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ESTUDIO DE CINÉTICAS DE NUCLEACIÓN NO ISOTÉRMICAS EN ORGANOGELES UTILIZANDO ACEITES VEGETALES Y CERA DE ABEJA
Abstract
The microstructure of organogels depends on the nucleation process. Nucleation is the initial process from which crystalline structures grow. The formulation of organogels can influence the nucleation process. The crystalline structures formed from the nucleation process depend on the type of nucleation itself (homogeneous or heterogeneous). It is possible to establish methodologies that allow studying the nucleation process from "easy access" equipment such as a spectrophotometer in addition to theoretical knowledge of fat crystallization and modeling. Therefore, the objective of the work was to to evaluate the effect of the type of oil and concentration of gelling agent on the nucleation process of organogels. organogels. The organogels were obtained by mixing vegetable oils (canola, olive and coconut) with different concentrations of gelling agent (wax). different concentrations of gelling agent (beeswax: 4 and 8% w/w). Non-isothermal nucleation kinetics nucleation kinetics were performed and photographs were taken under an optical microscope with a polarized light filter. As The result is that it is possible to evaluate the nucleation process by means of non-isothermal kinetics in a spectrophotometer. in a spectrophotometer. It was found that the concentration of gelling agent is a determining factor in the values of different different parameters accelerating the nucleation process in a general way. It was also found that the It was also found that the study has limitations due to the number of components that form the wax and that this can be this can be complemented with calorimetry tests (DSC).
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The effects of cooling rate during melt crystallization of rice bran wax, sunflower wax, candelilla wax and a commercial peanut butter stabilizer in peanut oil were evaluated and correlated to their oil binding capacity. Rapid cooling upon crystallization decreased crystal length, decreased network pore area fraction, increased the fractal dimension of the crystal network, and lead to an increase in the oil binding capacity. Oleogels structured using 1 % sunflower wax exhibited the highest oil binding capacity, followed by candelilla wax and rice bran wax gels. The oil binding capacity of the commercial stabilizer was the lowest, but could be improved by crystallizing the material under high cooling rates. Linear correlation analysis revealed that the network fractal dimension decreases as pore area fraction increases, which was correlated to a greater oil loss. In general, the oil binding capacity of a gel can be significantly improved if the pore area fraction is decreased below 96 %, demonstrating how the fractal dimension and pore area fraction of a gel network can be modulated to tailor oil binding capacity.
Structuring liquid oils has become an active area of research in the past decade, mainly due to pressures to reduce saturated fat intake and eliminate trans fats from our diets. However, replacing hard fats with liquid oil can lead to major changes in the quality of food products. Recent strategies to impart solid-fat functionality to liquid oils include the addition of unusual compounds to oil, leading to its gelation. These include small-molecule organogelators such as phytosterols and 12-hydroxystearic acid, which self-assemble into crystalline fibers which trap oil. Other crystalline additives include waxes, ceramides, monoacylglycerides, and other surfactants. Recently, the polymer ethyl cellulose was reported to form a polymer gel in triacylglyceride (TAG) oils. Other non-conventional strategies also include the formation of protein-stabilized cellular solids with oil trapped within the cells. In this review, we summarize the research on each one of these components in order to provide a comprehensive overview of the state of the area in oleogel research and provide future perspectives.
Many waxes including plant waxes and animal waxes were evaluated for the gelation ability toward soybean oil (SBO) and compared with hydrogenated vegetable oils, petroleum waxes and commercial non-edible gelling agents to understand factors affecting the gelation ability of a gelator. Sunflower wax (SW) showed the most promising results and all SW samples from three different suppliers could make a gel with concentrations as low as 0.5 wt%. Candelilla wax and rice bran wax also showed good gelation properties, which, however, varied with different suppliers. Gelation ability of a wax is significantly dependant on its purity and detailed composition. A wax ester with longer alkyl chains has significantly better gelation ability toward SBO than that with shorter alkyl chains indicating that the chain length of a component in a wax such as wax ester is an important factor for gelation ability. The SW–SBO organogel showed increased melting point with increased SW content, showing the melting point range from about 47 to 65 °C with 0.5–10 wt% SW. The effects of cooling rate on crystal size and firmness of a gel were investigated. The dependence of firmness on cooling rate was so significant that the desired texture of an organogel could be achieved by controlling the cooling rate in addition to controlling the amount of gelling agent. This research reveals that a small amount of food grade plant waxes including SW may replace a large amount of the hardstock containing trans-fat or saturated fat.
Using safflower oil as the liquid phase we investigated the organogelation properties of stearic acid (SA), (R)-12-hydroxystearic acid (HSA), and different primary and secondary amides synthesized from SA and HSA. The objective was to establish the relationship between the gelator's molecular structure, solid content, and gels' microstructure that determines the rheological properties of organogels developed at two cooling rates, 1 and 20 °C/min. The results showed that the presence of a 12-OH group in the gelator molecule makes its crystallization kinetics cooling rate dependent, and modifies its crystallization behavior. Thus, SA crystallizes as large platelets while HSA crystallizes as fibers forming gels with higher solid content, particularly at 20 °C/min. The addition to HSA of a primary or a secondary amide bonded with an alkyl group, resulted in gelator molecules that crystallized as fibrillar spherulites at both cooling rates. Independent of the cooling rate, gels of HSA and its amides derivatives showed thixotropic behavior. The rheological properties of the amide's organogels depend on a balance between hydrogen-bonding sites and the alkyl chain length bonded to the amide group. However, might be also associated with the effect that the gelators' molecular weight has on crystal growth and its consequence on fiber interpenetration among vicinal spherulites. These results were compared with those obtained with candelilla wax (CW), a well-known edible gelling additive used by the food industry. CW organogels had higher elasticity than HSA gels, but lower than the gels formed by amides. Additionally, CW gels showed similar or even higher thixotropic behavior than HSA and the amide's gels. These remarkable rheological properties resulted from the microstructural organization of CW organogels. We concluded that microstructure has a more important role determining the organogels' rheology than the solid content. The fitting models developed to describe the organogels rheological behavior support this argument.
Colloidal particles are small solid particles suspended in a fluid. They are small enough that thermal energy ensures that they are equilibrated with the suspending fluid, but large enough that their positions and motions can be monitored with optical methods. They represent a powerful model system for the study of other phenomena in condensed matter physics, where the collective phase behavior of the solid particles mimics that of other condensed systems. We review three classes of interacting colloidal particles, crystals, glasses and gels, each of which represents fascinating properties of colloidal particles as well as a model for more general types of materials and their behavior. Expected final online publication date for the Annual Review of Condensed Matter Physics Volume 4 is February 6, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Organogels of 12-hydroxystearic acid (HSA) have been investigated to emphasize solvent-dependent relationships between rheological properties and nanostructures in this class of physical gels. Different length scales are considered: macroscopic with optical opacity, rheology, phase diagram data; nanoscopic with small-angle neutron scattering experiments and molecular with 1H NMR data. HSA networks are shown to be rigid fibrillar networks with rigid junction zones and behave as elastoplastic materials. Shear elasticities, yield stresses, and deformation behaviors appear connected to the crystallinity of networks through the cross-sectional shapes of fibers. Kinetics of molecular aggregation and flowing properties are also used to compare three classes of HSA gels (toluene, dodecane, nitrobenzene). The melting transitions as well as the concentration dependence of yield stresses exhibit remarkable behaviors analyzed in a context of molecular nanomaterials.
Solvent−gelator interactions play a key role in mediating organogel formation and ultimately determine the properties of the gel. The effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators. In solvents of the same class the gelation number (defined as the ratio of solvent molecules that gel per gelator molecule) decreased for trehalose 6,6‘-diacetate and 6,6‘-dibutyrate as the solvent Hildebrand solubility parameter increased. The opposite was observed for trehalose 6,6‘-didecanoate and 6,6‘-dimyristate. In general, the gelation numbers for all the gelators studied decreased in the order of esters > ketones > alcohols. Alcohols, which are capable of hydrogen bonding and can make substantial contribution to the total solvent−gelator interaction, significantly compromise gel formation. Optical microscopy and scanning electron microscopy revealed that for systems with high gelation numbers, such as trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in ethyl acetate and trehalose 6,6‘-didecanoate and 6,6‘-dimyristate in acetonitrile, thin, flexible, and highly entangled nanofibers were formed. Conversely, thick, rigid, and often highly clustered fibers accompanied systems with poor gelation, such as gels formed from trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in acetonitrile. Understanding the role of solvent in organogel formation is crucial in designing gels with desired structure and physicochemical properties. Such designed gels may provide controlled gelation by fine-tuning the solvent or the chemical environment of the gelator.
