A pulsed low resolution NMR study on crystallization and melting processes of cocoa butter
Pulsed low resolution nuclear magnetic resonance (NMR) was employed to measure the «melting» curves of different series of cocoa butter samples. The samples were prepared from completely liquid phase by cooling and tempering them at different temperatures Tc for varying time Δt. The «melting» curves were measured while keeping the sample at a fixed temperature Tm. The complex shape of each curve was interpreted in terms of cocoa butter polymorphism, and the results were compared with data obtained by other techniques available in the literature. Using just two tempering temperatures (+7 C and −18C), we were able to distinguish four solid phases and identify them with the phases II, III, IV, and V described in literature. Our data are in full agreement with literature. Several novel results have been also found. These include the kinetic constants of the melting processes of phases II and III, the rate constants of solidification of phase V, the conversion of phase III into phase IV before melting at temperatures ≥30 C, and the growth of phase V out of phase II at −18 C (including the rate constant of this process). We are convinced that NMR may serve as a principal tool in fat polymorphism investigations, especially if it is combined with other techniques such as differential scanning calorimetry. Its advantage, apart from rapidity of measurement, is the fact that the measurement itself does not interfere with the melting or solidification process studied. On the other hand, it does not distinguish in a direct way between different solid phases present in the sample; this can be done only in inference from the behavior upon melting.
Cocoa butter and confectionery fats. Studies using programmed temperature X-ray diffraction and differential scanning calorimetry
The polymorphic behavior and thermal properties of cocoa butter have been investigated by means of programmed temperature x-ray diffraction and differential scanning calorimetry. The relationship of this polymorphism to the technical problems of “tempering” and “bloom” development is discussed. Cocoa butter containing, respectively, milk fat and a bloom inhibitor, and some alternatives to cocoa butter have been studied. These results have provided information that will help determine process conditions for these particular fats.
The determination of the solids content of fats and oils by nuclear magnetic resonance
A nuclear magnetic resonance (NMR) method was developed for the determination of the solids content of fats and oils at various temperatures. This method is more rapid, accurate, and uni-versally applicable than the generally accepted solids fat index (SFI) by the dilatometric pro-cedure. A standard deviation of 1.0% solids, unaffected by parameter interactions and attain-able by inexperienced operators, indicates good reliability and reproducibility.The utilization of an NMR variable-tempera-ture accessory and a more precise mode of NMR tuning improves the precision and accuracy. The direct calculation of percentage of solids from the NMR signals eliminates the need for standards and compensates for the temperature variable. The results indicate that two separate labora-tories, using somewhat different methods and modes of NMR operation, agree reasonably well.