Encapsulation of citrus polyphenols in multi-phase nano-emulsion: Preservative potential, bio-accessibility and cytotoxicity studies

Phenolic compounds in Citrus reticulata peels offer established nutraceutical benefits, contributing to improved health and well-being. However, their applications in the food industry are limited due to susceptibility to chemical degradation from oxygen, light, and heat. This study explores a novel approach to address this challenge by using ultrasonication to encapsulate these phenolic compounds in nano-emulsion. The developed nano-emulsions exhibited an average droplet size of 332 ± 14.67 nm, a polydispersity index of 0.29 ± 0.002, and a ζ-potential of -19 ± 1.82 mV. The major phenolic compounds observed in the nano-emulsion using HPLC included gallic acid (356.5 ± 1.41), p-coumaric acid (201.43 ± 0.81), chlorogenic acid (373.93 ± 4.38), ferulic acid (1278.8 ± 9.09), hesperidin (1192.56 ± 8.61), naringenin (570.63 ± 0.88), and quercetin (419.75 ± 4.47) μg/g. Encapsulated extract showed higher bio-accessibility compared to non-encapsulated extract. Specifically, the bio-accessibility index for total phenolic content was 42.80% and 73.89%, TFC was 44.75% and 75.70%, DPPH activity was 71.68% and 78.57%, and FRAP activity was 50.10% and 69.35% for phenolic extract and nano-emulsion, respectively. During 90 days of storage studies, maximum stability was observed for emulsions stored under refrigerated conditions, with 82.65% retention of phenolic compounds and 88.14% retention of antioxidant activity. Moreover, in addition to enhanced stability and bioavailability, the nano-emulsions demonstrated notable antimicrobial activity against both Gram-positive and Gram-negative bacteria, as well as pathogenic molds, showcasing promising preservative potential. Further, it was observed that the nano-emulsion exhibited no cytotoxic effects on Vero-cell lines (cell viability >85%). These findings suggested the potential application of these nano-emulsions in various facets of the food industry.