Abstract
Casein hydrolysate with in vitro angiotensin-I-converting enzyme (ACE)-inhibitory activity of 48.2% was prepared from caseinate by Alcalase and modified by plastein reaction in propanol–water medium with extrinsic tyrosine or phenylalanine. By applying response surface methodology, suitable reaction temperature, Alcalase addition, substrate and propanol concentration were optimized as 46.8°C, 8.36 kU/g peptide, 56.8% (w/v) and 58.5% (v/v), respectively. A reaction time of 1 h conferred two modified hydrolysates the highest inhibitory activity (61.6–68.5%), while longer time (e.g. 6 h) brought them greater reaction extent but lower inhibitory activity (41.4–54.7%). Pepsic- and trypsic-digestion of the modified hydrolysates of the highest inhibitory activity (or of greater reaction extent) totally resulted in damaged (or enhanced) inhibitory activity. Twelve out of the obtained 16 digests had residual inhibitory activity about 48–70%, close or larger than casein hydrolysate. It is thus concluded that plastein reaction can enhance ACE inhibition and digestive stability of casein hydrolysate.
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