Determination of Total Phenolic and Flavonoid Contents in Carrot (Daucus carota L.) Root Extract by UV-Visible Spectrophotometry and Evaluation of Antibacterial Activity Against Gram-Positive and Gram-Negative Bacteria

Abstract

The increasing prevalence of antimicrobial resistance has become a major global health concern, prompting the research for plant-derived antibacterial agents. Carrot (Daucus carota L.) contains phenolic and flavonoid compounds that have been reported to possess antibacterial properties. However, studies integrating phytochemical quantification with antibacterial activity and membrane leakage mechanisms against both Gram-positive and Gram-negative bacteria remain limited. Carrot tubers were extracted by methanolic maceration. Total phenolic content was determined using the Folin–Ciocalteu method, while total flavonoid content was measured by the aluminum chloride colorimetric method using UV–Visible spectrophotometry. Antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa was evaluated using the agar disc diffusion method at extract concentrations of 50, 100, 200, and 300 mg/mL. Membrane damage was assessed by measuring nucleic acid and protein leakage using UV–Visible spectrophotometry and potassium (K⁺) and calcium (Ca²⁺) ion leakage using Atomic Absorption Spectrophotometry (AAS). The extract exhibited total phenolic and total flavonoid contents of 142.2650 ± 5.7364 mg GAE/g extract and 11.2634 ± 0.1066 mg QE/g extract. Phytochemical screening confirmed the presence of flavonoids, glycosides, saponins, and triterpenoids/steroids. The extract inhibited the growth of S. aureus and P. aeruginosa, with inhibition zone diameters ranging from 8.93–11.52 mm and 8.68–10.37 mm, respectively. Statistical analysis demonstrated significant membrane leakage in S. aureus (p ≤ 0.05), whereas no significant difference was observed in P. aeruginosa (p > 0.05). Increased extracellular K⁺ and Ca²⁺ concentrations further supported membrane disruption as the antibacterial mechanism. The methanolic extract of Daucus carota L. contains substantial levels of  phenolic and flavonoid compounds and exhibits antibacterial activity against both Gram-positive and Gram-negative bacteria. Its antibacterial effect appears to be associated with disruption of bacterial membrane integrity, resulting in the leakage of intracellular constituents, including nucleic acids, proteins, potassium ions, and calcium ions.

Keyword: Daucus Carota L., Total Phenolic Content, Total Flavonoid Content, Antibacterial Activity, Staphylococcus Aureus, Pseudomonas Aeruginosa.