## 1 Introduction  
The consumer demand for foods produced with natural ingredients is increasing. Commercial juices may contain synthetic colorants or color enhancers since they are stable when subjected to different preservation processes. Despite this advantage, the addition of colorants has been related to such health problems as indigestion, anemia, allergic reactions (asthma and urticaria), pathological brain lesions, tumors, cancer, paralysis, intellectual disability, abnormal offspring, growth inhibition, and ocular defects resulting in blindness [1]. An enormous variety of exotic fruit and vegetables are used to produce beverages as these contain various vitamins, minerals, and some bioactive compounds. A Mexican fruit with high nutritional value and good organoleptic properties associated with health benefits (functional foods) is the red prickly pear (_Opuntia ficus indica_). Inaddition to its nutritional value, the fruit provides other properties such as antiradical or antioxidant, anti-inflammatory, and other properties, which are attributed to the presence of betalains [2] and polyphenols [3]. Betalains are pigments that can be divided into two types, betaxanthins and betacyanins, and provide yellow-orange and purple-red colorations, respectively [4]. Betacyanins are most abundant in the red prickly pear, resulting in its characteristic color. Red prickly pear is mostly consumed fresh and near to production areas because of postharvest losses as it is highly perishable. These disadvantages can be addressed by processing beverages with functional and nutritional benefits. However, betalains are affected by changes in pH and water activity, the presence of light and oxygen, and high temperatures associated with processing [5], rendering thermal treatment inadequate. Several studies have reported betalains content reductions associated with thermal treatment. The pasteurization of betroot juice caused pigment losses of 39.9 and 42.28% for betacyanins and betaxanthins, respectively. However, an increase in these pigments (67.42 to 64.13%) and a reduction in antioxidant activity (63.87%) were observed during storage [6]. The ultra-pasteurization of prickly pear beverages caused betaxanthin and betacyanin losses of 45 and 26%, respectively, and a 52 and 45% reduction in total polyphenols and antioxidant activity, respectively [7]. A non-thermal method can be used to reduce the loss of compounds of interest, such as the application of short-wavelength ultraviolet (UV-C) radiation. UV-C is approved by the Food and Drug Administration and can preserve heat-sensitive compounds, among other advantages [8,9]. UV-C technology has been used in a variety of juices, including apple and grape [10], onion [11], orange [12], guava, pineapple, apple cider, and mango nectar [13]. The main objective of these studies was to prove the effectiveness of UV-C in the inactivation of bacteria, yeasts, and molds and to evaluate the behavior of these microorganisms during storage. However, the immediate and shelf-life changes in bioactive compounds, which contribute favorably to the nutritional and functional quality, or acceptability of the product, have not yet been evaluated in depth. Some studies have been reported on the study of changes in pigments such as carotenoids [14] and anthocyanins [15] related to acceptability attributes such as color. Recent studies have reported the effects of UV-C light on bioactive compounds and pigments. Pigments and phenolic compounds showed a reduction in pitaya (_Stencoreus griseus_) juice treated with UV-C, attributed to the action of photons produced by UV-C light. The photons could be absorbed by organic molecules such as betalains that have conjugated bonds and aromatic rings, provoking changes in the structure. However, the microbial reduction was not sufficient to consider it a safe product [16]. A cranberry-flavored beverage processed using UV-C treatment did not show changes in the content of anthocyanins [17].