Microbial Reduction in Fresh Salad Using Natural Antimicrobials Added to Active Packaging by Vapor Contact

Introduction: Vapor contact is an alternative when essential oils (EOs) and microorganisms are placed separately in some sealed environment and therefore microbial inhibition is achieved from a distance without direct contact of the antimicrobial agent with the food. When EOs applied in vapor phase could be effective against foodborne pathogens and spoilage microorganisms at relatively lower concentrations than when applied in liquid phase, thereby causing less effect on sensory attributes.

Purpose: The aim of this work was to analyze the microbial reduction in fresh salad using natural antimicrobials added to active packaging by vapor contact throughout 15 days of storage at 8ºC. 

Methods: Cinnamon and oregano EOs were incorporated to different polymer (starch or carboxymethylcellulose) film formation solutions at different concentrations (0.00, 0.25, 0.50, 0.75, 1.00, 2.00, or 4.00%), then were applied into PET packages covers and dried. A mixture of lettuce and spinach washed and rinsed were put in the boxes. Finally, complete packages were storage at 8ºC during 15 days. Mesophilic standard plate count and total coliforms were determined every three days.

Results: For both kind of films incorporated to active packaging vapor contact reaches its highest log reduction in mesophilic count (2.5 cycles) with oregano EO (2 and 4%) showed significant differences (P<0.05) with respect to films formulated without EO and cinnamon EO packages. For total coliforms log cycle reduction (1.5 cycles) was achieved only with oregano EO at high concentration. Salad shelf life was increased by 30%.

Significance: Starch or carboxymethylcellulose edible films incorporating Mexican oregano EO added to active packaging can reduce microbial concentration by vapor contact increasing shelf life of fresh packaged products.