Monoacid Triglycerides Research Articles

Unraveling the hierarchical structure of saturated monoacid triglycerides during crystallization: A comprehensive time-resolved X-ray Scattering study

Time-resolved studies are crucial for capturing the dynamic evolution of triglyceride structures during crystallization, providing insights into the self-assembly of diverse triglyceride structures across various length scales. While previous research...

Triglyceride mixtures: Cold-bursting and double emulsion formation

It was shown recently that a solid-to-solid phase transitions (α-to-β, gel-to-crystal), typical for many lipid substances, can lead to formation of nanoporous network inside lipid micro-particles dispersed in aqueous surfactant solutions (Cholakova et al. ACS Nano2020, 14, 8594). These nanopores are spontaneously infused by the aqueous phase when appropriate combination of water-soluble and oil-soluble surfactants is applied. As a result, the initial lipid micro-particles can spontaneously burst into much smaller nanoparticles, just by cooling and heating of the initial dispersion. Under certain conditions, the infused aqueous phase is entrapped in the moment of lipid particle melting and double emulsion of type water-in-oil-in-water (W/O/W) is formed. The current study aims to clarify how the composition of the lipid micro-drops and surfactants affect the observed phenomena. Selected mixtures of monoacid triglycerides are studied systematically. The results show that the bursting efficiency usually decreases when the complexity of the lipid mixture increases, due to the expanded temperature interval for lipid melting. Nevertheless, complete particle bursting and lipid nanoparticles with diameters down to 20 nm are formed even for the most complex lipid compositions under appropriate conditions. The key mechanisms leading to efficient fragmentation and double emulsion formation are clarified, and the main governing factors are explored. On this basis, we reveal that the system behavior can be switched between complete particle bursting and W/O/W emulsion formation by: (1) Change in the cooling and heating rates without any changes in the chemical composition, (2) Change in the concentration of oil-soluble surfactant, and/or (3) Change in the phase in which the oil-soluble surfactant is introduced initially. Thus, we have formulated guiding rules to control the formation of lipid nanoparticles and W/O/W emulsions with triglyceride mixtures promising multiple potential applications.

On the Relation of Entropy and Enthalpy of Fusion in Triglycerides

AbstractThis contribution presents an extensive literature survey of the calorimetric properties, namely enthalpy and entropy of fusion, of alkyl‐based molecules. Building on the well‐known linear correlation of the named properties to the carbon number in n‐alkanes, saturated fatty acids (FA), and saturated monoacid triglycerides (TAGs), the calorimetric properties of TAGs are reviewed. No straightforward correlation using a single ordering parameter, i.e., carbon number, can be derived for TAGs. This is not surprising due to the complexity of this particular class of molecules differing in alkyl‐chain distribution over the glycerol backbone and chain saturation. A linear correlation of enthalpy and entropy of fusion is evident for molecule classes for which both properties correlate linearly with the carbon number, e.g., n‐alkanes. Despite the complexity of TAGs, it is possible to establish a linear correlation between enthalpy and entropy of fusion even though no underlying single ordering parameter can be identified. A linear fit reveals discrepancies between saturated and unsaturated molecules but independence of polymorphic forms and chain length differences in mixed‐acid TAGs. Moreover, the slopes of the linear fits for data on n‐alkanes, saturated FA, and saturated mono‐acid TAGs are found to be in the vicinity of the melting temperature of polyethylene.

Revisiting a model to predict pure triglyceride thermodynamic properties: parameter optimization and performance

AbstractIn 1990, a well‐known model to predict pure component properties of triglycerides was presented by Wesdorp in “Liquid‐multiple solid phase equilibria in fats: theory and experiments” and has been shown to perform well despite making thermodynamically inconsistent predictions for certain test cases. In this study, the underlying parameter set is improved to deliver more physically consistent predictions, i.e., increasing melting point and enthalpy of fusion with increasing stability of the polymorphs, without deterioration of the primary model quality to describe the available experimental data. Interestingly, when a curated dataset containing only thermodynamically consistent data is compared to a broader dataset, it appears that the model's efficacy is highly dependent on the quantity of data, specifically the number of unsaturated triglycerides data. Quality and thermodynamic consistency of model predictions and the condition of a reliable description of monoacid triglycerides as a subset is discussed, addressing a potential interdependence.

