Monoglyceride Stabilized Oil in Water Emulsions: an Investigation of Structuring and Shear History on Phase Behaviour

Abstract

In this study we report on the effects of structuring, aging, temperature, and shear history on the polymorphism and stability of structured monoglyceride stabilized oil in water emulsions, or MAG gels. With knowledge that the structure of the gel is paramount towards its functionality, this study investigated how structuring of MAG gel affects proton relaxation and monoglyceride crystal polymorphism. The structured MAG gel was compared to its compositionally equivalent unstructured components containing either dry or hydrated monoglycerides. Proton relaxation studies were conducted using pulsed proton Nuclear Magnetic Resonance T2 relaxation analysis. Powder X-ray Diffraction was used to determine the monoglyceride crystal polymorphism within the system. Proton relaxation was greatly affected by the structuring of MAG gel components, with the structured MAG gel displaying faster relaxation times compared to its unstructured components. The structured MAG gel also displayed different polymorphic behaviour than its unstructured components, with structured gels exhibiting greater stability, and displaying both α and β monoglyceride polymorphic forms. The application of shear resulted in greater water mobility within MAG gels compared to non-sheared samples, as well as a greater proportion of the β polymorphic population. This study established a relationship between water mobility determined by T2 relaxation analysis and the proportion of the β polymorph population determined through XRD reflections. It clearly demonstrates that an increase in the β polymorph population leads to a decrease in the strength of water binding, and that shear enhances this process.