Purpose: This study investigated antimicrobial activity (AMA) of seven fruit extracts and juices against four Lm (Scott A, SFL0404, F5027, H0222) and four Salmonella strains (S. Weltevreden SFL0319, S. Newport ATCC 6962, S. Newport H1275, S. Typhimurium ATCC 14028) from human clinical samples, seafood, raw milk, produce, and meat sources.
Methods: Extracts (25-100% wt/vol) were prepared by blending fruit, or peel (1 min) and diluting with sterile distilled water. AMA was measured using well-diffusion assay on trypticase soy agar with 9 mm wells containing different concentrations of tested compounds (25-100%). For compounds that exhibited highest AMA, minimum inhibitory (MIC) and minimum bactericidal concentrations (MBC) were determined using tryptic soy broth (35°C, 48 h). Inoculum levels were ca. 6-7 log CFU/ml.
Results: Pomegranate peel extract (PPE) and cranberry juice (CJ) exhibited highest AMA, with average inhibition zones against Lm and Salmonella of 19.38 and 18.65 mm, respectively, for PPE, and 20.98 and 12.80 mm, respectively, for CJ. Limited inhibition (ca. 10 to 15 mm) was observed for blueberry, strawberry, plum meat, whole plum and pomegranate seed extracts. MBC of CJ against Lm and Salmonella was 25%, whereas MIC against Lm was 12.5%, but this concentration did not fully inhibit the growth of Salmonella strains. The MBC of PPE for tested strains was 37.5%, whereas the MIC of PPE against Lm and Salmonella were 13.5% and 22.5%, respectively.
Significance: This study demonstrates potential of PPE and CJ to be used as natural antimicrobials against Lm and Salmonella in RTE foods. However, more research is needed to optimize concentrations that exhibit effective AMA, but have minimal impact on sensory qualities of food products.