Combined Summer Applications of Talc Particles and Elicitors Modulates Yield, Quality and Functional Properties of Olive Oil Produced Under Rainfed Conditions in Greece

The present study investigated the combined effects of foliarly applied elicitors—chitosan (CHI) and harpin (HAR)—combined with TALC (T) on rainfed olive (Olea europaea L.) cv. “Amphissis” fruit and oil yield, physiological traits, and virgin olive oil (VOO) quality and functional properties. The combination of TALC with chitosan (T-CHI) demonstrated a notable agronomic response, achieving the highest olive yield (38.2 kg tree−1) and oil percentage per fruit (22.05%), resulting in an approximately 61% increase in oil production per tree (8.43 kg) compared to control (CON) (5.24 kg). While basic extra VOO (EVOO) quality indices (free acidity, K270, ΔK) were similar across all treatments, peroxide value was significantly reduced in T-CHI- and TALC-produced oils. Functional profiling revealed that CHI alone maximized total phenols (315.85 mg gallic acid equivalents kg−1 olive oil) and antioxidant capacities, whereas HAR and T-HAR significantly elevated o-diphenol levels and α-tocopherol concentration. Furthermore, T-CHI and T-HAR enhanced the accumulation of major health-promoting secoiridoids, specifically oleacein (up to 177.9 mg kg−1 olive oil) and oleocanthal (51.95 mg kg−1 olive oil). Volatile analysis demonstrated that T-HAR induced a surge in (E)-2-hexenal, favoring green-fruity notes, while CHI and HAR alone promoted (Z)-3-hexen-1-ol. Multivariate analyses (clustering heatmap correlation, constellation Plot) highlighted that TALC application in combination with elicitors acts as a powerful dual-action strategy to simultaneously optimize EVOO yield, functional properties, and possibly its aromatic complexity.