Biocatalytic synthesis of L-ascorbyl palmitate using oleic acid imprinted Aspergillus niger lipase immobilized on resin.

In order to improve the esterification efficiency of the enzymatic synthesis of l-ascorbic acid palmitate, the substrate analogue imprinting of the Aspergillus niger lipase-catalyzed esterification process was studied. Oleic acid was selected as the imprinting molecule, oleic acid imprinting immobilized lipase was prepared at pH 8.0, 0.1 g oleic acid, 1.5 mL of 95 % ethanol, and 0.1 g Tween-20. Through solubilization and supersaturation of Vitamin C, the reaction concentration of Vitamin C reached 5.00 % (m/v) in dioxane with 93.99 % esterification rate and 110.72 g/L of product concentration. Moreover, the Vitamin C reaction concentration can reach 8.00 % by using staged substrate feeding, and the esterification rate and product concentration of esterification after 28 h was 156.34 g/L and 82.96 %. Besides, the imprinting-induced conformational changes in enzyme proteins was characterized by fluorescence and infrared spectroscopy. This method provides a pathway for enzymatic production of l-ascorbic acid palmitate.

Corncob waste derived carbon with sulfonic acid group: An efficient heterogeneous catalyst for production of ethyl levulinate as biodiesel additives.

Alkyl levulinate is a biomass-based chemical compound used as a fuel additive. This research aims to produce ethyl levulinate from levulinic acid and ethanol using esterification with the assistance of a heterogeneous sulfonated carbon catalyst. The carbon sulfonate catalyst is obtained from corncob waste that has undergone carbonization at 300 °C and sulfonation using sulfuric acid at a temperature of 150 °C for 8 h. The catalyst is used for esterification with predetermined operating variables using Box-Behnken Design (BBD) on the response surface methodology (RSM). The result shows significant variables for ethyl levulinate esterification are catalyst loading and esterification time. The FTIR analysis indicates the presence of S=O bonds in the sulfonated carbon catalyst. The XRD and SEM analysis shows that the sulfonated carbon catalyst is in amorphous and mesoporous form. Catalyst reusability demonstrates that the corncob-derived carbon sulfonate catalyst can be used up to 3 times. The optimum condition for esterification is 9 h of reaction, 10 % catalyst loading, and a molar ratio of levulinic acid to ethanol of 1:10, which has 83.15 % conversion. These results present the optimum parameter conditions for an efficient heterogeneous catalyst from corncob for producing ethyl levulinate.

Tuning the Properties of Xylan/Chitosan-Based Films by Temperature and Citric Acid Crosslinking Agent.

Petroleum-based food packaging causes environmental problems such as waste accumulation and microplastic generation. In this work, biobased films from stable polyelectrolyte complex suspensions (PECs) of xylan and chitosan (70 Xyl/30 Ch wt% mass ratio), at different concentrations of citric acid (CA) (0, 2.5, 5, 7.5 wt%), were prepared and characterized. Films were treated at two temperatures (135 °C, 155 °C) and times (30 min, 60 min) to promote covalent crosslinking. Esterification and amidation reactions were confirmed by Fourier Transform Infrared Spectroscopy and Confocal Raman Microscopy. Water resistance and dry and wet stress-strain results were markedly increased by thermal treatment, mainly at 155 °C. The presence of 5 wt% CA tended to increase dry and wet stress-strain values further, up to 88 MPa-10% (155 °C for 60 min), and 5.6 MPa-40% (155 °C for 30 min), respectively. The UV-blocking performance of the films was improved by all treatments, as was thermal stability (up to Tonset: 230 °C). Contact angle values were between 73 and 84°, indicating partly wettable surfaces. Thus, thermal treatment at low CA concentrations represents a good alternative for improving the performance of Xyl/Ch films.

Construction of an Aspergillus oryzae △nptB△pyrG Host for Homologous Expression of Lipase and Catalytic Property Characterization of Recombinant Lipase.

