Application of Microbubbles Combining with Disinfectants to Inactivate Salmonella Typhimurium on Alfalfa Seeds and the Effects on Sprouting

Microbial contamination is the main safety concern of sprouts and seeds are the major source. High concentrations of sanitizers (>10,000 mg/kg) are recommended for effective sanitation. Microbubble (MB) was reported to elevate the sanitizer efficacy. Hence, MB combined with disinfectants, chlorine dioxide (ClO2, 500 ppm) and slightly acidic electrolyzed water (SAEW, 250 ppm), was used to inactivate Salmonella Typhimurium on alfalfa seeds. After fulfilling MB for 10 min, alfalfa seeds were washed in 10 L of water for 10, 20, or 30 min. Compared with untreated seeds, S. Typhimurium reductions obtained by SAEW-MB (SMB) and ClO2-MB (CMB) for 20 min were 3.8 and 3.3 log CFU/g, respectively. Conversely, the 20-min treatments of SAEW and ClO2 only obtained reductions of 0.9 and 1.1 log CFU/g, respectively. More surface ruptures on the seeds treated with CMB were observed under a scanning electron microscope compared with the ones treated by water and ClO2 only. No adverse effects on the seed germination rate and the weight yield of sprouts were observed when treated with CMB for 20 min. A MB device with capacity of 100 L was assembled and achieved reductions of 3.9 and 3.2 log CFU/g of natural microbes and S. Typhimurium, respectively, after 20-min CMB washing. Additionally, a MB device at 250 L was assembled and achieved 3.0 log CFU/g reduction of natural microbes. This study demonstrated that MB enhanced the efficacy of disinfectants and could be applied for industrial-scale operation.