Triglyceride Crystals Research Articles

Foams of vegetable oils containing long-chain triglycerides

HypothesisCan vegetable oils containing long-chain triglycerides be aerated to yield stable oil foams? This is based on the idea that cooling of vegetable oil results in the formation of crystals of certain triglyceride chain lengths and composition dispersed in liquid oil of other chain lengths and composition. Do such oleogels allow the formation of oil foams stabilised by adsorbed crystals? ExperimentsUsing two vegetable oils, the temperatures for crystal formation are determined. Crystal dispersions were characterised using rheology and optical microscopy. Oleogels were aerated using a double beater and the effects of temperature and aeration time were investigated. The stability and microstructure of the oil foams were studied visually and using microscopy. A stable oil foam was progressively destabilised on heating. FindingsUpon cooling/warming vegetable oils, crystals of high melting triglyceride form in a low melting liquid oil - an oleogel. Such oleogels can be whipped to fabricate oil foams stabilised by fat crystals. Optimum foaming yields an over-run of ~ 40% for peanut oil and ~ 110% for olive oil. Oil foams which do not exhibit drainage, coarsening or coalescence result. We show that high melting triglyceride crystals possess a higher fraction of saturated fatty acids than the original oil. Ultra-stable oil foams can be rendered unstable by heating upon approaching the melting point of the crystals.

Revealing the Nanostructure of Glyceryl Tristearate Crystals by Atomic Force Microscopy

Habit and morphology of triglyceride crystals are critical factors in the formulation of lipid-based colloidal systems such as pharmaceutical formulations and dairy products. Until now, triglycerid...

Simplifying Hansen Solubility Parameters for Complex Edible Fats and Oils

Hansen solubility parameters (HSPs), often used to predict the miscibility between two compounds, are an alternative tool in evaluating the ability of the solvent to interact via dispersion, dipole-dipole, and hydrogen bonding interactions. The aim of this paper is to find a simple way to calculate HSPs for complex mixtures of triglycerides (TAGs). HSPs were calculated using two approaches: the first assumes that the contributions to the dispersion, dipole-dipole, and hydrogen bonding interactions may be subdivided into larger functional moieties (i.e., fatty acids and fatty acid methyl esters) that are additive, while the second approach assumes that vegetable oils are comprised of mixtures of simple TAGs in the same mass fractions as the fatty acids. The HSPs obtained using the two approaches are compared to reference values determined using the “Hansen Solubility Parameters in Practice” software (HSPiP) considering the complex TAG profile for each vegetable oil.HSPs for vegetable oils, obtained with the HSPiP software, did not correspond well to the HSPs obtained from the group contribution approach, when using fatty acids, fatty acids + glycerol or fatty acid methyl esters. In contrast, the HSPs calculated for vegetable oils, assuming that all TAGs are simple and in the same mass fractions as the fatty acids, provide similar values to the HSPs obtained from the HSPiP software. Therefore, it is possible to calculate the HSPs for complex oils by simply knowing the fatty acid composition. Knowledge of HSPs may be used to rationalize the ability of certain low molecular weight molecules to develop organogels in vegetable oils as well as the crystallization of triglycerides.

The Effect of monoglycerides on the crystallisation of triglyceride

Abstract There has been increased interest recently in how different lipids interact with each other in solid phases and in the properties and consequences of the inter-lipid associations. The crystallisation behaviour of the triglycerides is noticeably influenced by the presence of monoglycerides. The main aim of this work was to extend studies of the influences of saturated and unsaturated monoglycerides on the crystallization of triglycerides. We aim to gain more insight into the effect of monoglycerides on miglyol oil, palm oil and olive oil crystallization. Optical microscopy, differential scanning calorimetry (DSC), small X-ray scattering (SAXS) and wide X-ray scattering (WAXS) were used in this study. Our results suggest that the presence of saturated monoglyceride affects the oil crystallization behaviour. Conversely, triglycerides with unsaturated fatty acid chains show little impact. The results provide evidence that saturated and unsaturated monglycerides are incorporated into the α- phase of palm oil.