Aspergillus oryzae is an ideal cell factory for protein expression with powerful protein processing and secretion capabilities. The current study aimed to explore the homologous expression of A. oryzae lipase AOL (GenBank: KP975533) by constructing an auxotrophic A. oryzae △pyrG△nptB and subsequently characterizing the immobilization and catalytic properties of recombinant lipase. Initially, the pyrG gene knocked out in wild-type A. oryzae by homologous recombination, followed by the creation of a uridine/uracil auxotroph transformation. Through this system, the protease gene nptB was precisely knocked out, leading to a substantial decrease in extracellular (39.04%) and intracellular (90.07%) protease activity. The A. oryzae △nptB△pyrG strain was used as host for homologous expression of lipase AOL. After transformation of linearized lipase-expression cassette, the engineered A. oryzae AOL-8 was screened out with the lipase gene copy number of 14, exhibiting extracellular and intracellular lipase activities of 1.75 U/mL and 46.4 U/g, respectively. Subsequently, the production and immobilization of the recombinant lipase, via physical adsorption on macroporous resin XRZ04B, were achieved through submerged fermentation of the AOL-8 strain. The results of esterification catalytic properties of immobilized recombinant lipase indicated that the lipase exhibited optimal catalytic activity with lauric acid and methanol as substrates, a reaction temperature of 35 °C, and n-hexane as the preferred solvent medium; its highest conversion rate can reach at 72.3%.

Mechanism regulation over dual-atom catalyst enables high-performance oxidative alcohol esterification.

The development of heterogeneous catalysts with well-defined uniform isolated or multiple active sites is of great importance for understanding catalytic performances and studying reaction mechanisms. Herein, we present a CoCu dual-atom catalyst (CoCu-DAC) where bonded Co-Cu dual-atom sites are embedded in N-doped carbon matrix with a well-defined Co(OH)CuN6 structure. The CoCu-DAC exhibits higher catalytic activity and selectivity than the Co single-atom catalyst (Co-SAC) and Cu single-atom catalyst (Cu-SAC) counterparts in the catalytic oxidative esterification of alcohols and a variety of methyl and alkyl esters have been successfully synthesized. Kinetic studies reveal that the activation energy (29.7 kJ mol-1) over CoCu-DAC is much lower than that over Co-SAC (38.4 kJ mol-1) and density functional theory (DFT) studies disclose that two different mechanisms are regulated over CoCu-DAC and Co-SAC/Cu-SAC in three-step esterification of alcohols. The bonded Co-Cu and adjacent N species efficiently catalyze the elementary reactions of alcohol dehydrogenation, O2 activation and ester formation, respectively. The stepwise alkoxy pathway (O-H and C-H scissions) is preferred for both alcohol dehydrogenation and ester formation over CoCu-DAC, while the progressive hydroxylalkyl pathway (C-H and O-H scissions) for alcohol dehydrogenation and simultaneous hemiacetal dehydrogenation are favored over Co-SAC and Cu-SAC. Characteristic peaks in the Fourier transform infrared spectroscopy analysis may confirm the formation of the metal-C intermediate and the hydroxylalkyl pathway over Co-SAC.

Low methyl-esterified ginseng homogalacturonan pectins promote longevity of Caenorhabditis elegans via impairing insulin/IGF-1 signalling.

Panax ginseng C. A. Meyer (ginseng) is a medicinal plant widely used for promoting longevity. Recently, homogalacturonan (HG) domain-rich pectins purified from some plants have been reported to have anti-aging-related activities, leading us to explore the longevity-promoting activity of the HG pectins from ginseng. In this study, we discovered that two of low methyl-esterified ginseng HG pectins (named as WGPA-2-HG and WGPA-3-HG), whose degree of methyl-esterification (DM) was 16 % and 8 % respectively, promoted longevity in Caenorhabditis elegans. Results showed that WGPA-2-HG/WGPA-3-HG impaired insulin/insulin-like growth factor 1 (IGF-1) signalling (IIS) pathway, thereby increasing the nuclear accumulation of transcription factors SKN-1/Nrf2 and DAF-16/FOXO and enhancing the expression of relevant anti-aging genes. BLI and ITC analysis showed that the insulin-receptor binding, the first step to activate IIS pathway, was impeded by the engagement of WGPA-2-HG/WGPA-3-HG with insulin. By chemical modifications, we found that high methyl-esterification of WGPA-2-HG/WGPA-3-HG was detrimental for their longevity-promoting activity. These findings provided novel insight into the precise molecular mechanism for the longevity-promoting effect of ginseng pectins, and suggested a potential to utilize the ginseng HG pectins with appropriate DM values as natural nutrients for increasing human longevity.

Insight into esterified and granular esterified-pregelatinized starch formation during esterification modification: Key role of temperature.

