Palm-based fat crystallized at different temperatures with and without high-intensity ultrasound in batch and in a scraped surface heat exchanger
The objective of this study was to compare the sono crystallization process of a palm-based fat in batch to a continuous set-up using a scraped surface heat exchanger (SSHE). The sample was crystallized at 32, 30, 28, and 26 ◦C (Tc). High-intensity ultrasound (HIU, 20 kHz, 12.7 mm horn, 50% amplitude, 57W) was applied using 10s pulses. After crystallization, samples were stored (48 h/25 ◦C) and analyzed for crystal microstructure, melting behavior, oil binding capacity (OBC), hardness, and viscoelastic properties. HIU improved all physical properties of the material when crystallized in batch at all Tc; however, SSHE at 26 ◦C was the only condition improved by HIU. G’ and hardness were the highest in sonicated SSHE samples crystallized at 26 ◦C (141 kPa, 4.5N) and these values were higher than the ones obtained in batch. OBC was also improved in sonicated SSHE samples (77%) but in lower magnitude compared to the OBC obtained in batch (82%). Crystal size was not affected by HIU in the SSHE, but a reduction in crystal size was observed due to HIU in batch for all Tc. Similar behavior was observed for Tp, however, Ton and ΔH were not affected by HIU.
Lipids are commonly used in foods, pharmaceutical, and cosmetic industries since they provide desired physical properties to final products. Palm oil and its fractions are among the most studied and used oils worldwide because of their availability and the unique functional properties inherent to these products, allowing their use in a wide range of products including margarines, shortenings, baking, and confectionary fats (DeMan, 1998). Previous studies on the effect of external factors such as shear on the crystallization of palm oil demonstrated that shear enhanced the primary crystallization and changed its microstructure (de Graef, Puyvelde, Goderis, & Dewettinck, 2009). Nutrition concerns regarding consumption of high levels of saturated fats as found in the palm oil and its high melting point fractions, have resulted in a growing demand to reduce the saturated fatty acid (SFA) content in fat-based products. This reduction requires increased crystallization rates and strengthening the crystal network of trans free and low saturated fat products by applying external factors to the crystallization processes (Sato & Ueno, 2011). One alternative explored by food scientists was the use of sonocrystallization using high-intensity ultrasound (HIU) (Ueno, Ristic, Higaki, & Sato, 2003). Studies have shown that the vibrational energy input from cavitation bubbles promotes nucleation over greater heat and mass transfer. In addition, HIU promotes heterogeneous or secondary nucleation, resulting in a change of micro- and macroscopic properties of the sonicated fat (Suzuki, Lee, Padilla, & Martini, 2010). Most of the studies on lipid sonocrystallization were performed in a batch system (Chen, Zhang, Sun, Wang, & Xu, 2013; Suzuki et al., 2010; Ueno et al., 2003). However, few studies have evaluated the effect of HIU in continuous systems including studies in a flow cell for palm (Ye & Martini, 2015) and milk fat blend (Gregersen et al., 2019), and in a scraped surface heat exchanger (SSHE) for a soybean and palm-based fat (da Silva, Danthine & Martini, 2020b; da Silva & Martini, 2019, 2020b, 2020a). Overall, sonocrystallization studies have shown that the effect of sonication is dependent not only on sonication conditions but also on the type of sample used. Kadamne, Ifeduba, Akoh, and Martini (2017b, 2017a) showed that sonication of stearic based samples resulted in greater changes in physical properties compared to sonication of palm-based ones. Some of our previous studies evaluated the effects of HIU processing parameters and position in the SSHE in a soybean based-fat (da Silva & Martini, 2019, 2020a; da Silva, Danthine et al., 2020b). These studies showed that when used in a SSHE a soybean-based fat crystallized at a lower supercooling resulted in the greatest improvement on the physical properties due to HIU (da Silva, Danthine et al., 2020b). For a palm-based fat, although HIU seems to have an effect on physical properties when used in the SSHE (da Silva & Martini, 2020b), the magnitude of this improvement was lower compared to the findings for a soybean based. This issue is normally not found in batch sonocrystallized samples, and due to the importance of palm oil in foods and the need to reduce SFA in fats, the objective of this study was to compare and evaluate the effects of HIU in an palm-based fat with low content of SFA (32%) in a batch and in a SSHE system using different supercooling levels to evaluate the difference in physical properties based on different crystallization systems.