Effect of Streptococcus thermophilus supernatant and inulin on Listeria monocytogenes in soft cheese

The antilisterial activity of 0.1, 0.5 and 1 ml of both Streptococcus thermophilus supernatant ( as derived probiotics) and inulin (as prebiotics) in soft ch eese for three co-incubation periods (24,48 and 72 h) was evaluated. The results showed that the supernatant of S. thermophilus inhibited growth of Listeria monocytogenes at all co-incubation periods, especially when use d 1 ml of supernatant ( 3 log reduction at 24 h and 2 log reduction at 48 and 72 h) compared with c ontrol (L. monocytogenes only). The S. thermophilus supernatant at 0.5 and 1 ml was more effective in reducing growth of L. monocytogenes compared with 0.1 ml of supernatant. No inhibition activity of inulin ag ainst L. monocytogenes was observed at all co-incubation periods. These results indicate that S. thermophilus supernatant has a protective action against L. monocytogenes in soft cheese .