Metabolic profiling of outer fruit peels from 15 accessions of pomegranate (Punica granatum L.)

Pomegranate (Punica granatum L.) fruit peels are known to enrich the nutritional value of pomegranate juice due to their highly abundant phenolic metabolites such as hydrolyzable tannins (HTs), anthocyanins, and flavonoids, as well as the whole-fruit-based industrial extraction process. These shikimate pathway-derived metabolites also provide protection against pests and abiotic stresses for the fruit, and are important for the commercial trait of fruit peel color. To better understand the chemical diversity and biosynthetic relationships of phenolic metabolites in the outer fruit peel, we conducted metabolite profiling of outer peels from 15 pomegranate accessions largely varied in peel color using ultra high-performance liquid chromatography-diode array detection (uHPLC-DAD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 48 metabolites were (tentatively) identified through comparison to authentic standards, as well as MS or MS/MS spectral data in metabolomics databases. The 15 pomegranate accessions differ greatly in levels of anthocyanins, HTs, flavonoids, and other shikimate pathway-related metabolites, with the largest variations observed in the anthocyanin content. Negative correlations between HTs and flavonoids/anthocyanins, and between anthocyanins and proanthocyanins were observed, suggesting that these metabolites may compete for the same biosynthetic precursors for their production and are coordinately regulated.