The Quality Evaluation of In-Vitro Antimicrobial, Antioxidant Effect of different Pharmaceutical Dosage Forms of Vitamin C Compounds

Abstract

Background: The quality of commercially available ascorbic acid preparations varies widely, raising concerns about substandard vitamin C products in the market. Since vitamin C exhibits both antimicrobial and antioxidant properties, evaluating these characteristics across different brands is essential for ensuring consumer safety and therapeutic effectiveness. Objective: This in vitro study aimed to assess the quality of various vitamin C formulations available in the market and to identify the type with superior antimicrobial and antioxidant activity. Materials and Methods: Six vitamin C products in tablet and effervescent dosage forms were purchased and coded as S2–S7, while pure ascorbic acid powder (S1) served as the standard. Ascorbic acid content was quantified using iodine redox titration and compared with S1. Antibacterial activity was evaluated using the agar diffusion method against standard Gram‑positive strains (Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 25923) and Gram‑negative strains (Klebsiella pneumoniae ATCC 13883, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Proteus mirabilis ATCC 29906). Minimum inhibitory concentrations (MICs) were determined for each sample. Antioxidant activity was assessed using DPPH radical scavenging measured by UV–VIS spectrophotometry. Data were analyzed using one‑way ANOVA with significance set at p < 0.05. Results: ANOVA revealed significant differences among the tested products (p < 0.05). Sample S4 (Zein Pharma® Vitamin C 1000 mg with 10 mg zinc) showed the closest ascorbic acid content to the standard and demonstrated the largest inhibition zones against S. aureus, B. subtilis, P. aeruginosa, and E. coli at 100 mg/mL. S4 also exhibited the lowest MIC values across all tested strains. Additionally, S4 displayed synergistic enhancement of antioxidant activity compared with pure ascorbic acid. Conclusion: Vitamin C combined with zinc demonstrated superior product quality, stronger antimicrobial activity, and enhanced antioxidant potential compared with other tested formulations.