## 4 Impacts of HTST and UHT on Food Quality  
### Microbiological Quality and Shelf-Life  
Occurrences of microorganisms in fruit and vegetable products are related to contamination of the raw materials' surfaces during harvesting and further processing. The heat resistance of microorganisms depends on many factors, such as pH, redox potential, water activity, moisture content, salt content, types of targeted microorganisms and activities of the enzymes [21; 33]. For selecting the preservation parameters, the most important factor to take into consideration is the pH. Products with a pH up to 4.5 are preserved with temperatures up to 100 \({}^{\circ}\)C (pasteurization), inactivating non-spore-forming bacteria, while products with a pH above 4.5 are preserved with temperatures above 100 \({}^{\circ}\)C (sterilization), inactivating non-spore-forming and spore-forming microorganisms [21; 23]. To ensure their safety, a 5-log reduction in microorganisms is needed [9]. Heat affects various parts of microbial cells and their functioning, ultimately leading to varying degrees of inactivation. The most relevant cellular events that occur in a vegetative bacterial cell associated with heat treatment are DNA alterations; increases in the mutation rate; denaturation and aggregation of proteins; loss of specific protein function; reduction in protein repair capacity; ribosome confirmation loss; outer- and inner-membrane permeabilizations; loss of membrane-associated functions; and loss of intracellular components [34]. A detailed summary of the effects of the UHT and HTST parameters on the preservation efficiency of juices, nectars and beverages is provided in Table 1. According to the literature, the UHT method is very effective in preserving liquid food products. [PERSON] et al. [25] showed that this method resulted in reducing the numbers of the total aerobic bacteria (TAB) and the yeasts and molds (Y&M) to below detection limits and provided a shelf-life for kiwifruit juice of 42 days at 4 \({}^{\circ}\)C. [PERSON] et al. [35] also observed TAB and Y&M contents below the detection limits for 12 weeks in purple sweet potato nectar stored at 4 \({}^{\circ}\)C and 25 \({}^{\circ}\)C. [PERSON] et al. [36] demonstrated complete inactivation of aerobics, psychrotrophs, _Escherichia coli Coliformis_ and Y&M in carambola juice after the process, as well as within 40 days of storage. [PERSON] et al. [24] compared different UHT temperatures within the same preservation time, showing that better inactivation occurred at 120 \({}^{\circ}\)C and 135 \({}^{\circ}\)C than at 110 \({}^{\circ}\)C. However, both of these temperatures effectively inactivated microorganisms to safe levels. [PERSON] et al. [37] achieved desirable 90-day shelf-life for pomergranate juice after UHT treatment. Also, other studies have shown the effectiveness of the UHT method in inactivating microorganisms immediately after processing [12; 17; 38; 39; 40], maintaining microbiological safety during storage over 20 days [40; 41], 25 days [42], 28 days [27], 90 days [43] and 16 weeks [44; 45]. Compared to innovative, emerging methods of preservation like HPP, UHT is much more effective [41]. The HTST method is also effective in ensuring appropriate microbiological stability. Heating peach juice at 72 \({}^{\circ}\)C for 15 s resulted in the destruction of _E. coli_ O157:H7 by 5 logarithmic cycles [31]. Heating sea buckthorn juice at a configuration of 100 \({}^{\circ}\)C/15 s reduced TAB and Y&M counts below detection levels and ensured microbiological safety for 31 days at 4 \({}^{\circ}\)C [30]. The good effectiveness of the HTST treatment in inactivating various microorganisms has been demonstrated in many other research works [5; 40; 46; 47; 48; 49]. [PERSON] et al. [5] indicated a shelf-life for cloudy apple juice of 9 weeks. Microbial counts for the HTST-pasteurized orange juice (94 \({}^{\circ}\)C/26 s) remained at or below detection limits over the entire study (168 days) [50].