Parameters affecting diacylglycerol formation during the production of specific-structured lipids by lipase-catalyzed interesterification

Diacylglycerols (DAG) are important intermediates in lipase-catalyzed interesterification, but a high DAG concentration in the reaction mixture results in a high DAG content in the final product. We have previously shown that a high DAG concentration in the reaction mixture increases the degree of acyl migration, thus adding to the formation of by-products. In the present study we examined the influence of water content, reaction temperature, enzyme load, substrate molar ratio (oil/capric acid), and reaction time on the formation of DAG in batch reactors. We used response surface methodology (RSM) to minimize the numbers of experiments. The DAG content of the product was dependent on all parameters examined except reaction time. DAG formation increased with increasing water content, enzyme load, reaction temperature, and substrate ratio. The content of sn-1,3-DAG was higher than that of sn-1,2-DAG under all conditions tested, and the ratio between the contents of the former compounds and the latter increased with increasing temperature and reaction time. The water content, enzyme load, and substrate ratio had no significant effect on this ratio. The DAG content was positively correlated with both the incorporation of acyl donors and the degree of acyl migration.     

Pilot batch production of specific-structured lipids by lipase-catalyzed interesterification: Preliminary study on incorporation and acyl migration

Effects of water content, reaction time, and their relationships in the production of two types of specific-structured lipids (sn-MLM- and sn-LML-types: L-long chain fatty acids; M-medium chain fatty acids) by lipase-catalyzed interesterification in a solvent-free system were studied. The biocatalyst used was Lipozyme IM (commercial immobilized lipase). The substrates used for sn-MLM-type were fish oil and capric acid, and medium chain triacylglycerols and sunflower free fatty acids for sn-LML-type. The observed incorporation with the time course agrees well with the Michaelis-Menten equation, while the acyl migration is proportional to time within the range of 20 mol% acyl migration (MLM-type: M _f =0.2225 T, R²=0.98; LML-type: M _f =0.5618 T, R²=0.99). As water content (wt%, on the enzyme basis) increased from 3.0 to 11.6% for MLM-type and from 3.0 to 7.2% for LML-type in the solvent-free systems, the incorporation rates in the first 5 h increased from 3.34 to 10.30%/h, and from 7.29 to 11.12%/h, respectively. However, the acyl migration rates also increased from 0.22 to 1.12%/h and from 0.56 to 1.37%/h, respectively. Different effects in the production of two totally position-opposed lipids can be observed. Presumably these are caused by the different chain length of the fatty acids. The relationships between reaction time and water content are inverse and give a quantitative prediction of incorporation and acyl migration in selected reaction conditions and vice versa. The acyl migration can not be totally avoided in present systems, but can be reduced to a relatively low level. Acyl migration during the downstream processing has also been observed and other factors influencing the acyl migration are briefly discussed.     

Production of specific-structured lipids by enzymatic interesterification: Elucidation of Acyl migration by response surface design

Production of specific-structured lipids (SSL) by lipase-catalyzed interesterification has been attracting more and more attention recently. However, it was found that acyl migration occurs during the reaction and causes the production of by-products. In this paper, the elucidation of acyl migration by response surface design was carried out in the Lipozyme IM (Rhizomucor miehei)-catalyzed interesterification between rapeseed oil and capric acid in solvent-free media. A five-factor response surface design was used to evaluate the influence of five major factors and their relationships. The five factors, water content, reaction temperature, enzyme load, reaction time and substrate ratio, were varied at three levels together with two star points. All parameters besides substrate ratio had strong positive influences on acyl migration, and reaction temperature was most significant. The contour plots clearly show the interactions between the parameters. The migration rates of different fatty acids were also compared from three different sets of experiments during the lipase-catalyzed reaction. The best-fitting quadratic response surface model was determined by regression and backward elimination. The coefficients of determination (R ²) of the model were 0.996 and 0.981 for Q ² value. The results show that the fitted quadratic model satisfactorily expresses acyl migration for the enzymatic interesterification in the batch reactor used.     

