Combination effect of nisin and red ginger essential oil (Zingiber officinale var. rubrum) against foodborne pathogens and food spoilage microorganisms

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The aim of this research was examined the antimicrobial activity of nisin, red ginger essential oil (Zingiber officinale var. rubrum) and their combination against foodborne pathogen and food spoilage microorganisms. Minimum inhibitory concentration (MIC) assay was performed to determine the antimicrobial activity of nisin and red ginger essential oil. Each antimicrobial agents were tested against four foodborne pathogens microorganisms (Salmonella typhimurium, Escherichia coli, Staphylococcus aureus and Bacillus cereus) and two food spoilage microorganisms (Pseudomonas fluorescens and Aspergillus niger). The checkerboard method was used to determine the synergistic effect of a combination of nisin and red ginger essential oils. Minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) assay were performed to determine the killing effect of nisin and red ginger essential oil combination. Red ginger essential oil was analyzed using GC-MS assay to obtain the chemical compound of red ginger essential oil. The MIC value of nisin against Salmonella typhimurium and Staphylococcus aureus was > 2000 IU/ml, against Escherichia coli and Pseudomonas fluorescens was 500 IU/ml, against Bacillus cereus was 200 IU/ml and against Aspergillus niger was 250 IU/ml. The MIC value of red ginger essential oil against Staphylococcus aureus was <0.0625%, against Escerichia coli was 0.0625%, against Aspergillus niger was 0.125%, against Bacillus cereus and Pseudomonas fluorescens was 0.25% and against Salmonella typhimurium was 1%. The combination of nisin and red ginger essential oil had synergistic effect against Bacillus cereus. The combination of nisin and red ginger essential oil shown no bactericidal effect against all five bacteria but performed fungicidal effect against Aspergillus niger at concentration 62.5 IU/ml of nisin and 1% of red ginger essential oil. The result of GC-MS assay showed that red ginger essential oil contained of Z-citral (23.332%), citral (18.87%), 1,8-cineole (12.18%), camphene (11.87%), geranyl acetate (3.82%), linalool (2.88%), α-pinene (2.6%), 5-hepten-2-one, 6-methyl-(2.32%), ar-curcumene (2.06%) and α-terpineol (2.05%).