Abstract: The condensed tannin (proanthocyanidin) content of dry bean has been determined by the vanillin assay in theinternational research, but inadaptable to the test with higher respective concentrations of hydrochloric acid and vanillin thatwould result in too long time for color formation, bad reproducibility and sometimes even coloring the blank solution. The papertried to modify the vanillin assay on the content of proanthocyanidin of grape seed by puting on a new method with lowconcentration of hydrochloric acid and vanillin, as compared with the regular method.The modified method showed betterveracity and reproducibility on the determination of the contents of proanthocyanidin in grape seed and stem. This modifiedvanillin assay was quick、simple and easy to practise for the qualitative and quantitative study of the extraction ofproanthocyanidin. In this study, the concentration of HCl was 4%, vanillin 0.5%, incubation time for the color formation 30minand the temperature for color formation 30±1℃.

Key words: grape seed, prodanthocyanidins, vanillin-HCl, determin content