Fat Crystal Network Research Articles

Micro-viscosity of liquid oil confined in colloidal fat crystal networks.

Molecular rotors may be utilized as non-invasive, non-disruptive and highly sensitive alternatives to conventional measures of bulk viscosity when the oil is entrained in a colloidal fat crystal network. Oil viscosity changes based on the molecular confinement of the oil, which is dependent on its molecular volume. Changes in micro-viscosity were not dependent on the solids content, but instead were strongly dependent on the box-counting fractal dimension in high-space filling colloidal fat crystal networks (i.e., D > 1.89). A bulk oil viscosity is often an overestimation of the actual viscosity of the entrained oil and may not be appropriate when predicting diffusion in multi-phase materials.

Edible oil structures at low and intermediate concentrations. I. Modeling, computer simulation, and predictions for X ray scattering

Triacylglycerols (TAGs) are biologically important molecules which form the recently discovered highly anisotropic crystalline nanoplatelets (CNPs) and, ultimately, the large-scale fat crystal networks in edible oils. Identifying the hierarchies of these networks and how they spontaneously self-assemble is important to understanding their functionality and oil binding capacity. We have modelled CNPs and studied how they aggregate under the assumption that all CNPs are present before aggregation begins and that their solubility in the liquid oil is very low. We represented CNPs as rigid planar arrays of spheres with diameter ≈50 nm and defined the interaction between spheres in terms of a Hamaker coefficient, A, and a binding energy, VB. We studied three cases: weak binding, |VB|/kBT ≪ 1, physically realistic binding, VB = Vd(R, Δ), so that |VB|/kBT ≈ 1, and Strong binding with |VB|/kBT ≫ 1. We divided the concentration of CNPs, ϕ, with 0≤ϕ= 10−2 (solid fat content) ≤1, into two regions: Low and intermediate concentrations with 0<ϕ<0.25 and high concentrations with 0.25 < ϕ and considered only the first case. We employed Monte Carlo computer simulation to model CNP aggregation and analyzed them using static structure functions, S(q). We found that strong binding cases formed aggregates with fractal dimension, D, 1.7≤D≤1.8, in accord with diffusion limited cluster-cluster aggregation (DLCA) and weak binding formed aggregates with D=3, indicating a random distribution of CNPs. We found that models with physically realistic intermediate binding energies formed linear multilayer stacks of CNPs (TAGwoods) with fractal dimension D=1 for ϕ=0.06,0.13, and 0.22. TAGwood lengths were greater at lower ϕ than at higher ϕ, where some of the aggregates appeared as thick CNPs. We increased the spatial scale and modelled the TAGwoods as rigid linear arrays of spheres of diameter ≈500 nm, interacting via the attractive van der Waals interaction. We found that TAGwoods aggregated via DLCA into clusters with fractal dimension D=1.7−1.8. As the simulations were run further, TAGwoods relaxed their positions in order to maximize the attractive interaction making the process look like reaction limited cluster-cluster aggregation with the fractal dimension increasing to D=2.0−2.1. For higher concentrations of CNPs, many TAGwood clusters were formed and, because of their weak interactions, were distributed randomly with D=3.0. We summarize the hierarchy of structures and make predictions for X-ray scattering.

Small Deformation Rheology for Characterization of Anhydrous Milk Fat/Rapeseed Oil Samples

