Rheological Behavior of Pineapple and Mango Pulps D. H. Pelegrine*, F. C. Silva and C. A. Gasparetto D. H. Pelegrine, C. A. Gasparetto: Department of Food Engineering, Food Engineering Faculty/UNICAMP, P.O. Box 6121, Code: 13.081-970, Campinas/S.P. (Brazil) F. C. Silva: Embrapa Agroindu´stria de Alimentos, Au. das Ame´ricas, 29501, CEP: 13083-970 – Campinas/SP, Brazil (Received October 1, 2001; accepted June 12, 2002) The rheological behavior of whole and centrifuged mango (Mangı´feraindica L. var. Keitt) and pineapple (Ananas comusus L. merr var Pe ´rola) pulps was analysed at 30 1C, in a rotational viscometer Haake Rotovisco RV-20. The experiments were conducted with measuring system of 45 mm diameter parallel plates (PQ45) with gap of 0.5 mm, at shear rates up to 874 s l . The rheograms were fitted with Casson, Ostwald-of-Waelle and Mizrahi–Berk (M–B) models. The Brix of pineapple and mango pulps were 16.6 and 13.3 1Brix, respectively, and the insoluble solids content was 0.108 g/kg for mango and 0.054 g/kg for pineapple. The best adjustment was obtained with M–B model. It was observed that the pulps presented pseudoplastic behavior, and the suspended solids had great influence on the consistency index. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: mango; pineapple; rheology; pulp Introduction Mangoandpineappleoccupyprominentpositionsinthe world market, being among the main fruits of great commercial importance. Besides the fruits ‘in nature’, their manufactured products, such as juices, nectars, ice creams and jellies, whose basic raw material is the pulp, which is used in the unit operations, such as pumps, agitation, heat exchanger and separations. For such industrial processes to be technically and economically feasible, it is important to have the knowledge of the physical–chemical properties. Among these properties, the rheological behavior is one of the most important, being useful not only as quality measure, but also in projects, evaluation and operation of the process equipments (Ibarz et al., 1996). Because every fruit liquid product is composed by solid particles dispersed in an aqueous phase, its rheological behavior will be influenced by the concentration, chemical composition, size, shape and arrangement of these particles that compose the dispersed phase (Costell and Dura´n, 1982). Queiroz (1998) studied the influence of suspended solids on mango and pineapple pulps and concluded that these particles had great influence on rheology of both pulps. Most fluid foods do not have the simple Newtonian rheological model; in other words, their viscosities are independent of shear rate or shear stress and not constant with temperature. Therefore, it is necessary to develop more complex models to describe their behavior (Holdsworth, 1971). Some of the most widely used rheological models are the Power Law with two parameters, the Casson with two parameters plus the yield stress, and the Mizrahi–Berk (M–B) with three parameters and yield stress. Usually, the Power Law is used to indicate pseudoplasticity due to dissolved solids, through the fluid behavior index n. Casson is used to demonstrate the effect of suspended material, and M–B model is an attempt to match these two effects. The Ostwald-de-Waelle (Power Law) model is described below as  ¼ K _  n Eqn ½1 where t is the shear stress (Pa); _  the shear rate (s 1 );the K the consistency index (Pas n ) and n the behavior index of the fluid. Several researchers used the Power Law model to describe rheological behavior of fruit pulps, juices and pure´e (Saravacos, 1968; Varshney and Kumbar, 1978; Guariguata,1981;Lombran˜aandDı´as,1985;Rao et al., 1985, 1986; Xu et al., 1986; Gunjal and Wachmare, 1987). Even so, some foods have the yield stress that is also an important characteristic so their experimental data are not adjusted to the Power Law model with greatprecision.Forthat,Cassonproposedthefollowing expression:  1=2 ¼  0C þ  C _  ðÞ 1=2 Eqn ½2 *To whom correspondence should be addressed. Fax: +55 19 378840227; E-mail: dhpeleg@ceres.fea.unicamp.br 0023-6438/02/$35.00 doi:10.1006/fstl.2002.0920 r 2002 Elsevier Science Ltd. All rights reserved. All articles available online at http://www.idealibrary.com on 645 Lebensm.-Wiss. u.-Technol., 35, 645–648 (2002)