Crystallization of cocoa butter with and without polar lipids evaluated by rheometry, calorimetry and polarized light microscopy Article uri icon

abstract

  • In this investigation, we evaluated the crystallization process of triacylglycerols (TAG) in unrefined cocoa butter (CB) and in CB without polar lipids (CB-WPL), under non-isothermal and isothermal conditions. These conditions were obtained by cooling from 80°C at a cooling rate of 1°C/min until achieving particular crystallization temperatures (i.e., 18.5°C, 19.0°C, 19.5°C, and 20°C), at which isothermal crystallization studies were done. Phase shift angle rheograms (δ) showed that the onset of crystallization during the non-isothermal stage, independently of the crystallization temperature (TCr) used, was 59.8 ± 3.7°C in CB and 39.5 ± 1.5°C in CB-WPL. These results pointed out the nucleating role of phosphatidylcholine (26.53 ± 0.04%25) and phosphatidylethanolamine (57.14 ± 0.07%25), the main phospholipids present in the CB used in this investigation. Under similar crystallization conditions, differential scanning calorimetry (DSC) provided an onset of crystallization during the non-isothermal stage of 15.0 ± 0.0°C in CB-WPL and of 15.5 ± 0.1°C in CB. Then, δ rheograms were more sensitive to detect the nucleating role of phospholipids than DSC. Under isothermal conditions, both DSC and δ rheograms showed that shorter times were needed in CB-WPL to complete crystallization than in CB. In the same way, at all TCr investigated, a higher crystallization rate was achieved in CB-WPL than in CB, this as measured by the crystallization rate constant (z) of the Avrami equation. These results showed that crystallization of α and β′ polymorphs took longer in CB than in CB-WPL, pointing out that polar lipids delayed the α-to-β′ polymorphic transition. Additional results confirmed that polar lipids affect the kinetics of TAG crystallization in CB. However, polar lipids do not affect the thermodynamic properties of the crystals [i.e., heat of fusion (ΔHM), temperature of fusion (T M′)], the storage modulus at the end of the crystallization process (i.e., G′ of pseudo-equilibrium), or the mechanism of crystal growth (i.e., the Avrami index, n). © 2005 Wiley-VCH Verlag GmbH %26amp; Co. KGaA.
  • In this investigation, we evaluated the crystallization process of triacylglycerols (TAG) in unrefined cocoa butter (CB) and in CB without polar lipids (CB-WPL), under non-isothermal and isothermal conditions. These conditions were obtained by cooling from 80°C at a cooling rate of 1°C/min until achieving particular crystallization temperatures (i.e., 18.5°C, 19.0°C, 19.5°C, and 20°C), at which isothermal crystallization studies were done. Phase shift angle rheograms (δ) showed that the onset of crystallization during the non-isothermal stage, independently of the crystallization temperature (TCr) used, was 59.8 ± 3.7°C in CB and 39.5 ± 1.5°C in CB-WPL. These results pointed out the nucleating role of phosphatidylcholine (26.53 ± 0.04%25) and phosphatidylethanolamine (57.14 ± 0.07%25), the main phospholipids present in the CB used in this investigation. Under similar crystallization conditions, differential scanning calorimetry (DSC) provided an onset of crystallization during the non-isothermal stage of 15.0 ± 0.0°C in CB-WPL and of 15.5 ± 0.1°C in CB. Then, δ rheograms were more sensitive to detect the nucleating role of phospholipids than DSC. Under isothermal conditions, both DSC and δ rheograms showed that shorter times were needed in CB-WPL to complete crystallization than in CB. In the same way, at all TCr investigated, a higher crystallization rate was achieved in CB-WPL than in CB, this as measured by the crystallization rate constant (z) of the Avrami equation. These results showed that crystallization of α and β′ polymorphs took longer in CB than in CB-WPL, pointing out that polar lipids delayed the α-to-β′ polymorphic transition. Additional results confirmed that polar lipids affect the kinetics of TAG crystallization in CB. However, polar lipids do not affect the thermodynamic properties of the crystals [i.e., heat of fusion (ΔHM), temperature of fusion (T M′)], the storage modulus at the end of the crystallization process (i.e., G′ of pseudo-equilibrium), or the mechanism of crystal growth (i.e., the Avrami index, n). © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.

publication date

  • 2005-01-01