Critical analysis of current methods for assessing the in vitro antioxidant and antibacterial activity of plant extracts

Abstract

Natural product research is an active branch of science, driven by the increased value placed on individual health and well-being. Many naturally-occurring phytochemicals in plants, fruits and vegetables have been reported to exhibit antioxidant and antibacterial activity; often touted as being beneficial for human health. In vitro screening is a common practice in many research laboratories as a means of rapidly assessing these properties. However, the methods used by many are not necessarily optimal; a result of poor standardization, redundant assays and/or outdated methodology. This review primarily aims to give a better understanding in the selection of in vitro assays, with emphasis placed on some common assays such as the total phenolic content assay, free radical scavenging activity, disc-diffusion and broth microdilution. This includes a discussion on the reasons for choosing a particular assay, its strengths and weaknesses, ways to improve the accuracy of results and alternative assays.

Keywords: 1,1′-Diphenyl-2-picrylhydrazyl (DPPH) (PubChem CID: 2735032); 2,2′-Azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) (PubChem CID: 5815211); 2,2′-Azobis-2-methyl-propanimidamide dihydrochloride (AAPH) (PubChem CID: 76344); AlCl(3) (PubChem CID: 24012); Bacterial susceptibility testing; DMSO (PubChem CID: 679); Ferric tripyridyltriazine (PubChem CID: 77258); Fluorescein (PubChem CID: 16850); Folin–Ciocalteu reagent; Free radical scavenging; Total phenolic content; Tween 80 (PubChem CID: 5281955); p-Dimethylaminocinnamaldehyde (DMACA) (PubChem CID: 5284506).