Physical, Chemical and Rheological Characterization of Red Palm Oil Pickering Emulsion Stabilized by Zinc Oxide Nanoparticles and Glycerol Monostearate

Abstract

In recent years, Pickering emulsions (PE) and particle-stabilized emulsions have attracted considerable interest owing to their biocompatibility, tunable properties, and their ability to resist coalescence. However, the wider application of inorganic solid particles in food products remains limited primarily because of their potential adverse effects to human health. In this study, we investigated the use of generally recognised as safe (GRAS) ZnO nanoparticles and glycerol monostearate (GMS) as coemulsifiers to fine-tune the stability of red palm oil-based Pickering emulsions. The emulsion system consisted of red palm oil and water in a 1:1 volume fraction, with a total emulsifier concentration ranging from 1.5-5% and ratios of 1:2, 1:1, and 2:1 between ZnO and glycerol monostearate. The effects of total emulsifier concentration and ratio on the properties of the emulsions were analysed. An increase in the total emulsifier concentration had a positive effect on the physical (static) stability of the emulsions. The chemical stability of red palm oil increased with increasing emulsifier concentration, as indicated by the flattening slope of the free fatty acid and carotenoid content. However, the difference in emulsifier ratio did not show a significant effect. Based on the rheological characterization, the emulsion system was categorised as a shear-thinning fluid with viscoelastic properties. The results indicated that increases in the total emulsifier concentration and GMS ratio were negatively correlated with the rheological stability of the emulsion, as demonstrated by hysteresis. Every emulsion prepared in this study showed unique properties, ranging from flowable to thick and margarine-like consistency. This study provides a new perspective for the formulation of emulsions using solid particles and molecular co-emulsifiers in food-grade Pickering emulsion systems.