Relationship between crystallization behavior, microstructure, and mechanical properties in a palm oil‐based shortening

Abstract

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...

Milk fat in structure formation of dairy products: a review

“…The structural stability and rheological behavior of butter and milk fat-based products is primarily determined by stabilization by the fat crystal network [42][43][44]. The fat crystal network is strengthened by formation of more and stronger crystal-crystal interactions due to mechanically interlinked fat crystals as occurring during crystal growth.…”

Compatibility of selected plant-based shortening as lard substitute: microstructure, polymorphic forms and textural properties

“…PLM (Olympus, Model BH-2, Tokyo, Japan) was used to determine the microstructure of the shortening (Litwinenkoa et al, 2002). The microscopical examination was conducted after placing a drop of shortening, which was removed immediately from the incubator (25 °C ± 1.0 °C) onto a glass slide covered by a glass slip and viewed under PLM connected to a video color camera (Leica Q500mc Qwin Vol 0.02, Leica Cambridge Ltd., Cambridge, UK).…”

“…According to Litwinenkoa et al (2002), TAG composition plays an important role in determining the physical and functional properties of shortening. LD had POL, POO, PPO, and StPO as the most dominant TAG molecules.…”

Computer simulation of fractal dimensions of fat crystal networks

“…To show that the change in the microstructure of the fat crystal networks causes the change in the rheological properties of the fat samples, it is necessary to have consistency between the rheology fractal dimensions and the microscopy fractal dimensions. Furthermore, several methods have been used to calculate the microscopy fractal dimensions including the extensively used box-counting and particle-counting methods (4)(5)(6)(7)(8)(9). Moreover, the fractal dimensions calculated by different methods often have different values and even display different trends when the microstructure of the fat crystal networks is changed (7)(8)(9).…”

“…The particle-counting fractal dimension, D f , relates the number of primary particles, N, that a fractal object contains with the linear size, R, of that object according to the equation: [3] To calculate the particle-counting fractal dimension, D f , of a fat crystal network, a square-shaped ROI (Region of Interest) with different side length, R, is drawn on the center of the image of the fat samples and the number of the microstructural element in each ROI is counted. The logarithm of the number of microstructural elements, ln(N(R)), is plotted against the logarithm of the side length of each ROI, ln(R), for varying values of R. The slope of the linear regression curve of this log-log plot is the particle-counting fractal dimension, D f (5). The particle-counting fractal dimension algorithm should be carried out within the range between 100% and 35% of the original image size (4,9).…”