# Old-Fashioned, but Still a Superfood--Red Beets as a Rich Source of Bioactive Compounds
## 3 Flavonoids and Polyphenolic Acids  
The high antioxidant capacity of beets is due not only to the high content of betalains, but also other phenolic compounds--flavonoids and polyphenolic acids. Significant amounts of catechins and polyphenolic acid (ferulic, protocatechuic, vanillic, p-coumaric, p-HBA, syringic, and caffeic) have been detected in beets [47; 48; 49; 50]. However, the composition  
Figure 3: The mechanism of action of _Beta vulgaris_ betanin on tumor cells. Reprinted with permission from [18]. of plant extract depends on many factors, including the original plant (variety, maturation state), conditions of its cultivation (climate, harvesting), as well as its storage condition [51]. [PERSON] et al. showed how much the total content of polyphenic compounds depends on the beet variety and the place of its cultivation [50]. The highest content of total polyphenols was found in the variety of Renova from Sliac, in Slovakia (1280.56 \(\upmu\)g\(\cdot\)g\({}^{-1}\)), followed by red beetroot from Zohor. In addition, the variety of Zohor, obtained from Siheline, had the lowest concentration of polyphenols (820 \(\upmu\)g\(\cdot\)g\({}^{-1}\)). In the case of the variety Monorubrawe, the highest value of total polyphenols was determined in samples from the area of Siheline (1201.6 \(\upmu\)g\(\cdot\)g\({}^{-1}\)), followed by red beetroot from Sliac (1023.21 \(\upmu\)g\(\cdot\)g\({}^{-1}\)) and Zohor (988.66 \(\upmu\)g\({}^{-1}\)). The variety-specific differences between the highest and lowest polyphenol contents were 460.56 \(\upmu\)g\(\cdot\)g\({}^{-1}\) in the Renova variety and 212.94 \(\upmu\)g\(\cdot\)g\({}^{-1}\) in the Monorubrawe variety. The authors concluded that the observed differences may be due to the high humus (4.0%) and potassium (520 \(\upmu\)g\(\cdot\)g\({}^{-1}\)) content in the soil. Studies conducted by [PERSON] et al. clearly showed that the total phenolics content decreases in order: peel (50%), crown (37%), and flesh (13%) [52]. The comparison of the phenolic composition in betalain extracts from intact _B. vulgaris_ cv. _Detroit Dark Red_ plants and hairy root cultures was described by [PERSON] et al. [11]. The authors proved that the concentrations of selected polyphenic compounds were even more than 100 times higher in extracts from hairy root cultures than in extracts obtained from intact plants. Moreover, rutin was present only in hairy root cultures, while chlorogenic acid was found only in intact plants. While quercetin was not reported in this study, [PERSON] and [PERSON] proved its presence in the purified extract of beetroot leaf [53]. In the study performed by [PERSON] et al., quercetin was detected in fresh red beet, fermented red beet, and commercial fermented beet juice, in concentrations of 0.023 \(\upmu\)g\(\cdot\)g\({}^{-1}\), 0.002 \(\upmu\)g\(\cdot\)g\({}^{-1}\), and 0.009 \(\upmu\)g\(\cdot\)mL\({}^{-1}\), respectively [47]. The results obtained by [PERSON] indicated that the extract of the hairy roots had substantially higher concentrations of the identified phenolic compounds than did the intact plants, as noted above [11]. Moreover, there were differences in the phenolic profiles of the studied extracts. Chlorogenic acid was present only in the extract from intact plants, while rutin was found only in the extract from hairy root cultures. As the authors emphasize, it is a valuable discovery as rutin interacts synergistically with many other biologically active compounds present in the plant material enhancing its antioxidant properties [54]. The fermentation process caused an increase in the content of phenolic acids and a reduction in the content of their conjugated forms, while the same process caused a decrease in the content of free flavonoids [47]. In the case of the studies described by [PERSON], significant differences in the concentrations of polyphenic acids were observed between the extracts from fresh and fermented beetroot [47].