ANTIOXIDANT AND ANTIMICROBIAL POTENTIAL OF METHANOLIC EXTRACTS OF SOME COMMONLY CONSUMED SPICES

Abstract

The present study was aimed at investigating the phytochemical constituents, antioxidant and antimicrobial potential of the seeds of Myristicafragrans, Tetrapleuratetraptera and Monodoramyristicaalong side the leaves of Piper nigrum and Ocimumgratissimum commonly used as spices in Nigeria. Phytochemical screening revealed the presence of tannins, saponins, alkaloids and flavonoids in all the studied spices and quantitatively, the highest tannins (24.21%) and saponins contents (8.35%) were observed for T. tetraptera while the least tannins and saponins contents were observed for M.myristica. The highest ascorbic acid (1.57mg/100g) and vitamin E content (2.5mg/g) was observed for O. gratissimum while the least ascorbic acid and vitamin E contents was recorded for M. myristica(0.24mg/100g) and M. fragrans (0.6mg/g) respectively. The results of the phenolic (mgTAE/g) and flavonoids contents (mg/gQE) showed that T.tetrapterahad the highest total phenolic (21.63) and total flavonoid contents (2.55) while the least values were observed for M. fragrans(4.53), (0.77). Similarly, the Ferric Reducing Antioxidant Power (FRAP) of the studied spices indicated that T.tetrapterapossesses the highest reducing power with the least reducing power observed for M.fragrans.In the same vein, the DPPH radical scavenging ability (%) and the total antioxidant (mg GAE/ g) activities of the studied spices also showed a higher value for T. tetrapteraand the least value observed for M. fragrans. Conversely, the highest phytate content (mg/100g) was recorded for P.nigrum(919.53), while the least value was observed for T. tetraptera (344.4). The antibacterial activities of the phenolic extracts of the studied spices at different concentrations (100, 50 and 30mg/ml)also revealed that T. tetraptera exhibited the highest antibacterial activity against all the tested organisms while the least inhibitory effect was recorded for M. fragrans. The study further revealed that the methanolic extracts of the studied spices exhibited a much higher antimicrobial action against the tested gram negative bacteria compared to the strains of gram positive bacteria. The phenolic composition of T. tetraptera having the highest antioxidant activity and antimicrobial action was partially characterized using HPLC/DAD/MS method. The HPLC analysis showed the presence of some phenolic compounds: vicenin-2, four unidentified flavonoids, luteolin derivative and caffeoyl derivatives. On the overall, the studied plants demonstrated some level of antioxidant and antimicrobial activities with T. tetrapteraranking the highest. The observed antioxidant and antimicrobialaction of T. tetraptera and the other studied spices could be attributed to the presence of some phenolic compounds. Hence, the utilization of these indigenous spices and T. tetraptera in particular as potential source of natural antioxidants and antimicrobial agents should be encouraged.