Kelp belongs to brown algae, which mainly includes two colors of pigment, one is green chlorophyll, the other is yellow or brown carotenoids, such as beta carotene, physcion, phycocyanin and so on. They are mainly stored in chloroplasts, and chlorophyll is bound to proteins. There is a hole in the center of the chlorophyll molecule. Normally, there will be a magnesium atom in it, and the chlorophyll will turn green. However, under acidic conditions, magnesium atoms will be driven away by hydrogen atoms, and chlorophyll will turn into yellow “magnesium free chlorophyll”. After the kelp is fished out of water, kelp cells lose their activity, chlorophyll and protein are separated, and organic acids in cells are released, resulting in magnesium ions escaping from chlorophyll molecules, and kelp turns yellow brown. There may be two reasons for the discoloration of kelp as soon as it is hot. One is that the stability of chlorophyll to heat is higher than that of carotenoids. In the process of blanching, some carotenoids are destroyed, so the green appears; the other is that the high temperature changes the acid-base environment of kelp, and the original yellowish brown magnesium free chlorophyll reacts with metal ions and shows green. Therefore, it is normal for kelp to turn green in case of boiling water, and it is usually the performance of fresh kelp. < p > < p > it should be noted that with the expansion of planting area, China has gradually tried to cultivate excellent kelp varieties, and green kelp is one of them. The roots of the kelp are still brown, but the upper parts of the leaves turn green. In other words, fresh kelp is brown and green, not fake. In addition, the color of kelp is also related to the local ocean light conditions and other factors.