Fast field cycling NMR relaxometry studies of molten and cooled cocoa butter

ABSTRACT

Due to its relevance in the confectionery industry, cocoa butter (CB) has been extensively studied. However, most studies focus on its crystallisation properties, whilst studies of its liquid state are lacking. Here, and for the first time, a study of the self-diffusion of CB at different temperatures is presented, using fast field cycling (FFC) nuclear magnetic resonance (NMR) further validated using pulsed field gradient stimulated echo (PGSTE) NMR. Measurements were performed upon heating CB to either 50°C or 100°C and cooling it to 22°C. No hysteresis was found between the different thermal treatments. However, the activation energy (28.7 kJ/mol) estimated from the cooling protocol of the 100°C treatment, was the closest to that reported in the literature for similar systems. This suggests that measurements using a wider range of temperatures, and starting with a liquid material are advisable. Additionally, samples were measured during isothermal crystallisation at 22°C, showing that the region below 1 MHz is the most sensitive to phase changes.

GRAPHICAL ABSTRACT

KEYWORDS:

• Cocoa butter
• triacylglycerols
• diffusion
• FFC-NMR

Acknowledgements

The authors would like to thank Dr Daniel Baker, from the University of Leeds, who helped with the set-up of both the PGSTE-NMR and the FFC-NMR. The experiments in the latter were made possible by the NMR Small Research Facility in the School of Physics and Astronomy of the University of Leeds. M.E.R. is a Royal Society Industry Fellow. The authors would also like to thank COST ACTION CA15209 who gave financial aid to Marjorie Ladd-Parada for her attendance to the Training School [NMR relaxometry for food and environmental applications].

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by the Consejo Nacional de Ciencia y Tecnología (México) [grant number 459910] in the form of a full scholarship for the PhD studies of Marjorie Ladd-Parada. Nestlé, Product Technology Centre, York, provided the cocoa butter used in this study, and Nestec, Ltd provided financial support for Marjorie Ladd-Parada’s PhD project; European Cooperation in Science and Technology [grant number CA15209].