Compound proteinase

The samples of Antarctic krill were provided by Dalian Marine Fisheries Group Cop.of Liaoning province (Dalian, Liaoning, China), which were transported to the laboratory at −20°C and stored at −50°C until use.
The standard mixtures of 37 fatty acid methyl esters (FAMEs), retinol and α‐, β‐, γ‐, and δ‐tocopherols (purity > 95%) were purchased from Shanghai ANPEL Science Instrument Co., Ltd. (Shanghai, China). Compound proteinase and acidic protease were purchased from Shanghai Yuan Ye Biotechnology Co., Ltd. (Shanghai, China). Alcalase and neutrase were purchased from JiangSu RuiYang BioTech (Jiangsu, China). Papain, pancreatin and anhydrous ethanol, petroleum ether (30~60°C) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

Pea peptides were prepared from the crude pea protein remaining from the production of pea starch by compound protease hydrolysis, and the ACE inhibition rate of pea peptides in vitro was determined according to the available literature method [27 (link)]. Clams (Ruditapes philippinarum) were from the local aquatic market in Hongdao (Qingdao, China). We hydrolyzed them with compound protease, and clam peptides were obtained after impurity removal as described previously [28 ]. The contents of pea and clam peptides were measured by the biuret method, and the average molecular weight of the pea and clam peptides was measured by high-performance liquid chromatography (HPLC) [10 (link)]. The two-peptide composite was prepared by mixing pea peptides and clam peptides in a 2:3 (W:W) ratio. Captopril was purchased from Shandong Xinhua Pharmaceutical Co., Ltd. (Shandong, China), and compound proteinase was provided by Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China).