2.7　Data analysis

Initial pretreatment of the raw chromatographic data included baseline correction，chromatogram alignment，noise reduction，and normalization by use of GCMS solution software.The metabolite peaks were then tentatively identified from their retention characteristics and mass fragmentation patterns，by use of the NIST mass spectrum database.The metabolite peaks were tentatively quantified on the basis of the corresponding peak intensity.(https://www.daowen.com)

Data analysis including principal-components analysis(PCA)，analysis of variance(ANOVA)，and multivariate analysis of variance(MANOVA)were performed in a Matlab environment.