Food spoilage due to microbial contamination is one of the major concern of the food industry. There is great interest in the use of antimicrobials from natural sources or safer compounds to reduce microbial food spoilage and to ensure food safety instead of synthetic chemical preservatives. Ascorbic acid is one of the major water-soluble vitamins and a powerful dietary antioxidant, and it has been shown to possess in vitro antimicrobial activity, presumably, attributable to acidification of the medium, i.e., lowering the pH, of the medium; and enhances the antibacterial activity antibiotics. The antibacterial activity of ascorbic acid was evaluated in Mueller hinton broth on Escherichia coli, Bacillus subtilis, and in MRS broth on acid-tolerant Lactobacillus plantarum, using micro-broth dilution technique. The growth curve of the bacteria in the liquid broth was compared in presence or absence of ascorbic acid for 24 hours at 37o C and the growth inhibition of ascorbic acid determined. Several concentrations of ascorbic acid were examined for its activity against the bacterial strains. There was complete inhibition of E. coli and B. subtilis at ascorbic acid concentration of 60 mM (solution pH, 3.2) and final liquid broth pH of 6.3. A complete growth inhibition of L. plantarum was observed with ascorbic concentration of 120 mM (solution pH, 2.5) and final liquid broth pH of 5. The minimum inhibitory concentration (MIC) of ascorbic acid against L. plantarum was 2-folds that against E. coli or B. subtilis, suggesting differences in the sensitivity of bacteria to ascorbic acid and its dissociated and non-dissociated forms. While the non-acid tolerant bacteria were sensitive to the dissociated form, the lactic bacteria were more sensitive to the non-dissociated form. The observations suggest that the antibacterial activity of activity may not be, for most part, due to the acidification or lowering of the pH, but it may entail specific action of ascorbic acid on cell membrane or cellular enzymes, and more work is required to understand its inhibitory mechanisms.

Antibacterial Activity of Ascorbic acid: pH effect, specific action or both?

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.