Production of specific-structured lipids by enzymatic interesterification: Elucidation of acyl migration by response surface design

Production of specific-structured lipids (SSL) by lipase-catalyzed interesterification has been attracting more and more attention recently. However, it was found that acyl migration occurs during the reaction and causes the production of byproducts. In this paper, the elucidation of acyl migration by response surface design was carried out in the Lipozyme IM (Rhizomucor miehei)-catalyzed interesterification between rapeseed oil and capric acid in solvent-free media. A five-factor response surface design was used to evaluate the influence of five major factors and their relationships. The five factors, water content, reaction temperature, enzyme load, reaction time and substrate ratio, were varied at three levels together with two star points. All parameters besides substrate ratio had strong positive influences on acyl migration, and reaction temperature was most significant. The contour plots clearly show the interactions between the parameters. The migration rates of different fatty acids were also compared from three different sets of experiments during the lipase-catalyzed reaction. The best-fitting quadratic response surface model was determined by regression and backward elimination. The coefficients of determination (R ²) of the model were 0.996 and 0.981 for Q ² value. The results show that the fitted quadratic model satisfactorily expresses acyl migration for the enzymatic interesterification in the batch reactor used.     

Modification of menhaden oil by enzymatic acidolysis to produce structured lipids: Optimization by response surface design in a packed bed reactor

Structured lipids from menhaden oil were produced by enzymatic acidolysis in a packed bed reactor. Response surface methodology was applied to optimize the reaction. Lipozyme IM from Rhizomucor miehei lipase was the biocatalyst, and caprylic acid was the acyl donor. Parameters such as residence time, substrate molar ratio, and reaction temperature were included for the optimization. High incorporation of acyl donor and retention of high levels of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in the original menhaden oil were obtained. Good quadratic models were obtained for the incorporation of caprylic acid and for the content of EPA plus DHA retained, by multiple regression with backward elimination. The coefficients of determination (R ²) for the two models were 0.91 and 0.87, respectively. The regression probabilities (P) were below 0.003 for both models. Also, the predicted values from the two models had linear relationships with the observed responses. All parameters studied had positive effects on the incorporation of caprylic acid, but only residence time and substrate molar ratio had negative effects on the content of EPA plus DHA retained. The optimal conditions generated from models were temperature =65°C, substrate molar ratio=4–5, and residence time=180–220 min. Incorporated caprylic acid did not replace DHA, but the content of EPA decreased somewhat with an increase in caprylic acid incorporation.     

Chemistryvis-à-vis maternalism in lace bugs (Heteroptera: Tingidae): Alarm pheromones and exudate defense inCorythucha andGargaphia species

The hawthorn lace bug,Corythucha cydoniae, and the eggplant lace bug,Gargaphia solani, possess alarm pheromones that are produced in dorsal abdominal glands (DAGs). WhenG. solani nymphs are grasped, they emit secretion from both DAGs; the posterior DAG secretion alone elicits alarm, but the anterior DAG secretion may hasten the response. InC. cydoniae, the response is due to a synergism between the anterior and posterior DAG secretions, and nymphs are apparently unable to voluntarily release their DAG secretions; both DAGs must be ruptured for the pheromone to escape. The alarm pheromones are interspecifically active in patterns matching the intraspecific activities. Compounds identified from tingid DAG secretions that are involved in the alarm messages are: (E)2-hexenal, (E)-4-oxo-2-hexenal, acetaldehyde, geraniol, and linalool. A new natural product of unknown function (designated nerolidol aldehyde) was identified from the anterior DAG secretions of both species.     

