China, as a contrary climate to the Mediterranean-climate region, is massive in planting olive (Olea europaea) cultivation as an important oil crop. Nonetheless, Chinese olive leaves have received little attention and there is little information about the phenols content. Therefore, in this study, a multiple-response optimization was performed to maximize the total phenolic and oleuropein content (TPC and OEC) by ultrasound-assisted extraction, and the aged and young leaves prepared from six Chinese cultivars from January to December were investigated concerning seven main phenolic composition. Under optimal conditions (power 260 W, time 10 min, liquid-solid ratio 30 mL/g, and 50% ethanol), the highest TPC (197.32 mg/g DM) and OEC (74.68 mg/g DM) were obtained. Findings revealed that the optimal olive leaves for phenolic compounds were the young leaves in spring and winter, being oleuropein and luteolin-4′-O-glucoside present in higher level, and the “Koroneiki” and “Jiufeng” cultivars were relatively stable. Furthermore, antioxidant potential of the phenol extract and oleuropein was also evaluated based on the reducing power and scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH)and superoxide radical assays, and a higher antioxidant effect of oleuropein was observed compared to the phenol extract. In addition, oleuropein showed anticancer activity against HeLa cells, with a minimum inhibitory concentration (EC₅₀) value of 0.19 mg/mL at 48 h. These findings revealed an attractive source of biological substances for further development and utilization of Chinese olive leaves.

Chinese Olea europaea leaves, rich in verbascosides, were extracted using ultrasound-assisted extraction (UAE) and wall-breaking extraction (WBE) with deep eutectic solvents (Optimal UAE: 55 min, 200 mL/g liquid–solid ratio, 20% moisture, yielding 206.23 ± 0.58 mg GAE/g total phenolic content (TPC) and 1.59 ± 0.04% verbascoside yield (VAY); Optimal WBE: 140 s, 210 mL/g, 30% moisture, giving 210.69 ± 0.97 mg GAE/g TPC and 1.33 ± 0.2% VAY). HPLC analysis showed that young leaves accumulated higher TPC and phenolic compounds. Among the five olive varieties, Koroneiki and Chemlal showed the highest TPC in UAE, while Arbosana and Chemlal excelled in WBE. WBE yielded a higher TPC and rutin, whereas UAE marginally increased other phenolics. Additionally, the DPPH^• assay showed that WBE-extracted verbascoside-rich extracts (VREs) of Chemlal exhibited high antioxidant activity (EC₅₀ of 57 mg/mL), but Koroneiki-VREs exhibited lower activity against the ABTS^•+ radical (EC₅₀ of 134 mg/mL). Remarkably, the UAE/WBE-extracted Chemlal-VREs promoted the normal esophageal Het-1A cell line at 25 μg/mL for 24 h; yet, the esophageal cancer Eca-109 cells were sensibly inhibited, especially at 50 μg/mL; and the cell viability decreased dramatically. The results confirmed WBE as a relatively efficient method, and the Chemlal variety may be an excellent source of verbascoside.

The main objectives of this study were to develop an optimized green extraction process to obtain high contents of oleuropein and flavonoids from olive leaves. A deep eutectic solvent (DES) combined with wall-breaking extraction (WBE) was employed. A DES composed of choline chloride and ethylene glycol in a 1:2 molar ratio with 30% moisture content outperformed lactic acid and methanol as extraction solvents. The optimal conditions, determined by response surface methodology, were 30% moisture content, 140 s of wall-breaking time, and a 230 mL/g liquid–solid ratio. Under these conditions, 88.87 mg/g DM oleuropein, 4.57 mg/g DM luteolin-7-O-glucoside, and 114.31 mg RE/g total flavonoids were obtained. Among three olive varieties (Arbosana, Arbequina, and Picholine) cultivated in China, young Picholine leaves exhibited the highest contents. The Picholine-enriched extract demonstrated higher antioxidant activity (ABTS^•+ 155.10 mg/mL, DPPH^• 44.58 mg/mL) compared to other DES-based extracts, although it was lower than that of purified compounds. Furthermore, the CCK-8 assay revealed significant inhibition of Eca-109 human esophageal cells by the Picholine-enriched extract at 25 µg/mL for 24 h, compared to Het-1A cells. This process effectively recovers bioactive compounds from olive by-product, and shows potential for applications in nutritional supplements, cosmetics, and the food industry.

To address severe seasonal drought affecting over 60% of China’s olive-growing regions, this study evaluates whether arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in elite olive cultivars (Arbequina and Koroneiki) under simulated arid conditions. A controlled pot experiment inoculated seedlings with two AMF strains (Rhizophagus intraradices [AMF1], Funneliformis mosseae [AMF2]) under full irrigation or a 32-day water deficit. Biomass, root colonization, photosynthesis, PSII efficiency, osmolytes, antioxidants, and lipid peroxidation were measured. Data were analyzed via two-way ANOVA, Pearson’s correlation, and principal component analysis (PCA). Under optimal hydration, both AMF strains colonized >60% of roots, significantly increasing Arbequina biomass by 25–35% (p < 0.05) and Koroneiki biomass. Drought reversed benefits in Arbequina but triggered resilience: AMF1 restored photosynthesis (18%), Fv/Fm (37%), and water potential (18%) (p < 0.05) while reducing lipid peroxidation (79%) (p < 0.01). In Koroneiki, AMF2 restored Ψw to 47% of pre-irrigation levels and increased root volume (137%), PSII efficiency (43%), osmolytes (100%), and carotenoids (28%) (p < 0.01). PCA ranked Arbequina–drought–AMF1 as the most resilient combination. Pairing AMF strains with specific cultivars offers a scalable, chemical-free strategy to stabilize olive productivity in southwest China’s aridifying climate, advancing climate-smart agriculture for drought-prone regions.