Process Modeling and Convective Drying Optimization of Raspberry Pomace as a Fiber-Rich Functional Ingredient: Effect on Techno-Functional and Bioactive Properties

This study aimed to transform raspberry pomace, a by-product of the berry industry, into a sustainable, fiber-rich functional ingredient using convective drying. Drying experiments were conducted at temperatures of 50, 60, 70, 80, and 90 °C to identify the optimal conditions that balance process efficiency and preservation of functional and bioactive properties. The best results were achieved at 70 °C, where a high drying rate (<i>DR</i>) of 0.46 kg H₂O·kg^-1 db·min^-1, effective moisture diffusivity (<i>D</i>_eff) of 1.53 × 10^-10 m²·s^-1, and activation energy (<i>E</i>_a) of 34.90 kJ·mol^-1 were observed. The Page model accurately represented the drying behavior (<i>R</i>² = 0.9965-0.9997). Total dietary fiber (TDF) content remained stable across temperatures (52.52-64.76 g·100 g^-1 db), while soluble dietary fiber (SDF) increased by 43.40%, resulting in a solubility (SOL) of 71.8%, water-holding capacity (WHC) of 8.2 mL·g^-1 db, and oil-holding capacity (OHC) of 3.0 mL·g^-1 db. High retention of bioactive compounds was achieved at 70 °C, including phenolics (32.10 mg GAE·g^-1 db) and anthocyanins (25.84 mg C3G·g^-1 db), resulting in significant antioxidant activities (DPPH: 33.29 mg AAE·g^-1 db, IC₅₀ 0.016 mg·mL^-1; ABTS: 35.85 mg AAE·g^-1 db, IC₅₀ 0.029 mg·mL^-1). These findings demonstrated the potential of convective drying at 70 °C to efficiently transform raspberry pomace into a high-quality functional ingredient. This process promotes sustainable production and waste reduction in the berry industry.