Evaluating the Efficacy of Ozone and Modified Atmosphere Packaging at Extending the Lag Phase of Native Microflora on Vegetables Stored at Non-optimum Temperatures

Introduction: Cold storage is not always readily accessible for small vegetable growers, as access to refrigerated trucks and cooling facilities is often limited.  This can be particularly problematic for farmers selling at wholesale markets, as quality and safety of the product may be negatively affected when stored at non-optimum temperatures.

Purpose: This research was conducted to determine if a postharvest ozone wash and passive modified atmosphere packaging (MAP), either alone or in combination, can restrict the growth of microbial populations on vegetables stored at non-optimum temperatures.

Methods: Broccoli, spinach and asparagus were collected at harvest from local vegetable farmers in Kansas.  Products were either 1) unwashed, 2) washed in 4°C water (1 minute) or 3) washed in ozonated water (1.0-1.5 ppm for 1 minute) prior to storage in an open produce bag or a MAP bag at 13°C with 85% RH.  As an indication of product safety, populations of yeasts, molds, psychrotrophs, total aerobic microorganisms and coliforms were quantified on days 0, 3, 5 for asparagus and broccoli and days 0, 3, 6, 9, 12, 15, 18 for spinach. 

Results: An atmosphere of 7% CO₂ and 6% O₂, 4% CO₂ and 7% O₂ and 12% CO₂ and 3% O₂ was equilibrated in MAP bags containing spinach, asparagus and broccoli, respectively. All treatments were statistically the same (P > 0.05) for all microorganisms and products evaluated. 

Significance: A post-harvest ozone wash and MAP packaging, implemented as either separate interventions or in combination, was not effective at extending the lag phase of native microflora on spinach, asparagus and broccoli stored at non-optimum temperatures.  Future research is necessary to determine if 1) increasing the concentration of ozone and/or the contact time, with or without MAP packaging, would be more efficacious and 2) other postharvest washing interventions are more efficacious.