Thermally stimulated shape-memory behavior of ethylene oxide-ethylene terephthalate segmented copolymer

A series of ethylene oxide—ethylene terephthalate segmented copolymers (EOET) with different long soft segments and different hard-segment contents were synthesized. The thermally stimulated shape-memory behavior of EOET segmented copolymer is characterized by the maximum recovery (R_f), the recovery temperature (T_r), and the recovery speed (V_r) or the temperature (T_M) of the maximum deformation recovery rate against temperature and the maximum recovery speed (V_M). These parameters show that the features of thermally stimulated shape-memory effects of EOET segmented copolymers are following: The crystallinity of soft segments determines the temperature T_r and T_M, and the parameters R_f, V_r, and V_M depend on the stability of the physical crosslinks formed by the hard segments, which at the same time are influenced by the length of soft segment. R_f, V_r, and V_M decrease with prolongation of the keeping time (t_k) and increasing stretching ratio. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2433–2440, 1997     

Four-factor response surface optimization of the enzymatic modification of triolein to structured lipids

The ability of an immobilized lipase to modify the fatty acid composition of (88.8% C_18:1, 4.3% C_16:0, 3.1% C_18:0, and 3.8% C_18:2 as determined by gas chromatography, and approximately 90% triolein) in hexane by incorporation of a medium-chain fatty acid, capric acid (C₁₀), to form structured triacylglycerol was studied. Response surface methodology was used to evaluate the effect of synthesis variables, such as reaction time (12–36 h), temperature (25–65°C), molar substrate ratio of capric acid to triolein (2:1–6:1), and enzyme amount (10–30% wt% of triacylglycerol), on the yield of structured lipid. Optimization of the transesterification was attempted to obtain maximum yield of structured lipid while using the minimum molar substrate ratio and enzyme amount as much as possible. Computer-generated contour plot interpretation revealed that a relatively high molar substrate ratio (6:1) combined with low enzyme amount (10%) after 30 h of reaction at 25°C gave optimum incorporation of capric acid. A total yield for combined monoand dicaproolein of up to 100% was obtained.     

Semiochemicals from the Predatory Stink Bug Eocanthecona furcellata (Wolff): Components of Metathoracic Gland, Dorsal Abdominal Gland, and Sternal Gland Secretions

Volatile compounds from the metathoracic glands (MTG), dorsal abdominal glands (DAG), and sternal setae of the generalist predatory stink bug Eocanthecona furcellata (Wolff) were studied by gas chromatography–mass spectrometry. MTGs of both male and female bugs contained (E)-2-decenal as the major component, with lesser amounts of (E,E)-2,4-decadienal, (E,Z)-2,4-decadienal, and (E)-2,9-decadienal. The relative amount of (E)-2,9-decadienal in the MTGs of female bugs was higher than in male bugs. There was no dimorphism in the morphology of the DAGs of adults. However, the DAG contents of adult bugs were different between the sexes. Geraniol was found only in the DAGs of males, and limonene and -terpineol were found only in the DAGs of females, whereas linalool oxide isomers, linalool, neral, and geranial were found in DAGs of both sexes. The DAG contents of nymphs were also analyzed, with 4-oxo-(E)-2-hexenal, 4-oxo-(E)-2-octenal, tridecane, and tetradecanal being major components. Male bugs but not females possess sternal setae, and 6,10,13-trimethyltetradecyl isovalerate was detected from extracts of the sternal setae of males. The possible biological significance of dimorphism in the contents of the glands in adults is discussed.     

Fatty acid and product selectivities of potato tuber lipid acyl hydrolase in esterification reactions with glycerol in organic media

Fatty acid [FA; butanoic (C₄); octanoic (C₈); tetradecanoic (C₁₄); and cis-9,12-octadecadienoic (C_18:2) acids] reaction selectivity and the corresponding acyl profiles in differentially accumulating acylglycerol (AG) products (mono-, di-, and triacylglycerols; MAG, DAG, TAG, respectively) were evaluated for Celite™-immobilized potato tuber lipid acyl hydrolase (LAH)-mediated esterification reactions in isooctane at 35°C and water activity of 0.19. The ordinal pattern of FA selectivities was C₈>C₁₄>C_18:2>C₄, and the AG products accumulating were α-MAG>DAG>β-MAG>TAG. A dimensionless expression for fatty acid partitioning coefficient (FAPC) was contrived to represent the partitioning patterns of specific FA into specific AG pools on the basis of an equivalent extent of FA reaction. These FAPC values indicated that preferential partitioning of FA was as follows: C₄ was preferentially partitioned into TAG, DAG, and β-MAG; C₈ was preferentially partitioned into DAG; C₁₄ was preferentially partitioned into α,β-MAG; C_18:2 was preferentially partitioned into α,β-MAG and TAG. These findings infer that the tendency for LAH-mediated esterifications to accumulate MAG is based, in part, on a constraint in reactivity of α-MAG of ≥10 acyl carbon groups to serve as acceptors for further esterification events. The general approach taken in this study may assist in identifying the discrete steps in assembling structured glycerides where different biocatalysts exhibit the greatest degree or control of reaction selectivity.     

