Release of pyrraline in absorbable peptides during simulated digestion of casein glycated by 3-deoxyglucosone

The glycation product 6-(2-formyl-5-hydroxymethyl-1-pyrrolyl)-l-norleucine (pyrraline), which is formed in the final stage of the Maillard reaction, is taken up in significant amounts with the daily diet. The high bioavailability of pyrraline known from human balance studies can be partly explained by the fact that pyrraline-containing dipeptides are substrates of the human peptide transporter 1 (PEPT1). In the present study we assessed whether pyrraline-containing peptides are formed during luminal digestion of glycated proteins. For this, casein and β-casein, respectively, were enriched with peptide-bound pyrraline by incubation with 3-deoxyglucosone (3-DG), and the modified casein samples were subjected to simulated gastrointestinal digestion. The digestibility of modified casein decreased with increasing pyrraline concentration as measured by analytical size-exclusion chromatography of the digested peptide mixtures. After digestion, 50–60 % of pyrraline was bound in peptides smaller than 1,000 Da isolated by ultrafiltration. Only