## 4 Impacts of HTST and UHT on Food Quality
### Volatile Compounds  
Volatile compounds determine the aroma and flavor of foods. Their transformations can lead to organoleptic changes that are unacceptable to consumers. As a result of UHT preservation, the areal content increased, while the germinal content decreased in cloudy ginger juice [37]. Also, [PERSON] et al. [24] showed the degradation of typical volatile contents of watermelon juice (C9 alcohol and C9 aldehyde) by 15.4%, 10.9% and 10.1% after applying the conditions of 110 \({}^{\circ}\)C, 120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C for 2 s, respectively. However, higher temperatures (120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C) reduced the ADH activity and had a greater degrading effect on the C9 alcohol content rather than C9 aldehyde content. [PERSON] et al. [43] investigated different preservation methods in watermelon juice. The typical volatile contents of UHT juice (135 \({}^{\circ}\)C/2 s) were significantly lower than those in unprocessed juice. The heated samples showed the presence of two compounds (acetic acid, 2-methyl butyric acid), which were absent in the raw sample. [PERSON] et al. [105], in watermelon juice processed at 126 \({}^{\circ}\)C/15 s, noticed an increase in the relative contents of esters (58.4%) and aldehydes but a decrease in alcohols (80.1%), ketones (59.5%) and alkanes compared to raw juice. Nonanal and 3,7-dimethyl-2,6-ocudadienal (characteristic compounds for watermelon flavor) decreased by 59.2% and 92.1% in UHT watermelon juice. In the UHT juice, the content of amyl butyrate increased (80.1%), accounting for the \"cooking flavor\". Also, [PERSON] et al. [18] pointed to the formation of the compound dimethyl sulfide, responsible for the \"cooked flavor\" of tomato juice, following heating at 110 \({}^{\circ}\)C/8.6 s. In addition, in raw tomato juice, the contents of alcohols, aldehydes, and ketones accounted for 46%, 18% and 23% of all flavor compounds, respectively, whereas in juice after UHT they were 36%, 34% and 18%, respectively. [PERSON] et al. (2022) [28] indicated that UHT has the effect of raising the contents of the esters and ketones responsible for the specific flavor of melon juice, while it causes a decrease in the contents of alcohols, aldehydes and total volatile components. [PERSON] et al. [54] indicated that 20 volatile compounds were present in the control sample, but following UHT (110 \({}^{\circ}\)C/8.6 s), only 13 remained in korla pear juice. In comparison, there were 17 compounds in the HPP-preserved sample. [PERSON] et al. [41] compared the UHT and HPP processes in an analysis of the key odorants of clear cucumber juice. In the case of (Z)-6-nonenal and (E,Z)-3,6-nonandien-1-ol, there was no significant difference between the processed and raw juices. (E,Z)-2,6-nonadienal and (E)-2-nonenal showed significant increases in their contents after preservation but to a much lesser extent in the UHT sample than in the HPP one. Other observations made by [PERSON] et al. [17] included that the heating of black carrot juice at 130 \({}^{\circ}\)C/5 s did not change the overall odor profile. [PERSON] et al. [49] compared blueberry juice after HTST and PEF preservation, indicating that the decreases in the compounds were considerably lower for PEF than with the HTST method, particularly in esters. HTST causes the aroma of blueberry juice to be less diverse. Passion fruit juice also showed HTST-preserved volatile compounds to a lesser extent than when using the HHP preservation technique. The concentrations of esters, alcohols, ketones and hydrocarbons decreased in the HTST sample by 23.9, 44.2, 12.5 and 39.7%, respectively [11]. The volatile acidities of a pomegranate fermented beverage, as a result of heating at 72 \({}^{\circ}\)C for 15 s, did not change significantly compared to the nonprocessedsample, while PEF and traditional pasteurization significantly lowered them [58]. A study by [PERSON] et al. [78] indicated that it was not possible to distinguish between the microwave- and HTST-treated samples of orange juice. [PERSON] et al.