Evaluating the effect of flavonoids in tomato exocarp on Salmonella enterica

Abstract

Introduction: The exocarp of tomato fruit are known to produce high levels of flavonoids, compounds with antimicrobial effects. The purpose of this study was to investigate flavonoid levels in peels of different tomato cultivars and their potential antimicrobial effects on Salmonella Newport and Montevideo. Methods: Phytocompounds were extracted from 20 mg of lyophilized exocarp of tomato fruit ‘Black Icicle’, ‘Midnight Roma’, ‘Dixie Red’, ‘Indigo Rose’, ‘Inigo Cherry’, ‘Heinz-1706’ and ‘Charger’ in 5% methanol for flavonoid and microbial analysis. Total flavonoids were measured using a colorimetric assay at 510 nm, quantified using catechin standard curve and expressed as mg catechin equivalent (CE)/g. Flavonoid finger-printing was performed on a UV-Vis spectrophotometer with a scanning range set to 240-400 nm. Extracts were inoculated with log 6 CFU/mL Salmonella Newport or Montevideo, incubated with shaking at 35°C and sampled at 2, 8 and 20 h post-inoculation. Bacteria were enumerated by serial dilution. Microbial data were analyzed statistically. Results: Salmonella counts declined over time in all cultivar extracts (p<0.01) and ‘Midnight Roma’ yielded the lowest counts.. No significant differences in Salmonella counts were detected within each time point by cultivar. ‘Indigo Rose’ had higher total flavonoids (85.38 mg CE/g), than ‘Charger’ (17.98 mg CE/g, p<0.01), ‘Heinz-1706’ (20.61 mg CE/g, p<0.01) and ‘Black Icicle' (27.25 mg CE/g, p<0.05). Flavonoid scan data showed cultivar differences. Significance: Flavonoid concentrations differed by cultivar. Salmonella decline in peel extracts over a 20 hour period was cultivar dependent.