AbstractSamples of anhydrous milk fat and rapeseed oil were characterized by small amplitude oscillatory shear rheology using nine different instrumental geometrical combinations to monitor elastic modulus (G′) and relative deformation (strain) at fracture. First, G′ was continuously recorded during crystallization in a fluted cup at 5C. Second, crystallization of the blends occurred for 24 h, at 5C, in external containers. Samples were gently cut into disks or filled in the rheometer prior to analysis. Among the geometries tested, corrugated parallel plates with top and bottom temperature control are most suitable due to reproducibility and dependence on shear and strain. Similar levels for G′ were obtained for samples measured with parallel plate setup and identical samples crystallized in situ in the geometry. Samples measured with other geometries have G′ orders of magnitude lower than identical samples crystallized in situ. This emphasizes the importance of gentle sample pre handling, temperature control and preventing slip.Practical ApplicationsSmall deformation rheology is widely used to study and evaluate textural behavior of fat‐based systems. As different research groups use different geometries, a systematic evaluation of data gained using different geometrical combinations is needed. By conducting a methodic evaluation, this work provides an increased knowledge of how to characterize fat‐based systems using small deformation rheology and evaluates the relations between geometries. Because of the rigid nature of fat‐based systems, wall slip is likely to occur. Moreover, when characterizing such systems during storage and/or produced at industrial scale, in situ crystallization is not possible. In such cases, the sample must be loaded at the geometry prior to analysis. Such loading will affect the fat crystal network to some extent and consequently the data obtained. However, as the physical conditions differ between the geometries available, they affect both the fat crystal network and the tendency of wall slip to occur differently.

The Effect of Capacity, Rotational Speed and Storage on Crystallization and Rheological Properties of Puff Pastry Butter

AbstractIn the margarine and butter industry, sustainable and more efficient refrigerants, such as CO2, are introduced to industrial scraped surface heat exchangers, allowing an increased capacity compared to conventional use of NH3. The effect of such changes in capacity and a varied rotational speed was studied in relation to the structural behavior of puff pastry butter during 4 weeks of isothermal storage at 20 °C. The physical properties of the fat crystal network were studied in detail at several length scales by combining X‐ray diffraction with differential scanning calorimetry, confocal laser scanning microscopy, LR‐NMR and rheology. Our data shows that a high capacity combined with high rotational speed decreases the brittleness of puff pastry butter after 7 days of storage. This effect is, however, diminished after 28 days of storage. Likewise, changes in capacity and rotational speed are shown to induce no microstructural and polymorphic differences after 28 days of storage. However, the degree of work softening is related to the manufacturing conditions: a high capacity and a high rotational speed increase the ability of the puff pastry butter to resist structural breakdown during working. With this being the only observed difference; a wide operational window exists on an industrial level to produce puff pastry butter with similar structural behavior.

The Effective Factors on the Structure of Butter and Other Milk Fat-Based Products.

Butter and other milk fat-based products are valuable products for the dairy industry due to their unique taste, their textural characteristics, and nutritional value. However, an increased consumer demand for low-fat-based products increases the need for an increased essential understanding of the effective factors governing the structure of milk fat-based products. Today, 2 manufacturing techniques are available: the churning method and the emulsification method. The first is typically used for production of butter with a globular structure, which has become increasingly popular to obtain low-fat-based products, typically without presence of milk fat globules. The microstructure of milk fat-based products is strongly related to their structural rheology, hence applications. Structural behavior is not determined by one single parameter, but by the interactions between many. This complexity is reviewed here. Parameters such as thermal treatment of cream prior to butter making, water content, and chemical composition influence not only crystal polymorphism, but also the number and sizes of fat crystals. The number of crystal-crystal interactions formed within the products is related to product hardness. During storage, however, postcrystallization increases the solid fat content and strengthens the fat crystal network. The fat crystal network is strengthened by the formation of more and stronger crystal-crystal interactions due to mechanically interlinking of fat crystals, which occurs during crystal growth. Postcrystallization is directly linked to chemical composition. The initially observed microstructural difference causing different rheological behavior will disappear during storage due to postcrystallization and formation of more crystal-crystal interactions.

