Chemoprofiling and <i>In vitro</i> antioxidant potentials of methanol water extracts from Nigerian ginger (<i>Zingiber officinale</i>)

Abstract

Ginger (Zingiber officinale) is one of the popular spices in Nigeria. It is highly utilised over the world as spice as well as for the treatment of inflammation, arthritis and other conditions involving reactive oxygen species (ROS), which are known to damage human cells. The proximate, phytochemical composition and antioxidant properties of the plant are reported in this work. Extraction by maceration was used for the pulverized rhizomes with methanol-water (50:50). Further partitioning of the extract was carried out using n-hexane, ethyl acetate and butanol into different fractions according to their polarity. The antioxidant activity was evaluated with 1,1-diphenyl-2-icrylhydrazyl (DPPH) radical scavenging assay, ferric reducing antioxidant power (FRAP) assay, nitric oxide radical scavenging activity (NOSA) and lipid peroxidation scavenging activity (LPSA). The proximate content was determined using conventional chemical methods. The FTIR analyses of n-hexane fraction of Z. officinale revealed some functional groups that may be present in two likely classes of secondary metabolites: terpenes and alkaloids. The ethyl acetate fraction produced flavonoid (121.31 mg/100 g; quercetin) and alkaloids because of the functional groups associated with them, while the butanol fraction with functional groups present revealed cardiac glycosides (4.88 mg/100 g; digoxin) and alkaloids (45.19 mg/100 g). The plant also contained reducing sugar (64.62 mg/100 g glucose), steroids (8.65 mg/100 g; cholesterol), tannins (56.82 mg/100 g; tannic acid) and phenolic compounds (110.64 mg/100 g; gallic acid) from the phytochemical analyses. The proximate analysis revealed that it has a high carbohydrate content (54.54%), but a relatively modest crude fibre (10.21%), moisture content (10.02%), total ash (9.30%), crude fat (8.80%) and crude protein (7.12%). The presence of these phyto-compounds could explain its customary use as oxidative stress inhibitor.