Convective Drying of Brown Seaweed (Lessonia spicata): Modeling, Energy Efficiency, and Impact on Bioactive Compounds and Functional Properties

Huiro negro (Lessonia spicata) is a brown alga with potential in the food, nutraceutical, and pharmaceutical industries. This study evaluated its convection drying at 30, 40, and 50 °C (2 ± 0.1 m/s; 83% RH), analyzing the kinetics using nine mathematical models. The Midilli–Kucuk model showed the best fit (R2 = 0.999). Drying at 50 °C significantly increased the fucoxanthin content (p ≤ 0.05) but had the highest energy cost (7.20 USD/kg). In contrast, 30 °C achieved the highest thermal efficiency (48.73%) and lowest cost (5.37 USD/kg), although with the lowest total phenolic compound (TPC) content. TPC was highest at 40 °C, while antioxidant capacity decreased to 30 °C and 40 °C, partially recovering at 50 °C. Higher temperatures also increased protein, fiber, and carbohydrates, while ash decreased. Tests on gastric cell lines (AGS and GES-1) showed low cytotoxicity at doses ≤ 1 mg/mL, with reductions in viability at concentrations ≥ 10 mg/mL. Overall, the extracts showed good biocompatibility at low doses and outstanding functional properties, especially after drying at 50 °C. The results show that the drying temperature significantly influences the nutritional and functional quality of L. spicata, favoring its use in functional foods.