par Becu, Mélanie ;Fonoll, Joan Rius;Hospied, Emeline;Haut, Benoît ;Debaste, Frédéric ;Liégeois, Sophie
Référence Biotechnologie, agronomie, société et environnement, 14, SPEC. ISSUE 2, page (537-538)
Publication Publié, 2010
Article révisé par les pairs
Résumé : In the food industry, the production process is often established in an empirical way, according to rules of good practice. These methods present gaps, in particular at the level of the production regularity. To model and optimize the processes, it is highly useful to determine the physico-chemical properties of the product. In this work, chocolate and margarine are studied, both aiming direct industrial application but also aiming a general enhancement of rheological mechanism understanding. Indeed, the chocolate is a suspension of solid particles in cocoa butter and the margarine is a water-in-oil emulsion. Rheological behavior of those fluids is therefore relying on different key phenomena. In this work the flow behavior of both products is characterized and a mathematical model describing the rheological behavior of chocolate is developed. For chocolate, the goal is to model the tempering process. To establish the rheological behavior of chocolate, viscosity measurements were realized in a SEARLE VT550 viscometer using a bob and cup geometry. To build the mathematical law, general tests following the International Office of Cocoa, Chocolate and Sugar Confectionery (IOCCC) recommended method (Servais et al., 2004) were performed. The obtained rheogram shows that the chocolate has a slightly thixotropic behavior. More focus is set on a smaller range of shear rate important for the industrial application (Debaste et al., 2008). Measures for various temperatures and various quantities of cocoa butter were realized. The results show a classical shear-thinning behavior. Further, a statistical analysis of the results was made to determine the parameters of a power-law describing this behavior. It appears that temperature and cocoa butter fraction have no influence on the exponent but well on the consistency parameter. For margarine, the goal is to model the flow in resting tubes, the last step in the industrial production (Herman et al., 2008). To determine the rheological behavior of the margarine two kinds of devices were used. First the SEARLE VT550 viscometer with a four blades impeller was used. And the results were not satisfying because the measured viscosity was often nulls. We suppose that the sample was broken into two blocks, one between the blades of the impeller and a second outside of the impeller. A HAAK MARS rheometer with a plate-plate geometry was also used. In both experiments we evaluate how a change of 1°C can affect the viscosity of margarine. The obtained flow curves show that the margarine has a plastic and thixotropic behavior and that a variation of 1°C affects margarine's rheology. With the chocolate rheological law, the perspective is to get a general model for concentrated suspensions. And for margarine, more measures with an adapted viscometer should be done to build a model.