## 3 Results
### Optical Properties of Red Pickly Pear Juice
Yeasts and molds are considered some of the most difficult microorganisms to eradicate because of their size and production of spores. Ultra-pasteurization and pasteurization were effective for the inactivation of yeasts and molds during the 20 days of storage time. Similarly, the UV-C doses used effectively eliminated the initial 3.26 and 2.32 log CFU/mL loads present in juices at pH 3.6 and 7 on day 0, respectively. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{8}{c}{**Total Coliforms (Log CFU/mL)**} \\ \cline{2-9}  & \multicolumn{4}{c}{**pH 3.6**} & \multicolumn{4}{c}{**pH 7**} \\ \cline{2-9}  & **Day 0** & **Day 5** & **Day 10** & **Day 20** & **Day 0** & **Day 5** & **Day 10** & **Day 20** \\ \hline Untreated juice (Control) & 4.94 \(\pm\) 0.05 & ND & ND & ND & 3.95 \(\pm\) 0.03 & 4.8 \(\pm\) 0.01 & 3.29 \(\pm\) 0.03 & ND \\ \hline UV-C (9.87 mJ/cm\({}^{2}\)) & ND & ND & ND & ND & ND & ND & ND & ND \\ \hline UV-C (15.13 mJ/cm\({}^{2}\)) & ND & ND & ND & ND & ND & ND & ND & ND \\ \hline UV-C (31.78 mJ/cm\({}^{2}\)) & ND & ND & ND & ND & ND & ND & ND & ND \\ \hline HTST (80 \({}^{\circ}\)C) & ND & ND & ND & ND & N/A & N/A & N/A & N/A \\ \hline UHT (130 \({}^{\circ}\)C) & N/A & N/A & N/A & N/A & ND & ND & ND & ND \\ \hline \multicolumn{9}{c}{**Yeast and Molds (Log CFU/mL)**} \\ \cline{2-9}
**Treatment** & \multicolumn{4}{c}{**pH 3.6**} & \multicolumn{4}{c}{**pH 7**} \\ \cline{2-9}  & **Day 0** & **Day 5** & **Day 10** & **Day 20** & **Day 0** & **Day 5** & **Day 10** & **Day 20** \\ \hline Untreated juice (Control) & 2.32 \(\pm\) 0.00 & 3.46 \(\pm\) 0.26 & 4.3 \(\pm\) 0.00 & 1.44 \(\pm\) 0.04 & 3.26 \(\pm\) 0.01 & 1.88 \(\pm\) 0.05 & 1.81 \(\pm\) 0.16 & 1.66 \(\pm\) 0.09 \\ \hline UV-C (9.87 mJ/cm\({}^{2}\)) & ND & 0.57 \(\pm\) 0.18 & 1.13 \(\pm\) 0.03 & 1.34 \(\pm\) 0.06 & ND & ND & ND & ND \\ \hline UV-C (15.13 mJ/cm\({}^{2}\)) & ND & ND & ND & 0.74 \(\pm\) 0.29 & ND & ND & ND & ND \\ \hline UV-C (31.78 mJ/cm\({}^{2}\)) & ND & ND & ND & ND & ND & ND & ND & ND \\ \hline HTST (80 \({}^{\circ}\)C) & ND & ND & ND & ND & N/A & N/A & N/A & N/A \\ \hline UHT (130 \({}^{\circ}\)C) & N/A & N/A & N/A & N/A & ND & ND & ND & ND \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effect of UV-C irradiation and thermal treatment on the microbiota of red prickly pear juice. Consistent with these reports, all juices with a pH of 7.0 presented no mold or yeast growth. However, juices treated with a low UV-C radiation dose (9.87 mJ/cm\({}^{2}\)) and a pH of 3.6 did contain yeasts and molds from day five of storage time. Yeast and mold growth were also reported in Aloe vera gel acidified with UV-C radiation [30]. The low efficiency of UV-C treatment in eliminating molds and yeast is attributed to the larger size and thickness of the cell wall [32]. A higher irradiation dose (31.78 mJ/cm\({}^{2}\)) and lower pH (pH = 3.6) prevented the growth of yeasts and molds during total storage time (20 days). Aerobic microorganisms, such as mesophiles and psychrophiles, showed inactivation of the initial load at all UV-C doses and pH 3.6. A microorganism inactivation level of 5 log CFU/mL is recommended by the FDA to consider UV-C radiation as a pasteuriza