Acyl Migration Rate Research Articles

Preparation of vacuum-assisted conjugated linoleic acid phospholipids under nitrogen: Mechanism of acyl migration of lysophospholipids

Sn-Glycerol-3-phosphatidylcholine (GPC) was prepared by hydrolysis of phosphatidylcholine (PC) catalyzed by phospholipase A1 (PLA1). Nitrogen flow assisted the esterification of conjugated linoleic acid (CLA) and GPC to produce conjugated linoleic acid lysophosphatidylcholine (LPC − CLA). The effects of different reaction conditions on the PC conversion and acyl migration rates were investigated, and the acyl migration mechanism under acidic and alkaline conditions was studied. In addition, the optimum conditions for the esterification of CLA and GPC were selected. The optimal condition for the hydrolysis of PC was an enzyme loading of 5 %, pH of 5, reaction temperature of 50 ℃, and reaction time of 3 h. The results also showed that the maximum esterification rate reached 82.37 % at an enzyme loading of 15 %, CLA/GPC molar ratio of 50:1, and vacuum pressure of 13.3 kPa. This study not only improved the bioavailability of PC but also effectively increased the content of LPC − CLA.

Purification of mono-saturated acid sn-1,3 diacylglycerols: Effects of acyl migration on the crystallization behaviors and physical properties

Sn-1,3 diacylglycerol (Sn-1,3 DAG) is widely applied as a functional lipid. Recently there has been escalating interest in understanding the acyl migration of sn-1,3 DAG that could bring about various physicochemical properties of the functional oils. In this study, 97.8% of sn-1,3 lauryl diacylglycerol (Sn-1,3 LDAG) and 98.3% of sn-1,3 palmityl diacylglycerol (Sn-1,3 PDAG) were synthesized by esterification and purified via crystallization using mixed solvent n-hexane: ethyl acetate = 92:8 (V/V) and n-hexane: ethyl acetate = 98:2 (V/V), respectively. Increasing temperature and system dispersion, enhanced the acyl migration rate (Km) of sn-1,3 DAGs and reduced its half-life (T1/2). As the acyl migration degrees (AMDs) of DAG increased, DAGs crystallization and melting were completed at a shorter temperature range and time while the crystal aggregation mode of DAGs shifted from disordered needle crystals to more organized Maltese cross-shape. Acyl-migrated LDAG forms β+β′ crystals, while acyl-migrated PDAG forms β+α crystals in 25 °C. The dynamics of acyl migration and crystallization of sn-1,3 DAGs can be applied to prepare high content sn-1,3 DAG products. The crystal morphology and polymorphism properties of sn-1,3 LDAG and sn-1,3 PDAG with different AMDs are beneficial to obtain functional sn-1,3 DAG customized products with desirable characteristics.

Acyl migration of 2-monoacylglycerols rich in DHA: Effect of temperature and solvent medium

Acyl migration of 2-monoacylglycerols (2-MAGs) rich in DHA is a universal reaction occurring during storage and structural lipid synthesis, and affects their nutritional value. In this study, their acyl migration was investigated under different systems and temperatures. The enhanced temperature promoted acyl migration, leading to a 5.6-fold increase from 20 °C to 50 °C. The kinetic study indicated rate constants followed the order: hexane > solvent-free > dichloromethane > ethanol ≈ acetone ≈ acetonitrile > t-butanol, and positively correlated with log P of solvent. During acyl migration in ethanol, acetone, acetonitrile and t-butanol at 40 °C, DHA content in 2-MAGs was higher than in 1-MAGs, indicating slow acyl migration of DHA; while at 50 °C, the difference of DHA distribution was small, due to increasing acyl migration rate. The results suggest that acyl migration of different fatty acids can be regulated by changing conditions to enrich DHA at sn-2 position.

