Stability of microemulsions containing red grape pomace extract obtained with a glycerol/sodium benzoate deep eutectic solvent

The valorization of red grape pomace is significant as grape is one of the most cultivated fruits worldwide and generated by-product quantities are enormous. For this purpose, numerous encapsulation techniques have been developed. However, the studies on microemulsions composed with deep eutectic solvent extracts are very limited. In this study, red grape pomace extract (RGPE) was first prepared by deep eutectic solvent extraction and characterized by HPLC analysis. Rutin, quercetin, catechin and caftaric acid were identified as the main non-pigment phenolic compounds. The RGPE was further encapsulated in microemulsions (MEs) following a low-energy approach using a mixture of low molecular weight surfactants, and the pseudo-ternary phase diagram was constructed. The physical and antioxidant stability of MEs containing 3–15 wt% RGPE was investigated for a period of 30 days. MEs were stable at an ambient temperature of 25 or 37 °C. The radical scavenging activity of encapsulated RGPE was improved up to 13% compared to the free extract. Our results indicate that microemulsions provide protection of valuable phenolic constituents especially under elevated temperature conditions and can therefore be used as systems for applications in nutraceuticals or cosmetics.