Isothermal crystallization of hydrogenated sunflower oil: II-Growth and solid fat content

HERRERA M.L.; FALABELLA C.; MELGAREJO M.; AÑON, MARÍA C.

JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY (JAOCS)

SPRINGER

Lugar: Berlin; Año: 1999 vol. 76 p. 1 - 6

0003-021X

Isothermal crystallization of sunflower seed oilhydrogenated under two different conditions was studied bymeans of pulse nuclear magnetic resonance (pNMR) and opticalmicroscopy. Solid fat content (SFC) curves showed two differentshapes depending on supercooling. When supercoolingwas high, hyperbolic curves were found, whereas with low supercoolingsigmoidal curves were obtained. Curves were interpretedwith the modified Avrami equation. Photographs of thecrystals were taken from the beginning of crystallization, every15 s until 15 min and every 5 min until 60 min. Samples whichexhibited hyperbolic curves showed a slight increase in crystalnumber, and crystals were needle-shaped in all cases. Sampleswhich had sigmoidal crystallization curves showed a markedincrease in crystal number with time, and crystals were sphericalin shape. Crystallization behavior was also in agreementwith the chemical composition of the samples. Samples whichhad the highest content of high-melting triacylglycerols (especiallytrielaidin) showed only hyperbolic curves. Supercoolingis a very important parameter that defines the way nucleationoccurs. Depending on the initial number of nuclei, two differentgrowth mechanisms were found: a uniform linear growth ofthe nuclei for a small initial number (sigmoidal curves) and anaggregate of the nuclei for a high initial number (hyperboliccurves).