Effect of cooling and heating rates on polymorphic transformations and gelation of tripalmitin Solid Lipid Nanoparticle (SLN) suspensions

Tarek S. Awad, Thrandur Helgason, Kristberg Kristbergsson, Eric A. Decker, Jochen Weiss, D. Julian McClements

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46 Citations (Scopus)

Abstract

Solid lipid nanoparticle (SLN) suspensions undergo a phase transition from the α- to β-polymorphic forms, which is accompanied by particle aggregation and gel formation. These processes are both time and temperature dependent, and so it is important to study the impact of cooling rates (CRs) and heating rates (HRs) on polymorphic transformations, particle aggregation, and gelation. Rheology measurements indicated that the temperature where gelation was first observed during cooling (T gel) decreased with increasing CRs, with SLN suspensions remaining fluid at HR≥5 °C/min. On the other hand, the temperature where gelation was first observed during heating of stable SLN suspensions increased with increasing HRs: 18, 24, 31, and 45 °C at 2, 5, 10, and 20 °C/min, respectively. When the melted SLN suspensions were cooled again, two exothermic peaks were observed in the differential scanning calorimetry scans at 39 (which was attributed to coalesced oil) and 19 °C (which was attributed to stable SLN). With increasing CR, the enthalpy of the coalescence peak (ΔH CO) decreased, while that of the supercooled SLN (ΔH SLN) increased. With increasing HR, ΔH CO decreased and ΔH SLN increased, with no coalescence being observed at HR≥10 °C/min. These results show that increasing the CRs or HRs retard the α→β polymorphic transformation, which increased the stability of SLN against aggregation and retarded gelation. In addition, this study shows that the careful selection of HRs and CRs is required to examine polymorphic transformations and the stability of SLN suspensions.

Original languageEnglish
Pages (from-to)155-162
Number of pages8
JournalFood Biophysics
Volume3
Issue number2
DOIs
Publication statusPublished - Jun 2008

Bibliographical note

Funding Information:
Acknowledgments This grant was supported by USDA CSREES Hatch grants (MAS 0911 and MAS 831) and grants by the USDA National Research Initiative Programs (Award number 2005-01357). Additional financial support was provided by the Leifur Eiriksson Foundation, Hrafnkellssjodur, and Rannsoknarnamsjodur, all located in Reykjavik, Iceland.

Other keywords

  • Crystallization
  • DSC
  • Gelation
  • Polymorphism
  • Rheology
  • Solid lipid nanoparticles
  • Stability

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