Flow behavior of Mexican sauces using a vane-in-a-large cup rheometer
´ L.P. Martınez-Padilla *, C. Rivera-Vargas
´ ´ ´ ´ Laboratorio de Propiedades Reologicas y Funcionales en Alimentos, FES Cuautitlan, Universidad Nacional Autonoma de Mexico. ´ ´ Av. Primero de mayo s/n, Cuautitlan Izcalli, Edo. de Mexico 54740,Mexico Received 3 June 2004; accepted 23 November 2004 Available online 7 January 2005
Abstract The rheological behavior of six diﬀerent commercial brands of Mexican sauces was studied. The sauces were considered to be homogeneous with ﬁne particles (‘‘Barbecue’’, ‘‘Chipotle’’ and ‘‘Valentina’’) and heterogeneous with coarse particles (‘‘Taquera’’, ´ ‘‘Ranchera’’ and ‘‘Verde Bufalo’’). Theconventional concentric cylinders geometry was used to validate the non-conventional vane-in-cup system. Two containers were tested for the vane-in-cup; a small cup (cup/bob radius ratio = 1.06) and a large cup (cup/bob radius ratio = 2). Rheological parameters were calculated using the Couette–Searle analogy, considering a non-Newtonian behavior and a large cup. The large cup contained eight baﬄesto avoid slippage at the wall. Homogeneous sauces with ﬁne particles were examined in all ﬁxtures, while the heterogeneous containing coarse particles, only in the vane-in-large cup. All sauces exhibited a shear-thinning behavior that could be correlated by the power-law model. Several shear stress and shear rate factors proposed in the literature for large gaps and power-law models were comparedto the average shear factors proposed in this study. The method proposed here was proved to be an alternative to characterize the ﬂow properties of coarse particles suspensions in a vane-in-a-large cup rheometer. Ó 2004 Elsevier Ltd. All rights reserved.
Keywords: Vane; Coarse suspensions; Rheometry; Power-law model; Shear factors
1. Introduction For the purpose of culinary uses, sauces can bedeﬁned as a ﬂuid product diﬀerent from condiment, which can be added to foods to give a better appearance, ﬂavor and texture. Under this deﬁnition sauces may include some spices. Sauces are a very common product consumed in Mexico characterized by the presence of coarse particles of tomato, hot peppers and the seeds of these two ingredients. The wide variety of hot peppers produced and consumed inMexico results in the manufacture of many types of hot sauces actually available in the
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marketplace, as well as, in new formulations trying to satisfy the large demand of this product. Typical sauces are multiphase dispersed systems formed mainly by solid rigidparticles, solid deformable particles, and sometimes liquid deformable particles such as oil droplets. Diﬀerent particle sizes and forms arise from diﬀerent vegetable tissues used in sauce preparation. A typical formulation of Mexican sauce includes 85% tomato, 5% hot pepper, 4% onion, 1% garlic and 2% salt. The continuous phase can be water or a solution of macromolecules in water, which include gums orpolysaccharides, as well as, proteins from vegetables or added proteins, mineral salts, organic acids and other components to get an acid pH and to preserve the product. The high concentration of particles, with a density close to that of water, is responsible for the
0260-8774/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2004.11.009
´ L.P.Martınez-Padilla, C. Rivera-Vargas / Journal of Food Engineering 72 (2006) 189–196
overall homogeneous appearance of some Mexican sauces as illustrated in Fig. 1. The importance of ﬂow properties in food processing and quality control has been widely described with particular reference to operations involving pipe ﬂow, mixing and heat transfer (Rao, 1999). The signiﬁcant increase of Mexican hot...