and [6]-shogaol, 1-(4-hydroxy-3-methoxyphenyl) dec-5-en-3-one (Ilic et al. 2014; El-Halawany et al.
2014; Escoubas et al. 1995). The oil derived from the seed was reported to contain volatile compounds such as α-humulene, β-caryophyllene, δ-cadinene and dibutyl phthalate (Markson et al. 2011; Ukeh et al. 2009; Ajaiyeoba and Ekundayo, 1999; Menut et al. 1991). Similarly, labdane dieterpenoids was recently isolated from the organic extracts of A. melegueta rhizome (Ngwoke et al. 2014). In our most recent study, the fruit and leaf ethanolic extracts were found to have eugenol, gingerol, capsaicin, 3- decanone, 1-(4-hydroxy-3-methoxyphenyl), ethyl homovallinate, oleic acid and other fatty acid derivatives (Mohammed et. al. 2015).
1.4.4 Ethnobotanical uses
A. melegueta has been widely used in food preparation as a spice and also locally in the treatment of various ailments. Various seed decoctions are used traditionally against bacterial infections, diarrhea, abdominal pain, snakebite and wounds healing in most parts of Africa (Akendengue and Louis, 1994; Kokwaro, 1993). Similarly, fruit, seed and leaf were also reported to be used in the treatment of DM and other metabolic diseases in Nigeria (Soladoye et al. 2012; Gbolade, 2012; 2009). It was also reported that leaf and stem of A. melegueta are used for wounds and bacterial infections (Akendengue and Louis, 1994). Additionally, the root has been a good remedy against snakebite and dysentery (Kokwaro, 1993).
1.4.5 Pharmacological importance
The A. melegueta seed extracts have been reported to demonstrate broad anti-microbial activities (Nneka and Jude, 2013; Doherty et al. 2010). Doherty et al. (2010) reported that seed ethanolic extract (5-50 mg/mL) exhibited higher anti-microbial (Salmonella spp, Escherichia coli, Shigella spp and klebsiella spp) action compared to the aqueous extract. In another study, the seed methanolic extract (5%-30%) has also shown anti-fungal activity against Helminthosporium solani, Aspergillus niger, Penicillium digitatum and Mucor piriformis (Nneka and Jude, 2013). In a more recent study, the dieterpenoids isolated from the organic extracts (0.97-250 mg/mL) of A. melegueta rhizome showed bactericidal activity in vitro against Escherichia coli, Listeria moncyogenes and Staphylococcus aureus strains (Ngwoke et al. 2014). The seed diethyl ether extracts (0.6 mg/mL) was reported to exhibit potent insect repellant activity against the maize weevil, Sitophilus zeamais (Ukeh et al. 2009).
Furthermore, the various extracts from A. melegueta seed showed anti-oxidative and potent inhibitory effects against α-glucosidase activity in vitro (Adefegha and Oboh, 2012a; Kazeem et al.
2012; Adefegha and Oboh, 2011; Etoundi et al. 2010). In another study by Adefegha and Oboh (2012a), the seed aqueous extract (0-3 mg/mL) demonstrated moderate radical scavenging ability (IC50:17.38 mg/mL) and the inhibition of the carbohydrate hydrolyzing enzymes (IC50 values:α-glucosidase: 2.14
mg/mL; α-amylase: 4.83 mg/mL). The same extract at the concentration of 0.2 g/mL was also reported to inhibit the α-amylase (30.61%) and lipase (8.91%) activities in vitro (Etoundi et al. 2010). It was also reported previously that the seed aqueous extract (0-3 mg/mL) attenuated the Fe2+-induced lipid peroxidation in normal rat’s brain (Adefegha and Oboh, 2011). Kazeem et al. (2012) have reported that seed polyphenolic-rich extract (0.1-1 mg/ml) exhibited good anti-oxidant action (IC50 values: DPPH:
0.11 mg/mL; anti-glycation: 0.125 mg/mL; Superoxide anion: 0.105 mg/mL). In a more recent study, treatment of seed ethanolic extract (100-400 mg/kg bw) daily for 4 weeks was reported to improve in vivo anti-oxidative status in normal rats (Onoja et al. 2014).
Similarly, the seed aqueous extract (4.8 g/kg bw/day) demonstrated hepato-protective effect in ethanol-induced toxic animals after 16 days oral intervention (Nwozo and Oyinloye, 2011). The seed ethanolic extract (0.5-1 g/kg bw) including paradol, gingerol, and shogaol isolated from the seed (0.15 g/kg bw) have showed anti-inflammatory activities in a rats paw edema model after 3 hour post- administration period (Ilic et al. 2014). Umukoro and Ashorobi (2008) had earlier reported that treatment of aqueous extract (50-200 mg/kg bw) daily for 4 days exhibited anti-inflammatory action in rats. Some previous findings have showed the potential of the seed extracts in ameliorating problems associated with reproductive function. Kamtchouing et al. (2002) have shown that treatment of aqueous extract (115 mg/kg bw/day) improved penile erection in rats. Subsequently, after 55 days treatment, the extract at the same dose increased the secretions of epididymis and seminal vesicle in animals (Mbongue et al. 2012). In another study, seed aqueous extract (25-200 mg/kg bw) showed anti-stress as well as anti-nociceptive potentials in mice after 30 minutes post-treatment period (Umukoro and Ashorobi, 2007; 2005).
Sugita et al. (2013) have recently reported that daily administration of A. melegueta capsule (10 mg) for 4 weeks activates brown adipose tissue and increases whole-body energy expenditure in healthy human subjects. In a preliminary study, Adesokan et al. (2010) reported that daily treatment of A.
melegueta seed aqueous extract (200, 400 mg/kg bw) demonstrated blood glucose lowering ability in alloxan-induced diabetic rats. Similarly, the leaf extract (50-200 mg/kg bw) was also reported to cause reduction of blood glucose level in alloxanized animals after 5 day post-treatment period (Mojekwu et al. 2011). Additionally, the seed ethanolic extract was reported safe up to a dose of 300 mg/kg bw (Akpanabiatu et al. 2013; Ilic et al. 2010). In another study, paradol, gingerol, and shogaol isolated from the seed have showed anti-inflammatory activity in a rats paw edema model (Ilic et al. 2014). El- Halawany et al. (2014) have also reported that diarylheptanoid, 8-dehydrogingerdione, 6- dehydroparadol,dihydrogingerenone, 6-gingerol, dihydroparadol, paradol and 6-shogaol demonstrated hepato-protective and anti-oxidative actions in CCl4 induced acute liver injury in rats.