N hippuryl l histidyl l leucine hhl

All chemicals, reagents and organic solvents of the highest grade available were purchased from Sigma-Aldrich (St. Louis, MO, USA) unless otherwise stated. DPPH, ACE from rabbit lung, N-Hippuryl-l-histidyl-l-leucine (HHL) and Hippuric acid were purchased from Sigma-Aldrich (St. Louis, MO, USA).
Deionized water was prepared by an Arium 611 VF system from Sartorius (Göttingen, Germany). Solid Phase Extraction (SPE) C18 cartridges were Bond Elut (Varian, Palo Alto, CA, USA).

Naked oat bran was purchased from Sanfen Oat Farm, Shuozhou, China. Trypsin (1 × 10⁴ U/g, derived from porcine pancreases), Pepsin (1 × 10⁵ U/g, derived from bovine stomachs), Flavourzyme (from Aspergillus oryzae, 2 × 10⁴ U/g), pancreatin (1 × 10⁴ U/g, derived from porcine pancreases), and Papain (3 × 10⁴ U/g) were purchased from Kangfukuai Biotech., Co. (Nanning, China). ACE, 4-(2-Pyridinazo)-resorcinol (PAR) and N-hippuryl-L-histidyl-L-leucine (HHL) were purchased from Sigma (St. Louis, MO, USA). Zinc sulfate heptahydrate (ZnSO₄·7H₂O), HEPES-KOH buffer, and other analytical grade chemicals were purchased from Jinyangkeji Co. (Taiyuan, China).

DOPK was provided by the Three Rivers Palm Garden (Haikou, China). Trypsin (1 × 10⁴ U/g, derived from porcine pancreas), papain (3 × 10⁴ U/g), and pepsin (1 × 10⁵ U/g, derived from bovine stomach) were purchased from Kangfukuai Biotechnology Co. (Nanning, China). ACE, 4-(2-Pyridinazo)-resorcinol (PAR), and N-hippuryl-l-histidyl-l-leucine (HHL) were purchased from Sigma (St. Louis, MO, United States). Dithiothreitol, HEPES-KOH buffer, and other chemicals were purchased from Jinyangkeji Co. (Linfen, China).