Phenolic Contents, Comparative Antioxidant Studies and Anti-Tubercular Activities of Commonly Used Spices in Abuja, Nigeria

Abstract

Spices are reported to be helpful against diseases of oxidative stress such as cardiovascular diseases and exhibit antimicrobial properties. The potential for their use in adjuvants in tuberculosis cases have not been explored. In this study, the in vitro antioxidant and anti-tuberculosis activities of nine Nigerian spices (Syzigium aromaticum, Thonnigii sanguinea, Piper nigrum, Zanthoxylum zanthoxyloides, Zingiber officinale, Cyperus articulatus, Xylopia aethiopica, Lepidum sativum, and Nigella Sativa) along with their phenolic contents, including total phenolics, total flavonoid, and total tannin contents were evaluated. Antioxidant activities were determined by DPPH scavenging and nitric oxide inhibitory assays. The anti-tuberculosis activity against Mycobacterium bovis and Mycobacterium smegmatis was evaluated using the broth micro-dilution method to determine the minimum inhibitory concentration (MIC). The ranges for the total phenolics, total flavonoids, and total tannins contents were 7.3-193.9 mg GAE/g, 0.0-12.5 mg QE/g, and 0.0-44.4 mg TAE/g, respectively, in all spices. The extracts presented strong DPPH scavenging and nitric oxide inhibitory activities with IC50 values ranging from 4.2-1098 µg/mL and 0.0025-28.65 µg/mL, respectively. S. aromaticum and T. sanguinea showed significant DPPH scavenging activities with IC50 of 4.2 and 7.7 µg/mL, respectively, which were comparable to that of ascorbic acid (3.6 µg/mL) (p ≤0.05). Z. zanthoxyloides and S. aromaticum also exhibited significant nitric oxide inhibitory activities (p ≤0.05) with IC50 of 0.0025 and 0.0051 µg/mL, respectively, which were comparable to the gallic acid value of 0.00088 µg/mL. A weak anti-tubercular activity was however observed with MIC values ranging from 25000-781 µg/mL and 12500-781 µg/mL for M. bovis and M. smegmatis, respectively. A correlation between anti-tubercular and antioxidant (NO and DPPH) activities of the spices was found for M. bovis and M. smegmatis (R =0.8957, 0.8241; R= 0.7681, 0.7030, p ≤ 0.05) respectively. The anti-tuberculosis properties of Thonnigii sanguinea and Lepidum sativum are being reported for the first time.