On the porous mesostructure of milk chocolate viewed with atomic force microscopy

Abstract

The surface structure of commercial milk chocolate is examined using atomic force microscopy. It is shown that its surface topography is complex, comprising a finely mottled, yet irregular texture with most structural elements measuring <3 μm in size. It is also demonstrated that a large number of microscopic pores exists at the surface. The morphology of these pores is highly variable, with observed cavities generally being conical in nature with irregularly shaped openings. Typical pore depths range from 1 to 3 μm and are randomly distributed on the surface of milk chocolate, without any defining features in their vicinity to suggest their existence. In the past, it has been postulated that such pores are opening to channels; these being responsible for liquefied cocoa butter transport and subsequent promotion of fat bloom formation. To shed light on any such relationship, milk chocolate is subjected to multiple (6, 12 and 24) temperature cycles (each from 25 to 27 °C and 25 °C over 2 h). Results show that following many cycles, there is crystal growth around some pores, but that the pores themselves are not appreciably altered. This suggests that, under these experimental conditions, they are not directly involved in bloom mediation or liquefied fat transport in milk chocolate.