Influence of structural variations on drug release from lipid/polyethylene glycol matrices

Different combinations of monoacid triglycerides and polyethylene glycol powders of different molecular weights were successfully extruded below their melting temperatures as a basis for oral dosage forms. The incorporated polyethylene glycols exhibiting different mean molecular weights were compared with respect to their effect on the dissolution rate for a model drug, and a mean molecular weight of 10,000 resulted in the most advantageous characteristics (fastest dissolution). Triglycerides with different fatty acid chain lengths provided additional options for the extrusion temperature which is beneficial for temperature sensitive active pharmaceutical ingredients. To obtain stable extrudates with desirable and reproducible dissolution characteristics a good understanding of the underlying processes during processing and storage is mandatory.

Influence of the composition of glycerides on the solid-state behaviour and the dissolution profiles of solid lipid extrudates

A monoacid triglyceride and a partial glyceride were extruded below their melting ranges alone and together in different mixture ratios to investigate the influence of the chemical composition of the lipid matrix on the solid-state properties and dissolution characteristics. The partial glyceride exhibits a faster release of the drug compared to the triglyceride due to its surfactant properties. The lipid mixtures show rather complex solid-state behaviour and hence unexpected dissolution characteristics. Adding 10% (w/w) partial glyceride to a triglyceride matrix led to increased incidence of the unstable α-form of the triglyceride leading to recrystallization of the stable β-form over time which causes fractal structures on the extrudate surface which decrease the dissolution rate. Adding 50% (w/w) partial glyceride to the triglyceride matrix also results in tristearin α-formation subsequently followed by recrystallization to the β-form. But as 50% of the matrix consists of the partial glyceride the dissolution rate was faster than the rate obtained by pure triglyceride or the 9 + 1 (w/w) mixture of triglyceride and partial glyceride. The results of this study help in understanding the complex solid-state behaviour of solid lipid extrudates with different composition and to manufacture suitable lipid-based oral dosage forms.

Understanding the solid-state behaviour of triglyceride solid lipid extrudates and its influence on dissolution

Three monoacid triglycerides differing in their fatty acid chain lengths were extruded below their melting temperatures. Physical characterization was conducted on the powders as well as the extrudates with a combination of DSC, XRPD and vibrational spectroscopy to get a deeper insight into the complex solid-state behaviour of lipids and solid lipid extrudates during processing and storage. The combination of extrusion temperature and friction was a key factor for the lipid polymorphic behaviour after extrusion. Polymorphic transitions had a strong influence on the dissolution behaviour due to crystallization of the stable β-form from the unstable α-form on the surface of the extrudate. These correlations help to understand the solid-state behaviour of lipids and to avoid process conditions which lead to unstable dosage forms. Tailor-made dissolution profiles for a model drug could be achieved using triglycerides of different fatty acid chain lengths as the dissolution rate is chain-length dependent. The solid-state form of the drug was unchanged after storage in accelerated conditions over 10 months. These studies demonstrate that although triglycerides are a promising basis for oral dosage forms, a good understanding and monitoring of the solid-state behaviour is mandatory to obtain reliable and reproducible dosage forms.

Investigation of dynamic processes in lipid-based nanoparticulate drug carrier systems with small and wide angle X-ray diffraction

Colloidal lipid-based particles offer interesting possibilities in drug delivery, in particular for the administration of poorly water soluble drugs, e.g. into the bloodstream. Such particles can be prepared by high-pressure homogenisation of the respective lipids in an aqueous phase with adequate stabilizers. Since thematerial properties of thematrix lipids in the colloidal state may differ significantly from those of the raw materials adequate characterization of the prepared particles is a very important part of the development work on such systems to ensure the formation of the desired particle properties. X-ray diffraction (XRD) in combinationwith complementarymethods such as, e.g., differential scanning calorimetry (DSC) and electron microscopy, has proven to be a very effective tool for this purpose. Examples will be shown from three different types of lipid drug carrier systems: solid lipid nanoparticles, supercooled smectic nanoparticles and nanoparticles of cubic phase. When solid lipid nanoparticles are prepared via triglyceride melts, a pronounced supercooling effect is often observed which may impair the formation of the desired solid state. Certain emulsifiers can increase the crystallization temperature and thus improve the solidification behaviour of the nanoparticles but their use is often accompanied by additional thermal events prior to triglyceride crystallization. According to XRD these additional thermal events correspond to the crystallization of a surfactant layer at the particle surface which may also include some of the triglyceride in dependence on the composition. The emulsifiers may also modify the polymorphic transitions of the triglycerides after crystallization. Generally, polymorphic transitions are faster in the nanoparticles than in the bulk and sometimes a more stable modification than observed for the bulk material is reached. Also within the colloidal size range different transition rates can be observed with smaller particles transforming faster than larger ones. For small nanoparticles from saturated monoacid triglycerides, a structured melting event is observed in DSC that is not caused by polymorphism but has to be attributed to a particle size effect according to XRD. An influence of the type of emulsifier is also observed for the crystallization behaviour of nanoparticles based on supercooled smectic phase cholesterol esters. The typical bimodal crystallization process observed in phospholipid-containing cholesteryl myristate dispersions is not due to polymorphism as confirmed by XRD but probably reflects the crystallization properties of particles with different shapes. The temperature dependence of different preparation processes for cubic phase nanoparticles based on aqueous monoolein/poloxamer systems seems to be related to the phase behaviour as indicated by results from small angle XRD. m37.o05

