# Evaluation of Different Drying Methods on the Quality Parameters of _Acanthopanax semicosus_ Fruits
## 4 Discussion  
This study comprehensively evaluated the influence of drying methods on color, bioactive compound retention, antioxidant activity, and metabolomic profiles in AS fruits, highlighting VFD as optimal across multiple quality parameters. Color, a vital indicator of quality, was best preserved by VFD, as reflected by superior L* values and reduced \(\Delta\)E. The low-temperature, low-oxygen conditions of VFD effectively suppressed non-enzymatic browning and polyphenol oxidation. Similar advantages were reported by [PERSON] et al. (2020), who observed enhanced color retention in freeze-dried apples [70]. Conversely, HD significantly accelerated Maillard reactions and polyphenol oxidation, negatively affecting color. VFD achieved the highest retention of TPC, TFC, and major phenolic and flavonoid compounds. Low-temperature drying processes mitigate the oxidation and degradation of phenolic compounds, whereas HD and MD significantly reduced these heat-sensitivecomponents. [PERSON] et al. (2023) also noted significant losses of phenolics and fiber in dragon fruit following hot-air drying [71]. Although VD avoids high temperatures, extended drying times may cause partial compound degradation. These results underscore the importance of controlling temperature and drying environment to preserve active components effectively. Amino acid analysis showed VFD notably preserved heat-sensitive amino acids such as Lys, Arg, and Glu. Lower temperatures reduce amino acid degradation kinetics, enhancing compound integrity. [PERSON] et al. (2024) similarly reported that VFD maintained higher amino acid-related metabolites in mushrooms compared with HD [72]. Additionally, PCA and OPLS-DA clearly demonstrated that drying methods significantly altered metabolomic profiles. VFD-treated samples formed distinct metabolite clusters, indicative of effective preservation, whereas high-temperature treatments caused notable degradation or transformation of thermolabile metabolites. Antioxidant activity, a crucial parameter for functional foods, was highest in VFD-treated samples, as reflected by elevated DPPH and ABTS scavenging capacities. This outcome correlates directly with VFD's superior retention of polyphenic and flavonoid constituents, thus limiting oxidative damage. Recent studies consistently support freeze-drying's superior retention of phenolics, flavonoids, and antioxidant activity. Freeze-dried plant materials exhibited greater antioxidant potential compared to heat-based drying methods [73; 74]. Conversely, HD and MD significantly compromised antioxidant activity due to heat-induced oxidative degradation, as corroborated by [PERSON] 2018, who reported lower antioxidant capacities in oven- and sun-dried samples [75]. Despite systematically evaluating the impact of different drying methods on the quality parameters, bioactive constituents, and volatile profiles of AS fruits, this study has several inherent limitations that warrant further investigation. There are some limitations in the chemical assays for phenolic and flavonoid quantification. Chemical assays commonly used for quantifying phenolics and flavonoids have inherent limitations. The Folin-Ciocalteu reagent is not specific to phenolics, interacting broadly with various reducing substances such as ascorbic acid, amino acids, and reducing sugars, potentially leading to the overestimation of total phenolic content (TPC) [76]. Nonetheless, it remains useful for the comparative, semi-quantitative evaluation of drying methods. Similarly, the aluminum chloride (AlCl\({}_{3}\)) method for TFC depends on flavonoid complexation with aluminum ions, but certain flavonoids lacking suitable hydroxyl groups may not react efficiently, causing false negatives [77]. Conversely, interference by organic acids and other polyphenols can yield false positives, inflating flavonoid content measurements [78]. The high correlations among TPC, TFC, and antioxidant activity measurements are anticipated, as these assays share underlying redox chemistry.