Evaluation of the Total Antioxidant Capacity of Three Selected Plants in Guyana

Aims: This study aimed to evaluate the leaf extracts of three commonly used medicinal plants in Guyana, namely Brassica juncea (mustard), Struchium sparganophora (antsbush), and Psidium guajava (guava), for their total antioxidant capacity. Study Design: Experimental-based study. Place and Duration of Study: The experiments were performed at the chemistry laboratory in the Faculty of Natural Sciences and the main laboratory in the College of Medical Sciences at the University of Guyana from September 2022 to August 2023. Methodology: The leaves of these plants were collected, washed, and air-dried at 280C for approximately one month, then pulverised in a sterilised food processor. Leaf extracts were then obtained by maceration with various solvents such as hexane, ethyl acetate, chloroform, and methanol; followed by filtration and rotary evaporation. The extracts obtained were then subjected to total antioxidant quantification via the phosphomolybdate method using a spectrophotometer. The total antioxidant capacity of the extracts was expressed as ascorbic acid equivalents. Results: Antioxidant activity was seen for all the extracts but in varying quantities. The highest antioxidant capacity was observed for the P. guajava extracts with a mean of 5.2 mg/mL. The least activity was observed for the S. sparganophora extracts, with a mean of 0.9 mg/mL. The ethanolic extracts showed the highest antioxidant capacity (10.6 mg/mL for P. guajava; 2.5 mg/mL for B. juncea). The hexane extracts had the least (0.33 mg/mL for P. guajava; 0.24 mg/mL for B. juncea). Conclusion: The leaves of B. juncea, S. sparganophora, and P. guajava have antioxidant capacity but those of P. guajava have greater potential for use as complementary and alternative treatments for chronic diseases.