In this study, the effects of cooling rate, degree of supercooling, and storage time on the microstructure and rheological properties of a vegetable shortening composed of soybean and palm oils were examined. The solid fat content vs. temperature profile displayed two distinct regions: from 5 to 25°C, and from 25°C to the end of melt at 45-50°C. A peak melting temperature of 42.7°C was determined by DSC. Discontinuity in the crystallization induction time (determined by pulsed NMR) vs. temperature plot at 27°C also suggested the existence of two separate groups of crystallizing material. Isothermal crystallization kinetics were characterized using the Avrami and Fisher-Turnbull models. In using DSC and powder X-ray diffraction, the α polymorph formed upon fast cooling (>5°C/min), and the β′ form predominated at lower cooling rates (<1°C/min). An α to β′ transition took place upon storage. Fractal dimensions (D f ) obtained by microscopy and image analysis showed no dependence on the degree of supercooling since D f remained constant (~1.89) at crystallization temperatures of 5, 22, and 27°C. Crystallization at 22°C at 1°C/min and 15°C/min yielded D f values of 1.98 and 1.93, respectively. Differences in microstructure were observed, and changes in particle properties increased the parameter λ at higher degrees of supercooling.Hydrogenation of unsaturated FA in edible oils allows for the conversion of liquid oils into semisolid fats. These fats are characterized by altered melting and textural characteristics and by a higher oxidative stability. Modified plastic vegetable fats are often the key ingredients in margarines and specialty tailored fats like shortening (1).Shortenings are commonly used in dough formulations where the fats need to be mixed with other ingredients at room temperature and possess a high level of stability at elevated baking temperatures. Therefore, a smooth material that is spreadable at room temperature and has a specific melting profile, solid fat content (SFC), and polymorphic behavior is desired.It is well known that the solid-like behavior of plastic fats is due to the presence of a fat crystal network (2-5). The influence of microstructure on the macroscopic rheological properties of shortening is therefore the focus of this study. The nature of this crystal network, including its spatial distribution, and the number, size, and shape of its constituent microstructural elements can be dramatically altered by changes in crystallization conditions. Effects of cooling rate, the degree of supercooling, and storage time on crystallization and melting behavior and mechanical properties, including the storage modulus (G′) and loss modulus (G″), were investigated. Powder X-ray diffraction (XRD) spectroscopy and DSC were also used to investigate the effects of various crystallization conditions on polymorphism in the shortening. MATERIALS AND METHODS Sample and chemicals.A commercially available allvegetable oil-based shortening (Golden Crisco Doré, Procter & Gamble, Toronto, Ontario, Canada) c...

The addition of 0.10% glycerol or Tween 60 increased the yield force of a 70:30 (w/w) mixture of triolein/HMF (high-melting fraction of milkfat) at 5 °C. Further increases in glycerol or Tween 60 caused a decrease in yield force. Solid fat content (SFC) versus time profiles at 30 °C (glycerol) and 28 °C (Tween 60) allowed for the determination of Avrami rate constants of crystallization (k) and Avrami exponents (n). Higher Avrami constants and lower Avrami indices (higher rate of crystal growth), smaller crystallites, and a shorter induction time of nucleation were observed in samples containing 0.10% Tween 60 relative to the control and 0.50% Tween 60. A 0.10% glycerol addition, on the other hand, yielded opposite results. The increase in hardness induced by small additions of Tween 60 could be attributed to decreases in crystallite size at constant SFC and fractal dimension. The increase in hardness induced by small additions of glycerol could only be attributed to increases in the crystal-melt interfacial tension, at constant SFC and fractal dimension, despite increases in crystallite size.

Fractionation of milk fat by short-path distillation changes the chemical composition and physical properties of the resulting fractions. Increases in distillation temperature from 125 to 250 degrees C increased distillate yield from 0.3 to 42.7% (wt/wt). The distillate was enriched in short- and medium-chain fatty acids and low molecular weight acylglycerols, while the retentate was enriched in long-chain saturated and unsaturated fatty acids as well as high molecular weight acylglyerols. As distillation temperature increased, dropping points of the distillate increased. Relative to native milk fat, the solid fat content (SFC) vs. temperature melting profile of the distillate was depressed and that of the retentate was augmented, which correlated with the saturated long-chain fatty acid content in the fractions. Retentate crystallization parameters obtained by fitting the Avrami model to SFC-time data, did not change as a function of distillation temperature, but varied as a function of the degree of undercooling. Changes in microstructure observed by polarized light microscopy also appeared to be solely a function of the degree of undercooling, with no observable differences between retentates obtained at the different distillation temperatures. In addition, no changes in the retentate's free energy of nucleation (deltaGc) as a function of distillation temperature were found. The compressive storage modulus of the crystallized retentate increased as a function of increasing distillation temperature.

This paper reviews the identification of the various levels of structure present in milk fat crystal networks, and the development of analytical techniques to quantify these levels. The relationship of the various levels of structure to macroscopic physical indicators of the mechanical strength of the network is discussed. The analysis of the microstructural level of the network via fractal geometrical methods is outlined, as well as mechanical models relating the structure to mechanical properties. The effect of processing conditions on the different levels of structure and mechanical properties also discussed.

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