Microscale Surface Roughening of Chocolate Viewed with Optical Profilometry

Microtopographical roughening and fat phase melting of milk chocolate subjected to three temperature cycles between 20 and 28, 30, 32, or 34 A degrees C were examined using optical profilometry and differential scanning calorimetry (DSC). Cycling to any of these temperatures did not lead to immediate visual bloom, though significant effects on microstructure and fat phase melting behavior were noted. The initial chocolate topography was lightly mottled and consisted of small asperities. DSC indicated the presence of form V crystals in control chocolates kept isothermally, with form VI crystals appearing with cycling to 30 and 32 A degrees C. The fat phase of the chocolates cycled to 34 A degrees C existed only in the form IV polymorph. As a result of cycling, the surface roughness of all samples increased, with the smallest rise seen with cycling to 28 A degrees C. Decomposition of the roughness into low and high-frequency components revealed a significant contribution of waviness (the low-frequency component) to overall roughness, particularly with cycling to 34 A degrees C. Furthermore, with the fat phase fully molten, the backbone structure consisting of the dispersed particulates also contributed to overall roughness. This study demonstrated that significant microstructural changes and deformation take place within chocolate as a result of temperature fluctuations prior to the onset of visible surface fat bloom.