Water-in-oil nanoemulsions loaded with Ardisia compressa K. bioactive compounds: evaluation of their physicochemical stability and functional activities

Abstract

Ardisia compressa K. (ACK) fruits are a potential source of antioxidant compounds like phenolics and anthocyanins. ACK extracts made with aqueous ethanol (E75) yielded the highest total phenolic content (TPC) and antioxidant activity (AA) by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assays. Water-in-oil nanoemulsions (NEW/O) were produced by spontaneous emulsification, in order to provide longer stability to functional activities from ACK extract, and formulated using ACK extract (10–30%wt.), rosemary essential oil (REO), and Tween 80:Span 80 (10–30% wt.). Resultant NEW/O were placed in a pseudo-ternary phase diagram and classified based on their visual performance, like phase separation, opacity, or translucent-stable systems. The latter displayed smaller hydrodynamic droplet sizes and better stability and were selected for physicochemical characterization. Physical stability through the hydrodynamic diameter, turbidity, and color attributes was monitored until 93 d at 25 °C under light exposure (LE) and dark. A first-order model was used for the first two variables, with rate kinetic constants (k) from 10−6 to 10−8 s−1. Color index (CI) showed higher reduction when NEW/O were stored under LE, whereas total color difference (TCD) values were higher than 5.5, indicating marked differences in visual color compared to fresh NEW/O (t =0 d). Chemical stability from NEW/O made with 30% w/w of ACK extract (NE30) displayed the best stability against pH changes, and TPC and AA during storage time, exhibiting also good antimicrobial susceptibility (AMS) against Gram-positive and Gram-negative bacteria with a synergistic effect of enhanced AMS than that observed in their respective individual components, even after storage time.