International Journal of Horticulture, 2025, Vol.15, No.1, 8-20 http://hortherbpublisher.com/index.php/ijh 9 For instance, the HuSWEET family of sugar transporters has been identified as crucial in regulating sugar accumulation during fruit development (Jiang et al., 2023). Additionally, the interplay between sugars, organic acids, and other metabolites, such as betalains, further affects the fruit's quality and visual appeal (Wu et al., 2019). This study systematically explores the impact of sugar and organic acid metabolism on the flavor and nutritional quality of pitaya, focusing on the biochemical traits and metabolic pathways that determine its sensory and nutritional characteristics. The study intends to uncover key factors that enhance the sweetness, overall taste, and health benefits of pitaya. These findings are expected to provide valuable insights for future research and practical applications in pitaya cultivation and processing, ultimately improving its market competitiveness and consumer acceptance. 2 Composition and Metabolism of Sugars in Pitaya 2.1 Analysis of types and content of sugars Pitaya exhibits a diverse composition of sugars that significantly influence its flavor and nutritional quality. The primary sugars identified in various pitaya species include glucose, fructose, and sucrose. For instance, in the yellow-peel pitaya species ‘Wucihuanglong’ (Hylocereus undatus) and ‘Youcihuanglong’ (Hylocereus megalanthus), glucose is the dominant sugar in ‘WCHL’, while ‘YCHL’ contains higher levels of sucrose, fructose, and glucose (Xie et al., 2022; Xu et al., 2024). Hylocereus undatus presents a total sugar content of 9.83%, with glucose and fructose being the major components (Wei et al., 2019; Constantino et al., 2021). The study found that glucose is the primary sugar in mature fruit, followed by fructose, while sucrose content is relatively low and exhibits minimal variation. During the later stages of fruit development (30 to 40 days after artificial pollination), the levels of glucose and fructose significantly increased, reaching 12.2-fold and 6-fold of their initial levels, respectively (Figure 1). In contrast, H. megalanthus has a lower total sugar concentration of 5.93%, with a notable presence of sucrose. Compared to H. polyrhizus, H. undatus has lower total phenolic content and antioxidant potential but stands out in terms of sugar composition. The flesh of H. undatus, with its low acidity and high sugar content, is particularly suitable for making desserts and beverages (Arivalagan et al., 2021). These variations in sugar composition among different pitaya varieties are crucial for determining their sweetness and overall flavor profile. Figure 1 Glucose is the main sugar in mature pitaya fruit. (A) Photograph of pitaya fruit at different developmental stages. (B) Changes of soluble sugars (glucose, fructose, and sucrose) contents during fruit maturation. Fruit at 16, 21, 26, 30, 35, and 40 days after artificial pollination (DAAP) was sampled for analysis. Data represent mean values from three biological replicates (±S.E.) (Adopted from Wei et al., 2019)
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