Similar trends for the acidification activity of the three tested L. lactis strains were detected after double staining with cFDA/cFDASE and PI (Table 2). Compared with L. lactis subsp. lactis S1 and L. lactis subsp. cremoris S3, Ta and time to pH5.5 of L. lactis subsp. Lactis S2 were affected to a lower degree using cFDA/cFDA-SE in combination with TOTO-1. The final pH after 24 h was significantly (P < 0.05) higher afterdouble staining of L. lactis subsp. lactis S1 and S2with high concentrations of cFDA/cFDA-SE in combination with PI or TOTO-1.