ACE-inhibitory activity of seed storage proteins and hydrolysates from Job’s tears (Coix lacryma-jobi L.)

Though hypertension is a serious health problem, the inhibition of the angiotensin-I converting enzyme (ACE) provides a means to treat and manage it. In the present work work, we investigated the ACE-inhibitory activity of crude proteins and protein hydrolysates from Job’s tears (Coix lacryma-jobi L.). ACE inhibition of 22.15 ± 0.94% was observed with 400 µg of protein from Job’s tears as compared to captopril, a common ACE inhibitor, equalled to 53.7 ± 2.3 nmol captopril equivalent per mg of protein (IC50 of captopril towards ACE was 4.8 nmol). The crude proteins from Job’s tears were enzymatically hydrolysed for 1, 2, and 3 h (E/S of 1:20 by weight) using commercial proteolytic enzymes including Alcalase, Papain, Pronase, and Trypsin. All hydrolysates exhibited increased ACE-inhibitory activity. The protein hydrolysates (400 µg) prepared using Pronase for 2 h (CLPrH-2h) exhibited the highest inhibitory activity (78.38 ± 0.23% or 190.0 ± 0.5 nmol captopril equiv. per mg protein) and were ~3.5 times more active as compared to crude proteins. Fractionation of the peptides was performed using semi-preparative reverse-phase high-performance liquid chromatography (RP-HPLC), and all the fractions exhibited ACE-inhibitory activity. The most active fraction was F2 (41.58% inhibition) which was ~7.5 times more active than the crude proteins. These results suggested that seeds from Job’s tears could be an interesting source for developing functional foods with antihypertensive properties.