Effect of the Cooling Rate and the Surface Film Composition on the Colloidal Stability of Whey Protein Based Emulsions of Triacylglycerols

Sammanfattning: The goal of this project was to investigate the effect and interplay of formulation and processing parameters on the colloidal stability of emulsified triacylglycerols from a product quality perspective. Different methods to quantify and monitor this effect over time were evaluated. The results of this study were intended to lead to the development of industry relevant recommendations to optimise the processing conditions and formulation of a range of different products. Many commercially important products, including cosmetics, pharmaceuticals and foods such as UHT milk and heavy cream are based on triacylglycerols emulsified in a protein-rich continuous phase. Temperature fluctuations during long-term storage and distribution of these products can cause uncontrolled crystallisation of the disperse fat phase. This impairs the functional and sensory characteristics and the stability of the emulsion system. Product defects and product waste could be reduced by gaining a systematic understanding of the factors that govern the crystallisation behaviour of emulsified triacylglycerols and by finding mechanisms to induce a guided crystallisation process. In this study, a liquid emulsion system was produced from hydrogenated palm oil, consisting nearly entirely of triacyglycerols, and an aqueous continuous phase, containing !-lactoglobulin as emulsifier. Diffraction analysis, microscopic and calorimetric measurements were used to determine the colloidal stability of the model system over eight weeks of isothermal storage at 22 °C. Based on previous research, it was expected that the surface film composition of the dispersed palm oil droplets and the rate at which the emulsions are cooled from processing to storage temperature, would impact the stability of the system. Thus, the influence of a high, moderate and low cooling rate and the addition of two phospholipids, acting as complementary emulsifiers to !-lactoglobulin, were tested. No significant effect of the cooling rate on the stability of the emulsion system was noted over a storage period of eight weeks. The addition of phospholipids seemed to have altered the composition and thereby the properties of the emulsion interfaces. The emulsions showed a more uniform fat crystal size but also more extensive flocculation. It is therefore questionable whether the benefit of using phospholipids does not outweigh the costs. One of the two phospholipids even appeared to inhibit the crystallisation of the hydrogenated palm oil, which is unfavourable, when aiming for a fully crystalline fat phase. The results of this project suggest that a formulation without phospholipids and a slow cooling process are most cost and resource efficient to produce a stable emulsion system. Independent of the formulation or processing, there were signs for the migration of fat molecules between the emulsion particles. This can adversely affect the particles’ physicochemical properties and raises the need for further research into mechanisms to prevent mass transport processes in triacylglycerol emulsions.