Physical Properties, Antioxidant Activity, and In Vitro Digestibility of Essential Oil Nanoemulsions of Betel and Pandan Leaves

This study aims to produce stable essential oil nanoemulsions (EONEs) of betel and pandan leaves as functional ingredients in food applications. EONEs from betel leaf (Piper betel Linn.), pandan leaf (Pandanus amaryllifolius Roxb.), and a blend of betel/pandan leaf at 1:1 (v/v) were produced using the spontaneous emulsification (SE) method. The oil phase [5% (v/v) (essential oil (EO) and corn oil at the ratio 4:1)] was mixed with an aqueous phase [mixture of 15% (v/v) Tween 80 in 80% (v/v) distilled water] using magnetic stirring at 750 rpm at 25 °C. The particle size, polydispersity index (PDI), zeta (ζ) potential, particle size distribution (PSD), turbidity, morphology, antioxidant activity, in vitro digestibility, and physical stability of the EONEs were then investigated. Betel/pandan leaf EONE had the smallest size (24 nm), highest ζ potential (−33 mV), and lowest turbidity (86.66% transmittance), while betel leaf EONE exhibited the lowest PDI (0.23). From the transmission electron microscopy (TEM) micrographs, all EONEs were composed of spherical particles with sizes in the range of 20–100 nm. The betel leaf EONE showed the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (88.01%) followed by betel/pandan leaf EONE (79.24%) and pandan leaf EONE (43.12%). Betel/pandan leaf EONE showed the highest in vitro digestibility by exhibiting the highest free fatty acid (FFA) released. Betel leaf EONE appeared to be the most physically stable after 8 weeks of storage at 4 °C. Overall, nanoemulsions containing betel leaf EO showed great potential as functional ingredients for food applications as they exhibited small particle size, low turbidity and PDI, narrow PSD, high antioxidant activity, and physical stability.