A targeted metabolomics approach to understand differences in flavonoid biosynthesis in red and yellow raspberries

Phenolic compounds account for the most important class of secondary metabolites in raspberries and fulfill a broad range of biological functions in plants. Due to their presence in fruits they are also considered as important bioactive compounds in human nutrition and are closely related to fruit quality. In the present study a targeted UPLC-MS/MS method was used to screen various phenolic compounds in fruits of red and yellow raspberry cultivars. In total 50 phenolic compounds were detected above the quantification limit. Beside the obvious lack of anthocyanins, all yellow fruits analysed here lack procyanidin B1. The presence of this dimer, along with B3 dimers is described for the first time in raspberry fruits. Also for the first time, dihydrochalcone and stilbene derivatives and the quercetin metabolite, isorhamnetin with its glycosides, were identified in considerable concentrations in raspberries. Based on a PCA plot the red cultivar "Heritage" and the yellow "Alpen Gold" could clearly be separated from the other tested cultivars due to their distinct metabolite profiles/concentrations. This study allowed to obtain a comprehensive profile of the phenolic composition of the different raspberry varieties. The obtained data will lead to a better understanding of the overall biosynthetic network of polyphenols in raspberry and will help to explain responsible factors for the different metabolite profiles in ongoing studies.