## 4 Impacts of HTST and UHT on Food Quality
### Basic Physicochemical Characteristics
#### 4.2.5 Color  
Color is affected by the presence of color substances, such as anthocyanins (from red to purple or blue in color), chlorophylls (different intensities of green hues), carotenoids (from yellow to orange or red in color) and betalains (betacyanins--red to violet in color; betaxanthins--yellow to orange in color) [29]. The direction of the change depends on the chemical composition of the food and the preservation conditions. During preservation and storage, the presence of oxygen in the container, enzyme activity or chemical transformations of pigments (for example, degradation, polymerization and Maillard reactions) are also important [39; 63]. An increase in the preservation temperature, at the same time, results in a greater color change [24]. [PERSON] et al. [32] showed a significant increase in L*, a* and b* and \(\Delta\)E = 6.6 compared to raw juice using 110 \({}^{\circ}\)C/8.6 s parameters for UHT. [PERSON] et al. [25] showed the difference between clear and cloudy juices--in the case of the former,the L*, a* and b* parameters increased significantly after thermal preservation (\(\Delta\)E = 2.3), while in the latter juice, the L* and b* parameters decreased (\(\Delta\)E = 4.6). In addition, their colors continued to change significantly during storage. Visible color changes (\(\Delta\)E > 3) were also demonstrated by other studies [12; 36; 38; 42; 49; 53]. An intense color change was demonstrated by [PERSON] et al. [63] where \(\Delta\)E = 11.4 was obtained after preservation of lime juice (136\({}^{\circ}\)/4 s), and was associated with decreases in L* of 12.5% and a* of 59.7% and an increase in b* of 85.4%. Smaller color changes were indicated by [PERSON] et al. [41] (\(\Delta\)E = 3.0), [PERSON] et al. [35] (\(\Delta\)E = 3.0), [PERSON] et al. [37] (\(\Delta\)E = 2.4), [PERSON] et al. [39] (\(\Delta\)E = 1.2) and [PERSON] et al. [27] (\(\Delta\)E = 0.1), but they confirmed the discoloration process during storage. [PERSON] et al. [35] observed that \(\Delta\)E = 8.0 at 12 weeks of storage at 4 \({}^{\circ}\)C and \(\Delta\)E = 5.4 at 25 \({}^{\circ}\)C, while [PERSON] et al. [41] \(\Delta\)E = 24.0 at 20 days of storage at 4 \({}^{\circ}\)C. In contrast, [PERSON] et al. [53] noted no obvious color changes after the process (\(\Delta\)E = 2.0) or during a 21-day storage period (\(\Delta\)E between 1.8 and 2.5). Small \(\Delta\)Es may be due to the inactivation of enzymes. However, it is emphasized that UHT leads to much larger color changes compared to HPP [37; 41]. [PERSON] et al. [70] compared HTST (85 \({}^{\circ}\)C/30 s) with UHT (110 \({}^{\circ}\)C/8.6 s). Cloudy pomegranate juice preserved at a higher temperature and for a shorter time achieved a higher value of \(\Delta\)E = 6.8 than that at a lower temperature and for a longer time, at \(\Delta\)E= 5.5. Heating peach juice at 72 \({}^{\circ}\)C for 15 s resulted in slight decreases in the L* and a* parameters and a significant increase in the b* value immediately after HTST preservation compared to raw juice. There was a significant change in the brightness and proportion of the yellow color during 28 days of storage. After HTST, the peach juice became more yellow and darker [31]. In contrast, heating at 80 \({}^{\circ}\)C for 30 s resulted in increases in the L*, a* and b* values of cloudy pomergranate juice [32]. [PERSON] et al. [64], on the basis of the thermal processing of two jules and a lemonade, showed different effects for the same HTST preservation conditions on the color parameters. In lemonade, there were significant increases in a* and b* values of 5.6% and 3.9%, respectively. In citrus juice, there was an increase in the a* value of 60.0%, and in green juice there were changes in all three color parameters (L* of 14.1%, a* of 120.0% and b* of 4.9%). The consecutive \(\Delta\)Es for these products were 0.3, 1.4 and 8.0, respectively.