Structure and functionality of edible fats

Fat-structured food materials are an important component of our diet. The role that fat plays in material functionality, flavor perception, texture and health characteristics is due in large part to its physical properties. An understanding of these physical properties is relevant from scientific, technological and medical perspectives. The physical properties of fat materials, are, in turn, governed by a complex confluence of the various structural levels in a fat material beginning with triglyceride molecules. The formation of nanoscale structural elements by these molecules is the first step in the formation of a fat material as we know it. This review shows how these microstructural elements can be imaged and characterized. It is also shown that the formation of these nanocrystals is affected by the attendant crystallization parameters. Through simulation and a discussion of van der Waals forces, it is shown that these nanoscale elements assemble into colloidal aggregates with fractal character. The influence of microstructure on the mechanical properties of a fat material is explained using a variety of mechanical models. Lastly, this review examines methods by which the properties and characteristics of the various structural levels can be engineered. Shear has been shown to affect the polymorphism and phase transition kinetics of triglyceride crystals. As well, shear has been shown to modify the aggregation of nanocrystals, with consequences for the porosity and diffusivity of oil through the fat crystal network.

W/O/W Emulsions Stabilized by Fat Crystals - Their Formulation, Stability and Ability to Retain Salt

The potential of fat-crystal stabilised W1/O emulsions containing salt to be incorporated into a W1/O/W2 double emulsion was studied. 30% W1/O emulsions stabilised by monoglyceride and triglyceride crystals, and containing 1.6% KCl in the W1 phase, have been mixed with equal amounts of oil and incorporated into double emulsions (W1/O/W2), where the W2 phase contained different levels of different types of emulsifiers (e.g. Na-caseinate). The resulting double structures were monitored over the course of 8 weeks. It was found that double emulsions remain relatively stable during this time depending on the species used to stabilise the external o/w2 interface.

Fat-crystal stabilised w/o emulsions for controlled salt release

The potential of fat-crystal stabilised w/o emulsions to control the release of salt contained within their aqueous phase has been investigated. A mixture of mono- and triglyceride crystals was used to obtain Pickering-stabilised 60:40 w/o emulsions. Salt release was monitored by placing small amounts of these emulsions into a bulk aqueous phase (this was either pure water or glucose aqueous solutions in order to vary osmotic pressure gradients) and measuring changes in conductivity over time. Less than 5% of total salt was released after 1 month in emulsions containing a mixture of mono- and triglycerides. Emulsions containing only monoglycerides released more than 40% salt in this period. SEM pictures showed that crystals have sintered at the interface to give total surface coverage with no or very few defects. Stability measurements at varying temperatures and Differential Scanning Calorimetry (DSC) indicate that any release is the result of partial melting of the crystals. Finally, varying the osmotic pressure gradient has no impact on salt release.

Effects of high pressure on anhydrous milk fat crystallization in emulsion

Anhydrous milk fat crystallization was compared either in bulk phase or in oil in water emulsion by studying melting curves obtained by calorimetry measurements. Emulsions were submitted to a high pressure (HP) treatment (200 MPa/10 min). An aging period of 72 h was required to obtain the highest amount of crystallized fat at 4 °C. Emulsification promoted the crystallization of low melting point (LMP) triglycerides. The effect of HP on anhydrous milk fat crystallization depended on the aging time. For short aging periods (30 min and 1 h), HP treatment favored the crystallization of LMP triglycerides, thus amplifying the effect of emulsification compared with the crystallization in bulk phase. However, for a long aging time, i.e. 48 h, the amounts of crystallized matter in emulsion with or without HP treatment were comparable. This result was interpreted in terms of a different polymorphic form crystallizing under HP.

The effect of ultrasonication on crystallization of triglycerides

The effect of ultrasonication on crystallization of triglycerides

Shear stability of sodium caseinate emulsions containing monoglyceride and triglyceride crystals

Shear destabilization of sodium caseinate oil-in-water emulsions has been investigated under carefully controlled conditions. Protein stabilized emulsions with tristearin (TS) crystals in the groundnut oil phase were cooled and destabilized under strictly controlled shearing conditions using a Bohlin CVO rheometer. Glycerol monooleate (GMO) was added as emulsifier in order to promote shear sensitivity in the emulsions. Emulsion systems with monoglyceride contents or triglyceride crystal concentrations, which exceeded certain well-defined limits, could be readily destabilized under shear. Shear-induced destabilization occurred very suddenly at a certain critical shear stress. The critical destabilizing stress was found to decrease with increasing levels of GMO, but shear-sensitive emulsions containing up to 3.25 wt.% GMO in the oil phase were found to be stable to quiescent storage over a time-scale of weeks. The shear sensitivity of emulsions was also found to be dependent on the concentration of triglyceride crystals within the droplets. The enhanced shear-sensitivity of crystal-containing emulsions with added GMO can be interpreted partly to a displacement of protein from the interface and partly to a template effect, with triglyceride crystals being encouraged by the emulsifier to grow beyond the droplet surface.

