Fig. 3

PCA and PLS-DA analysis of intracellular metabolites at different fermentation time points. The samples were withdrawn from the cultivation at 24, 72, 120 and 156 h. a PCA scores scatter plot in positive ion scan modes. b PCA scores scatter plot negative ion scan modes. c PLS-DA scores scatter plot in positive ion scan modes. d PLS-DA scores scatter plot in negative ion scan modes. In order to assess the accuracy and stability of the equipment state during detection and collection process, the quality control samples (the mixture of all samples) were prepared in advance, and then were carried out every 10 samples