## 4 Impacts of HTST and UHT on Food Quality
### Enzymes Activity  
Preservation using high temperatures results in a significant reduction in the activity or complete inactivation of enzymes responsible for changes in the quality characteristics \begin{table}
\begin{tabular}{c c c c c} \hline
**Matrix** & **Parameters** & **Phenolic Compounds** & **Vitamins** & **Other Bioactive Ingredients** & **References** \\ \hline \multirow{6}{*}{Valencia orange juice} & \multirow{6}{*}{73.9 \({}^{\circ}\)C/30 s} & \multirow{6}{*}{-} & \multirow{6}{*}{Asorbic acid 3.8\(\%\)\(\downarrow\)} & Total carotenes 5.5\(\%\)\(\uparrow\) & \multirow{6}{*}{[96]} \\  & & & and 14.0\(\%\)\(\downarrow\) & & 14.0\(\%\)\(\downarrow\) \\  & & & & TC 8.5\(\%\)\(\uparrow\) and 13.6\(\%\)\(\downarrow\) & \\  & & & and 2.6\(\%\)\(\downarrow\) & Total carotenoid fatty acids & \\  & & & & esters 7.7\(\%\)\(\uparrow\) and 15.1\(\%\)\(\downarrow\) & \\  & & & & \(\upalpha\)-carotene 12.5\(\%\)\(\uparrow\) and 7.1\(\%\)\(\downarrow\) & \\  & & & & \(\upbeta\)-carotene 20.6\(\%\)\(\uparrow\) and 4.1\(\%\)\(\uparrow\) & \\ \hline Orange juice & 90 \({}^{\circ}\)C/60 s & - & Vitamin C 17.6\(\%\)\(\downarrow\) & - & [97] \\ \hline Apple and cranberry juice blend & \multirow{2}{*}{72 \({}^{\circ}\)C/26 s} & TPC 3.0\(\%\)\(\downarrow\) & \multirow{2}{*}{-} & \multirow{2}{*}{[98]} \\  & & & Cyanidin-3-O-glucoside 14.6\(\%\)\(\downarrow\) & - & \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._and sensory attributes of food. The higher the temperature, the lower the enzymatic activity remains [37]. The application of appropriate heat treatment can lead to complete inactivation of enzymes (Table 4). The main enzymes found in raw fruits and vegetables are polyphenyl oxidase (PPO), peroxidase (POD), pectinomethylesterase (PME) and phenylalanine ammonia lyase (PAL). They are responsible for numerous reactions, most often leading to changes in quality characteristics [20]. PPO and POD are enzymes largely responsible for enzymatic browning reactions in fruits and vegetables (undesirable brown color). Their action also leads to an unpleasant taste and a loss of nutritional properties [99]. PAL is responsible for the biosynthesis of phenolic compounds in plants, converting phenylalanine into flavonoids, phenolic acids or anthocyanins [84]. PME causes cloud loss by allowing for calcium pectates to precipitate and clarify the juice [4; 31]. Enzyme inactivation usually involves the destruction of secondary and tertiary structures by physical (heat, ultrasound, and high pressure) and chemical factors [2]. In the storage process, changes in enzyme activity can occur. For example, changes in phenolic enzyme (PPO and POD) activity can arise because of reactions between phenolic compounds and proteins or phenolics oxidation. The first reaction leads to the formation of an inactive enzyme-substrate complex or a change in the enzyme's catalytic site. The second leads to a reduction in the amount of substrate and the formation of products that inhibit enzymes [74]. The combination of temperature and exposure time can affect enzyme inactivation differently. A detailed summary of the effects of the applied UHT and HTST preservation temperatures. A one enzymatic activity in juices, nectars and beverages is included in Table 4. [PERSON] et al. [24] showed that UHT conditions of 120 \({}^{\circ}\)C/2 s and 135 \({}^{\circ}\)C/2 s resulted in more than a 10% PPO residual rate in watermelon juice, while 110 \({}^{\circ}\)C/2 s resulted in about a two times higher PPO residual rate. Because of the residual PPO activity in the juice, an inverse relationship occurred in the phenolics content. PPO is responsible for catalyzing the \(o\)-hydroxylation of \(o\)-phenols and \(o\)-diphenyl. Juices preserved at 120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C for two seconds did not differ in phenolics content from nonpreserved juices, while juice treated at 110 \({}^{\circ}\)C had significantly lower levels of phenolics. Prolonged exposure to high temperature can effectively increase the inactivation of tissue enzymes. [PERSON] et al.