Mayonnaise and Margarine

Abstract

The margarine spread on toasts, the milk for breakfast and the mayonnaise for dressing the salad for lunch shown in Fig. 1.1 in Chap. 1 are all emulsions. Further, the creamer used in the after-lunch coffee is as well an emulsion. Our daily diet is in fact composed of many foods that are classified as emulsions (or regarded as emulsified foods). The foods like margarine, milk, and mayonnaise discussed in Chap. 1 are typical emulsified foods. Although knowledge concerning emulsion has been burgeoning in recent years along with the advancement in interfacial science, we will learn about the fundamentals of emulsion-forming process holding basically mayonnaise up as an example. Emulsions and liquid food polymers display combined viscous and elastic flow behaviors which are different from those of ordinary fluids (Newtonian fluids) like water. Fluids of this kind are called viscoelastic fluids, the basics of fluid flow of which will be further elaborated in this chapter.

Exercise

• 5.1 Name some example of O/W and W/O emulsions around us.

• 5.2 Look up the methods for determining the viscosity of fluids.

• 5.3 The surface tension (at 25 °C) of the aqueous solutions of a surfactant prepared at various concentrations is shown in Table 5.4. What are the critical micelle concentration, the surface excess, and the area occupied by a single surfactant molecule at the interface?

  Table 5.4 Concentration, C, and surface tension, γ

• 5.4 Table 5.5 summarizes the shear stress measured of a tomato ketchup sample at prescribed deformation rates (shear rates). Determine the parameters that describe the flow property of the sample.

  Table 5.5 Flow curve of a tomato ketchup sample

• 5.5 Derive Eq. (5.17) that expresses the relaxation curves of viscoelastic fluids.

• 5.6 A Maxwell fluid was subjected to sinusoidal strains of γ ₀ cosω t using a rheometer to characterize its flow property. At ω = 2 and an angular velocity of 5 s⁻¹, the loss angle, δ, was determined to be 0.375 and 0.158, respectively. (a) Prove that this set of data is valid and determine the relaxation time, λ. (b) The oscillation amplitude of τ/γ ₀ in Eq. (5.21) was 2.32 kg/(m² · s) during the measurement at ω = 2 s⁻¹. Determine the viscosity, μ, of the fluid.