The Variations, Including Structures and Attenuation to Hemolysis, of Peptide Purified from Dendrobium aphyllum During In Vitro Gastro-Intestinal Digestion and Caco-2 Uptake and Transportation

In a previous study a crude peptide extract was obtained from Dendrobium aphyllum , and this study focused on the functional characterization of the peptide fraction (named DPP) after being purified by DEAE Sepharose. The DPP with high purity contained 16 types of free amino acids and 6 polypeptides. DPP could act as the AAPH-free radical scavenger to protect the erythrocyte under oxidative stress, and the attenuation significantly increased after intestinal digestion. Moreover, the results of the Caco-2 cell models indicated the high absorptive and transfer rates of DPP, in which the passive diffusion was the major transfer pathway. Through the LC-TOF/MS-MS analysis, the peptide sequences Asp-Asp-Asp-Tyr and Asp-Tyr-Asp-Asp were very sensitive to the gastric environment and were completely degraded by Caco-2 cells. While Ser-Ser-Arg, Ala-Val-Thr-Phe , and Met-Leu-Cys-Ala resisted the gastric condition; and sequence Met-Leu-Cys-Ala maintained its structure after the subsequent intestinal digestion and the Caco-2 cells’ uptake.