## 3 Results  
### Optical Properties of Red Pickly Pear Juice  
Optical properties are the most important characteristics to consider when exposing a beverage to UV radiation as a preservation method. Juices were analyzed before treatment to verify their optical properties and to determine the effectiveness of UV-C radiation treatment. Table 1 shows the properties of turbidity, absorption coefficient, and penetration length of the diluted and non-diluted red pickly pear juice. The three optical properties of the diluted juice samples differed significantly (\(p\) < 0.05). Non-diluted juice presented different optical property values as it was made from fruit and had an opaque appearance, mainly due to the soluble solids present, as well as the color of the pigments of the fruit [28]. The absorption coefficient determined in diluted samples, both acidified and non-acidified, was approximately 6/cm. This was similar to the result communicated by [PERSON] and [PERSON] [29], who reported coefficient values of absorption of 5.63 \(\pm\) 0.01/cm for clarified grape juice, higher than those reported in Aloe vera and pitaya blends [30]. An absorption coefficient of less than 15/cm is desirable to ensure a 5 log of Escherichia coli K12 reduction in fruit juices [31]. The penetration depth was 75% less in the undiluted juice than that in both diluted juices (acidified and non-acidified), favoring UV-C radiation efficiency. The penetration depth (0.16 and 0.17 cm) was lower compared to the Aloe vera and pitaya blend [30]. This is likely because the juice they studied only contained 5% pitaya juice. The turbidity of non-diluted juice was 274.8 \(\pm\) 0.56 NTU, and the opacity is caused by the intense redness of red pickly pear juice. The turbidity, absorption coefficient, and depth penetration were reduced when the juice was diluted (1:3), making the red pickly pear juice prepared (PPJP) suitable for efficient UV-C processing (Table 1). Effects of UV-C Irradiation and Thermal Treatment on the Natural Microbiota of Red Pickly Pear juice (PPJP)  
The UV-C radiation doses (9.87, 15.13, and 31.78 mJ/cm\({}^{2}\)) for both juices at pH 3.6 and 7 effectively reduced the aerobic plate count, total coliforms, yeasts, and mold counts. The \begin{table}
\begin{tabular}{l c c c} \hline  & **T (NTU)** & **\(\alpha\) (1/cm)** & **\(\lambda\) (cm)** \\ \hline Juice no-diluted & 274.8 \(\pm\) 0.56  & 24.36 \(\pm\) 0.31  & 0.04 \(\pm\) 0.00  \\ PPJP at pH 3.6 & 21.35 \(\pm\) 0.14  & 5.97 \(\pm\) 0.03  & 0.17 \(\pm\) 0.00  \\ PPJP at pH 7.0 & 68.70 \(\pm\) 0.30  & 6.09 \(\pm\) 0.07  & 0.16 \(\pm\) 0.00  \\ \hline \end{tabular}
\end{table} 
Table 1: Optical properties of red pickly pear juice. thermal treatments (80 \({}^{\circ}\)C for 30 s, and 130 \({}^{\circ}\)C for 3 s) eliminated the microbial load after treatment at any pH (pH 3.6, 7) or day (0, 5, 10, and 20). Table 2 shows the microbial load of the untreated red prickly pear juice (control), juices treated with UV-C (three doses), and thermal treatment (HTST and UHT), respectively. Total coliforms, yeasts and molds, and aerobics microorganisms grew in untreated juice at pH 7, but from day five of storage, a decrease was observed. This is related to the pH of the juice (Table 3); although the juice was at a pH of 7, storage for more than five days caused an increase in the microorganism's growth, reducing the pH, increasing the acidity of the juice, and inhibiting the growth of the microbiota. Total coliforms are indicators of contamination and can be used to evaluate food safety. UV-C radiation was effective in both pHs (3.6 and 7) as no total coliform growth was observed after treatment. However, the total coliforms were better controlled in acidified juice. This was observed with the control storage time, where these microorganisms were not detected at a pH of 3.6 after five days. An acidic pH helps generate an environment that is not suitable for most microorganisms that harm consumer health and food quality [19].