Conformational influences of the polymorphic forms on the C [dbnd]O and C–H stretching modes of five saturated monoacid triglycerides studied by Raman spectroscopy at various temperatures

A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at various temperatures in two separate spectral ranges: 1780–1700 and 3100–2650 cm −1. The samples are studied in polycrystalline phase at room temperature, in isotropic liquid phase, and in polycrystalline phase after cooling from the isotropic liquid phase. The C O stretching mode of these triglycerides changes significantly according to the temperature: we observe three components, or an unresolved doublet, or a resolved doublet. The I(2845)/ I(2880) ratios (in the C–H stretching spectral region) of the different saturated monoacid triglycerides vary also according to the temperature. The study of these two indicators (the C O stretching mode and the I(2845)/ I(2880) ratio) has permitted us to determine the polymorphic forms of the studied triglycerides.

Raman spectroscopy investigation of various saturated monoacid triglycerides

A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at room temperature in the 3100–500 cm −1 spectral range. The splitting of the C O stretching mode leads to conclude on the existence of two or three geometries of C O in the “knot” group O C O. The C O stretching mode seems to be a good tool for distinguishing the polymorphic forms of the studied triglycerides. The assignments of the different C H stretching modes are performed in the 1500–500 cm −1 spectral range. The I(2845)/ I(2880) (in the C H stretching spectral region) and I(1445)/ I(1296) intensity ratios (between the maximal intensity I(1445) of the CH 2 scissoring mode and the maximal intensity I(1296) of the skeletal vibration of (CH 2) n in-phase twist) seem to depend on the type of polymorphic forms of these molecules.

Self-Assembly of Triglyceride Nanocrystals in Suspension

The interparticle interactions in aqueous monoacid triglyceride nanosuspensions prepared by melt homogenization are strongly influenced by the thickness distribution of the platelet-shaped particles. Small-angle X-ray scattering and transmission electron microscopy investigations on the native, undiluted tripalmitin dispersions stabilized with phospholipids and sodium glycocholate indicate that the dispersed nanocrystals can form aggregates of particles which are oriented in the same direction (stacked lamellae) with interparticle distances around 20 nm. The relative concentration of the particles in the stacks increases with the total triglyceride concentration in a dispersion. The stacked lamellae almost disappear after dilution with the aqueous phase or by increasing the temperature just below the onset of melting of the tripalmitin nanocrystals. This observation indicates that the energy gained by the formation of a stack is of the order of kBT. The tendency to form stacked lamellae is reduced for tri...

Investigations on the melting behaviour of triglyceride nanoparticles

Suspensions of triglyceride nanoparticles have been proposed as carrier systems for intravenous administration of poorly water soluble drugs. Such nanosuspensions can easily be produced by homogenization of the melted triglyceride in an aqueous phase. Using special emulsifier blends it is possible to obtain suspensions with an average size of the recrystallized particles below 100 nm (photon correlation spectroscopy z-average). As can be observed by transmission electron microscopy the particles are very thin platelets with thicknesses in the range of only a few molecular layers. Nanoparticles of saturated monoacid triglycerides (smaller than 200 nm) exhibit uncommon melting behaviour, which is expressed in their differential scanning calorimetry curve by multiple endothermal peaks over a temperature range of about 10 °C. This effect was attributed earlier to the particle thickness distribution in the suspension rather than to polymorphic transitions since all the material exists in the stable β modification. Here we present experimental investigations on the correlation between the melting behaviour of trilaurin nanosuspensions and the particle thickness distribution determined by analysis of difference X-ray diffraction patterns recorded at progressively higher temperatures in the melting range of the particles. Because of the weak X-ray scattering of the systems investigated synchrotron radiation was used besides conventional sources. The Fourier analysis of the difference diffraction patterns is described in detail and the advantages and difficulties in using this method are discussed. It was observed that the melting temperatures of the nanoparticles increase with increasing particle thicknesses. Simultaneously a decrease in the interplanar (001) spacing with increasing particle thickness was found.

