Chocolate is a complex food system. Indeed, different types of chocolate are composed of various chemical compounds such as carbohydrates, proteins, polyphenols with similar chemical composition, and traces of minerals; and they may also present different crystallographic structures. Both the composition and the structure influence the physical properties of chocolate, for example the melting point and the density, which in turn influence the chocolate properties and the sensory perception. The relevant length scales involved in food systems extend from the macroscale to the nanoscale, and the different features at these scales are important in the food processing and preparation.<br/>Here, we propose to use atom probe tomography (APT) to analyze a typical dark Belgian chocolate. APT is a powerful technique based on the evaporation of the sample, atom by atom, layer by layer, the analysis by mass spectrometry, and further detection by a position-sensitive detector. APT is used for the characterization of both the composition and the 3D structure of materials at the atomic-scale, allowing to reach for sub-nanoscale spatial resolution, ppm elemental sensitivity and high mass resolution in the most favorable cases. Due to the versatility of the most recent atom probe instruments, it is now possible to study samples that were not imaginable only a few years ago: minerals, biominerals and geological samples, or even biological samples such as bacteria.<br/>Since the structure of chocolate samples consists of a suspension of cacao particles, milk and sucrose in a continuous semi-solid fat phase, its analysis by APT requires a challenging sample preparation using a modified lift-out method by FIB-SEM. Due to the complexity of the sample, the resolution could still be optimized, but it is possible to distinguish two different phases of the chocolate suspension that can be distinguished by their MS signal.<br/>To conclude, the experiments proved that dark chocolate bars can be analyzed by atom probe tomography as any other hard/soft matter systems [1], and thus be seen as a model system for the analysis of soft matter food systems. Further experiments are however required to unravel the details of the composition as well as to explore the possibility of observing crystallography on chocolate samples [1].<br/>

Belgian chocolate as a model system for food analysis by atom probe tomography

2019 Spring National Meeting

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