Metabolite profiling of red and blue potatoes revealed cultivar and tissue specific patterns for anthocyanins and other polyphenols

Metabolite profiling of tuber flesh and peel for selected colored potato varieties revealed cultivar and tissue specific profiles of anthocyanins and other polyphenols with variations in composition and concentration. Starchy tubers of Solanum tuberosum are a staple crop and food in many countries. Among cultivated potato varieties a huge biodiversity exists, including an increasing number of red and purple colored cultivars. This coloration relates to the accumulation of anthocyanins and is supposed to offer nutritional benefits possibly associated with the antioxidative capacity of anthocyanins. However, the anthocyanin composition and its relation to the overall polyphenol constitution in colored potato tubers have not been investigated closely. This study focuses on the phytochemical characterization of the phenolic composition of a variety of colored potato tubers, both for peel and flesh tissues. First, liquid chromatography (LC) separation coupled to UV and mass spectrometry (MS) detection of polyphenolic compounds of potato tubers from 57 cultivars was used to assign groups of potato cultivars differing in their anthocyanin and polyphenol profiles. Tissues from 19 selected cultivars were then analyzed by LC separation coupled to multiple reaction monitoring (MRM) to detect quantitative differences in anthocyanin and polyphenol composition. The measured intensities of 21 anthocyanins present in the analyzed potato cultivars and tissues could be correlated with the specific tuber coloration. Besides secondary metabolites well-known for potato tubers, the metabolic profiling led to the detection of two anthocyanins not described for potato tuber previously, which we tentatively annotated as pelargonidin feruloyl-xylosyl-glucosyl-galactoside and cyanidin 3-p-coumaroylrutinoside-5-glucoside. We detected significant correlations between some of the measured metabolites, as for example the negative correlation between the main anthocyanins of red and blue potato cultivars. Mainly hydroxylation and methylation patterns of the B-ring of dihydroflavonols, leading to the formation of specific anthocyanidin backbones, can be assigned to a distinct coloring of the potato cultivars and tuber tissues. However, basically the same glycosylation and acylation reactions occur regardless of the main anthocyanidin precursor present in the respective red and blue/purple tissue. Thus, the different anthocyanin profiles in red and blue potato cultivars likely relate to superior regulation of the expression and activities of hydroxylases and methyltransferases rather than to differences for downstream glycosyl- and acyltransferases. In this regard, the characterized potato cultivars represent a valuable resource for the molecular analysis of the genetic background and the regulation of anthocyanin side chain modification.