Influence of various drying conditions on the functional pigments and antioxidant properties of Undaria pinnatifida

Undaria pinnatifida, a widely consumed seaweed in Korea, is valued for its pleasant flavor and rich nutritional value. Owing to its substantial moisture content, drying is a critical processing step that significantly impacts its quality. This study examined the influence of various drying methods (freeze, hot-air, and microwave drying) on the functional pigments and antioxidant properties of U. pinnatifida. Freeze-drying obtained the highest levels of carotenoids (155.37 μg/g), fucoxanthin (104.77 μg/g), chlorophylls (2,431.41 μg/g), total polyphenols (1,360.60 μg GAE/g), phlorotannins (1,887.1 μg PGE/g), and flavonoids (14.35 μg QE/g). Additionally, it demonstrated the strongest DPPH (226.39 μg GAE/g) and ABTS (1.19 mg AAE/g) radical scavenging activities. Heat-drying methods exhibited reduced compound retention, but microwave drying was significantly better than hot-air drying, with lower reduction rates except in chlorophylls. Microwave-dried samples retained 5-6% higher carotenoids and fucoxanthin, 13% more flavonoids, 19% higher polyphenols, 35% more phlorotannins, and 8% greater DPPH radical scavenging activity, than hot-air dried samples. These results suggest that pigments and antioxidant compounds in U. pinnatifida are particularly sensitive to prolonged heat and air exposure. Given the shorter processing time and lower operational costs of microwave drying, it emerges as a promising method for processing U. pinnatifida compared to freeze and hot-air drying, offering superior pigment retention, enhanced antioxidant properties, and greater cost efficiency.