E: Food Engineering & Physical Properties The Influence of Different Processing Stages on Particle Size, Microstructure, and Appearance of Dark Chocolate Virginia Glicerina, Federica Balestra, Marco Dalla Rosa, Bjorn Bergenhst˚ al, Eva Tornberg, and Santina Romani Abstract: The effect of different process stages on microstructural and visual properties of dark chocolate was studied. Samples were obtained at each phase of the manufacture process: mixing, prerefining, refining, conching, and tempering. A laser light diffraction technique and environmental scanning electron microscopy (ESEM) were used to study the particle size distribution (PSD) and to analyze modifications in the network structure. Moreover, colorimetric analyses (L ∗ , h°, and C ∗ ) were performed on all samples. Each stage influenced in stronger way the microstructural characteristic of products and above all the PSD. Sauter diameter (D [3.2]) decreased from 5.44 μm of mixed chocolate sample to 3.83 μm, of the refined one. ESEM analysis also revealed wide variations in the network structure of samples during the process, with an increase of the aggregation and contact point between particles from mixing to refining stage. Samples obtained from the conching and tempering were characterized by small PS, and a less dense aggregate structure. From color results, samples with the finest particles, having larger specific surface area and the smallest diameter, appeared lighter and more saturated than those with coarse particles. Keywords: appearance, chocolate, ESEM, manufacture stages, microstructure, particle size distribution Practical Application: Final quality of food dispersions is affected by network and particles characteristics. The deep knowledge of the influence of single processing stage on chocolate microstructural properties is useful in order to improve or modify final product characteristics. ESEM and laser diffraction are suitable techniques to study changes in chocolate microstructure. Introduction Dark chocolate can be defined as a concentrated suspension made up of solid particles (sugar and ground cocoa particles) dis- persed in a Newtonian fluid, generally cocoa butter (Afoakwa and others 2008). Quality and stability of final products are affected by a number of factors, such as particle size (PS), particle size distribution (PSD), and interaction between them and are strictly related to the raw materials but also to the manufacture process (Servais and others 2002; Granger and others 2005; Sato and oth- ers 2009; Baldino and others 2010). The physicochemical and microstructural properties of chocolate depend on many factors besides the ingredients and their proportions. The different process steps (mixing, prerefining, refining, conching, and tempering) of chocolate manufacture and the different adopted process param- eters can affect chocolate properties that, in turn, determine the behavior and the characteristics of the final product. An effec- tive control of the technological parameters is required in order to achieve a constant and desirable quality of the final product (Muller-Fischer and others 2005; Baixauli and others 2007). The MS 20131759 Submitted 11/26/2013, Accepted 4/19/2014. Authors Glice- rina, Balestra, and Rosa are with Interdepartmental Centre for Agri-Food Indus- trial Research, Alma Mater Studiorum, Univ. of Bologna, Piazza Goidanich, 60, Cesena, Italy. Author Romani is with Interdepartmental Centre for Agri-Food In- dustrial Research and with Dept. of Agri -Food Science & Technologies, Alma Mater Studiorum, Univ. of Bologna, Piazza Goidanich, 60, Cesena, Italy. Au- thors Bergensthal and Tornberg are with Dept. of Food Technology, Engineering and Nutrition, Lund Univ., Lund, Sweden. Direct inquiries to author Glicerina (E-mail: virginia.glicerina2@unibo.it). processing of foods and in particular of dark chocolate brings several changes in their microstructure. During chocolate man- ufacturing, mixtures of sugar, cocoa, and fat are heated, cooled, pressurized, and refined (Beckett 2000). These steps not only affect PS reduction, but also break agglomerates and distribute lipid and lecithin-coated particles through the continuous phase, modifying the microstructure of final chocolate (Afoakwa and others 2009). The interactions between the suspended particles and the contin- uous phase provide information about the existing network and consequently can be associated with the properties and character- istics of the dispersions (Sato and others 2009). Since macroscopic properties of foods, such as the appearance attributes and color, are strongly determined by the microstructure of the food material, evaluation of the microstructure of food and its components is necessary for understanding its macroscopic properties (Aguilera and Stanley 1999). PS values of chocolate are influenced by its for- mulation, and in particular as known by literature (Awua 2002), optimum PS for dark chocolate should be lower than 35 μm of diameter. Environmental scanning electron microscopy (ESEM) is one of the most suitable techniques used to investigate microstructure of foods and to highlight the changes in the different structures ob- tained during the manufacturing process (Kalab and others 1996). ESEM, in fact, is a technique producing high-resolution images of chocolate specimen due to the way the image is obtained; ESEM images have a characteristic 3-dimensional appearance and let to investigate the macroscopic properties of a sample (Dahlen- borg and others 2010). Laser diffraction analytical method is also a very spread technique used for PS analysis, based on the laser C  2014 Institute of Food Technologists R  doi: 10.1111/1750-3841.12508 Vol. 79, Nr. 7, 2014  Journal of Food Science E1359 Further reproduction without permission is prohibited