The phase behavior of fully hydrogenated canola oil in soybean oil was investigated using iso-solid lines from temperature-controlled pulse-NMR along with DSC data, with the rate of cooling of crystallized samples kept constant. The molecular diversity within the fat system was investigated using HPLC and GC. The microstructure of the fats was determined using a temperature-controlled polarized light microscope, and the polymorphism of the solidified fat structures was determined via a temperature-controlled X-ray diffractometer. Hardness was measured by a temperature-controlled Instron mechanical analyzer with a penetration cone. The phase behavior predicted by the DSC and iso-solid lines did not account for the hardness trends observed, as the microstructure and polymorphism of the fat also played a significant role. The addition of hard fat to a system did not consistently increase the hardness of the fat system. Furthermore, the solution behavior demonstrated by the iso-solid line diagram did not account for all trends in melting behavior, as both intersolubility and polymorphic changes occurred simultaneously. It was found that variations in hardness can be inferred from structural changes, although the structural level causing variation differs.A phase is a domain, homogenous with respect to chemical composition and physical state (1). A natural fat is an example of a system of coexisting homogeneous domains in equilibrium. The relationship and occurrence of phase change in a fat system is referred to as the phase behavior of the fat. Phase behavior, characterized by the study of the solid fat content (SFC), is important in optimizing production processes and maintaining production quality, and has been used to predict important attributes such as mouthfeel and hardness in fat-containing food products. Studies on phase behavior also lead to a better understanding of the ways in which fat blends interact-an important understanding, because the large-scale industrial production of shortenings and other fat-containing products often requires blending of lipids from many different sources.The use of iso-solid lines to characterize phase behavior is important in illustrating some aspects of intersolubility but is ultimately limited in scope. In many instances, iso-solid line behavior may not indicate changes in polymorphism of the samples and certainly does not impart information beyond the prediction of hardness by SFC, a method that has been shown to be imperfect (2-4). On the other hand, DSC phase measurements can reflect changes in polymorphism as well as intersolubility. However, such changes are not attributable to either polymorphic or intersolubility effects alone when utilizing purely DSC data. Therefore, it is important to study phase behavior by using a number of different techniques, such as X-ray diffraction (XRD; 5), microstructure analysis, GC, and cone penetrometry.The fat systems used in this study are mixtures of fully hydrogenated canola and soybean oils. These two lipids were selected for stu...

The Avrami model was developed to model the kinetics of crystallization and growth of a simple metal system. The original assumptions of the model do not apply for high-volumefraction crystallizing lipids, although it is incorrectly and frequently applied. A modified form of the Avrami model, wellsuited to complex lipid crystallization kinetics, is developed. It produces excellent fits to experimental data and allows the prediction of physically meaningful parameters, such as changes in nucleation rate and type, growth rate, morphology, and dimensionality. Morphological changes highlighted by time-resolved temperature-controlled polarized light microscopy support its application to crystallizing lipids. The kinetics of crystallization for six separate lipid samples were monitored by pulsed NMR, and fits were performed using the classical and modified Avrami model. In all cases, the modified model provided superior fits to the data compared with that of the classical model. The modified model supports the theory that lipids crystallize and grow into networks via very specific growth modes. Furthermore, the case is made that it is useful for interpreting crystallization kinetics of other systems such as polymer melts, which have nonconstant growth rates, dimensionalities, and nucleation conditions, and whose growth become diffusion-limited within specific regimes.Paper no. J11426 in JAOCS 83, 913-921 (November 2006).The Avrami model is frequently used to evaluate the kinetics of crystallization and growth of lipids, and is purported to relate experimentally determined kinetics to growth modes and structure of the final lipid network. Unfortunately, the application of the Avrami equation in lipid crystallization literature is inconsistent. Three different fits of the Avrami model have produced significantly different values for the Avrami exponent and constant (see below). Some researchers suggest that only a portion of the crystallization curve should be fitted with the model, thereby ignoring important information about the entire crystallization process. It has also been suggested that there are a number of line segments within a typical data set that can each be fitted with the Avrami model, and researchers have arbitrarily chosen one segment to fit with the model, without any justification. In fact, the crystallization kinetics of most lipid systems are not characterized by conditions that the Avrami model assumes are valid.This communication reviews the development of the Avrami model and examines crystallization data from a number of lipid systems. A modification to the Avrami model is proposed that does not violate the assumptions of the original model and provides excellent fits of crystallization data from lipids.Assumptions of the Avrami model. The Avrami equation is used extensively to model the crystallization behavior of metallic melts, polymers, and more recently, lipids, and is related to the problem of impinging waves, a problem first solved by Poisson (1). It is important to note that essentially i...

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