RESUMO
This paper aimed to study the antioxidant properties of two Nigerian plants Psidium guajava (guava) Myrtaceae and Aloe vera Liliaceae plants which have a broad application in phytomedicine. The plants were assessed by quantifying their individual chemical contents and their 1:1 (mass/mass) homogenous combination (guava+A. vera) simultaneously. The non-antioxidant phytochemical quantified included total alkaloids. There was a significant difference in the total alkaloids content (measure on dry weight basis, mg/g) in the analysed plant materials in the order of guava (111.13±0.45)>guava+A. guava (65.99±0.37)>A. vera (22.86±0.15). The antioxidant properties measured were the levels of total phenol, tannin, total flavonoid, total saponin, vitamin C, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging ability and trolox equivalent antioxidant capacity (TEAC). P. guajava recorded significantly higher (p<0.05) antioxidant phytochemicals contents than A. vera except for vitamin C where it recorded significantly lower (p<0.05) value. There was no significant difference (p>0.05) in the vitamin C contents of A. vera and the combined plant materials, guava+A. vera. Guava had also significantly higher (p<0.05) DPPH scavenging ability (0.056 mg/ml), and TEAC (12.51±0.40 mM/gdw) than A. vera. The combined plant materials guava+ A. vera showed synergistic properties in the DPPH free radical scavenging ability (0.15 mg/ml) and antagonistic activity in the TEAC (4.58±0.17 mM/gdw). This study suggests that while guava may be a better antioxidant than A. vera when used separately, the combined plant materials produces synergistic