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During mechanical harvesting, the above-ground biomass (sugar beet leaves) is routinely cut and left on the field as green fertilizer and represents a underuti-lisation of a seasonal stream of biomass with provable potential of bioactive compounds. The aim of this study was to show the distribution of polyphenol and protein content in the leaf blade and petioles in different sugar beet cultivars and different harvest times. Quantified total polyphenols and delineated the phenolic composition of SBL using complementary HPLC-DAD and LC-MS methods. In sugar beet leaf blades, protein content was from 19% to 29% and significantly affected by Individual cultivars and harvest date. Petioles showed a significantly lower protein content, typically ranging from 4.9% to 9.5%. The total polyphenol content (TPC) quantified using vitexin as a standard and was in the range of 7.8-11.0 mg/g DW for blades and 0.8 – 2.7 mg/g DW for petioles and it also depended on the harvest date for individual varieties. Leaf blades contained substantially higher concentration of vitexin derivatives (mean 7.4 ± 2.3 mg/g DW) than petioles (1.1 ± 0.6 mg/g DW). The percentage contribution of vitexin derivatives in to total polyphenol content in SBL blades and petioles was high across all samples (above 70%) and decreased with the delay in harvest time.