Microbial and Antioxidant Activities of Some Common Spices from Southeast Nigeria

Abstract

The aim of this research was to evaluate the antioxidant and antimicrobial properties of Piper guineense, Xylopia aethiopica, Tetrapleura tetraptera, Monodora myristica Njameja. The total phenol contents and antioxidant activities of the indigenous spice extracts were determined using Folin-Ciocalteau´s reagent; ABTS (2,2´-azinobis-(3-ethylbenzothiazoline-6-sulponic acid) diammonium salt; DPPH (2,2-diphenyl-1-picrylhydrazyl) and ORAC (Oxygen Radical Absorbance Capacity). Phenolic content of the spices was correlated with the anti-oxidant properties. Antimicrobial properties of some of the spices against known food spoilage and pathogenic microorganisms were also determined. Xylopia aethiopica, Tetrapleura tetraptera, Piper guineense, Monodora myristica, and Njameja contained high levels of total phenols and strong antioxidant activity. Total phenolic content ranged from 869.11 to 1536.40 mg GAE/100g/dw. Antioxidant activity measured by ABTS varied from 1043.74 to 5978.50 mg Trolox Equivalent (TE)/100g/dw, DPPH from 1165 to 13038.92 mg Trolox Equivalent (TE)/100g/dw, and ORAC, from 261.05 to 379.28 ± 2.14 mg Trolox Equivalent (TE)/100g/dw respectively. A positive linear correlation was obtained between total phenol content and ABTS (R2= 0.854). Correlation coefficient between total phenolic content and DPPH was lower (R2= 693), and even lower between total phenolic content and ORAC (R2= 549). The assay methods correlated well with each other (R2= 828-932). The positive linear correlation between total phenolic content and antioxidant activity values show that phenolic compounds in the tested spice extracts contributed significantly to the strong antioxidant activity. In this study, Xylopia aethiopica and Tetrapleura tetraptera showed higher values for phenolic compounds and higher antioxidant activities indicating that they can scavenge free radical actions and prevent lipid peroxidation. X. aethiopica showed bactericidal properties against  S. aureus, Salmonella, Klebsiella, Lactobacillus and E. coli. None of the spices was inhibitory to fungi at concentrations used for the experiments. Further analysis is required to decipher the nature of their phenolic constituents with a view to determining the potentials of these natural antioxidants for commercial ssexploitation.