Ternary Phase Diagram of β‐Sitosterol–γ‐Oryzanol–Canola Oil

Abstractβ‐Sitosterol and γ‐oryzanol have been shown to form unique structures in canola oil that have the potential to act as saturated and trans fat replacers [1–7]. The ternary phase, reported herein, illustrates numerous interesting physical systems. At high canola oil ratios with low β‐sitosterol and γ‐oryzanol concentrations, the system has a crystal structure capable of mimicking fat crystal networks. Four mesophases are identified based on Bragg's ratios using small angle X‐ray scattering. Two mesophases are lamellar crystals, one is the cubic P phase, and the fourth is an amorphous material due to the low solids content. Wide‐angle X‐ray further subcategorized the phases based on polymorphic divisions of the hydrocarbon side chain packing. In all, six distinct phases are reported, ranging from lamellar crystals, to liquid crystals to what appears to be a lipid glass.

Rheology and microstructure of pastes with crystal network

This article reviews scientific studies which have been focused on the structure–property relationships of pastes with crystal network by considering fat crystal network as the key example. The review illustrates how rheology can be a valuable tool to characterize the mechanical behavior in these pastes and also provide information about the underlying microstructure in conjunction with various complimentary techniques. Rheological tests which can be adopted to determine the yielding behavior of the crystal network containing pastes are also presented. We have used these methods and concepts to characterize fatty acid crystal network to study a system emulating a skin cream formulation. It is hoped that the rheological fundamentals and the microstructural characterization techniques discussed in context of fat crystal network can be translated to other experimental systems where crystal-forming components are added to impart pasty material characteristics.

Effect of Temperature on the Crystalline Form and Fat Crystal Network of Two Model Palm Oil-Based Shortenings During Storage

Fat products experienced undesirable microstructural property changes due to the temperatures during transportation and storage. In this study, the lipid composition and solid fat content (SFC) of two model palm oil-based shortenings, which are denoted as shortening A (melting point of 35.1°C) and shortening B (melting point of 51.2°C), were evaluated, and their crystallization behavior and polymorphism during storage at various temperatures (−10 °C to 30 °C) was examined by X-ray diffraction (XRD) and polarized light microscopy (PLM). The fractal dimension (D b) was calculated to qualify the change in the crystal network during storage. The aggregation of high-melting triacylglycerols (TAGs) nanostructure and the formation of the most stable β polymorph were observed in shortening at higher temperatures (≥0 °C) during storage. At the same temperature, the intensity of β crystals in the two samples increased as the storage time increased, and this trend was obvious at high temperatures (≥10 °C). In addition, the intensity of the β crystals in the two samples gradually increased as the temperature increased, and the size of the crystalline particles became larger. The crystal size in shortening A was larger than that in shortening B at high temperatures (≥10 °C). The crystal network of shortening B was denser than that of shortening A. The D b value reached a maximum at 10 °C and 30 °C for shortening A and B, respectively. These findings have important implications on the storage stability and functional properties of palm oil-based shortenings.

Impact of pre-crystallization process on structure and product properties in dark chocolate

Dark chocolate microstructures with different structure densities, i.e., close-packing of the fat crystal lattice, and homogeneity i.e., evenness and connectivity of the fat crystal network, were created by βVI-seeding or conventional pre-crystallization with various degrees of temper and were evaluated with respect to storage stability. The structure characterization was conducted by measuring the strength of the cocoa butter crystal network with traction tests combined with DSC melting curves. Subsequent storage stability was evaluated with DigiEye technique for fat bloom development and gravimetrical techniques for fat/moisture migration. The two pre-crystallization processes generated significantly different structures and storage stability. Well-tempered βVI-seeding resulted in a dense and homogenous chocolate structure directly after solidification, which was optimal in order to retard fat bloom and fat migration. However, a too high structure density generated heterogeneous structures with reduced ability to withstand fat bloom. A lower structure density exhibited optimal resistance against moisture migration.

