Fig. 2

Principal component analysis (PCA) plots and two-dimensional (2D) clustering plots describing the trend of separation between 26 independent samples between two groups. The Large and Small groups are represented by green and purple circles, respectively. The red circles are the QC samples. a The plots of PCA score in the ESI positive ion mode. b The plots of PCA score in the ESI negative ion mode. c OPLS-DA score plot demonstrating separation between the two groups in ESI positive and negative ion modes, based on the regression model. The OPLS-DA shows a prediction power (Q2) of 0.489 and a correlation index (R2Y) of 0.972, according to cross-validation. Samples from the Large group are indicated by red nodes; the samples from the Small group are indicated by green nodes. d Volcano plots presenting the statistical significance of metabolites in the FF samples in ESI positive and negative ion modes. e Change trends of 30 differential metabolites; the horizontal axis shows the VIP score of each substance. A VIP score is a measure that summarizes the contribution of a given variable to the regression model