Effect of particle size in chocolate shell on oil migration and fat bloom development Hanna Dahlenborg a,b,⇑ , Anna Millqvist-Fureby a , Björn Bergenståhl b a SP, Technical Research Institute of Sweden, Box 5607, SE-114 86 Stockholm, Sweden b Lund University, Department of Food Technology, Engineering and Nutrition, P.O. Box 124, SE-221 00 Lund, Sweden article info Article history: Received 26 February 2014 Received in revised form 15 August 2014 Accepted 2 September 2014 Available online 16 September 2014 Keywords: Chocolate Cocoa butter Particle size Fat bloom Migration Surface structure abstract The effects of chocolate shell particle size were investigated by means of its influence on rate of oil migra- tion and fat bloom development. The particle size of the non-fat particles in the chocolate, i.e. sugar and cocoa particles was varied between 15, 22 and 40 lm. A novel set of analytical techniques was used and by combining migration results with surface topology results clear differences could be observed between the samples. At 23 °C storage the samples with a particle size of 15 lm showed higher rate of oil migration and further, the earliest development of fat bloom at the surface. This could be observed both macroscopically and microscopically. Thus, it appears as a larger specific surface area of the non- fat particles facilitates migration of filling oil, possibly due to a more heterogeneous and coarser crystal network with higher permeability. Molecular diffusion cannot explain the level of oil migration observed and, thus, convective flow is assumed to be an important contribution in addition to the molecular diffusion. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Migration of the internal filling fat into the surrounding choco- late shell in chocolate pralines is a major concern for the confec- tionery industry. This migration leads to textural quality loss in addition to fat bloom development, giving the product a dull, whit- ish haze resulting in rejection by the consumers (Ghosh et al., 2002; Hartell, 1999; Lonchampt and Hartel, 2004; Smith et al., 2007; Talbot, 1990). The driving force behind this migration is usu- ally explained by a triacylglycerol (TAG) concentration gradient between the liquid filling fat and the liquid cocoa butter (CB) in the chocolate shell, tending towards a thermodynamic equilibrium (Ziegleder et al., 1996a,b; Ziegleder and Schwingshandl, 1998). However, the mechanism of oil migration in chocolate pralines is not yet fully understood, and it has been explained by molecular diffusion (Deka et al., 2006; Lee et al., 2010; Maleky et al., 2012; McCarthy and McCarthy, 2008; Miquel et al., 2001; Ziegleder et al., 1996a,1996b; Ziegleder and Schwingshandl, 1998), capillary flow (Aguilera et al., 2004; Choi et al., 2007; Guiheneuf et al., 1997; Marty et al., 2005; Quevedo et al., 2005; Rousseau and Smith, 2008) and a pressure driven convective flow (Altimiras et al., 2007; Dahlenborg et al., 2011, 2012; Loisel et al., 1997). Due to migration of liquid fat from the filling, the solid fat con- tent (SFC) is reduced in the chocolate shell in addition to polymor- phic changes within the solid fat phase (Motwani et al., 2011; Timms, 1984). These polymorphic changes are usually connected to formation of fat bloom, where form b 1 VI, the most stable CB TAG polymorph, has developed within the chocolate fat matrix (Smith et al., 2007; Wille and Lutton, 1966). Further, when the nee- dle shaped b 1 VI crystals are formed on the chocolate surface and these are larger than 5 lm, a whitish haze, connected to fat bloom, appears due to scattering of light (Hartell, 1999; Kinta and Hatta, 2005; Lonchampt and Hartel, 2004). In contrast, when producing chocolate products the desired crystalline form or polymorph of the CB TAGs is b 2 V, which is achieved when it undergoes a con- trolled crystallisation during production. The rate of oil migration can be influenced by different param- eters. Higher storage temperatures have shown to increase the migration rate (Ali et al., 2001; Altan et al., 2011; Dahlenborg et al., 2014; Guiheneuf et al., 1997; Khan and Rousseau, 2006; Miquel et al., 2001; Ziegleder and Schwingshandl, 1998), and the chocolate shell microstructure has also been shown to affect the migration rate (Dahlenborg et al., 2014; Lee et al., 2010; Maleky et al., 2012; Miquel et al., 2001; Motwani et al., 2011; Svanberg et al., 2011, 2013). Studies have demonstrated that by using http://dx.doi.org/10.1016/j.jfoodeng.2014.09.008 0260-8774/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: SP, Technical Research Institute of Sweden, Box 5607, SE-114 86 Stockholm, Sweden. Tel.: +46 10 516 60 62 (Dir), mobile: +46 70 587 60 62; fax: +46 8 20 89 98. E-mail address: hanna.dahlenborg@sp.se (H. Dahlenborg). Journal of Food Engineering 146 (2015) 172–181 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng