# Old-Fashioned, but Still a Superfood--Red Beets as a Rich Source of Bioactive Compounds
## 2 Betalains  
Betalains are water-soluble secondary metabolites that occur in many plants of the order _Caryphyllales_. They have a higher solubility in water compared to anthocyanins, and are stable in the pH range of 3-7, thus, can be used in low-acid and neutral foods [18; 19]. Betalamic acid is a component of all betalains and its substituent type defines the class of betalain [20]. Betalamic acid can spontaneously condense with cyclo-DOPA (3,4-dihydroxy-phenylalanine, a precursor of betalain pigment in plants) yielding the violet betacyanins, or with amines or amino acids to produce yellow betaxanthins [21]. Their general chemical structures are presented in Figure 2 [18]. Red beets are the main edible source of these compounds. According to [PERSON] et al., betacyanins content in beetroot accounts for 75-95% of the total pigments, the remaining 5-25% corresponds to betaxanthins [22]. The violet betacyanin is the most studied of all the betalain groups. Beetroot contains also its epimer, isobetanin, as well as other pigments like betaxanthins vulgarisanthin I and miraxanthin V [23]. Four betacyanins (betanin, prebetanin, isobetanin, neobetanin) and three betaxanthins (vulgaxanthin I, vulgaxanthin II, indicaxanthin) were identified in the water fractions of crude extracts of beetroot peel [24]. In beetroot juice samples, the  
Figure 1: Main bioactive compounds present in red beetroots. presence of red pigments was reported in ranges of 797.5-421.7 mg\(\cdot\)L\({}^{-1}\) for betanin and 321.7-423.1 mg\(\cdot\)L\({}^{-1}\) for vulgaxanthin [25]. Concentrations of both dyes in purchased organic betroot juice were higher than those in freshly squeezed juice [26]. However, the characteristic color quickly lost its intensity after storage at 20 \({}^{\circ}\)C, and after some time it was possible to notice the presence of a flocculent precipitate. Degradation products of betanin are isobetanin, decarboxylated betanin, betalamic acid, and cyclodopa glucoside [27]. [PERSON] et al. determined higher concentrations of betalains in pure beetroot juices in comparison to those combined with other components (e.g., apple, lemon) [28]. Betalains can exert their action by different mechanisms, such as scavenging free radicals, regulating their content produced during biochemical reactions, and protecting cells from oxidative stress and damage. In food science, the term \"antioxidant\" is commonly used to describe compounds that prevent oxidative reactions, such as lipid peroxidation, maintaining the freshness of food products. In health science, this term includes free-radical scavenging of reactive oxygen species, reducing agents, and chelators of metal ions; thus, they have roles in preventing different chronic diseases [29]. However, many antioxidants at high concentrations could act as prooxidants and induce toxicity. Several studies confirmed the high radical-scavenging activity of betalains [30; 31; 32]. While betanin exhibits a high radical-scavenging activity at pH > 4, the highest activity of betanidin was reported at a pH range of 2-4 [30]. In betacyanins, acylation raises the antioxidant potential, whereas glycosylation decreases their activity. The highest potential was reported for betanin, followed by nebetanin, vulgaxanthin I, and indicaxanthin [32]. The losses of red pigments in the betalin solution (heated at 90 \({}^{\circ}\)C for 30 min in a water bath without access to light) increased, along with rising pH levels, due to their degradation [33]. The opposite correlation was observed for yellow pigments; the most pronounced increase in their levels was observed at a pH of 6.5-7.0. However, during heating, the antioxidant capacity of the solution was subject to only minor changes in the pH range of 4-9. Many studies demonstrated the health-promoting effects of betalains. Most of these reports focus on their antioxidant, anti-inflammatory, and anti-carcinogenic properties, as was mentioned earlier [9; 10; 12; 13; 14].