DSC Study of Effects of Addition of Sucrose Fatty Acid Esters on Oil Phase Crystallization of Oil in Water Emulsion

Abstract

Differential scanning calorymetry (DSC) was conducted to clarify the crystallization behavior of n-hexadecane dispersed in oil-in-water emulsions (n-hexadecane : water=20 : 80). Tween 20 was used for emulsification and four sucrose fatty acid esters; sucrose laurate (L-195), sucrose palmitate (P-170), sucrose stearate (S-170) and sucrose oleate (O-170) were added to n-hexadecane. Crystallization temperature (Tc) of n-hexadecane in the emulsion system was 3.4°C and the melting temperature (Tm) was 17.4°C. Tc and Tm were 16.9°C and 18.5°C for bulk n-hexadecane, respectively. P-170 and S-170 addition resulted in considerable increase in Tc of n-hexadecane/water emulsions but L-195 had only slight effect. O-170, possessing oleic acid moieties as its hydrophobic portion had no effect on Tc of n-hexadecane/water emulsions. In bulk liquid, none of the sucrose esters showed any effect on Tc or Tm of n-hexadecane.With the addition of P-170 and S-170, small endothermic peaks appeared at 3.6°C and 4.1°C (on heating) and exothermic peaks at -3.2 and -3.0°C (on cooling) appeared in addition to the crystallization and melting peaks of n-hexadecane. These peaks corresponded to phase transitions of molecular aggregates formed emulsion interfaces. The mechanisms for acceleration of crystallization of n-hexadecane and molecular aggregate formation are discussed with consideration to interface adsorption and mesophase formation due to sucrose fatty acid ester addition in n-hexadecane.