Fig 1.
a) Truncated (1100-1850nm) raw spectra (n = 4500) of the analyzed 15 Lactobacillus strains acquired between 40 min and 20 h of the cultivation time; b) Growing dynamics of L. bulgaricus S6 determined at λ = 665 nm; c) Calculated ratio between the distances of group centers and standard deviations (SD) of probiotic, moderate and non-probiotic groups in the plain of PC2 and PC3 of MW-PCA calculated on the truncated (1100-1850nm) NIR data in the function of the cultivation time.
Table 1.
Growth rates, maximal optical densities, bile’s MICs and yields of biomass after low pH stress in presence of pepsin of the strains.
Fig 2.
a) PCA Bi-plot calculated on the reference data (strains growth rates, maximal optical densities, bile MIC and the yield of biomass after three hours stay at pH 1.80 in presence of pepsin (9000 U/ml), reference data in Table 1); b) MW-PCA analyses using the 1100–1850 nm wavelength interval—Score plot calculated on spectral data (n = 150) at the cultivation time of 11.4–12 h.
Probiotic (red symbols), moderate (green symbols) and non-probiotic (blue symbols) groups; c) loadings of PC2 (blue line) and PC3 (black line) of MW-PCA model highlighting the bands.
Fig 3.
OPLS-DA model built on the spectral data of the 15 strains in the monitoring time between 11.4–12 h (n = 150) using the 1100–1850 nm wavelength interval to classify the probiotic, moderate and non-probiotic groups a) score plot and b) loadings plots.
Fig 4.
PLSR models on spectral data obtained between 11.4–12 h (n = 150) of the cultivation process, wavelength interval 1100–1850 nm a) Quantified MICs vs. NIR-predicted MICs of bile tolerance of the Lactobacillus strains.
Calibration (blue line and points), “one strain out” cross-validation model (red line and points) and strains not included in the modeling dataset (green dots); b) Quantified optical densities at 665 nm vs. NIR-predicted optical densities for strains cultivated in MRS after 3 h treatment at low pH and pepsin, c) PLS regression vectors, indicating the bands of biggest importance for the discrimination.
Fig 5.
Aquagram on the spectra of culture media of groups of probiotic, moderate and non-probiotic strains.
Averaged values of normalized absorbance values of the water matrix coordinates for every group are plotted on each axis. Results were calculated on spectral data obtained between 11.4–12 h.
Table 2.
Measured wavelength and calculated wavenumbers of the bands found with PCA, SIMCA, OPLS-DA and PLSR methods and their assignment based on the corresponding references.