Undaria pinnatifida is a seaweed native to Japan, where it is cultivated and sold commercially as food. Fresh seaweed commonly blanches before consumption. However, the effects of blanching on metabolites present in different parts of U. pinnatifida, namely, Wakame (leaf) and Mekabu (sporophyll), are not well understood. Here, we investigated changes in metabolites in these two seaweed parts after blanching for different periods. The samples were freeze-dried and extracted using methanol-water, and metabolite concentration was quantitated using liquid chromatography mass spectrometry and capillary electrophoresis mass spectrometry. The concentration of most metabolites was the highest in raw samples, decreasing drastically within 20 s of blanching in Wakame and decreasing gradually in Mekabu. In contrast, the concentration of some fatty acids, such as octanoate, increased in both parts. During blanching, seaweed color changed from brown to green, and blanching did not significantly affect amino acid or the sugar composition. Finally, a relationship was found between metabolite and blanching-related characteristics, such as color and drying percentage.
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