The effect of initiator‐to‐monomer ratio on the properties of the polybutadiene‐ol synthesized by free radical solution polymerization of 1,3‐butadiene

Polybutadiene‐ol was synthesized by solution radical polymerization of 1,3‐butadiene in the presence of hydrogen peroxide as initiator and 2‐propanol as solvent. The ratio of initiator to monomer molar concentration, [I₀]/[M₀], was varied while temperature, reaction time and the type and amount of solvent were kept constant. The effects on the M_n; M_w; M_v; PDI, OH‐number and functionality of the synthesized polyols were studied. By taking several samples during a polymerization batch and analyzing them, the time of reaction was chosen as 100 min, after which the PDI changed dramatically. M_n decreased exponentially with increasing [I₀]/[M₀] according to the relationship M_n = 565.55 ([I₀]/[M₀])^?0.7553. The decrease observed in M_w gradually levelled off with increasing [I₀]/[M₀] and molecular weight distribution broadened at larger values of [I₀]/[M₀]. The OH‐number increases with [I₀]/[M₀]. In addition to the number‐average molecular weight, functionality is dependent on the number of hydroxyl‐terminated chain radicals in the reaction medium. Copyright © 2003 Society of Chemical Industry     

Production of specifically structured lipids by enzymatic interesterification in a pilot enzyme bed reactor: process optimization by response surface methodology

Pilot production of specifically structured lipids by Lipozyme IM-catalyzed interesterification was carried out in a continuous enzyme bed reactor without the use of solvent. Medium-chain triacylglycerols and oleic acid were used as model substrates. Response-surface methodology was applied to optimize the reaction system with four process para-meters, these being volume flow rate, water content in the substrates, reaction temperature, and substrate ratio. The incorporation of acyl donors, product yields, and the content of diacylglycerols were measured as model responses. Enzyme activity was not identical for the sequential experiments in the same enzyme bed due to the deactivation of the Lipozyme IM. Therefore, the results were normalized based on enzyme deactivation models. Well-fitting quadratic models were obtained after normalizing the data for the incorporation of oleic acid and the production of mono-incorporated and di-incorporated structured lipids with multiple regression and backward elimination. The coefficient of determination (R²) for the incorporation was 0.93 and that for the diincorporated products was 0.94. The optimal conditions were flow rate, 2 ml/min; temperature, 65 °C; substrate ratio, 5.5; and water content, 0.1%. The production of diacylglycerols was not well correlated with any of the parameters, and the yield generally decreased with the experimental sequence. This was due to the stoichiometric water in the substrate mixture in the packed enzyme bed being complicated by the water binding and absorption of the immobilized lipase. The main effects of parameters were also examined, and conclusions in agreement with our previous results were made.     

Discussion of three models used for the investigation of insertion/extraction processes by the potential step chronoamperometry technique

Three models used in electrochemical literature to fit experimental data for insertion/extraction processes investigated by the potential step chronoamperometry (PSCA) technique are examined and compared in this article. The first model (M_I) gives a theoretical expression of Faradaic current transient taking reaction kinetics at the electrode surface, diffusion process in the host material and Ohmic drop effects into consideration. The ‘cell-impedance controlled diffusion’ constraint is used in the second model (M_II) together with the diffusion equations and boundary conditions. Finally, the third model (M_III) applies when the diffusion flux of injected/extracted species at the electrode surface is limited by interfacial charge transfer kinetics represented by the Butler-Volmer equation. The use of a finite-difference method is required to numerically solve models M_II and M_III. First, the theoretical predictions from models M_I, M_II and M_III are compared when a small potential step is applied on the electrode. It is stated that the theoretical expression of current transient derived from model M_I is the analytical solution of both models M_II and M_III under small-signal (linearization) conditions. Next, the three models are numerically compared under Langmuir isotherm conditions, assuming a constant diffusion coefficient of guest species in the host material. It is shown that the ‘cell-impedance controlled diffusion’ constraint used in model M_II does not work very well when a large potential step is applied on the electrode. Finally, an alternative formulation of the boundary condition at the host material|electrolyte interface (model M_III) is used to study the influence of Ohmic drop, together with the use of large potential steps.     

