Simulated digestion of proanthocyanidins in grape skin and seed extracts and the effects of digestion on the angiotensin I-converting enzyme (ACE) inhibitory activity

This study investigated the effect of in vitro gastrointestinal digestion on the stability and composition of flavan-3-ols from red grape skin and seed extracts (raw and purified, which are high in proanthocyanidins (PAs)). In addition, the effects of digestion on the angiotensin I-converting enzyme (ACE) inhibitory activities of these extracts were evaluated. The extracts were digested with a mixture of pepsin-HCl for 2 h, followed by a 2 h incubation with pancreatin and bile salts including a cellulose dialysis tubing (molecular weight cut-off 12 kDa) at 37 °C with shaking in the dark and under N2. Under gastric conditions, the mean degree of polymerisation (mDP) of seed extracts, raw (mDP ≈ 6, p < 0.05), and purified (mDP ≈ 10, p < 0.05) was stable. The mDP of the raw skin extracts increased from 19 to 25 towards the end of the digestion. The PAs were significantly degraded (up to 80%) during the pancreatic digestion, yielding low-molecular-weight compounds that diffused into the serum-available fraction (mDP ≈ 2). The overall mass transfer coefficient (K) of the seed extracts was 10−7 m2/s. After simulated gastrointestinal digestion, over 80% of ACE inhibition by raw seed and skin extracts was preserved. However, the purified seed and skin extracts lost their ability to inhibit ACE after intestinal digestion.