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., P-1(water-insoluble large peptides) and P-2 (water-soluble small peptides, precipitable by ethanol), were collected. The FTIR analysis on Pepsin-HPH suggested that P-1 and P-2 peptides had different Zn2+-binding sites where N-H and C=O were the primary sites in P-1 and P-2, respectively. Although the Zn2+-binding capacity (P-1 and P-2 combined) of HPHs was lower than that of nonhydrolyzed hemp protein, the P-2-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.