Impact of Weighting Agents and Sucrose on Gravitational Separation of Beverage Emulsions Ratjika Chanamai and D. Julian McClements* Biopolymers and Colloids Research Laboratory, Department of Food Science, University of Massachusetts, Amherst, Massachusetts 01003 The influence of weighting agents and sucrose on gravitational separation in 1 wt % oil-in-water emulsions was studied by measuring changes in the intensity of backscattered light from the emulsions with height. Emulsions with different droplet densities were prepared by mixing weighting agents [brominated vegetable oil (BVO), ester gum (EG), damar gum (DG), or sucrose acetate isobutyrate (SAIB)] with soybean oil prior to homogenization. Sedimentation or creaming occurred when the droplet density was greater than or lower than the aqueous phase density, respectively. The weighting agent concentrations required to match the oil and aqueous phase densities were 25 wt % BVO, 55 wt % EG, 55 wt % DG, and 45 wt % SAIB. The efficiency of droplet reduction during homogenization also depended on weighting agent type (BVO > SAIB > DG, EG) due to differences in oil phase viscosity. The influence of sucrose (0-13 wt %) on the creaming stability of 1 wt % soybean oil-in-water emulsions was also examined. Sucrose increased the aqueous phase viscosity (retarding creaming) and increased the density contrast between droplets and aqueous phase (accelerating creaming). These two effects largely canceled one another so that the creaming stability was relatively insensitive to sucrose concentration. Keywords: Creaming; sedimentation; emulsions; beverages; weighting agents INTRODUCTION The term “beverage emulsion” is used to describe a group of products that have similar compositions, preparation procedures, and physicochemical properties, for example, fruit drinks, cordials, punches, and sodas (Tan, 1997). Beverage emulsions are oil-in-water emul- sions that are prepared in a concentrated form that is diluted prior to consumption either by the manufacturer or by the consumer. The oil phase consists of some combination of vegetable oil, flavor oil, weighting agent, and antioxidants, whereas the aqueous phase consists of water, emulsifier, sweetener, salts, acids, and pre- servatives. The low concentration of droplets in diluted beverage emulsions (<0.3 wt %) accounts for their slightly turbid or “cloudy” appearance and the fact that their viscosities are similar to that of the aqueous solution that surrounds the droplets (Trubiano, 1995; McClements, 1999). Beverage emulsions are thermodynamically unstable systems that tend to break down during storage. The most common manifestations of beverage emulsion deterioration are “ringing” and “oiling-off” (Trubiano, 1995; Tan, 1997, 1998). Ringing is the formation of a whitish “ring” around the neck of the container, whereas oiling-off is the formation of a shiny oil slick on top of the product. Ringing and oiling-off are the result of a variety of physicochemical mechanisms that occur within the beverage emulsion, including gravitational separa- tion, flocculation, and coalescence (Dickinson and Stains- by, 1982; Dickinson, 1992; McClements, 1999). A better understanding of the origin and nature of these insta- bility mechanisms would enable beverage manufactur- ers to develop products with enhanced shelf lives. Previous researchers have examined the influence of emulsifier characteristics (Dickinson et al., 1989; Ray et al., 1995; Kim et al., 1996; McNamee et al., 1998; Garti, 1999), oil composition (Freeburg et al., 1994), weighting agents (Trubiano, 1995; Tan, 1997, 1998), temperature (Tse and Reineccius, 1995), and pH and ionic strength (Jayme et al., 1999) on the stability of beverage emulsions. In this study, we examine the influence of weighting agents and sucrose on gravita- tional separation in beverage emulsions. The rate at which an isolated rigid spherical particle moves in a Newtonian liquid is given by Stoke’s law (Hunter, 1986) where U is the creaming velocity, η is the shear viscosity, r is the particle radius, g is the acceleration due to gravity, F is the density, and the subscripts 1 and 2 refer to the continuous and dispersed phases, respectively. The sign of U determines whether the particle moves upward (+) or downward (-). Stoke’s law gives a good description of the creaming velocity of isolated fluid spherical droplets, provided that there is little movement of the liquid within the droplets (McClements, 1999). This condition is met when the viscosity of the disperse phase is significantly greater than that of the continuous phase (i.e., η 2 /η 1 > 5) or when the droplets are surrounded by an emulsifier membrane that resists deformation (McClements, 1999). Equation 1 is therefore applicable to beverage emulsions because the oil phase has a much higher viscosity than the aqueous phase (η 2 /η 1 > 5) and the droplets are * Corresponding author [fax (413) 545-1262; e-mail mcclements@foodsci.umass.edu]. U Stokes )- 2gr 2 (F 2 -F 1 ) 9η 1 (1) 5561 J. Agric. Food Chem. 2000, 48, 5561-5565 10.1021/jf0002903 CCC: $19.00 © 2000 American Chemical Society Published on Web 09/29/2000