Ultrasonic studies of the crystallization behavior of two palm fats O/W emulsions and its modification

Abstract

Based on the difference between the speed of sound in solids and liquids, an ultrasonic velocity technique was employed to monitor the phase transition, nucleation and crystal growth of two palm oils dispersed as oil-in-water (O/W) emulsions. The O/W emulsions of palm mid-fraction (PMF) and palm kernel oil (PKO) crystallized at 12 and 0 °C, respectively. The degree of supercooling of PMF emulsion was 18 °C, while that of PKO emulsion was 28 °C. The effects of different hydrophobic emulsifier additives on the interfacial heterogeneous nucleation, induced at the oil/water interface of emulsion droplets, and crystal growth were studied by monitoring the sound velocity ( V) during isothermal crystallization. Sucrose oligoesters (SOEs) having stearic (S-170) and palmitic (P-170) fatty acid chains accelerated nucleation, yet SOEs having short chains such as lauric (L-170) showed no effect in the two fats. A polyglycerine ester (DAS-750) had a lesser and different effect on the nucleation of PKO compared to PMF. Moreover, the crystal growth was retarded in the two oils at different degrees by the addition of S-170. Solubility measurements indicated that the solubility degree of DAS-750 was more than that of S-170. In addition, the solubility of DAS-750 was higher in PKO than in PMF. The effects of the additives were thus discussed in terms of their molecular structure in relation to the oil phase composition.