Zinc-binding behavior of hemp protein hydrolysates: Soluble versus insoluble zinc-peptide complexes

Proteins and peptides when forming complexes with zinc can increase zinc bioavailability. Such complexation was investigated on hemp protein hydrolysates (HPHs) in the present study using Pepsin, Alcalase, Flavourzyme, Papain, Protamex, and Trypsin. Two solubility fractions of Zn²⁺–HPH complexes, i.e., P₁ (water-insoluble large peptides) and P₂ (water-soluble small peptides, precipitable by ethanol), were collected. The FTIR analysis on Pepsin-HPH suggested that P₁ and P₂ peptides had different Zn²⁺-binding sites where N–H and C[dbnd]O were the primary sites in P₁ and P₂, respectively. Although the Zn²⁺-binding capacity (P₁ and P₂ combined) of HPHs was lower than that of nonhydrolyzed hemp protein, the P₂-bound Zn²⁺ was more abundant in HPHs (up to 63.4%) than in nonhydrlyzed protein (29.6%). Isothermal titration calorimetry corroborated with Zn²⁺-binding capacity for different HPH samples. Peptides produced with Flavourzyme had the highest Zn²⁺-binding activity (88.8%) while those with Pepsin exhibited the maximum solubility.