The non-isothermal nucleation rate of a self-assembling fibrillar network of 12-hydroxystearic acid in canola oil was found to be inversely proportional to the undercooling time exposure of the system. Moreover, fiber growth kinetics could be adequately modeled using the Avrami equation. Both nucleation and fiber growth kinetics displayed two distinct regimes, above and below 5 °C/min. The abrupt change in the rate of nucleation, crystal growth rate constant, and the degree of branching at this cooling rate are related to whether the nucleation and crystal growth processes are governed by mass transfer or thermodynamics. At rapid cooling rates, above 5 °C/min, the driving force for both nucleation and crystal growth is the time-dependent chemical potential difference between the molten solid in solution and the crystallized solid (the degree of undercooling or supersaturation). At low cooling rates, however, the rate of crystallization is no longer determined by this dynamic chemical potential difference, but rather only limited by time. In the slow cooling regime, we show that there are no noncrystallographic mismatches which would lead to fiber branching. Using the models developed and adapted in this work, we could accurately predict the fiber length, rate of nucleation, rate of crystal growth, induction time of nucleation, and the degree of branching of a 12HSA SAFIN.
This paper describes the relationship of viscosity with the crystallization process in a binary system formed by sasame oil
and different concentrations of tripalmitin (TP) and tristerian (TS) (0.0, 0.032, 0.098, 0.18, 0.26, 0.344 g/dL). The behavior
of the reduced viscosity (ηred) indicated that TP and TS affected the native bilayer lamellar organization of sesame oil triacylglycerides. The behaviour
of ηred at TP or TS concentrations ≤0.098 g/dL suggested that, as a result of intermolecular interactions between the saturated triacylglyceride
and the unsaturated triacylglycerides of sesame oil, the oil solution developed lamellar structures with a smaller size than
the native structures in sesame oil. At TP or TS concentrations >0.098 g/dL, the behavior of ηred indicated that TP or TS segregated out of the lamellar structure as the temperature was decreased. The kinetics of the segregation
phenomenon was a function of the concentration of saturated triacylglyceride and the type of triacylglyceride (i.e., TP or
TS), and was favored by an increase in the shear rate. In all situations, the temperature of nucleation was achieved when
ηred=0, which may represent the point at which the interfacial energy between sesame oil and the developing nuclei achieved its
maximum value. The higher the intermolecular interaction between the TP or TS and the triacylglyceride structure of the sesame
oil, the lower the temperature at which ηred=0 in the oil solutions. As a result, the diffusion term (i.e., viscosity of the liquid phase) became a limiting factor for
crystal growth rate, especially at TP and TS concentrations ≤0.18 g/dL.
The unique physical, functional, and nutritional properties of edible oil organogels has caught the eye of the food and pharmaceutical industries. These organogels are formed upon self-assembly of surfactant-like small molecules into crystalline fibers, sometimes hundreds of micrometers in length, which eventually lead to gelation of oil. Of particular interest is the ability of organogelator systems to structure and immobilize liquid triacylglycerols at very low concentrations (∼2%), which could be exploited for a variety of purposes in food products, from the manufacture of spreads to the solubilization, stabilization and delivery of lipid-soluble nutraceuticals. The purpose of this review is to outline the potential applications of edible oil organogels and to summarize the work that has been carried out to evaluate the functionality of organogelators in food systems.
The solvent type strongly affects the nucleation behavior of 12HSA and therefore strongly influences the peak nucleation rate, fiber length, spatial distribution of mass, and degree of branching. Using nonisothermal kinetic models, a correlation was established among the activation energy of nucleation, fiber length, and induction time of 12HSA nucleation in different solvents. However, there was no correlation between any measurable parameter and solvent polarity. Activation energies varied from 2.2 kJ/mol in methyl oleate to 15.8 kJ/mol in glycerol. Nucleation behavior and structure were strong functions of the cooling rate, with distinct regions observed above and below 5-7 degrees C/min for fiber length, induction time, rate constant, and peak nucleation rate. The abrupt changes in the rate of nucleation, crystal growth rate constant, and degree of branching around this cooling rate are related to whether the nucleation and crystal growth processes are governed by mass transfer or thermodynamics. Furthermore, the Avrami equation accurately predicted several structural features of the fibrillar network such as fiber length and, to a lesser extent, induction time.
Fractals in crystallizing food systems". Current Opinion in Food Science
- B Joshi
- S Beccard
- T A Vilgis
Joshi, B., Beccard, S., y Vilgis, T. A. "Fractals in crystallizing food systems". Current Opinion in Food Science, 21,
p. 39-45, 2018.