Abstract: Provided are methods of producing a novel collagen peptide composition, and a DPP-4 inhibitor and antihyperglycemics that comprise the above-mentioned collagen peptide composition. Ginger rhizome-derived enzymes are added to and break down a collagen and/or gelatin solution to generate peptide compositions comprising peptides represented by X-Hyp-Gly (wherein X represents an amino acid residue other than Gly, Hyp, and Pro). The thus obtained collagen peptide composition has a high DPP-4 inhibitory activity and an excellent antihyperglycemic effect.

Abstract: A DPP-4 inhibitor comprising a peptide represented by the formula (1): Xe-Pro/Ala/Hyp-Xa-Xb-Xc-Xd (SEQ ID NO: 16) (wherein Xe is an amino acid residue with an isoelectric point of 5.9 to 6.3; Pro/Ala/Hyp represents Pro, Ala, or Hyp; Xa is an amino acid residue other than Hyp, Pro, and Arg, or deletion; 5 Xb is Gly, Pro, or deletion; Xc is Pro, Ala, or deletion; and Xd is an amino acid residue or deletion) as an active component. The inhibitor can be expected to bring out an effect of lowering blood glucose levels by enhancing effects of incretins; and the inhibitor may be used as a therapeutic agent for diabetes and, in addition, can act on the immune system or the like to be thus used in 10 treatment for skin diseases or the like.

Abstract: Provided are methods of producing a novel collagen peptide composition, and a DPP-4 inhibitor and antihyperglycemics that comprise the above-mentioned collagen peptide composition. Ginger rhizome-derived enzymes are added to and break down a collagen and/or gelatin solution to generate peptide compositions comprising peptides represented by X-Hyp-Gly (wherein X represents an amino acid residue other than Gly, Hyp, and Pro). The thus obtained collagen peptide composition has a high DPP-4 inhibitory activity and an excellent antihyperglycemic effect.

Abstract: A DPP-4 inhibitor comprising a peptide represented by the formula (1): Xe-Pro/Ala/Hyp-Xa-Xb-Xc-Xd (wherein Xe is an amino acid residue with an isoelectric point of 5.9 to 6.3; Pro/Ala/Hyp represents Pro, Ala, or Hyp; Xa is an amino acid residue other than Hyp, Pro, and Arg, or deletion; Xb is Gly, Pro, or deletion; Xc is Pro, Ala, or deletion; and Xd is an amino acid residue or deletion) as an active component. The inhibitor can be expected to bring out an effect of lowering blood glucose levels by enhancing effects of incretins; and the inhibitor may be used as a therapeutic agent for diabetes and, in addition, can act on the immune system or the like to be thus used in treatment for skin diseases or the like.

Abstract: Large amounts of hairs and feathers can be decomposed and refined by treatment in an oxygen-containing gas stream with a fungus that can decompose hairs and feathers. The resulting decomposed and refined hairs and feathers are useful as a fertilizer.