Comparative Evaluation of Drying-Induced Changes in Selected Edible Brown Seaweed Powders

This research assessed the impact of oven drying (40°C, 50°C, and 60°C) and freeze-drying on the drying characteristics, nutritional makeup, functional traits, color, and microstructure of Sargassum wightii, Zonaria variegata, and Padina boergesenii. Moisture extraction occurred primarily during the falling-rate phase, and the Midilli-Kucuk model accurately represented the drying kinetics, with high R² values (0.9965 to 0.9978). Fresh samples had elevated moisture content (79.05 ± 0.55% to 88.02 ± 0.53%), which dropped to below 9% after drying. Freeze-dried samples exhibited the least residual moisture (7.88 ± 0.11% to 7.98 ± 0.13%) and demonstrated superior retention of protein, pigments, and rehydration characteristics. The protein content in freeze-dried Sargassum wightii was 21.96 ± 0.24%. In contrast, the levels of fucoxanthin and chlorophyll were relatively higher (ranging from 2.34 ± 0.06 to 2.84 ± 0.08 mg/g DW and reaching up to 4.34 ± 0.11 mg/g DW, respectively). The freeze-dried samples exhibited the highest rehydration ratios (5.18 ± 0.13 to 5.64 ± 0.15). In comparison, drying in an oven at 60°C enhanced techno-functional attributes, including water absorption capacity (3.42 ± 0.15 to 3.82 ± 0.18 g/g), swelling power (6.36 ± 0.30 to 7.06 ± 0.34 g/g), and dispersibility (80.24 ± 2.82%). Color analysis and microscopic examinations showed increased structural collapse and pigment deterioration in oven-dried samples, while freeze-drying preserved a more porous and intact structure. In general, freeze-drying proved to be superior for maintaining nutritional and structural quality, whereas moderate oven drying improved functional traits beneficial for food and nutraceutical uses.