Phase evolution,crystal structure,and microwave dielectric properties of gillespite-type ceramics

A gillespite-structured MCuSi₄O₁₀ (M = Ba_1-xSr_x, Sr_1-xCa_x) ceramics with tetrahedral structure (P4/ncc) were prepared by solid-state reaction method. X-ray diffraction and thermogravimetry with differential scanning calorimetry (TG-DSC) were employed to study the phase synthesis process of BaCuSi₄O₁₀. Pure BaCuSi₄O₁₀ phase was obtained at 1075°C and decomposed into BaSiO₃, BaCuSi₂O₆, and SiO₂ when calcined at 1200°C. The relationships between the crystal structure and microwave dielectric properties of MCuSi₄O₁₀ ceramics were revealed based on the Rietveld refinement and P-V-L complex chemical bond theory. The dielectric constant (ε_r) decreased linearly with decreasing total bond susceptibility and ionic polarizability. Quality factor (Q × f) was closely dependent on bond strength and lattice energy. The temperature coefficient of resonant frequency (τ_f) was controlled by the stability of [CuO₄]⁶⁻ plane in MCuSi₄O₁₀. Optimum microwave dielectric properties were obtained for SrCuSi₄O₁₀ when sintered at 1100°C for 3 hours with a ε_r of 5.59, a Q × f value of 82 252 GHz, and a τ_f of −41.34 ppm/°C. Thus, SrCuSi₄O₁₀ is a good candidate for millimeter-wave devices.     

Correlation between structural characteristics and microwave dielectric properties of walstromite BaCa2M3O9 (M = Si,Ge) ceramics

Novel BaCa₂M₃O₉ (M = Si, Ge) microwave dielectric ceramics were prepared via solid-state reaction with sintering at 1125°C–1275°C for 5 h. Single-phase BaCa₂M₃O₉ (M = Si, Ge) ceramics were obtained according to stoichiometry. The single-phase BaCa₂Ge₃O₉ ceramic was confirmed through Rietveld refinement and high-resolution transmission electron microscopy/selected area electron diffraction and synthesized for the first time. The BaCa₂M₃O₉ (M = Si, Ge) exhibited a triclinic structure with a P$\overline{1}$ space group and good microwave dielectric properties. The ε_r, Q × f, and τ_f values of BaCa₂M₃O₉ (M = Si, Ge) ceramics are mostly dominated by the relative density, ionic polarizability, relative covalence, and bond energy of M–O bond, respectively. A high Q × f value (61 800 GHz at 16.3 GHz) was obtained in BaCa₂Ge₃O₉ ceramic due to its high r_c (Ge–O) and low intrinsic dielectric loss. The BaCa₂Si₃O₉ ceramic exhibited small |τ_f| value (‒36.4 ppm/°C) due to its large E_Si-O. Excellent microwave dielectric properties (ε_r = 8.31, Q × f = 61 800 GHz, and τ_f = ‒58.7 ppm/°C) were obtained for the BaCa₂Ge₃O₉ ceramic.     

Cationic copolymerization of 1 ,3-pentadiene-with isoprene

The cationic copolymerization of 1,3-pentadiene (PD) with isoprene (IP) initiated by AICl₃, was carried out in toluene. The microstructure of the copolymer chain was characterized by IR and ¹H NMR. IP is incorporated in the copolymer chain mainly in cyclic segments. The PD–IP copolymer has a much higher cyclic content than the PD homopolymer, which shows that the cyclization reaction during PD polymerization is enhanced by the addition of IP. In addition, the reactivity ratios for IP(M₁) and PD(M₂) determined by the Kelen–Tudos method from low-conversion data are r₁ = 1.22 and r₂ = 1.09.     