Study on the stability of intermediates in the process of enzymatic hydrolysis of phosphatidic acid by phospholipase A1

In the degumming process of crude soybean oil by phospholipase A1 (PLA1), the content of free fatty acids (FFA) in the product increases excessively. In this study, PLA1 was used to hydrolyse simulated crude soybean oil. It was found that the acyl group at the sn-2 position migrated to the sn-1 position, the content of FFA in the oil was as high as 1.26 ± 0.03 g/100 g, and the acyl migration rate was up to 38.9 ± 0.10% after 2.8 h. Under the conditions of H3BO3 addition of 2 g/100 g, pH of 5, enzymatic hydrolysis temperature of 50 °C and enzymatic hydrolysis time of 2 h, the acyl migration rate of sn-2-HPA was 16.8 ± 0.50%, the content of FFA was 1.14 ± 0.02 g/100 g, and the enzymatic hydrolysis efficiency was increased by 28.57 ± 0.07%.

Effect of Solvent on Acyl Migration of 2-Monoacylglycerols in Enzymatic Ethanolysis.

Acyl migration occurs in many reactions and is the main obstacle for structured lipid synthesis. In this study, 2-monoacylglycerol (2-MAG) was prepared by enzymatic ethanolysis in three different media to evaluate the effect of environment on product composition. The contents of 2-MAG obtained in ethanol, hexane + ethanol, and t-butanol + ethanol systems were 30.6, 15.7, and 32.4%, respectively, after 3 h reaction. Afterward, the acyl migration kinetics of 2-MAG were studied in solvent and solventless systems without the use of lipase. Results indicate that 2-MAG in the solventless system had the highest acyl migration rate. The isomerization was efficiently prevented by the use of polar solvents, especially t-butanol. The rate constants were shown to be the highest and activation energy values were the lowest in solventless systems. The novel finding in this study was that solvent had inhibitory effect on 2-MAG isomerization, but the nonpolar hexane had the lowest inhibition of acyl migration compared to other solvents.

Kinetics and Mechanism of Solvent Influence on the Lipase-Catalyzed 1,3-Diolein Synthesis.

1,3-Diacylglycerol preparation has roused increasing attention in recent years as the 1,3-diacylglycerol-rich oils can suppress the deposition of visceral fat and prevent the body weight increasing. Lipozyme TL IM-mediated esterification of oleic acid with monoolein was effective for 1,3-diacylglycerol production. During the esterification process, the solvent shows obvious influence on the diolein synthesis as well as the 1,3-diolein production. This work investigated the related kinetics and mechanism of the solvent effect on the esterification and Lipozyme TL IM performance. The results indicated that both the esterification rate constant and the acyl migration rate constant positively correlated with the logP of the solvent, while the site specificity of lipase has negative correlation with solvent logP. The acylation toward the 2-position of 1-monoolein was more sensitive to the solvent logP compared to the 1-position of glycerides. Molecular dynamics simulation revealed that solvents with different logP influenced the structure of Lipozyme TL IM including RMSD, hydrogen bond, and radial distribution function to a large extent, which subsequently led to the catalytic activity and selectivity variation of the lipase.

Enzymatic synthesis of 1,3-oleic-2-medium chain triacylglycerols and strategy of controlling acyl migration: insights from experiment and molecular dynamics simulation