Effect of Particle Size on Colloidal Solid Triglycerides

The size-dependent behavior of different crystalline, colloidal monoacid and complex triglycerides in aqueous dispersion is investigated, mainly by differential scanning calorimetry and X-ray diffraction. With decreasing particle size the melting range of the triglycerides broadens and shifts to lower temperatures. The melting of particles in small-size dispersions (e.g., with mean particle sizes around 100 nm) of even, saturated monoacid triglycerides such as tripalmitin and trimyristin is characterized by a sequence of discrete sharp transitions which are not due to polymorphism. This complex melting process is observed with different types of stabilizers. The sequence of melting events originates from the shape and layered structure of the triglyceride nanocrystals leading to successive discrete transitions corresponding to the melting of particle fractions with different thickness. In dispersions of complex triglycerides, the individual transitions are less sharp or even undetectable. The heat of fusion and the crystallization temperature of the nanoparticles decrease slightly with decreasing particle size whereas the rate of polymorphic transitions increases. Moreover, dispersions containing extremely small nanoparticles display an X-ray diffraction pattern indicating the presence of a crystal form that seems not to have been described previously for these triglycerides.

Characterization, quantitation and evolution of monoepoxy compounds formed in model systems of fatty acid methyl esters and monoacid triglycerides heated at high temperature

Monoepoxy compounds formed after heating methyl oleate and linoleate, triolein and trilinolein at 180°C for 5, 10 and 15 hours, were characterized and quantitated after derivatization to fatty acid methyl esters by using two base-catalyzed procedures. Structures were identified by GC-MS before and after hydrogenation. A complete recovery of the epoxy compounds was obtained by comparing results from methyl oleate and linoleate before and after transesterification, and good repeatability was also attained. Similar amounts of epoxides were found for methyl esters and triglycerides of the same degree of unsaturation, although formation was considerably greater for the less unsaturated substrates, methyl oleate and triolein, possibly due to the absence of remaining double bonds in the molecule which would involve a lower tendency to participate in further reactions. On other hand, independently of the degree of unsaturation of the model systems and of the period of heating, significantly higher amounts of trans isomers were formed. Finally from comparison between the amounts of epoxides and the level of polar fatty acids in samples, it was deduced that monoepoxy compounds were one of the major groups formed under the conditions used.

Characterization of membrane‐bound lipase from a thermophilic Rhizopus oryzae isolated from palm oil mill effluent

AbstractThe characteristics of the membrane‐bound lipase from a thermophilic Rhizopus oryzae were studied. The pH and temperature optima for lipase activity were at 7.0 and 37°C, respectively. The enzyme was stable and acidic conditions, retaining more than 80% of its initial activity at pH 4.0 after 30 min incubation. It was stable up to 50°C with 70% of initial activity retained after 3 h incubation. The enzyme is 1,3 specific and exhibits substrate preference. Monoacid triglyceride substrates were hydrolyzed better than methyl esters, polyoxysorbitan and sorbitan substrates.

Calf pregastric lipase catalyzed hydrolysis of short and medium chain-length monoacid triglycerides: Temperature, pH and lipid concentration effects

Calf pregastric lipase catalyzed hydrolysis of short and medium chain-length monoacid triglycerides: Temperature, pH and lipid concentration effects

Physicochemical characterization of lipid nanoparticles and evaluation of their drug loading capacity and sustained release potential

