Flavonoids are one of the most abundant classes of natural products present in plant kingdoms. They are crucial dietary polyphenols and are abundant in various foods such as fruits, vegetables, nuts, and tea (Slimestad et al. 2008), (Marks et al. 2007). Structurally, the carbon backbone of the flavonoids is the C6-C3-C6 where the two C-6s make the A and B rings while the C-3 makes the C ring. Based on the position of the bond of the B-ring to the C-ring (benzopyrano moiety), the C-15 molecules (flavonoids) are mainly classified into three different classes: flavonoids, isoflavonoids, and neoflavonoids. According to the saturation level in the C-ring, the degree of oxidation, and the presence of additional rings, flavonoids are further categorized into eight different subclasses (Pandey et al. 2016). They play a vital role in protecting plants against adverse climatic, biological, and physical environments. In addition, they act as signal molecules, UV-B protectants, and coloring pigments of fruits and flowers. To date, more than 10,000 flavonoid derivatives have been characterized, and synthesized, utilizing techniques like glycosylation, methylation, hydroxylation, methoxylation, prenylations, acylations, and others (Xiao et al. 2011), (Cao et al. 2015), (Overwin et al. 2016). Flavonoids exhibit a diverse array of properties, ranging from antioxidant, anti-proliferative, and anti-inflammatory effects to protecting neurodegenerative conditions like Alzheimer's and Parkinson's disease. Also, they have shown effective results in anti-tumor, anti-viral, anti-allergic, and anti-carcinogenic properties (Santos et al. 2013), (Pandey et al. 2014), (Barreca et al. 2014), (Xiao et al. 2011), (Stoclet and Schini-Kerth 2011), (Obrenovich et al. 2011). Flavonoids have a wide range of biological impacts on living beings including humans. However, their natural abundance falls short of meeting the demand due to their limited concentration in plants, tedious, costly, necessitating intricate and time-consuming extraction and purification procedures that often involve environmentally unfriendly processes. Additionally, the industrial application of flavonoids, including flavone compounds, encounters hurdles arising from their vulnerability to instability when exposed to factors such as light, pH variations, and elevated temperatures. Furthermore, the insufficient solubility and stability of flavone compounds pose significant challenges to their utilization in various industries (Panche et al. 2016), (Zhang et al. 2013), (Kawabata et al. 2011). The glycosylation process plays a crucial role in shaping the solubility, accessibility, and chemical properties of flavonoids, resulting in notable changes in their physical and chemical stability, as well as their solubility and biological characteristics (Choi et al. 2012), (Mestrom et al. 2019), (Luzhetskyy et al. 2008). Due to their high potential health advantages, flavonoid glycosides have attracted significant attention, leading to research aimed at creating innovative variations for potential applications across diverse sectors such as food, dietary supplements, and therapeutic uses (Cao et al. 2015).
Various methods can be used for glycosylating flavonoids, including chemical synthesis, enzymatic modification, and microbial biosynthesis, each with its advantages and drawbacks in producing glycosylated products. The glycosylation of flavonoids using amylosucrase from Deinococcus geothermalis (DgAS) stands out for its effectiveness, speed, simplicity, and cost-efficiency, utilizing sucrose as an economical source of glucose. This versatile enzyme, DgAS (ASase, EC 2.4.1.4), exhibits a range of activities, including isomerization, polymerization, hydrolysis, and transglycosylation (Thapa et al. 2023), (Kim et al. 2019). Even for compounds belonging to the same class of flavonoids, the occurrence of glycosylation and their conversion rates vary significantly. This study aimed to investigate the reasons behind these differences under common conditions and explore them from multiple perspectives. As a result, it was confirmed that the conversion rate of flavonoids into their glycosylated derivatives varies due to the acidity of hydroxyl groups, stereochemistry, and band gap energy (∆E).