Effects Of Ultrasound On The Crystallization Behavior Of Palm Oil Based Blends

The crystallization behavior of palm oil (PO) without and with the application ofhigh-intensity ultrasound (HIU) was investigated as a function of irradiation time (20,60,120,and240s), power level (47.5,95,270, and475W) and crystallization temperature (Tc=20,25,30, and36°C). The induction time (tind) for crystallization, crystallization rate, microstructure,hardness, viscosity and the melting behavior of crystallized samples were evaluated.Results indicated that HIU had positive effect on the crystallization rate of PO and theeffects were more significant at higher power level (47.5~475W) and longer irradiation time(20~120s). However, no significant (P>0.05) increase was observed when240s of HIU wasapplied, which suggested that HIU might cause thermal effect. Temperature variation studyindicated that the thermal effect generated by HIU was more pronounced with higher powerand longer irradiation rime. Therefore, suitable power level and irradiation time should beconsidered together. The effect of HIU was greatly related to the super-cooling degree.Markedly promotion on crystallization rate was observed at temperatures above25°C, butthere was no significant difference (P>0.05) at20°C. At36°C, with extremely lowsuper-cooling, HIU also prevented the separation of solid phase and liquid phase ofcrystallized sample and led to a uniform distribution of crystalsThe induction time for crystallization were significantly reduced by more than50%at allTc with95W60s of HIU. It indicated that HIU might cause similar effect as low temperature,which means to increase the driving force for crystallization. The effects of HIU on themicrostructure of crystal were summarized as follows: reducing the crystal cluster size;increasing the quantity of crystals; altering the growth mechanism of crystals into irregularshapes. The mean diameter caculated for crystals formed at25and30°C without HIU were65.68and74.37μm, respectively. However, when different HIU conditions were used, theygreatly reduced to16.91and12.79μm, respectively. Besides, the hardness and viscosity ofsample were significantly increased, which suggested that HIU might produce stronger crystalnetwork structure. The melting peaks of sample crystallized with HIU were sharper and withnarrower melting range. However, the melting enthalpies had no signifcant diferencecompared to controlled samples. It indicated that HIU promoted crystallization mainly on thegeneration of small crystals rather than the total amount of crystallized materials.HIU has no significant effect on the fat acid composition (FAC), trans-fatty acid (TFA),triacylglycerol compound (TAG) and the oxidation stability of PO. However, an unpleasantmetallic odour was observed in all sonicaiton samples, which were identified as short carbon chain compounds. These results suggested a probability for the generation of short carbonchains compound due to the cavitation effect，which provide an extremely conditions forchemical reactions such as bones broken or generation of free radicals.