The formation conditions and functional property differences of esterified starch (ES) and granular esterified-pregelatinized starch (EPS) synchronously prepared by octenyl succinic anhydride (OSA) modification remain unclear. In this study, we explored the formation conditions and physicochemical properties of ES and EPS after OSA modification. The modification temperature controlled the formation amount and time for both starch types during OSA modification. Compared to ES, EPS exhibited a higher degree of substitution, cold-water swelling power, water-absorption capacity and apparent viscosity in cold water. The structural characterization confirmed the molecular weight and short/long-range molecular order of ES and EPS decreased. Moreover, scanning electron microscopy indicated EPS retained its granular morphology. The X-ray diffraction patterns confirmed the presence of more starch-lipid complexes formed in EPS than in ES. This study provides a novel method for preparing esterified and granularly esterified-pregelatinized starches that could be used as promising additives in low-energy formula foods.

Candida antartica lipase-catalyzed esterification for efficient partial acylglycerol synthesis in solvent-free system: Substrate selectivity, molecular modelling and optimization.

Partial acylglycerols are valued for their emulsifying and stabilizing properties, yet precise green synthesis remains challenging due to low yield and selectivity. This study aimed to elucidate the "lipase selectivity-substrate structure-product composition" relationship to enhance the yield of targeted partial acylglycerol. The results showed that lipase exhibited a greater selectivity towards fatty acids with shorter chain lengths and higher unsaturation. Hydroxyl donors also affected the esterification process, with the enzyme-acyl complex exhibiting selectivity towards hydroxyl donors as follows: glycerol > monoacylglycerol > diacylglycerol. Substrate ratio significantly influenced enzymatic reactions; a 10:1 ratio favored triacylglycerol formation (>80 %), while a 1:1 ratio produced > 90 % partial acylglycerols. Molecular docking simulations revealed that substrates primarily interacted with lipase through hydrogen bonding and hydrophobic interactions. A comprehensive understanding of lipase selectivity patterns could facilitate the design of more efficient reaction systems, enabling the conversion of basic lipid resources into desired high value-added products.

Sex-Specific Dysregulation of Placental Lipid Metabolism in Preeclampsia.

Background: Preeclampsia (PE) is a hypertensive disorder of pregnancy associated with adverse maternal and fetal outcomes. While placental dysfunction is implicated in PE pathogenesis, the impact of PE on placental lipid metabolism and its potential sexual dimorphism remains poorly understood. Methods: We conducted a comprehensive analysis of term placentas from PE and normotensive pregnancies with male and female fetuses. Lipid profiles were quantified using mass spectrometry, and mRNA expression of genes involved in fatty acid oxidation, esterification, and transport was assessed using qPCR. Results: Placentas from PE pregnancies exhibited elevated lipid levels, with male placentas showing a more pronounced increase in triacylglycerols, cholesteryl esters, and free cholesterol compared to female placentas. Gene expression analysis revealed sexually dimorphic alterations, with male PE placentas exhibiting upregulation of genes involved in fatty acid uptake, oxidation, and esterification, while female PE placentas showed a more complex response with both upregulation and downregulation of certain genes. Notably, peroxisomal fatty acid oxidation was upregulated in male PE placentas but suppressed in female PE placentas. Conclusions: Our findings reveal sexually dimorphic alterations in placental lipid metabolism in PE, suggesting that male placentas may be more vulnerable to lipotoxicity. These insights may have implications for understanding the pathogenesis of PE and developing sex-specific interventions to improve maternal and fetal outcomes.

Enhancing the sodium storage performance of hard carbon by constructing thin carbon coatings via esterification reactions.

Hard carbons derived from pitch are considered a competitive low-cost anode for sodium-ion batteries. However, the preparation of pitch-based hard carbon (PHC) requires the aid of a pre-oxidation strategy, which introduces unnecessary defects and oxygen elements, which leads to low initial Coulombic efficiency (ICE) and poor cycling stability. Herein, we demonstrate a new surface engineering strategy by grafting chemically active glucose molecules on the PHC surface via esterification reactions, which can achieve low-cost nano-scaled carbon coating. Thin glucose coating can be carbonized at a lower temperature, which results in a more closed pore structure and fewer functional groups. The as prepared PHC exhibits a high reversible capacity of 328.5 mAh/g with a high ICE of 92.08 % at 0.02 A/g. It is noteworthy that the PHC can be adapted to a variety of cathode materials for full-cell assembling without pre-sodiation, which maintains the characteristics of high capacity and excellent cycling stability. The performance of resin-based hard carbon coated with a similar method was also improved, demonstrating the universality of the technique.

