Whippable emulsions based on vegetable fat are increasingly used as replacement for dairy whipping creams. One of the quality criteria of whippable emulsions is that it should be low-viscous prior to whipping, but sudden viscosity increase or even solidification during storage and transport is a prevalent problem causing deteriorated products. Increased viscosity is a consequence of aggregation of dispersed fat globules, which is referred to as physical instability. The aim of the project was to obtain detailed knowledge of the destabilization mechanisms in whippable emulsions by understanding the impact of ingredient composition, with focus on low-molecular-weight (LMW) emulsifiers. Three monoglyceride-based LMW-emulsifiers were selected: Lactic acid ester of saturated monoglyceride (LACTEM), unsaturated monoglyceride (GMU), and saturated monoglyceride (GMS).
LMW-emulsifiers had major impact on physical stability of whippable emulsions. Addition of LACTEM increased emulsion viscosity considerably at 20 °C, but low viscosity could almost be entirely regained by cooling the emulsions to 5 °C under appliance of shear. GMS did not induce fat globule aggregation in emulsions which remained low viscous despite appliance of shear and temperature changes from 5 to 20 °C. Globule aggregation induced by LACTEM was impeded when used in combination with GMS. On the contrary, GMU induced very dense fat globule networks in emulsions which transformed emulsions into very firm solid-like pastes. This effect was enhanced when GMU was added in combination with LACTEM.
Physical stability of whippable emulsions was also influenced by concentrations of proteins and stabilizers, and type of dispersed fat phase. Factors related to the dispersed fat phase with effect on emulsion stability was solid fat content, broadness of the melting range, and possibly fatty acid composition, crystal conformation and wettability of crystals. Polymorphism of dispersed triacylglycerides was found not to be related to physical instability of emulsions.
Interfacial protein displacement by LMW-emulsifiers was not prerequisite for physical instability in emulsions, and conversely physical instability was not necessarily accompanied by protein displacement. GMS and LACTEM efficiently displaced caseinate from the fat globule interface into the serum phase, while caseinate molecules remained partly attached to the interfacial globule layer in emulsions with GMU.
Three different mechanisms of GMU, LACTEM, and GMS in emulsions were proposed based on the emulsifiers’ effect on emulsion stability and protein displacement from the interface of fat globules. A flocculated network of fat globules was formed in emulsions with LACTEM due to formation of a hydrated α-gel at the interface of globules which linked globules together. Crystals of GMS composed a physical barrier around fat globules ensuring high stability against aggregation in emulsions. For emulsions with GMU, caseinate molecules were involved in formation of a partial coalesced fat globule network.