ABSTRACT Medium- and long-chain triacylglycerols (MLCTs) with high 1,3-oleic-2-medium chain (OMO) triacylglycerols content were synthesized by the acidolysis reaction between Cinnamomum camphora seed oil (CCSO) and oleic acid, catalyzed by lipozyme RM IM. In addition, the simultaneous rate of acyl migration (RAM) was investigated during the esterification process. The maximal yield of OMO-structured triacylglycerols (YST) was up to 64.45% under the optimum condition: the molar ratio of CCSO to oleic acid, 1:4; enzyme dosage, 10 wt%; temperature, 60°C; and reaction time, 24 h. RAM was 28.66% at same time. It is shown that YST positively related to RAM at single experiments of the molar ratio (r2 = 0.999, P< .01), enzyme dosage (r2 = 0.988, P< .01), below 60°C of temperature (r2 = 0.923, P< .05) and within 24 h of reaction time (r2 = 0.940, P< .05). However, YST was negatively correlated with RAM at a temperature higher than 60°C (r2 = −0.682, P> .05) or a reaction time longer than 24 h (r2 = −0.594, P> .05). The effect of temperature on the reaction could be verified by molecular dynamics simulation, opened enzyme lids were increased with temperature elevated, and helped substrates invade into catalytic triad. When temperature rose to higher than 333 K (60°C), rearrangement of the catalytic triad was promoted, which resulted in both decreasing enzyme catalytic activity and irritating acyl migration. This study could help understand the trigger cause of acyl migration at high temperature, and conclusively reaction temperature was a vital factor to balance YST and RAM in a solvent-free system. OMO-structured triacylglycerols might possess a potential application as a new type of nutritional lipids for daily diet.

Trace water activity could improve the formation of 1,3-oleic-2-medium chain-rich triacylglycerols by promoting acyl migration in the lipase RM IM catalyzed interesterification

New structured lipids with 1,3-oleic-2-medium chain (OMO) triacylglycerols were synthesized by promoting acyl migration in Lipozyme RM IM catalyzed interesterification between coconut oil (CO) and high oleic rapeseed oil (HORO). Results from an orthogonal design L25(55) showed that the maximal yield of OMO-structured triacylglycerols was 45.65% under the following conditions: the molar ratio of CO to HORO, 50:50; enzyme dosage, 12 wt%; reaction temperature, 60 °C; reaction time, 2 h; water activity, 0.07. Low water activity showed a high rate of acyl migration (10.86% vs 5.07% no water system), which promoted OMO synthesis due to medium-chain fatty acid migration to the sn-2 position. In a low water content (5%) system of the molecular dynamics simulation, water molecules stabilized the whole structure of RM IM through hydrogen bonding, which helped fix lipase-catalyzed active sites, making substrates more easily inserted into active sites, resulting in increased enzyme activity.

A Density Functional Theory (DFT) Study of the Acyl Migration Occurring during Lipase-Catalyzed Transesterifications.

Acyl migration (AM) is the main side reaction in the large-scale, regio-specific lipase catalyzed production of structural triglycerides (STs). A detailed understanding of the mechanism of AM was obtained during the process of lipase-catalyzed schemes (LCSs), which play a vital role in improving the quality and total yield of STs. However, currently, the mechanism of AM remains controversial. Herein, the two mechanisms (non-catalyzed (NCM) and lipase-catalyzed (LCM)) of AM have been analyzed in detail by the density functional theory (DFT) at the molecular level. Based on the computational results, we concluded that the energy barrier of the rate-limiting step in the LCM was 18.8 kcal/mol, which is more in agreement with the available experimental value (17.8 kcal/mol), indicating that LCM could significantly accelerate the rate of AM, because it has an energy barrier ~2 times lower than that of the NCM. Interestingly, we also found that the catalytic triad (Asp-His-Ser) of the lipase and water could effectively drop the reaction barrier, which served as the general acid or base, or shuttle of the proton.

Rate of acyl migration in lysophosphatidylcholine (LPC) is dependent upon the nature of the acyl group. Greater stability of sn-2 docosahexaenoyl LPC compared to the more saturated LPC species.

