Optimal condition to remove mercury in yellowfin tuna protein isolates and ACE-inhibitory property of peptide prepared using commercial proteases

Response surface methodology (RSM) was performed to maximize the mercury (Hg) reduction from yellowfin tuna (Thunnus albacare) by products protein isolates (YBPI). The optimal condition of Hg reduction (89.3%) was 10.5 mM CaCl₂ and a Water:YB of 12.9:1, while other variables were fixed at 5 mM citric acid, 60 min incubation, pH 11 and 8,000 x g for 15 min of centrifugation. At these conditions, the significant protein recovery (80.1%) was obtained. Hydrolysates sequentially hydrolyzed with G6 followed by GN exhibited the highest angiotensin I-converting enzyme (ACE) inhibitory activity than other enzyme preparations. Fractionated yellowfin tuna by products protein hydrolysate (YBPH) increased in ACE-inhibitory activity when peptide size decreased. In-vitro gastrointestinal (GI) digestion significantly increased bioactive property. ACEinhibitory activity of YBPH with and without simulated GI digestion significantly increased after incubating against ACE, demonstrating pro-drug type peptides.