The effects of phospholipids on crystallisation and crystal habit in triglycerides

Many food products contain a network of fat crystals. The sizes and shapes of these triglyceride crystals are extremely important in producing the good physical properties and texture for a high-quality final product. Control of crystal habit can affect a fat's structure and hence the resultant behaviour. In this work the effects of phospholipids on the crystal habit of triglyceride crystals have been investigated. Optical and scanning electron microscopy, DSC, and X-ray diffraction have been used. The effects of certain phospholipids on the crystallisation of fats have been shown, and large changes to crystal habit have been demonstrated. These changes are caused by the interactions of the phospholipid molecules with the crystallising triglyceride molecules. Interference with the crystallising molecules causes changes to the shape and size (habit) of the resultant fat crystals. Effects on nucleation and crystal growth are demonstrated. These dramatic changes to the crystal habit can have a significant effect on the properties of the resultant fat system. For example the process of fat fractionation could be significantly enhanced. Alternatively, the network structure of fatty products could be controlled or altered opening up the possibility of the development of new and improved products.

Phase transition of triglycerides during semi-hard cheese ripening

Sixteen semi-hard cheeses varying by their protein (20.2–24.1%), fat (23.7–31.1%) and dry matter (50.2–57.9%) contents were manufactured and ripened in controlled conditions. Fluorescence (vitamin A) and mid-infrared (2780–3000 cm−1 region) spectra were collected on the 16 different cheeses at 1, 21, 51 and 81 days of ripening. The data tables containing the mid-infrared and fluorescence spectra of the different cheeses were analyzed by principal component analysis and canonical correlation analysis methods. The obtained similarity maps showed that it was possible to discriminate the cheeses at the four different ripening times from the infrared and fluorescence spectra. In addition, the interest to combine the two spectroscopies was demonstrated since a better discrimination of the four stages was obtained using canonical correlation analysis. The examination of the spectral patterns associated with the principal components and the canonical variates showed that the structure of triglycerides acyl chains in fat globules was modified during cheeses ripening. The shift of the methylene bands in the infrared region and the changes of the shape of vitamin A fluorescence spectra agree with partial crystallization of triglycerides from 21 to 81 days of storage.

Polymorphism of milk fat studied by differential scanning calorimetry and real‐time X‐ray powder diffraction

AbstractThe crystallization behavior of milk fat was investigated by varying the cooling rate and by isothermal solidification at various temperatures while monitoring the formation of crystals by differential scanning calorimetry (DSC) and X‐ray powder diffraction (XRD). Three different polymorphic crystal forms were observed in milk fat: γ, α, and β′. The β‐form, occasionally observed in previous studies, was not found. The kind of polymorph formed during crystallization of milk fat from its melted state was dependent on the cooling rate and the final temperature. Moreover, transitions between the different polymorphic forms were shown to occur upon storing or heating the milk fat. The characteristic DSC heating curve of milk fat is interpreted on the basis of the XRD measurements, and appears to be a combined effect of selective crystallization of triglycerides and polymorphism.

Biological reference materials for the verification of sample preparation and measurement by low resolution NMR

The measurement of the solid fat index is of great importance to determine the technological quality of fats used in the agro-food industry. Pulse or continuous wave low resolution nuclear magnetic resonance may be used to perform the measurements fairly rapidly, and very simply. IUPAC has published several methods for sample preparation, with precise indications as to the procedure to follow. The reproducibility is however often inadequate, whereas the repeatability is very good. This may simply be due to an incorrect calibration of the apparatus, introducing a constant bias in the results of a particular laboratory. It may also be due to slight differences in the tempering the samples undergo. Because of their polymorphism, the crystallization of triglycerides is in fact greatly influenced by this thermal pretreatment. A need for reference samples was therefore felt, in part to verify the instrument adjustment but, more important, in order to control the whole sequence of actions performed before the measurement itself. The French Institut National Agronomique and the Institut des Corps Gras carried out a ring test involving 9 experienced French laboratories to determine standard SFI curves, using several thermal pretreatment procedures. Reference samples and the corresponding SFI values for 4 of the most commonly used fats are now available to quality control laboratories. This study is now to be extended, through the BCR, to the rest of Europe.

