## 4 Discussion
### Application of TLC Fingerprint for Extraction Quality Control  
Effect of Ethanol Concentration and Wetting Time on Fingerprint  
The polarity of the solvent and the physicochemical properties of the flavonoid components play an important role in extraction [47]. Differences in flavonoid peak number and intensity indicate variations in solubility due to the structural differences [48]. The flavonoid content is influenced by temperature, solvent concentration, and extraction time [49]. Increasing ethanol concentration and wetting time in the extraction process increases the concentration of flavonoid glycosides and organic acids [1]. Adequate wetting time ensures that the solvent thoroughly permeates the plant material, causing it to swell and then facilitating the dissolution of flavonoids that reflect the flavonoid peak detected in the sample [50]. Flavonoids typically dissolve in polar solutions, and their fingerprint profiles vary depending on ethanol concentration and wetting time. The PCA and PLSDA loading plots reveal that peak P10, P12, and P13 equivalent to standardized extracts are not observed when using 40% and 50% ethanol with a 30 min wetting time. These peaks are thought to represent flavones, flavonols, and di-hydro flavonols. Flavones, commonly found in the leaves, fruits, and flowers in the form of glucosides, have a double bond at positions 2 and 3 and a ketone group at position 4 of the C ring. The differences among flavones are based on substitution with the hydroxyl group in the phenyl rings [36]. Flavones of the luteolin type have been detected in the leaf extract of the _Ipomea batatas_ cultivar [PERSON] [41]. Luteolin has 4 hydroxy groups in C-5, C-7, C-3\({}^{\prime}\), and C-4\({}^{\prime}\) positions [37]. Flavonols, another subgroup of flavonoids, have a ketone group and a hydroxyl group at position 3 of the C ring, which can also be present in glycosylated form [36]. According to the flavonoid biosynthesis pathway, flavonoids are synthesized from flavones in two stages as follows: hydroxylation by flavone hydroxylase followed by dehydrogenation catalyzed by flavonoid synthase [51]. _Ipomea batatas_ L. contains various flavonoids, including kaempfer, quercetin, isoquercitrin, rutin, and hyperoside [41]. Kaempfer contains 3 hydroxyl groups at positions C-5, C-7, and C-4\({}^{\prime}\), while quercetin has 4 hydroxyl groups at positions C-5, C-7, C-3\({}^{\prime}\), and C-4\({}^{\prime}\), respectively [37]. In this study, using 60% ethanol with a 3 h wetting time resulted in the highest number and concentration of flavonoids. This may be because a 3 h wetting period activates the hydroxylase enzyme, facilitating the conversion of flavones to flavonoids. Flavanols, also known as flavan-3-ol, dihydroflavonols, or catechins, are 3-hydroxy derivatives of flavanones. Unlike other flavonoid subgroups, flavanols lack double bonds at positions 2 and 3 [36]. This group of flavonoids often appears in the form of polymers known as tannins, forming catechin molecules. The difference between catechin derivatives is determined by the hydrogen group and esterification with the gallate group [37]. Catechin has also been found in the leaf extract of the orange-fleshed _Ipomoea butatas_ cultivar Bophelo [52]. Based on this study, 60% ethanol is an effective solvent for extracting flavanols comparable to the standardized extract of _Ipomoea butatas_ L.  
This study nevertheless has limitations since, despite its widespread use in industry, the extraction technique is still conventional. In comparison, there are several advanced or contemporary extraction techniques that might be more effective at boosting yield. Contemporary techniques, including microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE), outperformed conventional techniques by achieving high extraction yields in a shorter amount of time (a few minutes), utilizing less solvent, requiring less work, and improving selectivity [34].