Bioactive Compounds of Sea Mustard (Undaria pinnatifida) Waste Affected by Drying Methods

Sea mustard (<i>Undaria pinnatifida</i>) is a brown macroalga extensively cultivated and consumed in South Korea. However, the high volume of seaweed production in the country results in substantial waste generation. To mitigate this issue, the bioactive compounds of sea mustard waste parts (sporophyll, root, and stem) were assessed under different drying conditions (freeze, oven, and microwave drying) to evaluate their potential as functional ingredients. The sporophyll contained the highest levels of total chlorophyll (540.38 μg/g), fucoxanthin (165.87 μg/g), flavonoids (5.47 μg QE/g), phytomenadione (332.59 μg/100 g), and cobalamin (5.92 μg/100 g). In contrast, the root exhibited the highest antioxidant activities (DPPH: 1582.37 μg GAE/g; ABTS: 0.93 mg AAE/g), total polyphenol (2718.81 μg GAE/g) and phlorotannin (4298.22 μg PGE/g) contents. Freeze drying achieved the best retention rates for most bioactive compounds, except for fucoxanthin, which was highest in microwave-dried samples. These results demonstrate the potential of sea mustard waste as a valuable source of bioactive compounds, with the retention of these compounds being influenced by drying methods, depending on the specific part of the seaweed.