NMR relaxation studies to explore the role of emulsifier in tristearin polymorphic transformation

AbstractProton magnetic resonance measurements were performed onα andβ polymorphs of tristearin crystals. T1 relaxation time was measured with the Bruker PC Minispec at 20 MHz and 37° on the pure triglyceride crystals and therefore on tristearin crystallized in the presence of different solid surfactants. A significant negative correlation for T1 values and different compositions ofα andβ polymorphs in a mechanical mixture was found. The shortening of T1 relaxation time of theβ form was found to be different for the various types of the added surfactants while they have no effect on the relaxation time of theα form. A model was proposed according to which the presence of additives, such as surfactants, generates vacancies within the crystal lattice of triglyceride and enhances the freedom of rotation of the fat molecule about the terminal carbon‐carbon bond.

On the Structure of Triglycerides in the Liquid State and Fat Crystallization

AbstractBased on X‐ray diffraction and Raman spectroscopy studies of trimyristin, a structure of triglycerides in the liquid state is proposed. The order in the melt is quite constant, even if the temperature is raised as much as 40° C above the melting point. The homologue series of simple triglycerides, together with 1‐monomyristin and 1,2‐dimyristin have been studied with the same techniques. The order of different segment in the hydrocarbon chains varies when different chain length, i. e. a long chain is more disordered at the methyl endgroup plane compared with a short one. The crystallization of triglycerides is also discussed based on diffraction pattern versus temperature studies. Due to different cooling rates and different chain length a melt can crystallize not only in α but directly in β' or β.

Polymorphism of rapeseed oil with a low content of erucic acid and possibilities to stabilise the β′‐crystal form in fats

AbstractThe polymorphism of hydrogenated rapeseed oil with a low content of erucic acid was investigated by X‐ray diffraction. The triglyceride composition in the hydrogenated oil was determined by a combination of gas chromatography and high‐performance liquid chromatography. A characteristic feature of this oil is its rapid transition to the β‐form. Possibilities of influencing the β′→ β transition are discussed. The addition of diglycerides appears to provide a means for delaying the β′rarr; β transition. Thus, 1,2‐diglycerides show a strong stabilising effect on the β′ triglyceride crystals form, which is considered to be of technical interest.

Physicochemical Analyses of the Bovine Milk Fat Globule Membrane. II. Electron Microscopy

Samples of cream and milk fat globule membrane fractions from bovine milk were examined by electron microscopy with thin sectioning and freeze-etching. Certain components of the fat globule membrane aggregated inside the continuous envelope surrounding the globule. At the site of aggregates the trilaminar electron microscopic image is similar to that of a normal cytoplasmic membrane. However, most of the membrane, contiguous with fat of the globule, exhibited no trilaminar structure. This difference in the structure of the membrane at various points is probably due to a re-arrangement of its components. Freeze-etching provided further evidence of the orientation of a layer of triglyceride crystals adjacent and parallel to the membrane in fat globules.

Micro heat-flow calorimeter for investigating the melting and phase transition behaviour of triglyceride crystals

A micro heat-flow calorimeter has been developed to investigate the melting and phase transition behaviour of triglyceride mixed crystals. Samples of about 1 mg can be investigated even if heating rates as low as 0·04-0·15 deg C min−1 are used. Calibration experiments with palmitic acid show an accuracy to 1·4% in the determination of the heat of fusion. Provided that the maximum temperature difference is below 0·1 degC, the accuracy with which the `clearpoint', i.e. the temperature at which the melting process is finished and the sample becomes optically clear, can be determined is 0·3°C. Possible effects of amount of sample, heating rate and differences in heat flow on the heat effects and clear points are also described.

Crystallization of triglycerides at low supercooling

Recrystallization was studied for a number of dispersions consisting of crystals of saturated triglycerides in oil by measuring the specific surface area of the crystals as a function of time. Since the crystals had a stable modification, the main driving force of the recrystallization process was due to the smallness of the crystals. The specific surface area was measured by means of permeametry. In most cases it was found that it decreased by about 30% over a period of, e.g., 10 days, depending on composition and temperature of storage. The results were compared with recrystallization theories for diffusion-controlled processes. It is concluded that the experimental results cannot be explained in this way, but that the rate-determining step is the incorporation of the molecules into the growing crystal.