Identification Of Plant Extracts And Phenolic Compounds With The Potential Of Inhibiting Fish-Spoiling Bacteria
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Date
2016-08
Authors
Anantham, Joshua Jeyenthiren
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Abstract
The aims of this project were to identify plant species and phenolic
compounds that exhibited antioxidant and antibacterial activities. Samples studied
were plant organs that are commonly used in the preparation of fish cuisines. The
bacterial strains involved in this study were Pseudomonas fluorescens (ATCC
13525), Serratia liquefaciens (ATCC 27592), Aeromonas hydrophila (ATCC
35654), Staphylococcus xylosus (ATCC 700404), Listeria monocytogenes (ATCC
19115) and Listeria innocua (ATCC 33090) while the assays deployed to gauge
antioxidant potentials were the 1,1-diphenyl-2-picrylhydrazyl-hydrate (DPPH),
ferric-reducing antioxidant power (FRAP), 2,2-azino-bis-3-ethylbenzthiazoline-6-
sulphonic acid (ABTS) and metal-chelating assays. From the preliminary screenings
in which 34 different samples extracted using 80% methanol were involved, the
rhizome extract of Curcuma longa exhibited the highest antibacterial properties with
minimum inhibitory concentration (MIC) values ranging from 15.6 to 62.5μg/ml
against all six bacteria. This was followed by the leaf extract of Murraya koenigii
which recorded MIC values between 62.5 and 125μg/ml when screened against P.
fluorescens, S. xylosus, L. monocytogenes and L. innocua. The antioxidant assays
revealed Persicaria minor to have the highest potential in the DPPH (EC50 of 19.2 ±
0.3μg/ml) and FRAP (EC50 of 40.0 ± 0.3μg/ml) assays. It also recorded the highest
total phenolic content (59.1 ± 0.2μg GAE/mg sample) among the tested plant
samples. These three extracts were subjected to fractionation using paper
chromatography to yield seven fractions each for both P. minor and M. koenigii
using the BAW (butanol : acetic acid : distilled water) solvent in a ratio of 4:1:5 and
five fractions for C. longa using a combination of 10% and 50% acetic acid solvents.
The fractions were viewed as distinct bands under ultra-violet illumination and were
collected separately before being subjected to antibacterial and antioxidant assays as
their respective extracts. The ensuing ultra-performance liquid chromatography
(UPLC) analysis conducted onto promising fractions of each shortlisted sample
revealed that curcumin (C. longa) and ρ-coumaric acid (M. koenigii) were
responsible for the antibacterial effects while quercetin-3-O-rutinoside contributed to
the antioxidant property of P. minor. This outcome provides us with alternative
preservatives to delay the spoilage of fish products caused by bacteria and oxidation.
Description
Keywords
To identify plant species and phenolic compounds that exhibited antioxidant , and antibacterial activities.