Anthocyanin belongs to flavonoids in phenolic compounds. The basic structure consists of two benzene rings connected by a three-carbon unit (C6-C3-C6). Anthocyanins are produced through phenylpropionic acid pathway and flavonoid biosynthesis pathway, and are catalyzed by many enzymes. There are six aglycones, namely geraniol, cyanidin, delphinidin, paeoniflorin, petunia and mallow. Anthocyanins show different colors due to different hydroxyl groups (-OH), methylation, glycosylation, sugar types and connection positions (Fan, 1998). The expression of color is influenced by the changes of biochemical environmental conditions, such as anthocyanin concentration, color effect and pH value in fluid cells (Clifford, 2000). Orange and yellow are the functions of carotene. 19 10 found β -carotene in carrots, and then found two other isomers of carotene in * * * *, namely α, β and γ. β -carotene has been patented by 1958 (US2849495,1958 on August 26th, patentee: Hoffman Roche), which is mainly extracted from the ocean and can also be artificially synthesized.
There are more than 300 different anthocyanins in nature. They come from different kinds of fruits and vegetables, such as purple sweet potato, blueberry, cranberry, blueberry, grape, elderberry red, blackcurrant, purple carrot and red cabbage, and their colors range from red to blue. These anthocyanins mainly include Delchindin, cyanidin, petunia and paeoniflorin.