Lyophilized cell-free supernatants of the oral probiotics Streptococcus salivarius M18 and Streptococcus salivarius K12 show promises for milk safety.

The functional food ingredients market has been growing due to the preferences for healthier, nutritional, environment-friendly, and convenience foods. Here, we evaluated the antimicrobial potential of the lyophilized cell-free supernatants of the two most promising oral probiotic strains Streptococcus salivarius M18 and S. salivarius K12 on Pseudomonas aeruginosa to be applied for safety purposes in the milk. We showed that the lyophilized culture supernatant of the strain M18 inhibited the pathogen growth in milk by about 75%, 70%, and 60% when incubated at 37°C, room temperature, and +4°C, respectively. The inhibition levels were about 50%, 30%, and 45% for the lyophilized K12 cell-free supernatant. Besides, the lyophilized culture supernatants of the oral probiotics, especially of S. salivarius M18, exhibited anti-cancer activities on colon cancer cells in vitro. Thus, the results of this manuscript suggest that the cell-free supernatants of the M18 and K12 strains are potential candidates, which merit more investigation for their applications, as biopreservatives in foods and beverages and as anti-cancer biotics for human health.