Insight into divergent chemical modifications of chitosan biopolymer: Review.

Chitosan is used in many applications due to its biodegradability, biocompatibility, nontoxicity, nonadhesiveness, and film-forming capabilities. Chitosan has antibacterial and antifungal activities, which are two of its other desirable attributes. However, chitosan can only dissolve in acidic liquids (1-3 % acetic acid), limiting its practical application. The hydroxyl and amino functional groups in the chitosan backbone are essential for chemical modification, which is a viable alternative for overcoming this obstacle. So, N- or O-, and N, O-substituted chitosan may yield derivatives with increased water solubility, biocompatibility, biodegradability, and bio-evaluation. In the same manner, the physicochemical properties of chitosan, including its mechanical and thermal properties, can be improved by cross-linking reactions. This review provides an overview of chitosan, including its origins and their solubility. Also, the review extend and discuss in details most of all chemical reactions that happened on the amino group, hydroxyl group, or both amino group and hydroxyl group to create modified chitosan-based organic materials. Finally, the problems that still need to be solved and probable future areas for study are discussed.

Pectic polysaccharides from Tartary buckwheat sprouts: Effects of ultrasound-assisted Fenton treatment and mild alkali treatment on their physicochemical characteristics and biological functions.

Buckwheat sprouts are rich in pectic polysaccharides, which possess numerous health-improving benefits. However, the precise structure-activity relationship of pectic polysaccharides from Tartary buckwheat sprouts (TP) is still scant, which ultimately restricts their applications in the food industry. Hence, both ultrasound-assisted Fenton treatment (UAFT) and mild alkali treatment (MATT) were utilized for the modification of TP, and then the effects of physicochemical characteristics of original and modified TPs on their bioactivities were assessed. Our findings reveled that the UAFT treatment could precisely reduce TP's molecular weight, with the levels decreased from 8.191 × 104 Da to 0.957 × 104 Da. Meanwhile, the MATT treatment could precisely reduce TP's esterification degree, with the values decreased from 28.04 % to 4.72 %. Nevertheless, both UAFT and MATT treatments had limited effects on the backbone and branched chain of TP. Moreover, our findings unveiled that the UAFT treatment could notably promote TP's antioxidant, antiglycation, and immunostimulatory effects, while remarkedly reduce TP's anti-hyperlipidemic effect, which were probably owing to that the UAFT treatment obviously reduced TP's molecular weight. Additionally, the MATT treatment could also promote TP's immunostimulatory effect, which was probably attributed to that the MATT treatment significantly decreased TP's esterification degree. Interestingly, the MATT treatment could regulate TP's antioxidant and antiglycation effects, which was probably attributed to that the MATT treatment simultaneously reduced its esterification degree and bound phenolics. Our findings are conducive to understanding TP's structure-activity relationship, and can afford a scientific theoretical basis for the development of functional or healthy products based on TPs. Besides, the UAFT treatment can be a promising approach for the modification of TP to improve its biological functions.

Enzyme-esterified grape seed proanthocyanidin derivatives as novel lipid-lowering agents.

Grape seed proanthocyanidin (GSP), as a natural antioxidant, has great potential to be developed into a lipid-lowering agent, but its low lipophilicity and stability greatly limit its application. In this study, an enzymatic esterification strategy was developed to introduce fatty acid chains into GSP, resulting in the successful synthesis of a series of new GSP derivatives. The results showed that up to 85% conversion of GSP and 35% TAG inhibition rate of GSP derivatives were achieved. The structures of GSP derivatives were identified by UPLC-MS/MS, and seven derivatives were confirmed as catechin-3'-O-laurate, epicatechin-3'-O-laurate, epicatechin gallate-3″,5″-di-O-laurate, epicatechin gallate-3',3″,5″-tri-O-laurate, procyanidin B1-3',3″-di-O-laurate, procyanidin B2-3',3″-di-O-laurate and procyanidin C1-3',3″,3‴-tri-O-laurate by NMR. GSP derivatives exhibited higher inhibitory effects on lipid accumulation, intracellular TAG and TC than parent GSP. These results indicate that GSP derivatives have potential as lipid-lowering agents for utilization in the food industry.

Extraction, Characterization, and Antioxidant Activity of Pectin from Lemon Peels.

