Effect of emulsifiers on the crystallization of kinetics of triglycerides and cocoa butter

The polymorphic transformation and isothermal crystallization kinetics of a model triglyceride, tristearin (SSS), were studied by DSC. Three beta' sub-forms for SSS were observed. The isothermal temperature and holding time are the key factors in determining the sub-form present. Transformation from a to a more stable form could occur either during isothermal holding or during heating. Higher isothermal holding temperatures resulted in longer induction times. Avrami analysis results showed that the Avrami exponent (n) values were constant over a range of temperature. At higher isothermal temperatures high n values were obtained. It is difficult to deduce the exact crystallization mechanisms from these data.; Effects of three emulsifiers, distilled monoglycerides (DMG), sorbitan monostearate (Span60) and sorbitan tristearate (Span65), on the crystallization kinetics of SSS, 1,3-dipalmitoyl-2-oleoylglycereol (POP), 1-palmitoyl-2-oleoyl-3-stearoylglycerol (POS), and 1,3-distearoyl-2-oleoylglycereol (SOS) were studied by DSC. In constant cooling crystallization, all three emulsifiers did not change the nucleation behavior of SSS but slowed down the crystal growth rate and the polymorphic transformations. In contrast all three emulsifiers increased the initial crystallization temperature of POP, POS and SOS, and had different effects on the melting behaviors and polymorphic transformations. Avrami analysis results showed no change on the n values for SSS, while for POP, POS, SOS, different results were obtained from different emulsifiers. Effects of tripalmitin (PPP) on the crystallization behavior of SSS were also studied. PPP decreased the growth rate of SSS and significantly changed the polymorphic forms of SSS obtained while Span65 did not.; Effects of four emulsifiers on the crystallization kinetics of cocoa butter were studied by DSC and NMR. Acetic acid monoglyceride esters (AAE) had almost no effect on the nucleation and melting behaviors of cocoa butter while DMG, Span60 and Span65 all increased the initial crystallization temperature and changed the melting behaviors of cocoa butter. The Avrami analysis results from both DSC and NMR indicated that all emulsifiers decreased the n value and increased the k value. At higher isothermal temperatures, higher n values were obtained. In addition, the n values from DSC results were higher than those obtained from NMR results.