Formation and characterisation of high-internal-phase emulsions stabilised by high-pressure homogenised quinoa protein isolate

Abstract

High pressure homogenised (HPH) quinoa protein isolates (QPI) suspensions (1, 3, and 5 wt%) were used to prepare high-internal-phase emulsions (HIPEs) (ɸ=0.8). The viscoelastic behaviours of HIPEs were characterised by oscillatory rheology, while the oil droplet size distribution and microstructural characteristics were examined by static light scattering and confocal laser scanning microscopy (CLSM). At all QPI concentrations, HIPEs behaved as viscoelastic gels due to network formation as a result of interactions between jammed oil droplets and protein aggregates. As the QPI concentration increased, the oil droplet size decreased from ~80 to~40 µm and the elastic modulus G´(1 Hz) increased from ~100 to~580 Pa. Effects of prolonged storage (30 days) and heat treatment (80 °C, 30 min) on the rheological behaviour and microstructures of HIPEs were also investigated. All emulsions showed excellent stabilities against phase separation, oil coalescence, and creaming during storage or under heat treatment. Prolonged storage induced a substantial increase in G´, while no significant change in oil droplet size was observed. CLSM revealed that the interfacial layer became thicker and large protein aggregates were formed during storage, which led to a more dense and compact packing of droplets and greater gel strength. Heat treatment induced a 3–5 folds enhancement in the gel strength due to protein denaturation and proteins and oil droplets aggregation. These findings provide useful information for the design and preparation of HIPEs stabilised by quinoa proteins.