Isolation and characterization of potential food preservative peptide from Momordica charantia L.

Abstract

Antimicrobial agents (AMAs) also known as preservatives are being used to keep food safe and unspoiled from microorganism. These preservatives, derived from plant sources or synthesized chemically are mostly non-proteinaceous AMAs. Less attention has been given to proteinaceous AMAs which may be used as preservative in food. Thus, there is a need to explore proteinaceous AMAs having antimicrobial activity with potentials to be used as an alternative to the presently used preservatives which are mostly synthetic. Therefore, the present study was carried out systematically to isolate and characterize peptides having antibacterial activity from different parts of bitter melon (Momordica charantia L.). Crude aqueous extracts of seeds, pulp and skin were prepared in phosphate buffer saline (PBS) and antibacterial activity was checked on Luria Bertani (LB) broth agar plates against a number of bacteria such as Escherichia coli, Staphylococcus aureus, Salmonella typhi and Pseudomonas aeruginosa. Since antimicrobial activity was observed only in seeds therefore, seed extract was used for peptide(s) precipitation with 75% ammonium sulfate solution and purification by gel filtration chromatography (GFC) using Sephadex G-100. Antimicrobial activity was also checked in dissolved ammonium sulfate precipitate and GFC peak fractions (1–4). Further, homogeneity and molecular mass of GFC pooled fractions along with crude extract and dissolved ammonium sulfate precipitate were determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). One peptide with molecular mass ∼10kDa with antimicrobial activity was obtained from peak 3. The purified peptide was stable at 4–50°C, active between 5–7 pH and inactivated by trypsin and proteinase K. Based on minimum inhibition concentration (MIC) values of purified peptide S. aureus was found to be the most sensitive strain. The use of this strain with minced meat showed significant viable count decreased i.e. from 8.0 to 3.77log CFU with P<0.001 at concentration of 40μg peptide. The results of our study suggest that antibacterial peptide obtained from seeds of M. charantia L. may be used as an alternative natural biopreservative source for minced meat products. However, further studies need to be carried out to check the effect of this peptide on more microorganisms, characterization and its toxicological analysis.