Sanitizer efficacy in reducing microbial load on commercially grown hydroponic lettuce

Area of Science:

• Food Science
• Microbiology
• Agricultural Science

Background:

• Hydroponic lettuce is often packaged with intact root balls, posing a microbial contamination risk from peat moss substrates.
• Current practices omit sanitizer washes due to the perceived lack of substrate contact with edible portions.

Purpose of the Study:

• To evaluate the efficacy of sanitizer washes on microbial load reduction in hydroponic lettuce.
• To assess the impact of storage time and substrate properties on microbial populations.

Main Methods:

• Assessed aerobic plate counts (APC) and coliform bacteria (CB) on lettuce leaves, roots, and substrate after sanitizer application (chlorine, peroxyacetic acid).
• Monitored microbial changes during storage.
• Evaluated microbial growth on different commercial peat moss substrates with varying physical properties.

Main Results:

• Peroxyacetic acid significantly reduced APC on leaves, roots, and substrate.
• Microbial populations, particularly fungi and APC, increased with storage time, with roots showing the highest APC increase.
• Drier, compacted substrates (Com4) supported less microbial growth compared to wet, spongy plugs.

Conclusions:

• Sanitizer washes (chlorine, peroxyacetic acid) effectively reduce microbial load on hydroponic lettuce leaves without compromising visual quality.
• Substrate physical properties significantly influence microbial hosting capacity.
• Sanitizer efficacy is linked to initial microbial load and storage duration.