## 2 Phytochemicals Present in Beetroot
### Betalains  
It is well known that betalains are the most important compounds present in beetroot. They are plant secondary metabolites with similar chemical properties, biological functions, and color spectrums as anthocyanins. However, anthocyanins and betalains never coexist together in plants [20]. Betalains are hydrophilic nitrogenous pigments, which could be subdivided into two main groups according to their chemical structure and color [26]. Betacyanins present a red-violet color, while the betaxanthins are yellow pigments (Table 1). Thus, these compounds had an extreme potential for their use in meat products as natural colorants. In the literature, there are discrepancies regarding the proportions between betacyanins and betaxanthins in beetroot, although it seems clear that the content of betacyanins in beetroot is much higher than that of betaxanthins. Some authors reported that the betacyanins represented about 80-90% of total betalains [28; 29], while others found that the concentration of betacyanins was between 50-70% of total betalains [20; 30]. The variation in these proportions determines the coloration of the root, and the higher content of betacyanins confers its typical red-purple pigmentation [3]. More than 90 different betalains (60 betacyanins and 33 betaxanthins) have been found in nature [9]. Despite the large number of compounds referred to by the term betalains, the betacyanins that are found in the highest concentration in beetroot are, in decreasing order, betanin, isobetanin, neobetanin, and probetanin (Figure 2). In the case of the betaxanthins present in beetroot, also in descending order, they are vulgaxanthin I, vulgaxanthin II, indicaxanthin, miraxanthin, and portulaxanthin (Figure 3) [3; 5; 24; 31]. Despite this, different studies have observed a large number of betalains in beetroot. In a previous study, the authors detected a total of 20 betacyanins and 11 betaxanthins in dried extracts from beetroot [30]. In addition to the betalains discussed above, important contents of 17-decarboxy-isobetanin, 15-decarboxy-betanin, betanidin and 17-decarboxy-neobetanin (betacyanins) and \(\gamma\)-aminobutyric acid-betaxanthin, isoleucine-betaxanthin, and isovulgaxanthin IV (betaxanthins) were detected. Similarly, in more recent research, other authors have identified 18 betacyanins and 12 betaxanthins in different beetroot varieties [32]. In addition to the majority of betalains, this research also observed high amounts of other betacyanins (2,17-bidecarboxy-betanin/isobetanin, 2,17-bidecarboxy-neobetanin, 17-decarboxy-neobetanin, 17-decarboxy-betanidin/isobetanidin, 17-decarboxy-betanin), and betaxanthins (valine-betaxanthin, vulgaxanthin IV, 3-methoxyytramine-betaxanthin, \(\gamma\)-aminobutyric-acid-betaxanthin, and vulgaxanthin III). In the same way, fermented grated beetroot and juiced beetroot were described with a total of 32 betalains, including 24 betacyanins and 8 betaxanthins [28]. On the other hand, although betalains are chromoalkaloids, they have no toxic effects [33] and are a potential natural alternative to replace synthetic colorants in the food industry [21]. Due to this fact, betanin was approved for use as a natural food coloring, both in Europe (additive E-162) and the United States (Food and Drug Administration, Title 1 of Code of Federal Regulations, 21 DFR 73, 40) [3,21]. However, its application as a food colorant agent is conditioned by its sensitivity to degradation to different processes in the industry [21]. According to their stability, it should be noted that betalains maintain their structure through a wide pH range (between pH 3 and 7) [33,34]. This makes these pigments suitable for use in both low-acid and pH-neutral foods [35]. This is an advantage compared to other natural compounds such as anthocyanins, as the color is stable over wider pH and temperature ranges [18].