ORIGINAL ARTICLE Antimicrobial activity of flavonoids extracted from bergamot (Citrus bergamia Risso) peel, a byproduct of the essential oil industry G. Mandalari 1,3 , R.N. Bennett 2 , G. Bisignano 3 , D. Trombetta 3 , A. Saija 3 , C.B. Faulds 4 , M.J. Gasson 1 and A. Narbad 1 1 Commensal and Microflora Programme, Institute of Food Research, Norwich Research Park, Colney, Norwich, UK 2 CECEA – Departamento de Fitotecnia e Engenharia Rural, Universidade de Tra ´ s-os Montes e Alto Douro (UTAD), Vila Real, Portugal 3 Department of Pharmacobiology, University of Messina, Messina, Italy 4 Sustainability of the Food Chain Exploitation Platform, Institute of Food Research, Norwich Research Park, Norwich, UK Introduction There is increasing epidemiological evidence for the bene- ficial health effects of regular intake of fruits and vegeta- bles as part of a healthier diet (Dauchet et al. 2004). Polyphenols from fruits, vegetables and cereals, herbs and spices have been shown to have beneficial effects on human health, and some extracts of polyphenol-rich plants have been used in functional foods or as supple- ments. Among polyphenols, flavonoids are secondary metabolites well documented for their biological effects, including anticancer, antiviral, antimutagenic and anti- inflammatory activities (Benavente-Garcia et al. 1997; Vuorela et al. 2005). There is also evidence suggesting that dietary flavonoids can influence gastrointestinal bac- terial populations, and there is considerable in vitro data on the direct and indirect (toxin inhibition) activity of polyphenols, such as naringenin and hesperetin, against Keywords antimicrobials, bergamot, flavonoids, MIC, synergism. Correspondence Arjan Narbad, Institute of Food Research, Norwich Research Park, Colney, NR4 7UA Norwich, UK. E-mail: arjan.narbad@bbsrc.ac.uk 2007 ⁄ 0035: received 10 January 2007, revised 26 March 2007 and accepted 16 April 2007 doi:10.1111/j.1365-2672.2007.03456.x Abstract Aims: To evaluate the antimicrobial properties of flavonoid-rich fractions derived from bergamot peel, a byproduct from the Citrus fruit processing industry and the influence of enzymatic deglycosylation on their activity against different bacteria and yeast. Methods and Results: Bergamot ethanolic fractions were tested against Gram- negative bacteria (Escherichia coli, Pseudomonas putida, Salmonella enterica), Gram-positive bacteria (Listeria innocua, Bacillus subtilis, Staphylococcus aureus, Lactococcus lactis) and the yeast Saccharomyces cerevisiae. Bergamot fractions were found to be active against all the Gram-negative bacteria tested, and their antimicrobial potency increased after enzymatic deglycosylation. The minimum inhibitory concentrations of the fractions and the pure flavonoids, neohesperi- din, hesperetin (aglycone), neoeriocitrin, eriodictyol (aglycone), naringin and naringenin (aglycone), were found to be in the range 200 to 800 lg ml )1 . The interactions between three bergamot flavonoids were also evaluated. Conclusion: The enzyme preparation Pectinase 62L efficiently converted com- mon glycosides into their aglycones from bergamot extracts, and this deglyco- sylation increased the antimicrobial potency of Citrus flavonoids. Pairwise combinations of eriodictyol, naringenin and hesperetin showed both synergistic and indifferent interactions that were dependent on the test indicator organism. Significance and Impact of the Study: Bergamot peel is a potential source of natural antimicrobials that are active against Gram-negative bacteria. Journal of Applied Microbiology ISSN 1364-5072 2056 Journal compilation ª 2007 The Society for Applied Microbiology, Journal of Applied Microbiology 103 (2007) 2056–2064 ª 2007 IFR