Surface Characterization of Caramel at the Micrometer Scale

Abstract

The surface of caramel has been imaged using pulsed force atomic force microscopy (AFM) and scanning thermal microscopy, revealing shallow depressions in the surface of 1 to 10 m in dia that have a higher adhesion to the silicon AFM probe and a lower stiffness and different thermal character than the surrounding sample. This is consistent with the view of caramel as fat droplets within a matrix of sugars. As confirmation, the depressed regions were identified by infrared microscopy as consisting mainly of fat in a matrix of sugar. AFM also reveals that regions surrounding the depressions are decorated with thin (about 6nm) plate-like features that display a higher stiffness than the rest of the matrix. We propose that these are of crystalline origin and most probably consist of fat.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Sun et al [1226] found that annealing of octyltriethoxysilane films on glass at elevated temperature lead to breakup of films and formation of islands but coverage of the glass surfaces was still observed between islands according to stiffness and adhesion data. Morton et al [1227] found shallow depressions in the surface of caramel with 1-10 mm in diameter that exhibited higher adhesion to the silicon AFM probe and a lower stiffness than the surrounding sample. This is consistent with the view of caramel as fat droplets within a matrix of sugars.…”

Scientific basis of nanotechnology, implications for the food sector and future trends

“…By probing the surface of samples with a nanometrical tip, AFM has been used to probe molecular interactions via force spectroscopy (Morris, Woodward, & Gunning, 2011). Moreover, AFM has been demonstrated as an ideal platform to develop advanced techniques for nanomechanical characterization of samples (Passeri, Rossi, Tamburri, & Terranova, 2013), the potential of which for the analysis of Young's modulus, complex elastic modulus, hardness, tip-sample adhesion force has been only marginally explored in food derived samples (Goode, Bowen, Akhtar, Robbins, & Fryer, 2013;Morton et al, 2003;Scramin et al, 2011;Zdunek & Kurenda, 2013). As an example, Fig.…”

“…based technique which allows one to perform the quantitative characterization of mechanical parameters of soft samples (mainly, elastic modulus, tip-sample adhesion force and tip-sample dissipation) with nanometrical lateral resolution (Sahin & Erina, 2008;Sahin, Magonov, Su, Quate, & Solgaard, 2007). Also, thermal characterization at the nanoscale has been performed on caramel using SThM (Morton et al, 2003). Finally, even if only marginally, other SPM techniques have been used to study food derived samples, i.e., SNOM for the characterization of proteinsurfactant interactions by acquiring fluorescence images at sub-micrometer scale (Morris, 2004) and STM for the investigation of high molecular subunits of wheat glutenin (Tatham et al, 1999).…”

Artifacts in Atomic Force Microscopy of Biological Samples

“…If it is due to other reasons, one can scan faster (Eaton, 2010). If the sample is too sticky or too soft, an artifact due to multiple probe-sample contact points occurs (Morton et al, 2003;Sokolov, 2007). This problem is highly relevant to cells studies (Touhami, Jericho & Beveridge, 2004).…”

“…The sample can be too sticky or too soft. In this case, artifacts due to multiple probe-sample contact points occur (Morton et al, 2003;Sokolov, 2007). AFM image of a charged nonconductive sample may not correspond to topography.…”