Vitamin K is a substance with chlorophyll biological activity. There are several forms, such as K 1, K2, K3 and K4. Among them, K 1 and K2 are naturally occurring and belong to fat-soluble vitamins, that is, vitamin K 1 extracted from green plants and vitamin K2 synthesized by intestinal bacteria (such as Escherichia coli). K3 and K4 are synthetic water-soluble vitamins. The most important ones are vitamins K 1 and K2. Vitamin k is a yellow crystal with a melting point of 52℃ ~ 54℃. Usually oily liquid or solid, insoluble in water, but soluble in organic solvents such as oil and ether. The chemical properties of all vitamin K are relatively stable, acid-resistant and heat-resistant, with little loss in normal cooking, but sensitive to light and easily decomposed by alkali and ultraviolet rays. Danish chemist Damme first discovered and extracted vitamin K from animal liver and hemp seed oil in 1929.