Physical aspects of spreadable semi-solid animal protein emulsions

Abstract

This thesis investigates the physical aspects of semi-solid animal protein emulsions, specifically foie gras pâté and duck liver pâté, with the goal of developing a foie gras alternative without the need for force-feeding. By characterizing these systems using various analytical techniques, such as rheology, textural force measurements, differential scanning calorimetry (DSC) and coherent anti-stokes Raman scattering (CARS) microscopy, unique insights were gained into their textural properties and microstructure. A key focus was the comparison between foie gras pâté and a simplified duck liver pâté composed of rendered duck fat. Experimental findings showed that foie gras pâté exhibited significantly higher viscoelastic properties and hardness than the control pâté, attributed to its unique fat particle clusters, which support the protein network and contribute to its textural properties. These clusters, observed through CARS microscopy, acted as hard filler particles, increasing the pâté’s structural integrity but also causing rapid collapse under shear stress. Two approaches were explored to modify the properties of the liver-based emulsion: the systematic use of different emulsifiers and the alteration of fat structure via lipase treatment.\\ The study examined the effect of three stabilizers and emulsifiers — collagen, sodium stearate, and mono- and diglycerides (MDG) — on the physical properties and microstructure of the emulsion. Each emulsifier influenced the texture differently; collagen increased elasticity and hardness, sodium stearate increased hardness due to increasing electrostatic repulsion, and MDG affected rheological properties primarily in the unheated state. Additionally, emulsifiers led to a reduction in fat particle size and improved dispersion within the emulsion. A successful approach to mimicking foie gras pâté involved treating duck fat with lipase. The enzymatic modification altered the fat’s melting profile and solid fat content without changing its fatty acid composition. This lipase-treated fat replicated the structural characteristics of foie gras fat, leading to pâtés with similar rheological and textural properties and a similiar microstructure. Overall, this research demonstrates the importance of understanding emulsion-based food systems to effectively manipulate their properties. The findings highlight the crucial role of fat particle structure in determining foie gras pâté’s texture and provide a foundation for creating ethical and high-quality foie gras alternatives and enzymatic fat modification.