Polyphenolic Compounds in the Stems of Raspberry (Rubus idaeus) Growing Wild and Cultivated

The stems of Rubus idaeus L., a byproduct of the fruit-food industry, are known sources of bioactive compounds. The main objective of this study was to investigate the composition of polyphenolic compounds in R. idaeus stems. Seven cultivated raspberry varieties, thirteen garden samples, including five well-known raspberry varieties, and thirteen wild raspberry samples from different locations in Estonia were analyzed. The HPLC-MS method detected 62 substances, of which 42 were identified, 12 were tentatively identified, and 8 compounds remained unknown. Protocatechuic acid pentoside was dominant in most varieties and in all garden and wild raspberry samples. Dihydroxybenzoic acid hexoside 1, p-coumaroyl quinic acid 1, quercetin 4'-glucuronide, and p-coumaric acid glycoside were found in significant quantities. Correlations among the contents of individual compounds were established. When studying the dynamics of polyphenolic compound accumulation in, for example, the GR1 sample over a year, it was found that, in raspberry stems, the largest amount of them accumulated in April and slightly less in January and October. Investigating the dependence of the accumulation of polyphenols on the parts of the stem, it was found that the upper parts have the highest phenolic contents. Therefore, it is recommended to harvest approximately the upper third of the stem.