Ultrasound-assisted preparation of double nano-emulsions loaded with glycyrrhizic acid in the internal aqueous phase and skim milk as the external aqueous phase

Abstract

In this study, response surface methodology (RSM) based on central composite rotatable design applied to encapsulate glycyrrhizic acid (GA), within the ultrasound-assisted double emulsions. Three independent variables considered as the 10–30% weight of the internal aqueous phase (W1) in the primary-emulsion (W1/O), 6–10% of polyglycerol-polyricinoleate (PGPR) as the surfactant in the oil phase, and 4–6 min sonication-time; dependent variables for optimal W1/O emulsion fabrication were droplet-size, poly-dispersity-index (PDI), and sedimentation-index. Then, 5–25% wt. of the W1/O emulsion dispersed into the skim milk as an external aqueous phase (W2) to form double-emulsions (W1/O/W2) through sonication for 1–5 min. The lowest droplet-size and sedimentation-index obtained for the W1/O emulsions formulated by 19% W1 in the W1/O emulsion, 6% PGPR and a sonication time of 6 min. Two optimal-conditions for preparation of double-emulsions were determined based on the results of encapsulation efficiency, droplet-size, and viscosity as follows: the first optimum treatment (15% W1/O and 3 min sonication) and the second optimal conditions (24% W1/O and 4 min sonication). The encapsulation efficiency of GA in these double-emulsions was 92%. The emulsions stored for 7 days at 37 °C showed instability (2-phase separation). In addition, droplet-size and encapsulation-efficiency increased and decreased during storage, respectively.