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

LITWINENKO J.W., ROJAS A.M., GERSCHENSON L.N. Y MARANGONI A.G.

JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY (JAOCS)

AOCS Press.

Lugar: 2211 W. Bradley Ave., Champaign, IL 61821-1827 USA.; Año: 2002 vol. 79 p. 647 - 654

0003-021X

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 soy-bean and palm oils were examined. The solid fat content vs. temperature profile displayed two distinct regions: from 5 to 25 ºC, and from 25ºC to the end of melt at 45-50ºC. A peak melting temperature of 42.7ºC was determined by DSC. Discontinuity in the crystallization induction time (determined by pulsed NMR) vs. temperature plot at 27ºC also suggested the existance 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 a polymorph formed upon fast cooling (> 5ºC/min), and the b’ form predominated at lower cooling rates (< 1ºC/min). An a to b’ transition took place upon storage. Fractal dimensions (Df) obtained by microscopy and image analysis showed no dependence on the degree of supercooling since Df remained constant (» 1.89) at crystallization temperatures of 5, 22, and 27ºC. Crystallization at 22ºC at 1ºC/min and 15ºC/min yielded Df values of 1.98 and 1.93, respectively. Differences in microstructure were observed, and changes in particle properties increased the parameter l at higher degrees of supercooling.