Effect of Concurrent Extreme Temperatures and Water Deficit on the Phytochemistry, Antimicrobial and Antioxidant Activities of Portulacaria Afra Jacq Using Four Extraction Solvents

Abstract

The study focused on Portulacaria afra, a plant native to South Africa which is renowned for its traditional medicinal applications against oral and skin infections. This study aimed to explore, the phytochemical composition, antimicrobial, and antioxidant capabilities of the leaves, stems, and roots under concurrent extreme temperatures (hot and cold) and water deficit conditions to further validate its medicinal significance. To achieve this, the study subjected Portulacaria afra to various temperatures ranging from 0/5ºC to 35/45ºC combined with water deficit and evaluated its antimicrobial and antioxidant properties. Phytochemical compounds were extracted from different solvent extracts of P. afra and analysed. Antioxidant activity was assessed using metal chelating activity, hydrogen peroxide scavenging, and 2,2-diphenylpicrylhydrazyl (DPPH) free radical assays, while antimicrobial efficacy was determined using the agar-well diffusion method against three microbial strains: Staphylococcus aureus, Escherichia coli, and Streptomyces griseus. Results revealed an enhanced presence of 13 phytochemical groups in Portulacaria afra extracts compared to controls, with peak accumulation of phenolic and flavonoid compounds observed under extreme hot temperatures (35/45ºC) with water deficit. Extracts from these conditions exhibited superior inhibitory effects against Escherichia coli. Moreover, antioxidant activity peaked at hot temperatures (30/40ºC) for 2,2-diphenylpicrylhydrazyl (DPPH) and metal chelating assays, while the most effective hydrogen peroxide scavenging activity was observed under hot temperatures (35/45ºC) with water deficit. Antioxidant activity peaked at mid-range hot temperatures (30/40ºC) for DPPH and metal chelating, while the best hydrogen peroxide scavenging activity was observed during concurrent extreme hot temperatures (35/45ºC) with water deficit. The findings suggest that extreme temperature variations combined with water deficit significantly impact the biological activities of Portulacaria afra, highlighting the plant’s adaptability and resilience while retaining its therapeutic potential.