Control Escherichia coli O157:H7 growth on sprouting brassicacae seeds with high acoustic power density (APD) ultrasound plus mild heat and calcium-oxide antimicrobial spray

Sprouts and microgreens present unique food safety risks. This study aimed to enhance microbial food safety of sprouts and microgreens via seed sanitation and antimicrobial spray. Radish, broccoli, and kale seeds inoculated with Escherichia coli O157:H7 were sanitized by a high acoustic power density (APD) ultrasound and mild heat (55 °C water) combined treatment for 5 min (US-5) or 10 min (US-10) that was compared with the FDA-recommended 20 min, 20,000 mg/L chlorine treatment. E. coli O157:H7 populations of the seeds and sprouts/microgreens were enumerated immediately after seed sanitation, on day-4 of germination, and after 4 more days in storage, or at the time of harvesting (day 7) for microgreens. Sanitated seeds were planted into germination mix and sprayed with water, 0.1% or 0.2% of calcium oxide (CaO) solution three times a day for 7 days. The US-5 treatment achieved a comparable E. coli O157:H7 reduction and sprout yield as the 20,000 mg/L chlorine treatment. The US-10 treatment exhibited a significantly higher E. coli O157: H7 reduction in all three seed types than the chlorine treatment but with a lower germination rate (p < 0.05). The 0.1% CaO spray effectively inhibited E. coli O157:H7 growth in kale microgreens while maintaining the yield and germination rate. For the same varieties of seeds regardless of treatment, microgreens harvested without roots showed much lower microbial loads (3.0–3.9 log CFU/g) than sprouts (6.0–7.0 log CFU/g) with roots. Overall, the US-5 treatment can be an adequate and environmentally friendly alternative to the traditional chlorine treatment. This study provided a practical solution to ensure microbial safety of the sprouts and presented evidence that microgreens are generally safer than sprouts.