Elucidation of acyl migration during lipase-catalyzed production of structured phospholipids

Elucidation of acyl migration was carried out in the Lipozyme RM IM (Rhizomucor miehei)-catalyzed transesterification between soybean phosphatidylcholine (PC) and caprylic acid in solvent-free media. A five-factor response surface design was used to evaluate the influence of five major factors and their relationships. The five factors—enzyme dosage, reaction temperature, water addition, reaction time, and substrate ratio—were varied on three levels together with two star points. Enzyme dosage, reaction temperature, and reaction time showed increased effect on the acyl migration into the sn-2 position of PC, whereas increased water addition and substrate ratio had no significant effect in the ranges tested. The best-fitting quadratic response surface model was determined by regression and backward elimination. The coefficient of determination (R ²) was 0.84, which indicates that the fitted quadratic model has acceptable qualities in expressing acyl migration for the enzymatic transesterification. Correlation was observed between acyl donor in the sn-2 position of PC and incorporation of acyl donor into the intermediate lysophosphatidylcholine. Furthermore, acyl migration into the sn-2 position of PC was confirmed by TLC-FID, as PC with caprylic acid was observed on both positions. Under certain conditions, up to 18% incorporation could be observed in the sn-2 position during the lipase-catalyzed transesterification.     

Petrographic aspects of the hot strength of coke

The strength CSR of metallurgical coke after high-temperature reaction with CO₂ is determined by the depth of reaction and depends on the petrographic composition of the initial coal, the degree of metamorphic development, and the content of catalytically active ash components. Qualitative aspects of coke’s hot strength are reflected in the mathematical model, whose parameters include the vitrinite content Vt in the batch, the inertinite content I, the reflective index R _o,r of vitrinite, and the basicity index of the ash.     

Controllable τf value of barium silicate microwave dielectric ceramics with different Ba/Si ratios

Ba_1+1/M[Si₂O_5+1/M] low‐permittivity microwave dielectric ceramics are prepared using the conventional solid‐state method. Pure phases are obtained in barium silicates with M = 1, 3, 4, 5, and ∞, except for M = 7, in which two phases, Ba₅Si₈O₂₁ and BaSi₂O₅, are observed. As the complexity of the crystal structure described by the Shannon information per reduced unit cell increases, the τ_f value tends to change from a negative to a positive value, except for M = 5, which has the highest complexity. A single Ba₅Si₈O₂₁ phase with ε_r anomaly peak at ?180°C exhibits a rare positive τ_f value (+25 ppm/°C), which is a novel temperature compensator.     

Enhanced ferroelectric and ferromagnetic properties of BiFeO3-PbTiO3 multiferroic solid solutions with Ba substitutions

Dense 0.6(Bi_0.9La_0.1)(Ga_0.05Fe_0.95)O₃-0.4(Pb_1-xBa_x)TiO₃ (BLGF-PBT, x = 0, 0.1, 0.2, 0.3, and 0.4) ceramics with different Ba contents were prepared by the solid-state reaction method, and effects of Ba contents on the structure and multiferroic properties were investigated. X-ray diffraction results indicate that the Ba-modified BLGF-PBT ceramics exhibit single perovskite structure without detectable secondary phases, and a transition from tetragonal phase to rhombohedral one takes place with the increase of Ba content. The piezoelectric constant d₃₃, remanent polarization P_r, and remanent magnetization M_r are improved by the Ba substitution simultaneously. Values of P_r, M_r, and d₃₃ of BLGF-PBT ceramics for the composition of x = 0.3 with the coexistence of tetragonal and rhombohedral phases are 20 μC/cm², 0.05 emu/g, and 256 pC/N, respectively, much higher than those without Ba modification. The significantly improved d₃₃ and M_r indicate that BLGF-PBT ceramics with Ba modification provide alternative materials for multifunctional devices.