Abstract

Six proteolytic enzymes, including alcalase, flavourzyme, trypsin, neutrase, papain and pepsin, were employed to hydrolyze cottonseed protein to produce the hydrolysates of Angiotensin I-converting enzyme (ACE) inhibitory activity. The result indicated that the cottonseed protein hydrolysate (CPH) produced by papain had the highest ACE inhibitory activity. Therefore, papain was selected for enzymatic production of ACE inhibitor from cottonseed protein isolates (CPI). CPI was hydrolyzed with papain for 1 - 8 h, and the 6 h hydrolysate had the strongest ACE inhibitory ability. The product was separated into four ranges of molecular weight (UF-I, > 30 kDa; UF-II, 30 – 10 kDa; UF - III, 10 - 5 kDa; UF - IV, < 5 kDa) by using an ultrafiltration (UF) membrane bioreactor system. Among them, UF-IV showed the highest ACE inhibitory activity (IC₅₀ = 0.792 mg/ml). UF-IV was further fractionated with Sephadex G-25 gel filtration chromatography into four fractions (Fra I, Fra II, Fra III and Fra IV) that were composed of peptides of >2.43 kDa, 2.43 - 0.82 kDa, 0.82 - 0.35 kDa and <0.35 kDa, respectively. Fra II exhibited the strongest ACE inhibitory ability (IC₅₀ = 0.159 mg/ml) with the yield of 41.63%. It was suggested that Fra II with good ACE inhibitory activity can be a potential source of natural ACE inhibitor.

Key words: Cottonseed protein hydrolysate, peptide fractions, angiotensin I-converting enzyme inhibitory ability, ultrafiltration.

Abbreviation

Abbreviations: ACE, Angiotensin I-converting enzyme; CPH, cottonseed protein hydrolysate; CPI, cottonseed protein isolates; UF, ultrafiltration; RAS, rennin-angiotensin system; AT1, angiotensin type 1 receptors; AT1, angiotensin type 2 receptors; HHL, hippuryl-L-histidyl-L-leucine; DH, degree of hydrolysis; MWCO,molecular weight cut-offs of cardiovascular, renal and adrenal functions governing