Scale‐sensitive fractal analysis of the surface roughness of bloomed chocolate

Abstract

AbstractThe surface roughness of stored chocolate bars was studied by scanning laser microscopy and area‐scale fractal analysis. Topographic data were expressed by the statistical average roughness (Sa), by two parameters from area‐scale analyses—the fractal complexity (Asfc) and the scale of the rough‐to‐smooth transition (SRC)—and by the relative area as a function of scale. The roughness measured with Asfc showed extremely low correlation with the SRC, indicating that these two parameters can be considered to be independent. Asfc appeared to have some correlation (R2=0.82) with the Sa, indicating that for these data Asfc and Sa are somewhat related. As surface roughness (Asfc) increased during storage, gloss decreased in a linear fashion (R2=0.96), which is consistent with the proposal that surface roughness is intimately related to gloss. The scales of observation from about 0.5 to 100 μm2 were characteristic of the fat bloom interaction with chocolate surface and with the gloss. Fractal analysis provides parameters (Asfc and relative area) that are better than conventional arithmetic mean roughness for describing the surface changes during storage of chocolate. Both the complexity (Asfc) and the relative areas showed strong correlations with gloss (0.96 and 0.94, respectively), which is consistent with a facet‐based scattering model.