Refractance Window Drying of Yellow Passion Fruit Peel Puree: Effect of Hybrid Drying Configurations on Drying Kinetics and Bioactive Compound Retention

Yellow passion fruit peel is a bioactive-rich agro-industrial by-product with potential as a functional ingredient, but its high moisture content requires effective drying. Although refractance window (RW) drying can enhance dehydration and bioactive retention, its performance may depend on matrix structure, and evidence for passion fruit peel is limited. This study compared convective air drying (AC) with RW, RW with forced airflow (RW+AC), ultrasound-assisted RW (RW+US), and their combination (RW+US+AC) at 50, 60, 70 and 80 °C. Drying kinetics, activation energy, total phenolic content (TPC), and antioxidant capacity (ABTS) were evaluated. Page’s model accurately described drying curves (R2 > 0.994). AC reduced drying time by 37–59% versus RW, while RW+AC increased drying rate constants by 38–83%. Ultrasound alone provided no improvement, whereas RW+US+AC showed synergistic enhancement at 50–60 °C. AC at 80 °C achieved the highest TPC (10.54 mg GAE/g d.m.) and ABTS (14.31 mg Trolox eq./g d.m.), demonstrating the importance of matrix-specific drying selection.