Stability of Cotinus coggygria Scop. extract-loaded liposomes: the impact of storage on their physical and antioxidant properties

Smoke tree (Cotinus coggygria Scop., Anacardiaceae family) is an important source of essential oils and extracts, with a wide range of health-promoting effects, such as antioxidant, antibacterial, antigenotoxic, antimicrobial, hepatoprotective, and anti-inflammatory potential. The antioxidant activity of plant products is of great interest due to their ability to preserve food, pharmaceutical, and cosmetic formulations from the toxic and degrading influence of oxidants or free radicals. The encapsulation of various plant extracts within delivery systems can provide prolonged and controlled recovery and protection of their antioxidants. Hence, in the current research, the stability of C. coggygria extract-loaded liposomes (non-treated and UV-irradiated) was monitored for 60 days via the impact of storage on their physical and antioxidant properties. The vesicle size, polydispersity index (PDI), and zeta potential were determined using photon correlation spectroscopy in a 60-day storage study at 4 °C. The liposome size varied over a narrow range for the 60 days, from 3131.0±17.0 nm to 3078.0±42.0 nm (for non-treated) and from 2092.0±22.0 nm to 2136.0±37.0 nm (for UV-irradiated). The PDI values obtained were between 0.273±0.089 and 0.313±0.051 (for non-treated) and 0.829±0.074 and 0.911±0.078 (for UV-irradiated). The zeta potential was -28.2±0.4 mV on the 1^st day and -29.6 mV on the 60^th day for the non-treated sample, while for the UV-irritated liposomes, the zeta potential was -21.5±0.8 mV on the 1^st day and -22.0±1.1 mV on the 60^th day. The obtained extract-loaded liposomes neutralized 81.9±0.4% of the free DPPH radicals before UV irradiation and 80.9±0.4% after irradiation. In the case of the ABTS assay, UV irradiation also significantly reduced the antioxidant capacity of the extract-loaded liposomes, from 12.02±0.54 µmol Trolox equivalent (TE)/mL to 10.55±0.28 µmol TE/mL. Furthermore, the ABTS and DPPH radicals’ scavenging activity of the UV-irradiated liposomes significantly decreased after 60 days of storage (75.4±0.7% and 8.93±0.45 µmol TE/mL, respectively), whereas in the non-treated sample, this drop in antioxidant capacity was not observed.