Effects of addition of diacylglycerols on fat crystallization in oil-in-water emulsion

Abstract

The effects of addition of diacylglycerols (DAGs) on the crystallization behavior of n-hexadecane dispersed in oil-in-water emulsion (oil 20% and water 80%, v/v) were studied by differential scanning calorimetry (DSC) and ultrasonic velocity measurement. In an attempt to modify the crystallization rate of n-hexadecane, five DAGs having the fatty acid moieties of behenic (DAB), stearic (DAS), palmitic (DAP), lauric (DAL) and oleic acid (DAO) were added to n-hexadecane, which was mixed with water and Tween 20 for emulsification. The DSC study showed that the addition of DAB, DAS or DAP (1.0 wt-% with respect to n-hexadecane) increased the crystallization temperature (Tc) of a n-hexadecane/water emulsion from 3 °C (without DAG) to 8 °C, whereas the addition of DAL and DAO showed no effect. The ultrasonic velocity measurement also revealed that the addition of DAGs resulted in increasing the Tc of n-hexadecane in O/W emulsion. These effects were discussed by taking into account the formation of molecular aggregates at the interface due to the addition of DAGs, which act as a template for crystallization of n-hexadecane. The template-assisted crystallization depends on the structure of the fatty acid chains present in the DAG: the longer the fatty acid moiety of DAG, the more is the crystallization of n-hexadecane in O/W emulsion accelerated. La cristallisation de la phase huileuse dans une emulsion huile dans l'eau est une etape importante pour la coagulation de l'emulsion refrigeree, comme par exemple la desemulsification de cremes fouettees ou la congelation de glaces. Les effets de l'addition de diacylglycerols sur la cristallisation de n-hexadecane disperse dans une emulsion huile dans l'eau (20/80% vol.) sont etudies par analyse calorimetrique differentielle et mesure de vitesse de propagation d'ultrasons. On observe que plus la chaine d'acide gras du diacylglycerol est longue, plus la cristallisation du n-hexadecane est rapide.