Antimicrobial and antioxidant activity of crude onion (Allium cepa, L.) extracts


  • Jonathan Santas,

    Corresponding author
    1.  Department of Nutrition and Food Science, University of Barcelona, Av. Joan XXIII, s/n, 08028, Barcelona, Spain
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  • María Pilar Almajano,

    1.  Chemistry Engineering Department, The Technical University of Catalonia, Av. Diagonal 649, 08034 Barcelona, Spain
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  • Rosa Carbó

    1.  Department of Agri-Food Engineering and Biotechnology, The Technical University of Catalonia, Campus Baix Llobregat, C. Esteve Terrades 8, 08860 Castelldefels (Barcelona), Spain
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Antioxidant and antimicrobial activity of the ethyl acetate and water subfractions of methanolic extracts of three Spanish onion varieties were assayed. Flavonoids were mainly present in ethyl acetate subfraction being 34.92 ± 0.75, 7.95 ± 0.16, 0.38 ± 0.01 μmol of rutin eq. g−1 D.W. and its antioxidant capacity was 74.86 ± 1.77, 24.59 ± 0.67, 4.55 ± 0.44 μmol Trolox g−1 D.W. of Grano de Oro, Fuentes de Ebro and Calçot de Valls varieties, respectively. The antimicrobial activity of flavonol standards and onion extracts was evaluated against some food spoiler microorganisms. Quercetin and kaempferol were inhibitory against gram positive bacteria such as Bacillus cereus, Staphylococcus aureus, Microcroccus luteus and Listeria monocytogenes. Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa were less sensible to the antimicrobial effect of both flavonol standards and Candida albicans was totally resistant. Among the onion extracts tested only ethyl acetate subfraction showed antimicrobial inhibition.