Factors Affecting the Growth and Survival of Salmonella and Shiga Toxin-Producing Escherichia coli on Microgreens
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Date
2017-11-27
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Abstract
Microgreens are an emerging commodity within the vegetable group with high consumer demand due to their high nutritional value and flavor attributes. To date, there have been no reported outbreaks linked to the contamination of microgreens. In addition, there are only limited experimental data available on the microbiological safety of microgreens. Therefore, not enough knowledge exists on the safety of microgreens. Food safety concerns have been expressed surrounding the similarities that are thought to exist between sprouts and microgreens. Sprouts represent a high food safety concern because the conditions under which they are produced (temperature, time, humidity, and nutrient availability) are ideal for the proliferation of foodborne pathogens. Sprouts have been linked to numerous foodborne outbreaks. Since contaminated seeds have been identified as the main source of pathogenic bacteria in sprout-related outbreaks, this could be also true for microgreens.
The first objective of this research focused on analyzing the growth and behavior of Salmonella and STEC on alfalfa sprouts and microgreens obtained from inoculated seed with an initial concentration of 5 log CFU/g of each organism. Results indicated sprouts contained higher concentrations (8.0 log CFU/g) of target organisms compared to microgreens (7.0 log CFU/g) (P<0.05). The second objective of this research was to determine the effects of production practices and plant type on the growth and survival of Salmonella and STEC at harvesting. Results indicated that harvest period played a significant role in pathogen reduction. Broccoli, mustard, and clover microgreens had significant reduction of Salmonella (0.3 - 2.3-log) and STEC (0.2-2.1-log) populations at 4 weeks compared to 2 weeks (P <0.05). For production practices, our results indicated that microgreen plants cut at 6.5 cm above soil surface contained significantly lower bacterial counts compared to 2.5 cm for both broccoli and clover microgreens (P<0.05). The final objective of this research included determining the spatial distribution of Salmonella Poona after inoculation on microgreens. For clover and mustard microgreens, S. Poona was more prevalent on inedible portions (seed coats) than the edible portions (middle shoot and leaves), indicating that seed coats were the primary source for contamination of microgreens. Overall, the findings from this research provided new insight for the production of microgreens, such as harvest period and production practices that could aid in developing food safety practices for the microgreen industry. Not only does this research provide new awareness for microgreens, but also for other vegetables that are grown from seeds.
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Microgreens, Salmonella and STEC