Time-series based metabolomics reveals the characteristics of the color-related metabolites during the different coloration stages of Zanthoxylum bungeanum peel

As the most visualized evaluation indicator of the commercial quality, the color of Zanthoxylum bungeanum peels is an important external economic characteristic and largely impacts the purchase behavior of consumers. To explore the potential coloration mechanism, the popular cultivars of Z. bungeanum (Fengxian Dahongpao, FXDHP) were selected to investigate its pigment composition and intracellular metabolic characteristics. The results indicated that the red-color formation of FXDHP peels was along with the degradation of chlorophyll and carotenoid, and the accumulation of the total anthocyanin and flavonoids. Furthermore, a widely targeted metabolomics analysis was performed to analyze the changes of intracellular metabolism during five different coloration stages by ultra-performance liquid chromatography-tandem mass spectrometry. Among the identified 803 intracellular metabolites, the largest number of differential metabolites were flavonoids in each comparasion group. In particular, dihydrokaempferol and dihydroquercetin might be the important metabolic nodes during the red-color formation. Cyanidin-3-O-galactoside, keracyanin and kuromanin were the key pigments in the red-color formation of FXDHP peels. Except for red group, four distinct metabolic modules were identified to be specifically associated with the rest four coloration stages of FXDHP peels through the weighted correlation network analysis. Combined with characteristic metabolites and the enzymatic activities related to anthocyanin biosynthesis, the dynamic metabolic changes of anthocyanin accumulation were further clarified during the color transformation of FXDHP peels. The above information would provide novel insights into the red-color formation of FXDHP peels, and it will certainly assist in efforts to improve the outward appeal and quality of Z. bungeanum.