Nanoscale characteristics of triacylglycerol oils: phase separation and binding energies of two-component oils to crystalline nanoplatelets

Fats are elastoplastic materials with a defined yield stress and flow behavior and the plasticity of a fat is central to its functionality. This plasticity is given by a complex tribological interplay between a crystalline phase structured as crystalline nanoplatelets (CNPs) and nanoplatelet aggregates and the liquid oil phase. Oil can be trapped within microscopic pores within the fat crystal network by capillary action, but it is believed that a significant amount of oil can be trapped by adsorption onto crystalline surfaces. This, however, remains to be proven. Further, the structural basis for the solid-liquid interaction remains a mystery. In this work, we demonstrate that the triglyceride liquid structure plays a key role in oil binding and that this binding could potentially be modulated by judicious engineering of liquid triglyceride structure. The enhancement of oil binding is central to many current developments in this area since an improvement in the health characteristics of fat and fat-structured food products entails a reduction in the amount of crystalline triacylglycerols (TAGs) and a relative increase in the amount of liquid TAGs. Excessive amounts of unbound, free oil, will lead to losses in functionality of this important food component. Engineering fats for enhanced oil binding capacity is thus central to the design of more healthy food products. To begin to address this, we modelled the interaction of triacylglycerol oils, triolein (OOO), 1,2-olein elaidin (OOE) and 1,2-elaidin olein (EEO) with a model crystalline nanoplatelet composed of tristearin in an undefined polymorphic form. The surface of the CNP in contact with the oil was assumed to be planar. We considered pure OOO and mixtures of OOO + OOE and OOO + EEO with 80% OOO. The last two cases were taken as approximations to high oleic sunflower oil (HOSO). The intent was to investigate whether phase separation on a nanoscale took place. We defined an "oil binding capacity" parameter, B(Q,Q'), relating a state Q to a reference state Q'. We used atomic scale molecular dynamics in the NVT ensemble and computed averages over 1-5 ns. We found that the probability of the OOE phase separating into a layer on the surface of the CNP compared to being retained randomly in an OOO + OOE mix were approximately equal. However, we found that it was probable that the EEO component of an OOO + EEO mix would phase separate and coat the surface of the CNP. These results suggest a mechanism whereby many-component oils undergo phase separation on a nanoscale so as to create a transition oil region between the surface of the CNP and the bulk major oil component (OOO in the case considered here) so as to create the appropriate oil binding capacity for the use to which it is put.

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.

Effect of Fatty Acid Composition of Monoglycerides and Shear on the Polymorph Behavior in Water‐in‐Palm Oil‐Based Blend

AbstractEffect of the fatty acid composition of monoglycerides and shear on the polymorphic behavior in a water‐in‐oil (W/O) emulsion semi‐solid fats blend was investigated. The bulk fat blend and the W/O emulsion fat blend with added either unsaturated or saturated monoglycerides were prepared using a rapid cooling heat exchanger, and the polymorphic transitions from β′ to β‐form during storage were compared by X‐ray diffraction. The peak intensity of the β‐polymorph of the samples with added saturated monoglycerides was stronger than that of unsaturated monoglycerides, and the peak intensity of the β‐polymorph of the W/O fat blend emulsions was stronger than that of the bulk fat blends. The polymorphic transition to the β‐form during storage of the W/O emulsion fat blend was promoted by the applied shear. In contrast, that of the bulk fat blend was retarded by shear. These results suggested that fatty acids, which combined to monoglycerides on the surface of water droplets, influenced the polymorph transformation of the fat crystal network in a continuous semi‐solid fat phase because of the acyl–acyl interactions between the fatty acid residues of the monoglycerides and triacylglycerols in the fat crystal network.

Evolution of Fat Crystal Network Microstructure Followed by NMR

Model systems composed of tristearin in solid state and tricaprin in liquid state with different solid-fat content (SFC) and storage time have been investigated by relaxation NMR and NMR diffusometry. The T(2) relaxation of the tricaprin in the melt exhibited a bimodal distribution as previously observed. The SFC had a major effect on the T(2) relaxation. This effect was explained according to the fast diffusive exchange model in porous media. According to this model the changes in T(2) relaxation as a function of the SFC and storage time were explained by the decrease of the surface-to-volume ratio of the crystal induced by Ostwald ripening. The diffusion coefficient D of the tricaprin in the melt decreased for higher SFC. Since no significant variation of D was observed for different diffusion time, D reflected the long-range connectivity and the tortuosity was calculated. During storage the diffusion coefficient remained constant.

