In vitro Antioxidant Properties and α-Glucosidase Inhibition of Combined Leaf Infusions from Psidium guajava L., Syzygium polyanthum L., and Annona muricata L.

Introduction: Guava (P. guajava), bay (S. polyanthum), and soursop (A. muricata) known as natural medicine. Limited report is available on their antioxidant and α-glucosidase inhibitory activities of leaf infusion. The aims of this research were to compare the antioxidant and α-glucosidase inhibitory activities of leaf infusion from guava, bay, and either as individual or combined infusions, and to analyze the chemical composition of the leaf infusion. Methods: Air dried leaf powder of guava, bay and soursop were infused separately with boiled aquadest. The infusions were analyzed for their antioxidant activity against DPPH. The α-glucosidase inhibitory assay was conducted against α-glucosidase from Saccharomyces cerevisiae. Then the infusions scanned with UV-Vis spectroscopy and analyzed with LC-MS. The synergism activities of the combined infusion were measured. Results: Antioxidant activities of leaf infusions of guava and bay showed a comparable result IC₅₀ 12.53 ± 0.55 and 10.76 ± 0.20 μg GAE/mL, but the infusion of soursop showed lower (IC₅₀ 19.77 ± 0.35 μg GAE/mL) than BHT as positive control (11.6 ± 0.31 μg GAE/mL). If soursop infusion was not added, then the mixture of the guava and bay infusion showed an antioxidative synergistic effect. The α-glucosidase inhibitory activities of the guava, bay and soursop infusion (0.083 ± 0.01; 0.025 ± 0.007; 0.533 ± 0.039 μg GAE/mL, respectively) were stronger than acarbose (1285 ± 148 μg/mL). The α-glucosidase inhibitory activities of the combined infusions showed a synergistic effect. The main constituents of the guava infusion were identified tentatively as chrysin and caffeoylquinic acid, for the bay infusion it was caffeoylquinic, and for the soursop infusion it was luteolin. Conclusions: There is a significant synergism of antioxidant activity of Guava and Bay mixture. The combined infusion of Bay and Soursop or Guava and Soursop showed antagonistic effect.