Several previous studies reported that sn-2 acyl lysophosphatidylcholines (LPCs) undergo rapid isomerization due to acyl migration, especially at physiological pH and temperature. However, these studies have been carried out using mostly sn-2 palmitoyl LPC, whereas the naturally occurring sn-2 LPCs are predominantly unsaturated. In this study, we investigated the acyl migration in four naturally occurring sn-2 acyl LPCs (sn-2 16:0, sn-2 18:1, sn-2 20:4, and sn-2 22:6) stored at various temperatures in aqueous or organic solvents, employing LC/MS to analyze the isomer composition. At 37°C and pH 7.4, the order of acyl migration rates (from sn-2 to sn-1) in aqueous buffer was 16:0 LPC> 18:1 LPC> 20:4 LPC> 22:6 LPC. The rate of isomerization of sn-2 16:0 LPC was 2–5 times greater than that of sn-2 22:6 under these conditions. Complexing the LPCs to serum albumin accelerated the acyl migration of all species, but sn-2 22:6 LPC was least affected by the presence of albumin. The migration rates were lower at lower temperatures (22°C, 4°C, and -20°C), but the differences between the LPC species persisted. All the sn-2 acyl LPCs were more stable in organic solvent (chloroform: methanol, 2:1 v/v), but the effect of the acyl groups on acyl migration was evident in the solvent also, at all temperatures. Storage of sn-2 22:6 LPC at -20°C for 4 weeks in the organic solvent resulted in about 10% isomerization, compared to 55% isomerization for sn-2 16:0. These results show that the sn-2 polyunsaturated LPCs can be stored at -20°C or below for several days without appreciable isomerization. Furthermore, they demonstrate that the sn-2 polyunsaturated LPCs generated in vivo are much more stable under physiological conditions than previously assumed.

Acyl migration in enzymatic interesterification of triacylglycerols: Effects of lipases from Thermomyces lanuginosus and Rhizopus oryzae, support material, and water activity

The enzymatic interesterification of a solvent‐free, equimolar mixture of trilaurin and 1,3‐palmitin‐2‐olein was studied using three immobilized lipase preparations as catalysts. Analysis of triacylglycerol (TAG) content and fatty acid (FA) distribution monitored the lipase‐catalyzed interesterification in sn‐1,3 positions and FA exchange in the sn‐2 position caused by acyl migration. Lipase from Rhizopus oryzae immobilized on polypropylene showed high sn‐1,3 regioselectivity, and minimal exchange in the sn‐2 position. With lipase from Thermomyces lanuginosus on silica (Lipozyme® TL IM), completely randomized FA distribution was obtained in 24 h. T. lanuginosus lipase on polypropylene caused a moderate rate of FA exchange in the sn‐2 position. Thus, the T. lanuginosus lipase and silica promoted randomization of FA distribution, whereas the R. oryzae lipase and polypropylene did not. Higher water activity promoted hydrolysis and thereby increased concentrations of partial acylglycerols, but at the same time a decrease in the acyl migration rate of these intermediates was also observed. The net result was that at a certain degree of interesterification, there was no significant effect of water activity on the degree of exchange in the sn‐2 position. On the other hand, a low water activity had the major advantage of giving a high yield of TAG.Practical applications: Both the type and the position of FA affect the properties of TAG. In TAG interesterification, there are thus different requirements for regiospecificity in FA exchange, depending on which product is desired. According to our results, lipase‐based catalysts can be used for TAG interesterification either to achieve unchanged FA composition in sn‐2 position or fast FA randomization in all positions. This helps to broaden the application of lipases in interesterification. The production of TAG can be tailor‐made for lipid mixtures with particular TAG composition and FA distribution using proper lipases, support materials, water activity, and reaction time.The enzymatic LLL–POP model reaction was used to investigate effects of lipase, support material, and water activity on acyl migration. (Fig. A): effect of Lipozyme® TL IM, TLPP and ROPP at aw 0.26, (Fig. B): effect of aw between 0.15 and 0.80 using Lipozyme® TL IM as the example.

Toxicity of Carboxylic Acid-Containing Drugs: The Role of Acyl Migration and CoA Conjugation Investigated.