Pectin is a natural polymer that is found in the cell walls of higher plants. This study presents a comprehensive analysis of pectin extracted from lemon in two different geographic regions (Peddie and Fort Beaufort) in two consecutive years (2023 and 2024) named PP 2023, PP 2024, FBP 2023, and FBP 2024. The dried lemon peels were ground into a powder, sifted to obtain particles of 500 µm, and then subjected to pectin extraction using a conventional method involving mixing lemon peel powder with distilled water, adjusting the pH level to 2.0 with HCl, heating the mixture at 70 °C for 45 min, filtering the acidic extract, and precipitating pectin with ethanol. The yield of these pectin samples was statistically significant, as FBP 2024 had a maximum yield of 12.2 ± 0.02%, PP 2024 had a maximum yield of 13.0 ± 0.02%, FBP 2023 had a maximum yield of 12.2 ± 0.03%, and PP 2023 had a maximum yield of 13.1 ± 0.03%, The variation in yield could be due to the differences in the growing conditions, such as the climate and soil, which could have affected the pectin content in the lemons. The physicochemical characterization of all samples proved that our pectin samples could be used in the pharmaceutical and food industries, with anhydrouronic acid content which was greater than 65%, as suggested by the FAO. The scanning electron microscope analysis of all extracted pectin was rough and jagged, while the commercial pectin displayed a smooth surface morphology with a consistent size. FTIR confirmed the functional groups which were present in our samples. Thermogravimetric analysis was employed to investigate the thermal behavior of the extracted pectin in comparison with commercial pectin. It was found that the extracted pectin had three-step degradation while the commercial pectin had four-step degradation. Additionally, pectin samples have been shown to have antioxidants, as the IC50 of PP 2024, PP 2023, FBP 2023, FBP 2024, and Commercial P was 1062.5 ± 20.0, 1201.3 ± 22.0, 1304.6 ± 19.0, 1382.6 ± 29.9, and 1019.4 ± 17.1 mg/L, respectively. These findings indicate that lemon pectin has promising characteristics as a biopolymer for use in biomedical applications.

A Review of Cinnamic Acid's Skeleton Modification: Features for Antibacterial-Agent-Guided Derivatives.

Antimicrobial resistance has emerged as a significant danger to global health, and the need for more effective antimicrobial resistance (AMR) control has been highlighted. Cinnamic acid is abundant in plant products and is a potential starting material for further modification, focusing on the development of new antimicrobial compounds. In the following review, we describe the classification of critical antibacterial-guided reactions applied to the main skeleton structure of cinnamic acid derivatives over the last decade. Of all of the main parts of cinnamic acids, the phenyl ring and the carboxylic group significantly affect antibacterial activity. The results presented in the following review can provide valuable insights into considerable features in the organic modification of cinnamic acids related to antibacterial medication development and the food industry.

Effects of charge distribution and degree of methylesterification of pectin emulsifier on bioaccessibility of curcumin incorporated in nanoemulsions.

The objectives of this study were to elucidate the effects of degree of methyl esterification (DM) and charge distribution of pectin on the stability of emulsions and to analyze bioaccessibility of curcumin incorporated in emulsions stabilized by pectins. Three commercial pectins, CP72 (DM72), CP50 (DM50), and CP7 (DM7), were used. MP50 (DM50) with consecutive demethylesterified galacturonic acid residues was prepared from CP72 via demethylesterification to induce different charge distributions. Emulsions containing curcumin were prepared and were stored for 30 days. The CP72 and CP50 emulsions remained relatively stable for 30 days. However, MP50 and CP7 were less effective at forming stable emulsions. When the pectin emulsions passed through each phase of the simulated gastrointestinal tract (GIT), the CP72 and CP50 emulsions retained their initial droplet structures after in vitro mouth and gastric digestion, whereas the MP50 and CP7 emulsions exhibited gel-like clusters, although the gel-like formation of MP50 was distinct from that observed in CP7. MP50 emulsion showed a high degree of final lipid digestion and high bioaccessibility of curcumin while CP72 emulsion displayed a low degree of final lipid digestion. CP50 exhibited low bioaccessibility of curcumin, which might have been contributed by its fast lipid digestion profiles.

Crystal and mol-ecular structure of 2-methyl-1,4-phenyl-ene bis-(3,5-di-bromo-benzoate).

