The bioavailability and bioavailable forms of collagen after oral administration to rats were investigated in this study. The relative and absolute bioavailability of collagen were 57.8% and 49.6%, respectively, which was indirectly evaluated by the bioavailability of Hyp in collagen using a pharmacokinetic method. The amino acid profile of plasma showed that more than 63.4% of the collagen was absorbed from the intestine in the form of peptide, and there was a good linear correlation between the absorbed amount of an amino acid and its content in collagen (R2 = 0.9225). The collagen peptides in plasma were purified by Sephadex G10 and Eclipse XDB C18 chromatography and further indentified (Ala-Asn, Ala-Hyp-Gly, Asp-Glu, Glu-Asn, Glu-Asp, Glu-Met, Gly-Pro-Hyp, Leu-Hyp, Leu-Met, Phe-Gly-Asn, Pro-Gly-Leu, Pro-Leu, Ser-Gly-Met, Ser-Hyp, Ser-Pro-Gly, Tyr-Met) with UPLC–ESI-MS. These results may help to speculate about the molecular mechanism behind the physiological effects of collagen after oral administration.

•Simulated gastrointestinal digestion model was employed to investigate gelatin.•Hydrolysis degree and radical-scavenging rate of gelatin increased with time.•Bioavailability and bioactivity of gelatin were high suggested by ultrafiltration.•The radical-scavenging peptide was purified with multi-step chromatography.•The purified peptide was identified to be Gly-Pro-Met using UPLC–ESI-MS.The hydrolysis kinetics and radical-scavenging activity of gelatin were investigated under simulated gastrointestinal digestion in this study. In the gastric phase, the degree of gelatin hydrolysis increased from 0.17% to 1.20%, while the DPPH radical-scavenging rate increased from 6.27% to 24.56%. Further digestion in the intestinal phase brought the degree of hydrolysis and radical-scavenging rate to 26.08% and 44.76%, respectively. After digestion, the gelatin hydrolysates were separated into two fractions by ultrafiltration. The fraction with an average molecular weight of 312.98 Da exhibited the higher yield (78.26%) and radical-scavenging activity (IC50 = 2.09 mg/ml), suggesting the high digestibility and bioactivity of gelatin after oral administration. The fraction was further purified with multi-step column chromatography and identified to be Gly-Pro-Met (303.38 Da) by UPLC–ESI-MS. These results may help us to better understand its physiological effects and to use it properly in foods and pharmaceuticals.Graphical abstract

•Simulated gastrointestinal digestion model was employed to investigate collagen.•Dynamic changes of hydrolysis, hydrophobicity and activity of collagen was cleared.•Collagen was digested almost completely into oligopeptides or free amino acids.•Collagen hydrolysates exhibited high antioxidant activity in vitro.•Antioxidant peptide was purified by chromatography and identified with UPLC-ESI-MS.The hydrolysis kinetics and antioxidant activity of collagen from Nile tilapia were investigated under simulated gastrointestinal digestion in this study. From gastric to intestinal phase, degree of hydrolysis increased from 1.15% to 16.74%, while surface hydrophobicity decreased from 21.46% to 2.06%; DPPH radical scavenging increased from 18.22% to 31.79%, but inhibition rate of linoleic acid peroxidation reached 34.63% in 40 min and then kept stability. After digestion, the collagen hydrolysates were separated into three fractions by ultrafiltration. The fraction (86.70%) with average molecular weight of 436.80 Da exhibited the highest antioxidant activity, suggesting the high digestibility and bioactivity of collagen. The fraction was further purified with multi-step chromatography and identified to be Gly-Pro-Met (303.38 Da) by UPLC-ESI-MS with IC50 value being 25.64 µg/mL for DPPH radical. These results may help better understanding its physiological effects and utilize it in foods and pharmaceuticals.