Microgreens have gained increasing popularity as food ingredients in recent years because of their high nutritional value and diverse sensorial characteristics. Microgreens are edible seedlings including vegetables and herbs, which have been used, primarily in the restaurant industry, to embellish cuisine since 1996. The rapidly growing microgreen industry faces many challenges. Microgreens share many characteristics with sprouts, and while they have not been associated with any foodborne illness outbreaks, they have recently been the subject of seven recalls. Thus, the potential to carry foodborne pathogens is there, and steps can and should be taken during production to reduce the likelihood of such incidents. One major limitation to the growth of the microgreen industry is the rapid quality deterioration that occurs soon after harvest, which keeps prices high and restricts commerce to local sales. Once harvested, microgreens easily dehydrate, wilt, decay and rapidly lose certain nutrients. Research has explored preharvest and postharvest interventions, such as calcium treatments, modified atmopsphere packaging, temperature control, and light, to maintain quality, augment nutritional value, and extend shelf life. However, more work is needed to optimize both production and storage conditions to improve the safety, quality, and shelf life of microgreens, thereby expanding potential markets.

This study was conducted to investigate the effect of free chlorine concentrations in wash water on Escherichia coli O157:H7 reduction, survival, and transference during washing of fresh-cut lettuce. The effectiveness of rewashing for inactivation of E. coli O157:H7 on newly cross-contaminated produce previously washed with solutions containing an insufficient amount of chlorine also was assessed. Results indicate that solutions containing a minimum of 0.5 mg/liter free chlorine were effective for inactivating E. coli O157:H7 in suspension to below the detection level. However, the presence of 1 mg/liter free chlorine in the wash solution before washing was insufficient to prevent E. coli O157:H7 survival and transfer during washing because the introduction of cut lettuce to the wash system quickly depleted the free chlorine. Although no E. coli O157:H7 was detected in the wash solution containing 5 mg/liter free chlorine before washing a mix of inoculated and uninoculated lettuce, low numbers of E. coli O157:H7 cells were detected on uninoculated lettuce in four of the seven experimental trials. When the prewash free chlorine concentration was increased to 10 mg/liter or greater, no E. coli O157:H7 transfer was detected. Furthermore, although rewashing newly cross-contaminated lettuce in 50 mg/liter free chlorine for 30 s significantly reduced (P = 0.002) the E. coli O157:H7 populations, it failed to eliminate E. coli O157:H7 on lettuce. This finding suggests that rewashing is not an effective way to correct for process failure, and maintaining a sufficient free chlorine concentration in the wash solution is critical for preventing pathogen cross-contamination.

Washing is a critical step for maintaining quality and safety of fresh-cut produce during its preparation and is often the only measure taken to reduce microbial populations and remove tissue fluids. However, little is known about the effect of washing method on water quality or its consequence on microbial growth and finished product quality. This study was conducted to evaluate the effect of wash water reuse on changes in water quality and its subsequent effect on microbial growth and product quality of packaged fresh-cut Romaine lettuce ( Lactuca sativa L.). Romaine lettuce leaves were sliced and washed in water with chemical oxygen demand levels ranging from 9.8 mg·L ⁻¹ (fresh water) to 1860.5 mg·L ⁻¹ (reused water) and product-to-water ratios of 1:20 and 1:150. The washed samples were dried and placed into packages prepared from films with an oxygen transmission rate of 8.0 pmol·s ⁻¹ ·m ⁻² ·Pa ⁻¹ and stored at 5 °C for 14 days. Microbial growth and product quality were monitored at days 0, 4, 8, 11, and 14 during storage. Results indicate that as the quantity of lettuce dipped in 40 L of water increased from 2.0 kg to 18.0 kg, water chemical oxygen demand increased from 124 mg·L ⁻¹ to 1721 mg·L ⁻¹ and biological oxygen demand increased from 140 mg·L ⁻¹ to 526 mg·L ⁻¹ , whereas free and total chlorine levels declined from 151.5 mg·L ⁻¹ to 4.7 mg·L ⁻¹ and from 171 mg·L ⁻¹ to 31.5 mg·L ⁻¹ , respectively. Thoroughly washed lettuce in clean water with a small product-to-water ratio had the least off-odor development. Samples without wash treatment and those washed with reused water had 0.8 to 1.6 log cfu·g ⁻¹ higher populations of lactic acid bacteria than those washed with clean water at the end of storage.