Antimicrobial assessment of polyphenolic extracts from onion ( L.) skin of fifteen cultivars by sonication-assisted extraction method.

Onion skin possesses various health benefits due to its phenolic and antimicrobial components. In this study, sonication-assisted extracts of onion skin of differentially coloured cultivars (dark-red, red, pink and white) were investigated for their antimicrobial activity against six pathogenic bacteria. Antimicrobial efficacy of fifteen different coloured extracts was analysed by agar well-diffusion assay with principal component analysis (PCA) for comprehensive investigation. Result showed skin extracts of pink cultivars (cv.) significantly (P ≤ 0.05) effective against pathogenic bacteria followed by red and dark red skin. White skin showed least effect on the growth of bacteria. Skin of cv. 'Phursungi Local' (pink) and cv. 'Hissar-3' (pink) showed best range of inhibition against and compared to other. Only white skin extracts of cv. 'Bhima Shubhra' and 'Udaipur Local' inhibited the growth of up to 4.0 ± 0.0 mm. Minimum inhibitory concentration (MIC) of the effective extracts was also elucidated in the range between 0.09 - 9.0 mg/mL. Skin extracts of cv. 'Hissar-2' (red) and 'Bhima Shubhra' (white) showed better inhibition at the concentration of 0.45 and 0.72 mg/mL against and , respectively. As per correlation analysis, positive correlation was obtained between total flavonoids and inhibition rate of all the bacteria while a weak correlation (R = 0.3967) was observed against . The waste skin of the analysed cultivars can be utilised in food and health sector as natural preservative and antimicrobial agent.