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.
Applications of NMR to food science
This report reviews the literature on the applications of NMR to food science from 1995 until March 2001. In order to be able to keep the number of references to manageable proportions, the number of papers referred to has been limited to those applications where NMR plays a major role in the experimental programme. Applications where NMR is simply used as a routine structural tool have been left out. Following an introductory section, the report covers water in foods, biopolymers, analysis and authentication, complex systems, and new methods for food analysis.
Arachidonic, 5, 11, 14, 17-eicosatetraenoic and related acids in plants—Identification of unsaturated fatty acids
Arachidonic and related fatty acids which normally are found only in animals or microorganisms have been isolated and identified from several mosses and ferns. Fatty acids with a double bond in position 5, separated by more than one methylene group from other double bonds, have been found inGinkgo biloba andEquisetum. Analyses of fatty acids from numberous plants, in particular their chlorophyll containing parts, are listed according to components.The experimental part gives details on structure determination of the usual methylene-interrupted fatty acids by ozonization-hydrogenation-GLC. Alkaline isomerization combined with these procedures was applied to determine the unusual double bond structures. The method permits positional identification of an internal double bond.