In Situ Studies of Ultrasound-Stimulated Fat Crystallization Using Synchrotron Radiation

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The crystallization behavior of tripalmitin (PPP) and trilaurin (LLL) without and with the application of ultrasonic power is investigated in situ using synchrotron radiation time-resolved small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) simultaneous measurement. Without ultrasound application, both polymorphic forms β ‘ and β crystallized in the melt of each substance. With ultrasound treatment of the melt, the following effects were observed: (i) a marked decrease of induction times for crystallization of both PPP and LLL, (ii) an increased nucleation rate, and (iii) a crystallization of only the β form for both PPP and LLL under conditions of initial crystallization temperatures of 50 and 30 °C, respectively, and applied ultrasound of 2 s. The last finding demonstrates that ultrasound irradiation can be used as an efficient tool for controlling the polymorphic crystallization of fats. In addition to this, the crystallization of LLL under a lower initial crystallization temperature of 25 °C and with the same ultrasonication time of 2 s, revealed the presence of both β ‘ and β polymorphs. This suggests that the crystallization of only the β form depends not only on ultrasound treatment but also on the initial temperature of crystallization. On the basis of the dynamic nucleation of PPP and LLL crystals induced by collapsing caviatation bubbles, we argue that a pronounced decline in induction times and an increase in the nucleation rate result from the shift in the melting points due to high-pressure pulses associated with collapsing bubbles. The insufficiency of this approach in accounting for the nucleation of only the β polymorph or both β ‘ and β polymorphs was also considered.