Why do cooked seaweeds turn green?

Seaweeds, like any vegetable, can be prepared in a number of ways. They can be eaten raw, fried, baked, boiled, and dried. Each method changes the texture, taste, and in some cases, color.

If you haven’t seen the magic like color change of cooked seaweeds, watch the video below.

Here you see someone blanching kelp, where it turns from brown to bright green in seconds. This happens whenever a brown or red seaweed is heated, but why? As you probably remember from high school biology, plants get their green color from the light harvesting pigment chlorophyll. Seaweeds are no different, red, green, and brown seaweeds contain chlorophyll. However, brown and red seaweeds have additional pigments that give them a different colors; red seaweeds have phycoerythrin while brown seaweeds have fucoxanthin (image below).

It turns out that chlorophyll has a higher melting point (~150 C) than phycoerythrin and fucoxanthin. When Seaweeds are added to boiling water (100 C) the other pigments melt and dissolve leaving behind the bright green chlorophyll. This trick is used for the iconic seaweed salad (wakame). Just as in the video above, wakame starts out brown and is blanched to attain the attractive bright green color.

seaweed pigments.PNG