Thiolysis-HPLC analysis of proanthocyanidins in health foods and their materials

Abstract

Proantocyanidins (PCs) found in plant products, are reported to be beneficial to human health. A thiolysis-HPLC method was developed to determine PC in health foods and the basic PC material, grape seed extract (GSE). PCs were quantitatively resolved by acid-catalysis in the presence of benzyl mercaptan as nucleophiles. The reaction solutions of actual purchased products were injected into an HPLC and the gallic acid (GA), catechin (CT), epicatechin (EC), epicatechin gallate (ECG), epicatechin benzyl sulfide (EC-S), and epicatechin gallate benzyl sulfide (ECG-S) were separated and detected. The HPLC was performed on a Hypersil BDS C₁₈ (4.6 mm id × 250 mm, 5 μm) column at 35°C, formic acid (0.05%) was employed as mobile phase A, and methanol ∶ acetonitrile= 1∶2 (v/v) was employed as mobile phase B. The flow rate of gradient elution was 0.8 mL·min^−1, and the DAD detection was carried out at 280 nm. The relative standard deviation of CA, CT, EC, ECG, EGS and ECG-S followed by repeated reactions and injections were between 0.4%–4.2%, and the PC levels in six health foods were between 6.9–161.3 mg·g^−1 with the mean degree of polymerization (mDP) 2.2–4.2. In a GSE product, the PC content was 531.4 mg·g^−1, and the mDP was 9.0, which although higher than other products tested, was far below the labeled, claimed, concentration. Data showed this method to be accurate and sensitive and can be used for the quality evaluation of actual health products containing PC components.