Extraction of phenolic compounds from bigarade (Citrus aurantium L.) Leaves using water bath and infrared irradiation : determination of the antioxidant and antibacterial activities of extracts

Abstract

Citrus is a globally available and popular fruit crop that contributes essential nutrients to the human diet. C. aurantium L. plant parts contain many active ingredients that have several biological effects. Few studies highlighted the extraction techniques used to extract total phenolic compounds from C. aurantium leaves, and their antioxidant and antimicrobial activities. For the first time, an infrared assisted extraction technique was used to extract phenolic compounds from C. aurantium leaves. The conventional extraction method water bath was also performed. The study included the following experimental parameters: extraction time, particle sizes, treatment temperature, solid/liquid ratio, and type of the extraction solvent. The total phenolic content and the antioxidant activity of the extracts were determined. The antimicrobial activity of bigarade leaves powder was also tested against 8 microbial isolates: 2 strains of S. aureus, 2 strains of E. coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Salmonella enterica, and Candida albicans using disc diffusion assay, macro dilution broth method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) values, and agar well diffusion method. The two extraction techniques used in our study showed to be effective in the extraction of total phenolic compounds from bigarade leaves. The longer the extraction time, the better the TPC recovery. A reduction in particles size caused a considerable increase in the TPC yield. The temperature and the solvent that gave the highest TPC yields and antiradical activities in both techniques were 80ºC and 100% pure water. Moreover, the solid/liquid ratio that was chosen as the best extraction ratio for both techniques was 1 in 40. Infrared exhibited slightly better results as compared to water bath at all tested temperatures and at some of the tested solvents and ratios. Using the disc diffusion assay, the antifungal activity of bigarade leaf powder extracts was proven against C. albicans for the first time. The extract also exhibited an antibacterial activity against S. aureus 2. The macro-dilution broth method showed that the microbial load had diminished with an increase in the extract concentrations for C. albicans and S. aureus 2. Regarding the agar well diffusion method, the antimicrobial effect of the extract against S. aureus 2 and C. albicans was also proven and zones of inhibitions were detected at 25 mg/well concentration.