Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?—A Hypothesis Paper

Abstract

The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods.

Influence of calcium fortification on physical and rheological properties of sucrose-free prebiotic milk chocolates containing inulin and maltitol

“…In previous studies, differences in L* (38.3-43.5) and C* (11.0-14.4) were found to vary with the process conditions and storage (Aguilera et al 2004;Mexis et al 2010). In this study, chroma values varied within narrow ranges, such as 15.0±0.65-15.5±0.81 (Table 3); however, statistically significant variations were determined between the sample groups (P <0.01).…”

“…Relevant information related to colour has be acquired from modern technologies such as computer vision and calibrated colour imaging analysis according to the HunterLab and CIELab models (Afoakwa et al 2008;Briones and Aguilera 2005;Jahns et al 2001;Hatcher et al 2004;Lawless and Heymann 1998). Colour changes are likely to be specific to each chocolate sample (Aguilera et al 2004). In previous studies, differences in colour parameters were found to vary with the particle size distribution, packaging conditions and storage (Aguilera et al 2004;Mexis et al 2010).…”

“…Colour changes are likely to be specific to each chocolate sample (Aguilera et al 2004). In previous studies, differences in colour parameters were found to vary with the particle size distribution, packaging conditions and storage (Aguilera et al 2004;Mexis et al 2010). Hardness plays an important role in the sensory assessment of chocolate (Viaene and Januszewska 1999).…”

Mass Transfer Mechanisms during Dehydration of Vegetable Food: Traditional and Innovative Approaches

“…These definitions recognizes the importance of the three dimensional microstructure of food, stating that the mass transport of water is a more complex phenomena than in a non-porous material (Datta, 2007a). Starting from this idea, capillary forces flow must be considered as one of the most important mass transfer mechanism during drying (Datta, 2007a), rehydration (Saguy et al, 2005) as well as during frying, and fat migration in chocolate (Aguilera et al, 2004). As known, capillary forces are responsible to the attraction among liquid molecules and between them and the solid matrix.…”

“…So, capillary force are among the reasons of: a. the water transport from a region with more water to a region with less one due to the differences in capillary force; b. the difficulty to remove water from vegetable structure. Historically, Lucas-Washburn equation it is recognized as best equation to model capillary rise into a small pores (Aguilera et al, 2004). The equation shows that the pressure inside a cylindrical capillary is balanced by viscous drag and gravity (Lucas, 1912;Washburn, 1921;Krotov and Rusanov, 1999).…”