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Relationship between crystallization behavior, microstructure, and mechanical properties in a palm oil‐based shortening
Author(s) -
Litwinenko J. W.,
Rojas A. M.,
Gerschenson L. N.,
Marangoni A. G.
Publication year - 2002
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-002-0538-y
Subject(s) - supercooling , crystallization , microstructure , materials science , isothermal process , degree (music) , rheology , crystallography , analytical chemistry (journal) , thermodynamics , chemistry , chromatography , composite material , physics , acoustics
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.