Drug carrier systems based on lipid nanosuspensions prepared by melt emulsification present a number of severe stability problems such as a high gelation tendency, considerable particle growth and drug expulsion. Destabilization of the emulsified lipidic carriers is related to recrystallization of the lipids. The choice of stabilizers for colloidal lipid suspensions is, therefore, restricted. Systematic surface modifications are thus limited. In addition, the drug payload of crystalline nanosuspension particles is generally low. Improved stability and loading capacities were found for amorphous lipid nanoparticles which present the characteristic signals of supercooled melts in high resolution 1H-NMR. The NMR data indicate that such liquid but viscous carriers can, however, not immobilize the incorporated drug molecules to the same extent as a solid matrix. Sustained release over days or weeks as in slowly biodegraded solid matrices thus seems difficult to achieve with a supercooled melt. Attempts to combine the advantages of the solid crystalline lipids and the amorphous nature of the supercooled melts by generating solid but amorphous lipid suspension particles with a satisfactory long-term stability by a variation of the lipid matrix material have hitherto not been successful. Even a satisfactory stabilization of the α-modification using complex lipid mixtures to improve the loading capacity or to slow down the drug expulsion process could not be achieved. The rates of the polymorphic transitions were much higher in the colloidal lipid dispersions than in the bulk for the hard fats under investigation. Despite the fact that the properties of the lipids are superimposed with colloidal properties, significant differences between monoacid triglycerides and complex lipids were, however, found.

Hydrolysis Characteristics of Bovine Milk Fat and Monoacid Triglycerides Mediated by Pregastric Lipase from Goats and Kids

Commercial extracts from oro-pharyngeal tissues of goats and kids have been used as the source of pregastric lipase and have been processed to yield partially purified samples of the primary pregastric lipase. The activity of these lipases against tributyrylglycerol has been determined over a range of pH and temperatures. Optimum pH conditions for pregastric lipase ranged from pH 5.6 to 6.5 for goats and from pH 5.5 to 6.2 for kids, respectively; the optimum temperature ranged from 43 to 60°C. Optima for kid lipase extended slightly below pH 5.5 and higher than 60°C; which were the limits of the test conditions. The enzymes were also used as catalysts for the hydrolysis of monoacid triglycerides (C4:0 to C12:0) at40°C and pH 6.5; activity was maximum against tributyrylglycerol (C4:0). Values for the Michaelis-Menten constant, increased as carbon chain length of the carboxylic moiety on the triglycerides increased, but values were identical for pregastric lipases of both goats and kids. Anhydrous milk fat was hydrolyzed by the commercial extracts of pregastric lipases of goats and kids, and the resulting profiles for free fatty acids were very similar to one another and to the corresponding profile for a commercial sample of Parmesan cheese. There appear to be no significant differences in activity between the enzyme preparations from goats and kids.

Quantitative analysis of triglycerides using atmospheric pressure chemical ionization-mass spectrometry.

Atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) was used for quantitative analysis of triglycerides (TG) separated by reverse-phase high-performance liquid chromatography. APCI-MS was used for analysis of mono-acid TG standards containing deuterated internal standard, of a synthetic mixture of heterogeneous TG, of randomized and normal soybean oils and of randomized and normal lard samples. Quantitation of the TG by four approaches based on APCI-MS were compared, and these were compared to quantitation obtained using liquid chromatography (LC) with flame-ionization detection (FID). The APCI-MS methods were based on (i) calibration curves from data for mono-acid TG standards, (ii) response factors obtained from a synthetic mixture of TG, (iii) response factors calculated from comparison of randomized samples to their statistically expected compositions, and (iv) response factors calculated from comparison of fatty acid (FA) compositions calculated from TG compositions to FA compositions obtained by calibrated gas chromatography (GC) with FID. Response factors derived from a synthetic mixture were not widely applicable to samples of disparate composition. The TG compositions obtained using APCI-MS data without application of response factors had average relative errors very similar to those obtained using LC-FID. Numerous TG species were identified using LC/APCI-MS which were undetected using LC-FID. Two quantitation methods, based on response factors calculated from randomized samples or on response factors calculated from FA compositions, both gave similar results for all samples. The TG compositions obtained using response factors calculated from FA compositions showed less average relative error than was obtained from LC-FID data, and were in good agreement with predicted compositions for the synthetic mixture and for randomized soybean oil and lard samples.

Lamb pregastric enzyme-catalysed hydrolysis of 4-nitrophenylalkanoates and monoacid triglycerides

Three lamb pregastric enzymes, isolated from the commercial extract from the tongue and epiglottal region of lamb, have been used to catalyze the hydrolysis of a series of 4-nitrophenylalkanoate esters (C2–C12) at 37°C, pH 7.2 and maximum activity was obtained against the decanoate ester in all cases. Burst kinetics were observed for activity of the principal lipase component against the decanoate ester. This enzyme was also used as a catalyst for the hydrolysis of monoacid triglycerides (C4:0 to C10:0) at 35°C, pH 6.5 and maximum activity was obtained against tributyrin (C4:0). A suggestion is made for orientation of ester substrates within the active site of the enzymes.