 Retention time/min 12.173 13.080 14.223 15.600 Content/% 4.07 27.33 44.17 24.43 It can be seen from FIG. 13 and Table 8 that the target product obtained in Example 6 includes more than 40% of OPO- structured fat, and has a relatively-low content of the remaining palmitoyl triglycerides, which meets the requirements in the national standard. FIG. 14 is a gas chromatogram for the fatty acid composition of all TGs in the target product obtained in Example 6. Table 9 shows the fatty acid composition of all TGs in the target product obtained in Example 6 and the relative content of each component. Table 9 The fatty acid composition of all TGs in the target product obtained in Example 6 and the content of each component Fatty acid C16:9 C18:0 C18:1 C18:2 C20:0 C20:1 C22:0 C22:1 C24:9 Retention time/min 8824 11.697 12.478 13.632 15.385 16251 19.643 20.615 24.806 Content/% 32.33 3.07 50.18 4.65 0.35 0.79 1.48 1.85 1.36 FIG. 15 is a gas chromatogram for the Sn-2 fatty acid composition of TGs in the target product obtained in Example

6.

— 1 7 — Table 10 shows the Sn-2 fatty acid composition of TGs in the target product obtained in Example 6 and the relative content of each component. Table 10 shows the Sn-2 fatty acid composition of TGs in the target product obtained in Example 6 and the relative content of each component Fatty acid C16:0 C18:0 CI8:1 C18:2 C20:1 Retention time/min 8.789 11.683 12.402 13.617 16.783 Content/% 55.89 6.47 29.57 6.22 1.85 It can be seen from FIG. 14, FIG. 15, Table 9 and Table 10 that, in the target product obtained in Example 6, the content of Sn-2 position palmitic acids reaches 55.89%, and the total content of oleic acids is 50.18%. In summary, the physical and chemical indexes for the target product obtained in Example 6 are shown in Table 11. Table 11 Physical and chemical indexes for the target product obtained in Example 6 Index GB 30604 2015 Target product OPO content. w/% > 40 44.17 +£0.04 Percentage of 2-position palmitic acids in total palmitic acids/(%a) > 52 576+ 033 Content of palmitoyl triglycerides, w/% <10 4.07 + 0.20 AV/(mg/g) <30 1.86 + 0.01 PVXmmol/kg) <20 0.22 0.01 It can be seen from Table 11 that the target product obtained in Example 6 is a mixed ester rich in OPO-structured fat, which conforms to the national standard. The above description is merely an implementation of the present invention. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present invention, but such improvements and modifications should be deemed as falling within the protection scope of the present invention.

Aspects of the invention are itemized in the following section.

1. A method for preparing a mixed ester rich in 1,3- dioleoyl-2-palmitoyl triglyceride (OPO) -structured fat, comprising the following steps: 1) subjecting peanut oil with high oleic acid content to alcoholysis or medium-pressure hydrolysis to give reaction

- 18 — products, wherein, the peanut oil with high oleic acid content has an oleic acid content 2 70%, the reaction products of the alcoholysis are fatty acid ethyl esters (FAEEs), and the reaction products of the medium-pressure hydrolysis are fatty acids; and 2) mixing the reaction products obtained in step 1), palm stearin and Sn-1,3-specific lipase, and then subjecting the resulting mixture to interesterification to give a mixed ester rich in OPO-structured fat.

2. The preparation method according to claim 1, wherein the alcoholysis in step 1) is conducted at 60°C to 80°C for 1 h to 3 h.

3. The preparation method according to claim 1, wherein, the medium-pressure hydrolysis in step 1) is conducted at 240°C to 260°C for 8 h to 10 h; and the water is added at an amount 1 to 1.2 times that of the oil.

4. The preparation method according to claim 1 or 3, wherein the medium-pressure hydrolysis in step 1) is conducted under a pressure of 24 kg/cm? to 28 kg/cm?.

5. The preparation method according to claim 1, wherein the interesterification in step 2) is conducted at 50°C to 90°C for 1 h to 6 h.

6. The preparation method according to claim 1, wherein, in step 2), the reaction products and palm stearin are mixed at a mole ratio of 2:1 to 6:1.

7. The preparation method according to claim 1, wherein the Sn-1,3-specific lipase in step 2) is Novozyme immobilized lipase 40086, Novozyme immobilized lipase TL IM, immobilized Candida sp. 99-125 lipase, or immobilized porcine pancreatic lipase.

8. The preparation method according to claim 1 or 7, wherein, in step 2), the mass of the Sn-1,3-specific lipase is 2% to 10% of the total mass of the reaction products and palm stearin.

Claims

- 19 — CONCLUSIONS

A method for preparing a mixed ester rich in 1,3-dioleoyl-2-palmitoyl triglyceride (OPO) - structured fat, comprising the steps of: 1) subjecting high oleic peanut oil to alcoholysis or hydrolysis under medium pressure to give reaction products, wherein the high oleic peanut oil has an oleic acid content of 2 70%, the reaction products of the alcoholysis are fatty acid ethyl esters (FAEEs), and the reaction products of the medium pressure hydrolysis are fatty acids; and 2) mixing the reaction products obtained in step 1), palm stearin and Sn-1,3-specific lipase, and then subjecting the resulting mixture to interesterification to give a mixed ester rich in OPO structured fat.

The preparation method according to claim 1, wherein the alcoholysis in step 1) is carried out at 60°C to 80°C for 1 hour to 3 hours.

The production method according to claim 1, wherein the intermediate pressure hydrolysis in step 1) is carried out at 240°C to 260°C for 8 hours to 10 hours; and the water is added in an amount of 1 to 1.2 times that of the oil.

The production method according to claim 1 or 3, wherein the intermediate pressure hydrolysis in step 1) is carried out under a pressure of 24 kg/cm 2 to 28 kg/cm 2 .

The production method according to claim 1, wherein the interesterification in step 2) is carried out at 50°C to 90°C for 1 hour to 6 hours.

The preparation method according to claim 1, wherein in step 2) the reaction products and palm stearin are mixed in a molar ratio of 2:1 to 6:1.

The preparation method of claim 1, wherein the Sn-1,3-specific lipase in step 2) is Novozyme Immobilized Lipase 40086, Novozyme Immobilized Lipase TL IM, Immobilized Candida sp. 99-125 lipase, or immobilized porcine pancreatic lipase.

- 20 -

The preparation method according to claim 1 or 7, wherein in step 2) the mass of the Sn-1,3-specific lipase is 2% to 10% of the total mass of the reaction products and palm stearin.