Effects of Freeze-Drying, Hot-Air Drying, and Thermal Treatment on Physicochemical and Bioactive Properties of Domat and Gemlik Olive Seeds.

This study investigated the impact of different processing methods (freeze-drying, thermal treatment for 25 and 35 min, and hot-air drying at 60°C and 70°C) on the proximate composition, mineral profile, phenolic compounds, antioxidant activity, and color parameters of Gemlik and Domat olive seeds. Proximate analysis revealed comparable protein (∼21%) and lipid (∼30%) contents on a dry weight basis (DWB) for both varieties. Mineral concentrations generally decreased following fermentation and subsequent thermal processing. However, this reduction was significantly less in freeze-dried samples; for instance, potassium (K) levels in fermented Gemlik seeds dropped from 429.89 to 379.76 mg/kg after lyophilization. Thermal treatment enhanced gallic acid and 3-hydroxytyrosol contents in Domat seeds, whereas all drying treatments reduced these bioactives in Gemlik seeds. The Total Phenolic Content (TPC) of Domat seeds reached its highest value following 25 min of thermal treatment (18.19 mg GAE/g DWB). DPPH radical scavenging activity decreased across all treated samples for both varieties. Color analyses ( L ∗ , a ∗ , b ∗ ) indicated processing-induced changes in seed pigments, driven by pigment oxidation and Maillard reactions. These findings demonstrate that processing conditions can be tailored to preserve or modify specific bioactive and nutritional attributes of olive seeds for functional food and nutraceutical applications.