Development of a new thin-layer drying model and multicriteria assessment of phytochemical stability and antioxidant activity in olive leaves

Olive leaves, a by-product of the olive oil industry, are rich in bioactive compounds whose stability strongly depends on drying conditions. This study models drying kinetics and assesses temperature effects on phytochemical stability and antioxidant activity. Olive leaves were dried using hot air at four temperatures (40, 70, 95, and 120°C). Drying progress was monitored through continuous mass-loss measurements, and moisture ratios were calculated to characterize drying behavior. These data were fitted to 23 mathematical models, and moisture diffusivity and energy efficiency were determined. Ultrasound-assisted extraction was then performed to evaluate the effect of drying temperature on total phenolics, flavonoids, and antioxidant activity. The proposed kinetic model showed the best agreement with experimental data (R2= 0.999, χ2 = 1.60 × 10-4), demonstrating strong predictive performance. Effective diffusivity increased with temperature, accompanied by a substantial reduction in drying time. Lower temperatures (40°C) preserved the highest bioactive compound content, while 120 °C markedly accelerated drying (moderate compound loss). Intermediate temperatures (70-95°C) resulted in the lowest retention due to prolonged thermal exposure.