Aims:  To study the antimicrobial activity of naringin (NAR), a flavonoid extracted from citrus industry waste, and NAR derivatives [naringenin (NGE), prunin and alkyl prunin esters] against pathogenic bacteria such as L. monocytogenes, E. coli O157:H7 and S. aureus. The relationship between the structure of the chemical compounds and their antagonistic effect was also analysed. Methods and Results:  The agar dilution technique and direct contact assaying were applied. NGE, prunin and NAR showed no antimicrobial activity at a concentration of 0·25 mmol l−1. Similarly, fatty acids with a chain length between C2 and C18 showed no antimicrobial activity at the same concentration. However, prunin‐6″‐O‐acyl esters presented high antibacterial activity, mainly against Gram‐positive strains. This activity increased with increasing chain length (up to 10–12 carbon atoms). Alkyl prunin esters with 10–12 carbon atoms diminished viability of L. monocytogenes by about 3 log orders and S. aureus by 6 log orders after 2 h of contact at 37°C and at a concentration of 0·25 mmol l−1. The compounds examined were not effective against any of the Gram‐negative strains assayed, even at the highest concentration. Conclusions:  Addition of sugars to the aglycone did not enhance its antimicrobial activity. Attachment of a saturated aliphatic chain with 10–12 carbon atoms to the A ring of the flavonoid (or to sugars attached to this ring), seems to be the most promising modification. In conclusion, alkyl prunin esters with a chain length of C10–C12 have promising features as antimicrobial agents because of their high antilisterial and antistaphylococcal activity. Significance and Impact of the Study:  This study shows that it is possible to obtain NAR derivatives with important antimicrobial activity, especially against Gram‐positive pathogenic bacteria. It also provides guidelines on the structural modifications in similar molecules to enhance the antimicrobial activity.

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Aims:  To determine the antimicrobial potential of prunin (P), a flavanone glucoside resulting from the hydrolysis of naringin present in grapefruit, and of its prunin 6″‐O‐lauroyl ester (PL), synthesized by enzymatic catalysis. Methods and Results:  P and its lauroyl ester were tested against Gram‐negative and Gram‐positive bacteria, yeasts and moulds. P showed no inhibitory effect against the micro‐organisms assayed, but stimulated growth of Pseudomonas aeruginosa and different Bacilllus sp. However, 150 μg ml−1 of PL inhibited Escherichia coli, Salmonella enterica serovar Enteritidis, Salmonella enterica serovar Typhimurium, many Bacillus sp., Staphylococcus aureus ATCC29213, Enterococcus avium DSMZ17511, and different Listeria monocytogenes strains. In the last case, L. monocytogenes, sensitive or bacteriocin‐resistant cells, lost nearly 4‐log reductions after 30 min of contact. A bactericidal mode of action was determined using both scanning and transmission electronic microscopies. Conclusions:  PL could be used as a food additive, because at low concentration (150 μg ml−1) it exhibited antimicrobial activity against important food‐borne pathogens. A bactericidal effect was also determined on L. monocytogenes sensitive and bacteriocin‐resistant mutant strains. P did not show any antimicrobial property at all. Significance and Impact of the Study:  PL is a potential antimicrobial compound with a high anti‐Listeria property.

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