Angiotensin-I Converting Enzyme Inhibitory Peptides from Sweet Sorghum Grain Protein: Optimisation of Hydrolysis Conditions and Hydrolysate Characterization

In order to utilize sweet sorghum grain protein (SSGP) for food applications, SSGP was hydrolyzed by alcalase to produce the hydrolysates with ACE-inhibitory activity. The Plackett-Burman design (PBD) was used to identify the important factors influencing the ACE-inhibitory activity of SSGP hydrolysates. The result of PBD indicated that hydrolysis temperature, pH and alcalase dosage had significant influence (P andlt; 0.05) on the ACE-inhibitory activity of SSGP hydrolysates. Response surface methodology (RSM) was applied to optimize the three significant factors. The optimum hydrolysis conditions obtained from RSM were as follows: hydrolysis temperature 56 and#176;C, pH 8.0, alcalase dosage 5200U/g. Under the optimum conditions, SSGP hydrolysates contained 24.3% 1–5 kDa (IC50=0.305 mg/ml) and 15.2% andlt;1 kDa (IC50=0.116 mg/ml) peptide fractions having potent in vitro ACE inhibitory activities. Moreover, the inhibition pattern against ACE investigated using Lineweaver–Burk plots revealed that the peptides with molecular weights above 5 kDa in the SSGP hydrolysates were non-competitive inhibitors with inhibition constants (Ki) between 1.098 and 1.171 mg/ml, while the peptides with molecular weights below 5 kDa in the hydrolysates were competitive inhibitors with Ki between 0.110 and 0.184 mg/ml. The results of this study suggest that SSGP may be considered as a source of functional ingredients for the prevention of hypertension.