Purpose: The goal of this study was to investigate the efficacy of three cranberry extracts: Extract-A, Extract-B and Extract-C, as inhibitors of pathogenic and spoilage bacteria in vitro and in food models to determine their feasibility as natural antimicrobials for food products.
Methods: Cranberry extracts were tested against Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes cells and Bacillus cereus, B. licheniformis, and Paenibacillus lautus spores using agar dilution assay at pH 5.0 and 6.0 at 37°C. In food models, 2% milk (pH 6.7) and apple juice (pH 3.4) were used for further evaluation at 12.5 and 25°C over 48-h period.
Results: In vitro, Extract-C effectively prevented growth of vegetative pathogens at 0.05-1.0%, with L. monocytogenes being most susceptible. Extract-A and B at 1.5% were effective at pH 5.0 against L. monocytogenes. For spores, Extract-C was also the most effective product and activity was greater at lower pH. B. cereus spores were the most susceptible to Extract-C at 0.1% at pH 5.0. Extract-A at 2% inhibited all spores tested at pH 5.0. In milk, 1% Extract-C could slow the growth of E. coli and Salmonella over 48 h at 12.5°C, while none of bacterial spores were affected. Extract-C reduced E. coli, Salmonella and L. monocytogenes to undetectable level (~6.0-log reduction) within 24 h in apple juice at 12.5 and 25°C. About 0.7-log reduction of B. cereus was achieved with 0.25% Extract-C in apple juice at 48 h.
Significance: Overall, Extract-C was the most effective antimicrobial, with the highest total phenolics, compared to Extract-A and B, showing the potential for use in low-fat, low-protein foods (e.g., beverages and fruit products) and may be effective at higher pHs than most other commonly used traditional antimicrobials.