Antioxidant, Antimicrobial, and Antibiofilm properties of Opuntia stricta and Vachellia erioloba, and chemical characterization of volatile compounds
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Date
2023
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University of Namibia
Abstract
Vachellia erioloba, commonly known as Acacia erioloba belongs to the family
Fabaceae and is native to Namibia, Botswana, and South Africa. The plant is used
traditionally to treat ear infections, headaches, and toothaches. Opuntia stricta belongs
to the family Cactaceae and is found in Namibia. The plant is used in the management
of diseases such as diabetes, obesity, and cancer. This study was designed to
investigate the antioxidant, antimicrobial, antibiofilm activity, and chemical
characterization of V. erioloba and O. stricta. The radical scavenging capacity of
extracts was estimated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the reducing
power was determined using ferric reducing power assay. Moreover, the antimicrobial
activities of the extracts of these medicinal plants were tested against Staphylococcus
aureus, Streptococcus mutans, Escherichia coli, and Candida albicans. On the other
hand, antibiofilm activity was determined against Staphylococcus aureus. The
phytochemical analysis of V. erioloba and O. stricta was done using qualitative and
quantitative phytochemical analysis. Moreover, the characterization of the volatile
constituents was done for the seed extract of V. erioloba. Furthermore, chemical
characterization of the volatile constituents of the extract was performed using gas
chromatography-mass spectrometry (GC–MS). The radical scavenging assay revealed
IC50 values of 1.973 ± 0.012 and 972.0 ± 22.3 μg/mL for the seed pods and seed of V.
erioloba, respectively, while the IC50 values for the extracts of O. stricta were 53.74
± 0.18, 153.8 ± 0.9, 258.7 ± 0.7, and IC50 ˃ 1000 μg/mL for the seeds, flowers, fruits,
and leaves of O. stricta, respectively. In addition, the reducing power of both V.
erioloba and O. stricta extracts increased as the concentration of the extracts
increased, which confirmed the presence of antioxidants in the extracts. The
antimicrobial assay revealed that the various extracts of V. erioloba and O. stricta
ii
exhibited moderate antimicrobial activity with inhibition zones (IZ) ranging from 0 to
12 mm. Moreover, the MIC obtained from this study ranged from ≤ 0.63 to 10 mg/mL.
The biofilm inhibition demonstrated BIC50 values of V. erioloba and O. stricta extracts
ranged from ˂ 0.08 to 0.498 ± 0.017 mg/mL. Moreover, biofilm eradication revealed
BEC50 values ranged from < 0.08 to 0.172 ± 0.008 mg/mL. The GC-MS analysis of
V. erioloba seed extracts revealed the presence of phytosterols, acids, esters, α-
tocopherol and α-amyrin, which comprises a number of known bioactive compounds.
The results from this study show that V. erioloba and O. stricta extracts possess
antioxidant, antimicrobial, and antibiofilm properties, making these plants good
potential sources of antioxidants and antimicrobial agents. The findings of this study
support the traditional uses of V. erioloba and O. stricta.
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Biochemistry
Keywords
Traditional uses, Biofilm inhibition, Biofilm eradication, 2-diphenyl-1- picrylhydrazyl (DPPH), Gas chromatography-mass spectrometry (GC–MS), Namibia, University of Namibia