The aryl diester compound, 2-methyl-1,4-phenyl-ene bis-(3,5-di-bromo-benzoate), C21H12Br4O4, was synthesized by esterification of methyl hydro-quinone with 3,5-di-bromo-benzoic acid. A crystalline sample was obtained by cooling a sample of the melt (m.p. = 502 K/DSC) to room temperature. The mol-ecular structure consists of a central benzene ring with anti-3,5-di-bromo-benzoate groups symmetrically attached at the 1 and 4 positions and a methyl group attached at the 2 position of the central ring. In the crystal structure (space group P), mol-ecules of the title aryl diester are located on inversion centers imposing disorder of the methyl group and H atom across the central benzene ring. The crystal structure is consolidated by a network of C-H⋯Br hydrogen bonds in addition to weaker and offset π-π inter-actions involving the central benzene rings as well as the rings of the attached 3,5-di-bromo-benzoate groups.

Kinetic Aspects of Esterification and Transesterification in Microstructured Reactors.

Microstructured reactors offer fast chemical engineering transfer and precise microfluidic control, enabling the determination of reactions' kinetic parameters. This review examines recent advancements in measuring microreaction kinetics. It explores kinetic modeling, reaction mechanisms, and intrinsic kinetic equations pertaining to two types of microreaction: esterification and transesterification reactions involving acids, bases, or biocatalysts. The utilization of a micro packed-bed reactor successfully achieves a harmonious combination of the micro-dispersion state and the reaction kinetic characteristics. Additionally, this review presents micro-process simulation software and explores the advanced integration of microreactors with spectroscopic analyses for reaction monitoring and data acquisition. Furthermore, it elaborates on the control principles of the micro platform. The superiority of online measurement, automation, and the digitalization of the microreaction process for kinetic measurements is highlighted, showcasing the vast prospects of artificial intelligence applications.

Production of resistant starches via citric acid modification: Effects of reaction conditions on chemical structure and final properties.

Aiming to contribute to the current knowledge on the impact of reaction conditions on the chemical structure and target properties of starch citrates, in the current contribution different corn starch citrates were prepared by manipulation of reaction time, temperature and citric acid concentration. Modified starches were characterized in terms of chemical structure, morphology, crystallinity, swelling power and resistant starch content. For the first time, total substitution, crosslinking and monosubstitution degrees were quantitatively determined; and the relationship among final chemical structure, reaction conditions and target starch citrates properties was comprehensively analyzed. Products with total substitution values in the range of 0.075-0.24, crosslinking degrees in the 0.005-0.11 interval, and monosubstitution extents within the 0.05-0.12 range, were produced. By proper selection of reaction conditions products with almost 100 % of resistant starch were obtained. Results evidenced that starch citrates properties (mainly swelling power and RS content) depend on both chemical structure and the reaction conditions employed. Actually, the reaction temperature set (120 °C or 150 °C) proved to play a determinant role in the final products properties as evidenced from starch citrates with similar chemical structure and substantially different swelling and digestibility properties.

Intraperitoneally injected d11-11(12)-epoxyeicosatrienoic acid is rapidly incorporated and esterified within rat plasma and peripheral tissues but not the brain.

Epoxyeicosatrienoic acids (EpETrEs) are bioactive lipid mediators of arachidonic acid cytochrome P450 oxidation. In vivo, the free (unbound) form of EpETrEs regulate multiple processes including blood flow, angiogenesis and inflammation resolution. Free EpETrEs are thought to rapidly degrade via soluble epoxide hydrolase (sEH); yet, in many tissues, the majority of EpETrEs are esterified to complex lipids (e.g. phospholipids) suggesting that esterification may play a major role in regulating free, bioactive EpETrE levels. This hypothesis was tested by quantifying the metabolism of intraperitoneally injected free d11-11(12)-Epoxyeicosatrienoic acid (d11-11(12)-EpETrE) in male and female rats. Plasma and tissues (liver, adipose and brain) were obtained 3 to 4 min later and assayed for d11-11(12)-EpETrE and its sEH metabolite, d11-11,12-dihydroxyeicosatrienoic acid (d11-11,12-diHETrE) in both the free and esterified lipid fractions. In both males and females, the majority of injected tracer was recovered in liver followed by plasma and adipose. No tracer was detected in the brain, indicating that brain levels are maintained by endogenous synthesis from precursor fatty acids. In plasma, liver, and adipose, the majority (>54 %) of d11-11(12)-EpETrE was found esterified to phospholipids or neutral lipids (triglycerides and cholesteryl esters). sEH-derived d11-11,12-diHETrE was not detected in plasma or tissues, suggesting negligible conversion within the 3-4 min period post tracer injection. This study shows that esterification is the main pathway regulating free 11(12)-EpETrE levels in vivo.