Fig. 3
Chemical analysis of the commercial rhubarb samples. a OPLS-DA score plots of the relative peak area obtained from all batches of commercial rhubarb samples with cross-validation revealed predictive accuracy of 0.612 (Q2) and goodness-of-fit of 0.702 (R2), respectively; b OPLS-DA score plots of the contents of identified compounds obtained from all batches of commercial rhubarb samples with cross-validation revealed predictive accuracy of 0.541(Q2) and goodness-of-fit of 0.661 (R2), respectively; c, d Histograms comparing the contents of chemical compounds between two groups. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001; ns, no significant difference (two-tailed, unpaired Student’s t-test)