Resistance of casein-derived bioactive peptides to simulated gastrointestinal digestion

The resistance of six casein-derived peptides, including antihypertensive peptides RYLGY, AYFYPEL and YQKFPQY, to simulated gastrointestinal digestion and the effect on angiotensin-converting enzyme (ACE)-inhibitory activity were evaluated. After digestion, peptides RYLGY, AYFYPEL, and YQKFPQY were partly hydrolysed by the digestive enzymes. RYLGY and AYFYPEL maintained potent ACE-inhibitory activity, with IC50 values as low as 9.3 and 4.7 μg mL−1, respectively. Digestion fragments were sequenced and then synthesised to evaluate their activity. Several showed potent ACE-inhibitory activity, which could explain the in vitro activity of the digests. A notable antioxidant activity was also observed. Since AYFYPEL was less susceptible to digestion, we focused on the antihypertensive activity in spontaneously hypertensive rats of the main digestion fragments of RYLGY. Interestingly, these peptides showed moderate effects in vivo. This suggests that the undigested fraction could also contribute to the in vivo effects of RYLGY and AYFYPEL, and other minor fragments may also participate.