2.7.5. Determination of proanthocyanidins content

Procyanidin and vanillin were purchased from Shanghai Chunyou Biotechnology Co. (Shanghai, China). The content of procyanidin in the extract solution was determined using the standard vanillin‐Hydrochloric acid method (Fang et al., ²⁰²⁰). Vanillin/methanol solution (4 g/100 ml) of 3 ml and concentrated HCl of 1.5 ml were added to 1 ml of the extract solution in a 25 ml tube with plug (out of light), mixed well. Color development at room temperature for 15 min, with methanol as the control. The absorbance was measured at 500 nm using a Cari‐300 Bio Ultraviolet‐visible spectrophotometer, and the content of procyanidins was calculated by standard curve method.