ACE inhibitory peptides derived from de-fatted lemon basil seeds: optimization, purification, identification, structure–activity relationship and molecular docking analysis
The oil processing industry generates significant quantities of lemon basil seed residue which is not currently used to any significant extent. However, this by-product has important potential as a source of bioactive peptides which may play a role as ingredients in functional foods. This study therefore sought to optimize the preparation techniques used to obtain the necessary protein hydrolysate from de-fatted lemon basil seeds (DLBS), and subsequently to examine the ACE inhibitory capabilities of the resulting hydrolysate. Response Surface Methodology (RSM) was used for the hydrolysis of DLBS by Alcalase®, with observation of the resulting ACE inhibitory activity and degree of hydrolysis (DH). The optimum conditions were 55 °C and 103 minutes with a ratio of enzyme to substrate of 7.0% w/v. The hydrolysate was fractionated by ultrafiltration and purified through RP-HPLC. The results reveal that the F2 sub-fraction demonstrated the highest ACE inhibitory activity. The amino acid sequence of this peak was identified by mass spectrometry as LGRNLPPI and GPAGPAGL with a molecular weight of 879.06 and 639.347 Dalton, respectively. These peptides were classified as non-toxic and bitter peptides. For the synthesized version of these peptides, the ACE inhibitory activity values, measured by IC50, were 0.124 ± 0.02 mM and 0.013 ± 0.001 mM, respectively. Analysis of the Lineweaver–Burk plot confirmed that these peptides served as non-competitive ones. The study of molecular docking showed that the ACE inhibitory behavior of both purified peptides was mainly due to the interactions of the hydrogen bonds between the peptides and ACE. It is therefore suggested that DLBS may be a useful raw material allowing the production of antihypertensive peptides which can offer therapeutic and commercial benefits as an ingredient in functional foods.