PCA was applied to investigate relationships between treatments and physiological parameters as well as correlations among the physiological parameters. High concentrations of TOTO-1 in single and double staining resulted in no growth on solid and in liquid media for L. lactis S1 and S3. These samples were found to be outliers and were excluded for further PCA. Fig. 2 shows the scores and loadings for the first and second principal component (PC) of the PCA for the averaged data after autoscaling and outlier removal. In the score plot, the three tested L. lactis strains were separated into individual groups and for each strain a clustering of the respective control with some treatments was detected. Several extremes deviated from this cluster and displayed a trend towards decreasing viability in direction of PC1. The relative shift of all treatments compared with the control was larger for L. lactis subsp. lactis S1 than for the other two strains. For all tested L. lactis strains, higher impact of fluorescent labelling was positively correlated with increasing lag phase and decreasing acidification activity and negatively correlated with culturability. According to the loading plot, the three acidification descriptors were closely clustered and in a similar way the max specific growth rate and the asymptote provided comparable information. These two growth parameters and the culturability on plates (as log plate counts) were oppositely correlated in their loadings for PC1 to lag phase and the three acidification descriptors.