Optimization of Bioactive Phenolics Extraction and Cosmeceutical Activity of Eco-Friendly Polypropylene-Glycol–Lactic-Acid-Based Extracts of Olive Leaf

Olive leaf is a rich source of phenolic compounds with numerous activities related to skin health and appearance. In this study, a green extraction method was developed using eco-friendly solvents: polypropylene glycol (PPG), lactic acid (LA), and water. The optimal extraction conditions were established, including solvent, extraction time, technique (magnetic stirrer vs. ultrasound-assisted extraction), and herbal material/solvent ratio. The composition of the solvent mixture was optimized using a mixture design. The content of phenolic compounds, including oleuropein and verbascoside, was determined using high-performance liquid chromatography (HPLC) and spectrophotometric methods. Using different extraction conditions, three extracts were prepared and their phytochemical compositions and antioxidant and skin-related bioactivities were investigated. The extracts were excellent inhibitors of elastase, collagenase, tyrosinase, and lipoxygenase. The best activity was shown by the extract richest in phenolics and prepared using magnetic-stirrer-assisted extraction for 20 min, with 0.8 g of herbal material extracted in 10 mL of PPG/LA/water mixture (28.6/63.6/7.8, w/w/w), closely followed by the extract prepared using the same extraction conditions but with 0.42 g of herbal material. The investigated PPG/LA/water mixtures contributed to the overall enzyme-inhibitory activity of the extracts. The prepared extracts were appropriate for direct use in cosmetic products, thus saving the time and energy consumption necessary for the evaporation of conventional solvents.

Control of the Verticillium Wilt on Tomato Plants by Means of Olive Leaf Extracts Loaded on Chitosan Nanoparticles

In this research, a new ecofriendly and sustainable fungicide agent, with the ability to control Verticillium wilt, was developed. To this purpose, a green extract of olive leaf (OLE) was prepared by ultrasound-assisted extraction (UAE) and characterized in terms of polyphenol content and antioxidant activity. Then, OLE was loaded in chitosan nanoparticles (CTNPs) to combine the antifungal activity of CTNPs and phenolic compounds to obtain an important synergic effect. Nanoparticles were synthetized using the ionic gelation technique and characterized in terms of sizes, polydispersity index, Z-potential, encapsulation efficiency, and release profile. Qualitative and quantitative analyses of OLE were performed by the HPLC method. OLE-loaded CTNPs exhibited good physicochemical properties, such as a small size and positive surface charge that significantly contributed to a high antifungal efficacy against Verticillum dahliae. Therefore, their antifungal activity was evaluated in vitro, using the minimal inhibition concentration (MIC) assay in a concentration range between 0.071 and 1.41 mg/mL. Free OLE, blank CTNPs, and OLE-loaded CTNPs possessed MIC values of 0.35, 0.71, and 0.14 mg/mL, respectively. These results suggest an important synergic effect when OLE was loaded in CTNPs. Thereafter, we tested the two higher concentrations on tomato plants inoculated with V. dahliae, where no fungal growth was observed in the in vitro experiment, 0.71 and 1.41 mg/mL. Interestingly, OLE-loaded CTNPs at the higher concentration used, diminished the symptoms of Verticillium wilt in tomato plants inoculated with V. dahliae and significantly enhanced plant growth. This research offers promising results and opens the possibility to use OLE-loaded CTNPs as safe fungicides in the control strategies of Verticillium wilt at open field.