International Journal of Horticulture, 2025, Vol.15, No.1, 8-20 http://hortherbpublisher.com/index.php/ijh 11 genes associated with these metabolic pathways, highlighting their importance in the regulation of organic acid content in pitaya (Yin et al., 2015; Xie et al., 2022). Additionally, enzymes involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, are crucial for maintaining ascorbic acid levels in the fruit (Li et al., 2018). The regulation of organic acid metabolism in pitaya is complex and involves multiple layers of control, including transcriptional regulation. Studies have shown that the expression of genes involved in organic acid metabolism is tightly regulated during fruit development (Schvartzman et al., 2018). For instance, the expression of genes encoding enzymes like malate dehydrogenase and citrate synthase is modulated in response to developmental cues and environmental factors. Additionally, transcription factors such as WRKY and Dof have been implicated in the regulation of sugar and organic acid metabolism, further highlighting the intricate regulatory networks governing these processes (Wei et al., 2019; Mou et al., 2022). 3.3 Role of organic acids in flavor and acidity Organic acids are key contributors to the tartness and overall flavor profile of pitaya. Malic acid and citric acid, in particular, are responsible for the characteristic tartness of the fruit. The balance between these acids and sugars determines the perceived sweetness and acidity, which are critical factors influencing consumer preference (Constantino et al., 2021). The presence of ascorbic acid also adds a subtle tanginess, enhancing the fruit's flavor complexity (Xie et al., 2022). The balance of organic acids in pitaya significantly affects consumer preference. Fruits with a higher ratio of sugars to organic acids are generally perceived as sweeter and more palatable. For instance, H. undatus, with its higher sugar content and lower acidity, is preferred for fresh consumption and in desserts and beverages (Fernandes et al., 2018; Arivalagan et al., 2021; Singh et al., 2023). Conversely, H. megalanthus, which has a more balanced sugar-acid profile, is recommended for individuals on carbohydrate-restricted diets due to its lower overall sugar content (Constantino et al., 2021). Understanding the interplay between organic acids and sugars is essential for developing pitaya varieties that meet diverse consumer preferences. 4 Interaction between Sugar and Organic Acid Metabolism 4.1 Balance between sugar and acid content The sugar-to-acid ratio is a critical determinant of fruit taste, influencing consumer preferences and overall flavor perception. In pitaya, the balance between sugars such as glucose, fructose, and sucrose, and organic acids like malic and citric acids, plays a significant role in defining the fruit's taste profile (Constantino et al., 2021; Xie et al., 2022). Higher sugar content generally enhances sweetness, while organic acids contribute to tartness, creating a complex flavor profile that is appealing to consumers (Constantino et al., 2021). The specific ratios of these components can vary significantly among different pitaya species and cultivars, affecting their marketability and consumer acceptance. The balance between sugars and acids in pitaya changes dynamically during fruit ripening. Early stages of fruit development are characterized by higher starch accumulation, which is later converted into soluble sugars as the fruit matures. Concurrently, the concentration of organic acids tends to decrease, leading to a sweeter taste in fully ripened fruits (Xie et al., 2022). This shift in sugar-acid balance is crucial for achieving the desired flavor and nutritional quality in pitaya. For instance, fruits harvested at an advanced color stage exhibit higher soluble sugar concentrations and lower acidity compared to those harvested at the color-break stage, resulting in superior taste quality (Hua et al., 2018; Sobral et al., 2019). 4.2 Influence on pitaya’s overall flavor profile The interaction between sugars and organic acids contributes significantly to the complexity of pitaya's flavor profile. Sugars such as glucose and fructose are predominant in mature pitaya, while malic and citric acids are the main organic acids present (Constantino et al., 2021; Xie et al., 2022). This combination of sweet and tart flavors creates a balanced and complex taste that is highly valued by consumers. The presence of other metabolites, such as phenolic compounds and flavonoids, further enhances the flavor complexity by adding additional layers of taste and aroma (Wu et al., 2019; Xie et al., 2022).
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