Many carboxylic acid-containing drugs are associated with idiosyncratic drug toxicity (IDT), which may be caused by reactive acyl glucuronide metabolites. The rate of acyl migration has been earlier suggested as a predictor of acyl glucuronide reactivity. Additionally, acyl Coenzyme A (CoA) conjugates are known to be reactive. Here, 13 drugs with a carboxylic acid moiety were incubated with human liver microsomes to produce acyl glucuronide conjugates for the determination of acyl glucuronide half-lives by acyl migration and with HepaRG cells to monitor the formation of acyl CoA conjugates, their further conjugate metabolites, and trans-acylation products with glutathione. Additionally, in vitro cytotoxicity and mitochondrial toxicity experiments were performed with HepaRG cells to compare the predictability of toxicity. Clearly, longer acyl glucuronide half-lives were observed for safe drugs compared to drugs that can cause IDT. Correlation between half-lives and toxicity classification increased when "relative half-lives," taking into account the formation of isomeric AG-forms due to acyl migration and eliminating the effect of hydrolysis, were used instead of plain disappearance of the initial 1-O-β-AG-form. Correlation was improved further when a daily dose of the drug was taken into account. CoA and related conjugates were detected primarily for the drugs that have the capability to cause IDT, although some exceptions to this were observed. Cytotoxicity and mitochondrial toxicity did not correlate to drug safety. On the basis of the results, the short relative half-life of the acyl glucuronide (high acyl migration rate), high daily dose and detection of acyl CoA conjugates, or further metabolites derived from acyl CoA together seem to indicate that carboxylic acid-containing drugs have a higher probability to cause drug-induced liver injury (DILI).

Synthesis, Purification, and Acyl Migration Kinetics of 2‐Monoricinoleoylglycerol

Abstract2‐Monoricinoleoylglycerol (2‐MRG) was synthesized by the Novozym 435 catalyzed alcoholysis of castor oil in excess ethanol (1:70 mol:mol) at ambient temperature. Due to the fatty acid C12‐OH group, conventional liquid–liquid extraction methods developed for less polar, non‐hydroxylated 2‐monoacylglycerols (2‐MAG) proved inadequate for 2‐MRG purification. Alternatively, 2‐MRG was purified by normal‐phase flash chromatography (FC) on silica gel using a binary acetone‐hexane gradient mobile phase. Gram quantities of 2‐MRG were isolated in 63 % yield and contained no residual diacylglycerol (DAG), which fail to separate using liquid–liquid extraction methods. The 2‐MRG was obtained at ~90 mol% relative to 1‐MRG, proving that the FC method did not appreciably catalyze acyl migration. 1H‐NMR spectroscopy was used to monitor the spontaneous acyl migration of isolated 2‐MRG from 20 to 80 °C. The relative energy of activation calculated from the Arrhenius relationship of the 2‐MRG acyl migration rate constants was 82.9 kJ/mol. This was ~two‐fold higher than the theoretical ΔG298.15 calculated from molecular modeling using density functional calculations (B3LYP/6−31 + G*) of 2‐MRG, the ketal ring transition state, and 1‐monoricinoleoylglycerol (1‐MRG). The synthesis and isolation methods reported herein provide a convenient means to access useful intermediates for functionalized structured lipids.

Influence of Solid Supports on Acyl Migration in 2‐Monoacylglycerols: Purification of 2‐MAG via Flash Chromatography

AbstractSoybean oil 2‐monoacylglycerol (2‐MAG) was synthesized via the Novozym 435‐catalyzed ethanolysis of triacylglycerols and purified by conventional liquid–liquid extraction. The 2‐MAG was subjected to incubation at 20 and 40 °C in the presence of five solid commercial support materials, Lewatit, Silica Gel 60, Alumina–Neutral Brockman Activity 1, Amberlyst‐15, and SBA‐15, to determine their effects on acyl migration rates. Lewatit and SBA‐15 did not catalyze acyl migration rates after 144 h, while silica gel slightly increased migration rates. The more polar alumina and the cationic Amberlyst 15 significantly increased migration rates. Flash chromatography purification of 2‐MAG using silica gel as the immobile phase developed with an acetone/hexane binary gradient proved to be a comparable purification method to liquid–liquid extraction, resulting in 60 % 2‐MAG yield, no residual triacylglycerol, diacylglycerol, or glycerol co‐products, and a 95 mol% 2‐MAG purity vs. 1‐MAG, demonstrating that flash chromatography did not catalyze acyl migration.

