## 4 Impacts of HTST and UHT on Food Quality
### Hydroxymethylfurfurfural  
At high temperatures, Maillard reactions take place, leading to the formation of compounds such as hydroxymethylfurfural (HMF) and furfural. The reactions occur between amino acids and reducing sugars, in addition to ascorbic acid transformations. HMF and others are compounds characterized by genotoxic, cytotoxic and mutagenic risks [4; 19; 45; 47]. The allowed maximum level of 10 mg for HMF per liter of juice are recommended by the AJIN (European Fruit Juice Association) [74]. [PERSON] et al. [45] showed that heating at 110 \({}^{\circ}\)C/8.6 s increased the HMF content in mango nectar by 70.6% compared to nonpreserved juice. They also observed an increase in its content in UHT-preserved samples after 16 weeks of 55.2% at 4 \({}^{\circ}\)C and 177.8% at 25 \({}^{\circ}\)C. In apricot nectar subjected to UHT, HMF was not detected [20]. Varied changes are observed in the literature for the HMF content in samples preserved by the HTST method. [PERSON] et al. [74] indicated that in orange juice pasteurized by the HTST method, HMF was not immediately detected after the process; however, it started to accumulate after 20 weeks of storage at 20 \({}^{\circ}\)C, 8 weeks at 28 \({}^{\circ}\)C, 3 weeks at 35 \({}^{\circ}\)C and 4 days at 42 \({}^{\circ}\)C. The researchers reported that the appearance of HMF may have been related to a change in the composition of the sugars present in the product. Tests on orange juice were also performed by [PERSON] et al. [19] using the parameters of 90 \({}^{\circ}\)C/10 s and 90 \({}^{\circ}\)C/20 s. The HMF contents immediately after preservation were 1.7 and 4.7 ppb, respectively; at \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Matrix** & **Parameters** & **Enzymes—Residual Activities** & **Reference** \\ \hline \multicolumn{3}{c}{**UHT**} \\ \hline Mango nectar & 110 \({}^{\circ}\)C/8.6 s & Acid invertase 8.6\% * & [45] \\ \hline Watermelon juice & 110 \({}^{\circ}\)C/2 s, 120 \({}^{\circ}\)C/2 s, 135 \({}^{\circ}\)C/2 s & For 120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C, 2 times lower residual activity of PPO than at 110 \({}^{\circ}\)C & [24] \\ \hline Red grapefruit juice & 110 \({}^{\circ}\)C/8.6 s & PPO, POD and PME—completely inactivated & [53] \\ \hline Apricot nectar & 110 \({}^{\circ}\)C/8.6 s & PPO, POD and PME—completely inactivated & [20] \\ \hline red raspberry juice & 110 \({}^{\circ}\)C/8.6 s & PAL \(\downarrow\) *; PPO—completely inactivated; PPO—equal to that of fresh juice & [84] \\ \hline \multicolumn{3}{c}{**HTST**} \\ \hline Strawberry juice & 90 \({}^{\circ}\)C/60 s & 22.2\% * for PME, 76.2\% * for PG & [104] \\ \hline Strawberry juice & 90 \({}^{\circ}\)C/30 s & 48\% * for PME and 96.8\% * for PG & [102] \\ \hline Strawberry juice & 90 \({}^{\circ}\)C/60 s & Lipoxygenase 37.7\% * and 45.3\% *, b-glucosidase—slight increase in activity & [102] \\ \hline Sea buckthorn juice & 100 \({}^{\circ}\)C/15 s & SOD 51.3\% * & [56] \\ \hline Orange and carrot juice & 98 \({}^{\circ}\)C/21 s & PME—2\% * & [46] \\ \hline Cloudy apple juice & 98 \({}^{\circ}\)C/50 s & PPO and POD—completely inactivated & [5] \\ \hline Cloudy apple juice & 72 \({}^{\circ}\)C/15 s & PPO, POD and PME—up to 10\% * & \\ \multicolumn{3}{c}{85 \({}^{\circ}\)C/30 s} & PPO, POD and PME—completely inactivated & [74] \\ \hline Orange juice & 72 \({}^{\circ}\)C/20 s & PME 15\% *; POD—completely inactivated & [4] \\ \hline Peach juice & 72 \({}^{\circ}\)C/15 s & PPO 86.4\% * PME 87.0\% & [31] \\ \hline Orange juice & 70, 80, 90 and 100 \({}^{\circ}\)C and time 2, 5, 10, 15 and 30 s & PME—inactivation of 99\% was only achieved at 90 \({}^{\circ}\)C and 100 \({}^{\circ}\)C & [14] \\ \hline \multicolumn{3}{c}{\(\downarrow\)—decrease. * Statistically significant change. PPO—polyphenyl oxidase; POD—peroxidase; PAL—phenylalanine ammonia-lyase; PME—pectinmethylesterase; SOD—superoxide dismutase.} \\ \end{tabular}
\end{table} 
Table 4: Effects of UHT and HTST processing on enzymatic activity in different beverages. the same time, this compound was not observed in the raw sample.