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

Abstract

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 (DR) of 0.46 kg H2O·kg−1 db·min−1, effective moisture diffusivity (Deff) of 1.53 × 10−10 m2·s−1, and activation energy (Ea) of 34.90 kJ·mol−1 were observed. The Page model accurately represented the drying behavior (R2 = 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.

Keywords

• raspberry pomace
• convective drying
• drying kinetics
• mathematical modeling
• dietary fiber
• techno-functional properties