With the possible exception of sushi, seaweed is not usually a staple in the American diet. In Korea, Japan and China, seaweed has been used as a food since at least 600 B.C. At least 21 species are used in Japan and until recently seaweed comprised 10 percent of the Japanese diet. Ireland and Scotland also use some seaweed as food. Some seaweeds are roasted before use and roasting can affect nutrients such as enzymes.
Seaweeds Commonly Used as Food
Nori, kombu and wakame are the most important seaweeds for food in Japan. Kombu, also called kelp, is usually dried and either cut into strips or ground into a powder. Kombu is used in curries, sauces, soups and bean dishes or it may be added to rice. Wakame is usually dried; wakame soup is served with nearly every meal in Japan. Laverbread is picked from rocks in Wales after the tide has gone out, washed repeatedly and then cooked for several hours to make a dark green puree.
Toasting Seaweed
Nori is the seaweed most likely to be toasted -- seaweeds are not roasted in an oven but passed directly over a flame. The sheets of nori take on a green color after toasting. The seaweed is added to broths, soups and sauces, wrapped around cold rice, used in sushi or just soaked and eaten plain. Sea lettuce is another seaweed, or more properly sea vegetable, that is sometimes toasted.
Seaweed Enzymes
One enzyme that breaks down a sugar in the cell walls of red algae used to make nori has been found in the gut of some Japanese. The enzyme has not been found in other groups such as Americans; it is present only in a small percentage of the Japanese population. The enzyme helps people digest seaweeds. However, roasting destroys the enzymes in the seaweed, according to an article in the April 2011 “New Scientist.”
Heat and Enzymes
Several scientists who responded to a question on the Newton “Ask a Scientist” program stated that heat in any form will destroy enzymes. They point out that the process of digestion also breaks down enzymes into their component parts and that the human body makes the enzymes it needs for metabolic activities. Enzymes in food sources perform similar metabolic functions in the living state, but once heated are no longer effective as enzymes, only as individual amino acids.
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