Ultrasonic velocity measurement of crystallization rates of palm oil in oil-water emulsions

The crystallization behaviour of palm oil dispersed in oil-in-water emulsion (oil, 30 wt.%; water, 70 wt.%) was studied by ultrasonic velocity measurement under cooling and heating processes. Na caseinate, as a major surfactant, and hydrophilic sucrose polyesters, as minor components, were employed for emulsification. The rates of crystallization of palm oil were monitored by the changes in the ultrasonic velocity values, which increase with increasing amount of fat crystals in the palm oil phase. Effects of the addition of highly hydrophobic food emulsifiers of sucrose polyesters with HLB values of around 1, added in palm oil, were examined, in an attempt to modify the rate of crystallization of palm oil, Comparing the results in the emulsion systems with those in neat palm oil liquid, we have obtained the following results: (a) the rates of crystallization, particularly of nucleation, were retarded in the emulsion system compared with the neat liquid; (b) the addition of hydrophobic sucrose polyesters increased the nucleation rates in the emulsion systems, whereas it retarded the rates of crystal growth; (c) this opposing effect was most manifest for the sucrose polyesters with a stearic acid moiety, yet minimized for those with an oleic acid moiety. A mechanistic argument is given for the experimental results in terms of emulsifier-fat interactions. (C) 1997 Published by Elsevier Science B.V.