Impact of gastric structuring on the lipolysis of emulsified lipids

Understanding and manipulating how emulsion structure impacts on fat digestion is an important step towards understanding the role of fat in our diet. This article reports on the nature of emulsion structuring within the digestive tract and how it affects the dynamics of fat digestion. Emulsions were designed a priori to have specific structuring behaviours (stable, coalesced, partially coalesced and fully broken) under gastrointestinal conditions, through careful emulsifier selection and control of solid fat composition. The impact these structures had on lipolysis was then assessed in vitro using a digestion model and in vivo by measuring the postprandial change in blood triglyceride concentration as a marker of fat absorption. The major factor controlling the rate of fat digestion in vitro was the droplet surface area available for lipase adsorption, which was governed by emulsion instability. The rate of fat absorption in vivo was only affected by large changes in the droplet surface area, and only if these changes remained until the droplets reached the small intestine. This was most evident in emulsions that had undergone extensive partial coalescence under gastric conditions. Partial coalescence resulted in a dramatic reduction in triglyceride absorption, in part because the network of fat crystals provided the agglomerates with an internal scaffold to resist re-dispersion as they passed through the pylorus. The differences in fat absorption profile achieved by controlling emulsion structural stability during digestion provide a basis for examining the physiological effects of food structure on lipid metabolism, which will be the subject of a follow-up clinical paper.

Effects of Crystal Growth and Polymorphism of Triacylglycerols on NMR Relaxation Parameters. 1. Evidence of a Relationship between Crystal Size and Spin−Lattice Relaxation Time

Fat crystal networks confer their physical properties on fat-containing products. They are characterized by the solid fat content (SFC) and the design of the crystals, that is, their polymorphism and their size. Different techniques such as NMR, differential scanning calorimetry, and X-ray diffraction (XRD) are used to determine these parameters. Low-field NMR, the reference method for evaluation of SFC, has been proven to allow the determination of polymorphism through spin−lattice relaxation time (T1) and second moment (M2) measurements. However, this technique could provide more information on the system. On the basis of the effects of supercooling on the NMR parameters, the first evidence of a possible relationship between the size of the crystals and T1 was demonstrated. The effects of a liquid phase on the fat crystal network were investigated with liquid tricaprin and solid tristearin. It was demonstrated that the two triacylglycerols can cocrystallize, and that the liquid phase modified the polymorphic behavior of tristearin. The evolution of T1 over time could be related to the Ostwald ripening phenomenon. In view of this evidence, it was concluded that there was a relationship between T1 and the size of the crystals in the fat crystal network.

Thermo-mechanical method for the determination of the fractal dimension of fat crystal networks

The physical properties of a fat are determined by its thermal history, processing conditions, chemical composition, polymorphism and spatial distribution of mass. The mass fractal dimension of a fat crystal network can be determined from the slope of the log–log plot of the storage modulus (G′) versus the solid fat content (SFC). Different SFCs were obtained by melting the fat, diluting it to different extents in liquid oil, and crystallizing the blends under specific conditions. One of the major drawbacks of this method is the inability of characterizing the native structure of an already crystallized fat. In the thermo-mechanical method developed in this study, SFC is changed via temperature variations instead. At each temperature, the G′ and SFC were measured and the fractal dimension calculated as described above. The thermomechanical method proved to be a simpler and more reliable estimator of the fractal dimension of a fat crystal network than the dilution method.