Kinetics of transesterification of olive oil with methanol catalyzed by immobilized lipase derived from an isolated Burkholderia sp. strain

This work was carried out to investigate the acyl migration phenomena which has been considered as the factor having significant impact on kinetics of transesterification of oils catalyzed by a Burkholderia lipase with 1,3-regioselectivity. Transesterification of olive oil with methanol catalyzed by the immobilized lipase produces various intermediates, including 1-monoglyceride, 2-monoglyceride, 1,2-diglyceride, and 1,3-diglyceride. Migration kinetics of fatty acid groups from sn-2 of 2-monoglyceride and 1,2-diglyceride to 1-monoglyceride and 1,3-diglyceride were investigated for the temperature range of 25-65°C. The kinetics of transesterification of olive oil with methanol involving acyl migration in the presence of water was also systematically studied at 25, 40, and 65°C. Increasing temperature could increase the acyl migration rate. The overall biodiesel conversion was improved from 73.4% (at 25°C) to 90.0% and 92.4% when conducting at 40 and 65°C, respectively. Thermodynamics aspects of equilibrium state of the immobilized lipase-catalyzed transesterification were also discussed.

Acyl migration evaluation in monoacylglycerols from Echium plantagineum seed oil and Marinol

Production of 2-monoacylglycerols (2-MAGs) by selective hydrolysis of the triacylglycerols (TAGs) of Echium plantagineum seed oil and Marinol and further purification was carried out. Three purification methods, including silica gel column chromatography, liquid-liquid extraction and low-temperature crystallization were assayed. Partial acyl migration during the purification step is always observed. Acyl migration rates were similar both for the column chromatography and for the liquid-liquid extraction methods, and resulted in 1-MAG/2-MAG ratios higher than 1.0. Fatty acid (FA) profiles of 2-MAGs after enzyme hydrolysis showed that the major FAs were stearidonic acid (56.9% of total FA in 2-position) and docosahexaenoic acid (63.6% of total FA in 2-position) for E.plantagineum seed oil and Marinol, respectively.

Influence of Fatty Acid Desaturation on Spontaneous Acyl Migration in 2‐Monoacylglycerols

AbstractThe effect of desaturation from the C9 to the C15 carbon of 2‐monoacylglycerol (2‐MAG) fatty acids on spontaneous acyl migration is described. Three 2‐MAG species, 2‐monooleoylglycerol (C18:1 cis‐Δ9), 2‐monolinoleoylglycerol (C18:2 cis‐Δ9,12), and 2‐monolinolenoylglycerol (C18:3 cis‐Δ9,12,15) were synthesized by lipase‐catalyzed ethanolysis of their respective triacylglycerols and isolated in &gt;60 % yield and at 2‐MAG purities of &gt;95 % relative to 1‐monoacylglycerol (1‐MAG). 1H‐NMR spectroscopy was used to monitor the spontaneous acyl migration of the 2‐MAG species over a temperature range from 20 to 80 °C. The relative energies of activation calculated from the Arrhenius relationships of the 2‐MAG acyl migration rate constants were 73.3, 68.0, and 72.9 kJ mol−1 for the three 2‐MAG species, respectively. Density functional calculations performed using the B3LYP functional at the 6‐31+G* basis set on the three ketal ring intermediate of the three 2‐MAG species followed a similar trend with a lack of relative energetic preference associated with the degree of desaturation. The kinetically determined relative activation energies were approximately twofold higher than the theoretical relative Gibbs free energies of the intermediates, suggesting that other factors influence acyl migration. In general, increasing desaturation after the C9 carbon of 2‐MAG fatty acids had no appreciable effect on acyl migration rates.

