Properties of casein hydrolysate as affected by plastein reaction in ethanol-water medium

Abstract

Casein hydrolysate with in vitro ACE-inhibitory activity of 44.4% at 0.3 mg/ml was generated from casein by Alcalase and modified by the Alcalase-catalysed plastein reaction in an ethanol-water medium. Eight treated hydrolysates were prepared using the reaction time of 1-8 h under ethanol or substrate concentration, Alcalase addition and reaction temperature of 56.8% (v/v) or 56.8% (w/v), 8.4 kU/g peptides and 37.5°C, respectively. Most of the treated hydrolysates showed enhanced ACE-inhibition compared to casein hydrolysate, and a reaction time of 4 h brought about the highest ACE-inhibition. All treated hydrolysates had lower zinc- or calcium-chelation but slightly higher iron(II)-chelation than casein hydrolysate, and a reaction time of 4 or 2 h could grant the treated hydrolysates the highest zinc- or calcium-chelation. Kinetic evaluation indicated that casein hydrolysate and two treated hydrolysates were competitive inhibitors to ACE. ACE-inhibition of these evaluated hydrolysates originated from themselves but was uncorrelated with their zinc-chelation, while their CaCO₃ precipitation inhibition was clearly correlated with their measured calcium-chelation (P < 0.05).