A novel thiolysis‐high‐performance liquid chromatography method for the determination of proanthocyanidins in grape seeds

A novel thiolysis‐high‐performance liquid chromatography method for the quantitative determination of total proanthocyanidins and the mean degree of polymerization in grape seeds has been developed. Following thiolysis with formic acid and benzyl mercaptan, reaction products were separated and purified. Three proanthocyanidin monomers and three derivatives were obtained and their structures were identified by liquid chromatography‐mass spectrometry, FTIR spectroscopy, and NMR spectroscopy. A decomposition model of the thiolysis products and a correction formula for proanthocyanidins concentration were established. This thiolysis‐high‐performance liquid chromatography method displayed good calibration linearity (R2 > 0.999 over the concentration range 0.01 to 10 mg/mL), excellent accuracy (recoveries of 97.9–99.6%), and precision (repeatability relative standard deviations of 0.45–0.75%). This method is suitable for the quantitative analysis of proanthocyanidins in grape seed products.