Purification of 2‐Monoacylglycerols Using Liquid CO2 Extraction

AbstractThe fatty acid moiety of 2‐monoacyl‐sn‐glycerol (2‐MAG) undergoes spontaneous acyl migration to the sn‐1(3) position, resulting in a thermodynamic equilibrium of approximately 1:9 of 2‐MAG to 1(3)‐monoacyl‐sn‐glycerol (1‐MAG). Spontaneous acyl migration is an impediment to synthesizing and isolating specific 2‐MAG for use as intermediates in the synthesis of structured triacylglycerols. 2‐Monooleoyl‐sn‐glycerol was synthesized by the enzymatic ethanolysis of triolein and isolated by liquid CO2 extraction. The resultant MAG, diacylglycerol, and fatty acid ethyl esters were quantified by 1H NMR and supercritical fluid chromatography. The low polarity of the CO2 and mild extraction temperature (25 °C) resulted in very low spontaneous acyl migration rates, allowing the MAG to be isolated in 80% yield and in a very high 2‐MAG:1‐MAG ratios of ≥93 mol%.

팜중부유를 이용한 대칭형 Palmitoyl-Oleoyl-Stearoyl Triacylglycerol의 효소적 합성 반응 연구

본 연구에서는 palm mid fraction(PMF)와 stearic ethyl ester를 기질로 Lipozyme TLIM을 이용한 에스테르 교환반응을 실시하였으며 기질의 몰 비율과 효소양 및 시간에 따른 TAG 조성 변화와 함께 POS 구성율 및 acyl migration 정도를 알아보았다. sn-2 위치에서의 주요 지방산 조성 변화는 몰 비율과 효소양, 반응시간이 증가할수록 C18:1은 점차 감소하였고, C16:0과 C18:0은 증가함을 알 수 있었다. 이와 같은 변화는 특히 반응시간이 증가함에 따라 두드러지게 나타났으며 acyl migration 생성과 관계가 깊은 것으로 예측되었다. 그 결과 총 포화지방산의 함량은 최고 37.4 area%까지 증가한 수치를 보였다. 반응 합성물의 주요 TAG 조성으로는 POP, POS, SOS와 같은 대칭형 구조의 TAG가 확인되었으며 반응이 진행됨에 따라 POP는 감소하고 POS가 증가하는 경향을 보였다. Acyl migration과 POS 함량을 고려하였을 때 몰 비율 1:2, 효소양 3 wt%, 5시간 반응 조건에서 POS는 53.5 area%의 높은 함량을 보였으며 이때 총 포화지방산 함량은 반응 전 11.9 area%와 비교하여 약 2배 증가한 23.1 area%를 나타내었다. 한편, 전체 반응 조건 중 가장 높은 POS 함량은 55.4 area%의 수치를 보였는데, 이후 몰 비율과 효소양의 증가와 더불어 반응시간이 지속되었음에도 불구하고 POS는 오히려 감소하는 것을 확인할 수 있었다. 또한 반응이 진행되면서 acyl migration에 의해 sn-2 위치에 palmitic acid와 stearic acid가 전이된 PPS, PSS, SSS와 같은 TAG의 생성도 증가함을 알 수 있었다.

Dependence on the properties of organic solvent: Study on acyl migration kinetics of partial glycerides

During Rhizopus oryzae-mediated methanolysis of triglycerides for biodiesel production, the amount of 1,2-DG and 2-MG as well as the ratio of 1,2-DG/1,3-DG and 2-MG/1-MG differed significantly in different reaction medium, which indicated that solvent might be a crucial factor that would influence the acyl migration rate, leading to varied biodiesel yield. In this paper, the influence of solvent and their properties on acyl migration kinetics of both 1,2-diglyceride and 2-monoglyceride were investigated systematically. It was found that decreasing solvent polarity would give increasing acyl migration rate constants in general. Solvent polarity influenced the acyl migration rate through the influence of the charge dispersion of the transition state. High polarity of the solvent was unfavorable to the transition state charge dispersion, which would increase its energy state, and thus decreased the acyl migration rate and then led to relatively lower methyl ester yield.