Active edible coating and γ-irradiation as cold combined treatments to assure the safety of broccoli florets (Brassica oleracea L.)

Int J Food Microbiol. 2017 Jan 16;241:30-38. doi: 10.1016/j.ijfoodmicro.2016.10.010. Epub 2016 Oct 11.

Abstract

The antimicrobial activity of essential oils (EOs), organic acid (OA) salts and natamycin, a natural antifungal produced during fermentation by the bacterium Streptomyces natalensis, was assessed against four pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium and Aspergillus niger). The Minimum Inhibitory Concentration (MIC) of each antimicrobial (AM) was assessed to determine their efficiency on tested microbial species in order to select the most efficient. Then, the interactions between different antimicrobial compounds showing the lowest MIC were determined by the checkerboard method. The most effective antimicrobial formulation showing synergistic or additive effects was then encapsulated in an alginate matrix to protect the antimicrobial efficiency during storage. The effectiveness of the formulation was then evaluated in situ using broccoli as a food model. A combined treatment of active coating and γ-irradiation (0.4 and 0.8kGy) was also done in order to evaluate the possible synergistic effect between treatments. The results of this study allowed the selection of 4 EOs, one OA salt and the natamycin as an antifungal agent exhibiting lower MIC values. The interactive antimicrobial effects between them showed that an antimicrobial formulation composed of 300ppm of lemongrass EO, 5000ppm of sodium diacetate and 80ppm of natamycin resulted in an additive effect against A. niger, E. coli and S. Typhimurium and showing synergistic effect against L. monocytogenes. Finally, in situ analyses showed a synergistic antimicrobial activity between active coating and γ-irradiation and allowed the extension of the shelf-life of ready-to-eat (RTE) broccoli during storage at 4°C.

Keywords: Active coating; Natural antimicrobial compounds; Shelf-life; Spoilage bacteria; Synergy; γ-Irradiation.

MeSH terms

  • Acetates / chemistry
  • Anti-Bacterial Agents / chemistry*
  • Aspergillus niger / drug effects
  • Brassica / microbiology*
  • Cinnamomum zeylanicum / chemistry
  • Colony Count, Microbial
  • Consumer Product Safety
  • Cymbopogon / chemistry
  • Escherichia coli O157 / drug effects
  • Food Contamination / prevention & control*
  • Food Irradiation*
  • Food Microbiology*
  • Gamma Rays*
  • Listeria monocytogenes / drug effects
  • Microbial Sensitivity Tests
  • Natamycin / chemistry
  • Oils, Volatile / pharmacology
  • Salmonella typhimurium / drug effects
  • Satureja / chemistry
  • Thymol / chemistry
  • Thymus Plant / chemistry

Substances

  • Acetates
  • Anti-Bacterial Agents
  • Oils, Volatile
  • sodium diacetate
  • Thymol
  • Natamycin