Abstract: The single and compound enzymatic hydrolysis conditions of tilapia (Oreochromis niloticus) skin collagen were studied. Based on the assay of inhibitory activity of single enzymatic hydrolysates to ACE, Bromelain and Alcalase 2.4L were selected to be compound enzyme. The optimal hydrolytic conditions of skin collagen with the two enzymes were determined by orthogonal test. The results show that the optimal hydrolytic conditions of Bromelain and Alcalase 2.4L are temperature 45℃, pH4.5, E/S 4000U/g, time 4h and concentration of substrate 6% and temperature 55℃, pH7.5, E/S 6000U/g,time 2h and concentration of substrate 4%, respectively. Thereafter, hydrolytic experiments of compound enzyme were done. The results indicate that it is better to hydrolysis by Bromelain at first, then by Alcalase 2.4L.The hydrolytic degree of the prepared hydrolysates is 30.43%, the ACE inhibitory ratio is as high as 68.6% in vitro. The high activity ACE inhibitory fractions were separated and purified using the Sephadex G-25 and the Reverse-Phase High Performance Liquid Chromatography (RP-HPLC). The concentrations of the hydrolysates to inhibit 50% of ACE activity (IC50) were measured. The results showed that the IC50 of the original hydrolysate and the Sephadex G-25 filtrate were 2.82mg/ml and 0.65mg/ml, respectively.

Key words: tilapia skin, collagen, compound enzymatic hydrolysis, purification, angiotensin converting enzyme (ACE)