Enzymatically synthesized γ-[Glu](n≥1)-Gln as novel calcium-binding peptides to deliver calcium with enhanced bioavailability

•γ-[Glu](n≥1)-Gln have potential for the management of calcium deficiencies.•The process conditions were optimized and calcium-binding capacity was 35.2 mg/g.•Calcium chelation induced significant changes in the structure of γ-[Glu](n≥1)-Gln.•The calcium absorption and bioavailability were improved after the treatment of γ-[Glu](n≥1)-Gln.