Identification and synthesis of multifunctional peptides from wheat germ hydrolysate fractions obtained by proteinase K digestion

Abstract

Wheat germ protein hydrolysate (WGPH) was obtained by proteinase K digestion, in order to produce bioactive antioxidant and antihypertensive peptides. Response surface methodology (RSM) was used to optimize hydrolysis conditions (enzyme-to-substrate ratio, time, and temperature) for antioxidant activity of hydrolysates. The crude WGPH produced in this way significantly inhibited angiotensin-I converting enzyme (ACE) in a concentration-dependent manner. It was next fractionated by reversed-phase semi-preparative High Performance Liquid Chromatography (HPLC) into 12 fractions that were examined for antioxidant and antihypertensive activities. Fractions with antioxidant and ACE-inhibitory activities were then submitted to further analysis by nano-LC-ESI-MS-MS. Among the various peptides identified, MDATALHYENQK (IC₅₀ : 293.3 ± 6.5 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 265.5 ± 8.3 µg/ml) displayed antioxidant activity and VALTGDNGHSDHVVHF (IC₅₀ : 189.3 ± 4.05 µg/ml), VDSLLTAAK (IC₅₀ : 159.7 ± 0.33 µg/ml), MDATALHYENQK (IC₅₀ : 303.6 ± 2.47 µg/ml), IGGIGTVPVGR (IC₅₀ : 125.7 ± 2.3 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 128.2 ± 1.17 µg/ml) showed good ACE-inhibitory activity. PRACTICAL APPLICATIONS: Wheat milling industries produce massive amounts of wheat germ as by-product that can be converted into valuable compounds. The present research indicates that proteinase K is useful to hydrolyze wheat germ proteins in a search for bioactive peptides with antioxidant and ACE-inhibitory properties. The identified peptides can be regarded as functional food additives, or nutraceuticals to improve human health.

Keywords: ACE-inhibitory activity; antioxidant activity; bioactive peptides; proteinase K; wheat germ protein.