THE EFFECT OF TEMPERATURE ON THE RHEOLOGY OF BUTTER, A SPREADABLE BLEND AND SPREADS

ABSTRACT The texture of lipid‐based food materials is an important topic for investigation. In this study, the rheological properties of five edible fats were determined. A puncture test was performed to investigate the rheological properties of the food materials at 5C and at 19C using a texture analyzer. The force‐displacement measurements were converted to stress–strain by assuming incompressibility of edible fat food materials in a linear viscoelastic region (LVR). Young's modulus of each edible fat was calculated using stress–stain curves in a LVR. Shear elastic moduli of edible fats in a LVR were obtained using a rheometer. Further to that the effect of temperature on storage modulus and loss modulus and creep test were obtained using a rheometer. The tests showed good correlation between Young's modulus and shear elastic modulus for each material. The mechanical properties correlated well with the structural properties of each of the materials. PRACTICAL APPLICATIONSThe texture of butter, blends and spreads is determined by temperature, rheological properties, processing conditions and the composition of the material. Our research investigated the effect of temperature on the rheological properties of these foods. The results may be used to model the relationship between the microstructure and mechanical properties of the fat crystal network.

Novel structuring strategies for unsaturated fats – Meeting the zero-trans, zero-saturated fat challenge: A review

Numerous foods acquire their elastic properties (i.e., snap, mouth-feel, and hardness) from the colloidal fat crystal network comprised primarily of trans- and saturated fats. These hardstock fats contribute, along with numerous other factors, to the global epidemics related to metabolic syndrome and cardiovascular disease. A dire need for new technologies capable of structuring unsaturated edible oils, reducing the necessity for trans- and saturated fats, are required. At present, organogels are under-utilized in the food industry but numerous potential organogelators exist including: phytosterols and oryzanols, ceramides, monoglycerides and waxes. When examining these compounds as suitable ingredients for the food industry, they should be food grade, cost effective, have no negative health implications and one should be able to modify their physical properties. This review considers alternatives to colloidal fat crystal networks when structuring unsaturated oils as well as methods to modify their physical properties.

Structural and Mechanical Behavior of Tristearin/Triolein-rich Mixtures and the Modification Achieved by Interesterification

The effects of chemical and enzymatic interesterification on the structure and rheological behavior of blends of fully hydrogenated canola oil (FHCO) with high oleic acid sunflower oil in the range of 10–90% was studied. Relationships between chemical composition, crystallization temperature (20–50°C), solid fat content (SFC) of the blends, and their rheological properties, characterized using both small and large deformation mechanical testing, were investigated. The storage modulus (G′) and yield force increased with FHCO concentration in the blends and was affected strongly by interesterification. The SFC in the interesterified samples was lower than in the non-interesterified blends, but they had higher values of G′. This increase in G′ at 30°C upon interesterification was attributed to a decrease in the fractal dimension of the fat crystal network which translates into a decrease in crystal cluster size in the interesterified samples. The higher G′ in the chemically interesterified samples relative to the enzymatic interesterified samples, on the other hand, was due to a higher λ parameter which is directly proportional to the strength of interparticle interactions and inversely proportional to crystal size. Microscopy and nucleation kinetics studies allowed for the independent determination of λ.

Utilization of Olive‐Pomace Oil for Enzymatic Production of Cocoa Butter‐like Fat

AbstractRefined olive‐pomace oil (ROPO) was utilized as a source for the production of a cocoa butter (CB)‐like fat. Immobilized sn‐1,3 specific lipase‐catalyzed acidolysis of ROPO with palmitic (PA) and stearic (SA) acids was performed at various substrate mole ratios (ROPO:PA:SA) to produce major triacylglycerols (TAGs) of CB. Products obtained for various substrate mole ratios were compared to a commercial CB in terms of TAG content, melting profile, solid fat content (SFC) and microstructure. The fat produced at a substrate mole ratio of 1:2:6 was the most similar to CB. The product contained 11% POP, 21.8% POS, 15.7% SOS while commercial CB contained 18.9% POP, 33.1% POS and 24.7% SOS. The product had a melting peak of 29.9 °C while CB had one of 28.5 °C. Polarized light microscope (PLM) images showed that fat crystal network microstructures of this product and CB were very similar.