A powerful weapon for plants to resist environmental stress is to produce a variety of secondary metabolites. Anthocyanin is a kind of phenylpropane compound widely existing in higher plants, which makes flowers, fruits, stems and leaves of plants appear red, purple and blue.

Anthocyanins not only help plants resist harmful stresses such as ultraviolet rays, strong light, low temperature and nutrient deficiency, but also play an important role in the interaction between plants and insects. Therefore, the accumulation of anthocyanins is considered as an intuitive molecular marker to judge whether plants encounter adverse environment during their growth.

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Generally, free anthocyanins are rare in natural conditions and often form anthocyanins with one or more of glucose, rhamnose, galactose, xylose and arabinose. Glycosides and hydroxyl groups in anthocyanins can also form acidified anthocyanins with aromatic acids and fatty acids of one or several molecules such as coumaric acid, ferulic acid, caffeic acid and p-hydroxybenzoic acid through ester bonds.

Anthocyanin molecules have a highly molecular * * * conjugated system, contain acidic and basic groups, and are easily soluble in polar solvents such as water, methanol, ethanol, dilute alkali and dilute acid.

It has strong absorption in both ultraviolet and visible light regions. The maximum absorption wavelength in ultraviolet region is about 280 nm, and the maximum absorption wavelength in visible region is in the range of 500 ~ 550 nm. The color of anthocyanins changes with the change of pH value, which is red at pH = 7, purple at pH = 7 ~ 8, and blue at pH >: 1 1.