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Title: The effects of pressure and thermal history on the crystallisation of cocoa butter
Author: Ladd Parada, Marjorie
ISNI:       0000 0004 7431 1071
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2018
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Cocoa butter (CB) imparts most of the key sensory and stability characteristics in chocolate, when crystallised in the ß-V form. However, current processing methods can still be improved, since they do not account for the inherent compositional variations observed in products from different origin. Therefore, in-depth knowledge of the nanostructure of CB, and the different parameters affecting CB crystallisation is indispensable for new technologies to be developed. Two of these parameters which remain, surprisingly, under-reported are the temperature at which CB is molten prior to its crystallisation and application of medium pressure (<1000 bar). The nanostructure of the three main polymorphs of CB were determined from X-ray scattering experiments, and a novel structure in liquid CB is proposed. This is followed by the study of the effect of three thermal pre-treatments (50, 80 or 110 °C), using a multi-technique approach. Here, it was observed that by using a higher Timax, the crystallisation of the meta-stable phases was delayed, whereas the formation of the ß-V was enhanced, which is desirable for chocolate production. The differences between the 50 °C treatment and the other two treatments have been associated with the presence of crystallites of fully saturated TAG, DAG and MAG species, respectively. The effect of pressure was analysed by applying 100 to 600 bar to CB, which was subsequently cooled to 24, 26 or 28 °C, respectively. Initial post-processing analysis showed encouraging results, as crystallisation of the ß-V form appeared to be enhanced. However, these findings were not confirmed by in-situ experiments, where only the development of a-polymorphs was observed during pressurisation, which subsequently melted, to different extent, upon releasing the pressure. The observed differences might be caused by design-related issues of the pressuretreating machine used in the initial experiments.
Supervisor: Povey, Megan J. ; Rappolt, Michael ; Vieira, Joselio Sponsor: CONACYT ; Nestlé
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available