Relationship between Flow Characteristics and Composition of Fat Free “Dulce de leche”

Abstract

In order to follow the recommendations of the World Health Organization to limit the consumption of fat in the diet, since childhood and through out life, consumers must have healthy and tasty products available and the dairy industry is undergoing major transformations to meet these requirements. "Dulce de leche" (DL) is a rich, creamy, caramel-like milk-based sauce or spread. Widely consumed in Latin America, is also known as manjar, manjar blanco, and arequipe. In Argentina it is commercialized in at least four types of products to be used in different applications: traditional, reduced calories, reduced fat, and confectionary. They differ in their composition, caloric and lipid contents, and flow characteristics; so under the common name of "Dulce de leche" very different products are available to consumers. DL has a typical texture that is important for consumers when evaluating its overall acceptability. As fat content diminishes or water content increases DL becomes less viscous, so it is necessary to add thickeners to maintain flow characteristics in a "0% fat" product. In this chapter the rheological properties of fat-free "Dulce de leche" formulated with different contents of water and xanthan gum are discussed. DL samples with moisture contents ranging from 23.7% to 60.3% and xantham gum concentration between 0.173% and 0.555% were prepared. Steady-state flow curves (viscosity η versus shear rate ?) of the DL samples were evaluated with a controlled stress rheometer by increasing the shear rate in steps between 0.01 and 100 1/s. The obtained flow curves showed a shear-thinning behavior. Three models were tested to regress experimental steady-state flow curves (Casson, power law, and Herschel-Bulkley). From the analysis of residuals and correlation coefficients it was found that the Herschel-Bulkley´s model explained better the stress-strain experimental results. It was observed that the regressed parameters depended strongly on moisture content, increasing when moisture content decreased and much less markedly on xanthan gum content. Empirical polynomial expressions that correspond to Scheffe´s model with inverse terms included were obtained. From this set of equations it is possible to predict the most adequate composition to obtain fat-free "Dulce de leche" with the flow expected caracteristics according to it propose use.