Inactivation ofListeria monocytogenesandSalmonellaTyphimurium in strawberry juice enriched with strawberry polyphenols

BACKGROUND Low molecular-weight phenolic fractions (LMPFs) were extracted fromAlbion(LMPF-A) andCamarosa(LMPF-C) strawberry cultivars. Their antibacterial activity againstListeria monocytogenesandSalmonellaTyphimurium cocktailsin vitroandin vivowas investigated using strawberry juice as a food model. This study also sought to determine their antibacterial mechanism. RESULTS Quercetin was identified as a principal compound in both phenolic fractions. The minimum bactericide concentration (MBC) values were 750 and 850 mu g mL(-1)(LMPF-C) and 800 and 950 mu g mL(-1)(LMPF-A) againstS.Typhimurium andL. monocytogenes, respectively. The possible antibacterial activity of the phenolic extracts could be related to the release of phosphate and potassium ions, the effect of the disruption of membrane integrity on L. monocytogenes, and the effect of the inhibition of dihydronicotinamide adenine dinucleotide (NADH) oxidase activity on S. Typhimurium. Quercetin and kaempferol were the most active compounds in producing bacterial damage. Strawberry juice supplemented with the phenolic fractions and incubated at 37, 20, and 4 degrees C reduced bacterial viability; moreover, after treatment with the phenolic fraction at the lowest temperature, no viable cells were detected after 7 days' incubation.Salmonellawas more sensitive to the supplements thanListeriain strawberry juice. CONCLUSIONS This study could form the basis for the development of natural antibacterial agents that could be included in natural juice or used by the pharmaceutical industry. (c) 2020 Society of Chemical Industry

Automated summary

Low molecular-weight phenolic fractions extracted from Albion and Camarosa strawberry cultivars showed antibacterial activity against Listeria monocytogenes and Salmonella Typhimurium. Quercetin was identified as a principal compound in both fractions, with possible antibacterial mechanisms including release of ions, disruption of membrane integrity, and inhibition of enzyme activity. The study suggests potential development of natural antibacterial agents for use in juice or pharmaceutical industry.