Ultrasonic Enhancement of Aqueous Two-Phase Extraction and Acid Hydrolysis of Flavonoids from Malvaviscus arboreus Cav. Flower for Evaluation of Antioxidant Activity

Abstract

The ultrasonic-assisted aqueous two-phase extraction (UAATPE) of flavonoid glycosides from Malvaviscus arboreous Cav. flower (MACF) was developed using ethanol/ammonia sulfate systems, followed by the ultrasonic-assisted acid hydrolysis (UAAH) of the top extract with HCl solution. The optimization of UAATPE and UAAH processes was accomplished by single-factor experiments and response surface methodology. As a result, the flavonoid glycosides enriched in the top phase could achieve a maximum yield of 35.9 ± 1.1 mg/g by UAATPE and were completely hydrolyzed by UAAH deglycosylation. The flavonoid glycosides and their hydrolyzates were separated and characterized by high-performance liquid chromatography and ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry. Ultrasonic enhancement of the extraction and hydrolysis was explored by comparative study. Furthermore, the in vitro activity of the flavonoid glycosides and the aglycones were comprehensively evaluated by antioxidant activity assays, including ferric-reducing antioxidant power and scavenging DPPH, hydroxyl, and superoxide radicals. All of the IC50 values suggest that the antioxidant activity of flavonoid aglycones was stronger than that of their glucosides and even vitamin C, revealing that the deglycosylated flavonoids from MACF were the more powerful antioxidants. This study provided an effective and eco-friendly strategy for the extraction, separation, and purification of flavonoids from MACF, as well as for the development of the potential flavonoid antioxidants.

Combined analysis of inorganic elements and flavonoid metabolites reveals the relationship between flower quality and maturity of Sophora japonica L.

“…Tao et al (2023) reported that the addition of a glycoside at the C-3 position of quercetin-3-O-galactoside increased the bond dissociation enthalpy of the phenolic hydroxyl groups, resulting in weakened antioxidant activity. Furthermore, Yuan et al (2022) found that the antioxidant activity of aglycones is stronger than that of their glucosides and vitamin C. When the 3-OH group of flavonols is replaced by glycoside groups, steric hindrance impedes the binding of the inhibitor to the active site of the enzyme . This phenomenon was verified in another study, in which the FS extract showed better inhibition of tyrosinase activity after treatment with a weak acid than before treatment (Lai et al, 2014).…”

“…Flavonoids are polyphenolic compounds with a benzo-g-pyrone structure and are divided into seven main subclasses: flavones, flavonols, isoflavones, flavanols, flavanones, anthocyanins, and chalcones (Shen et al, 2022). The biological activities of flavonoids are structure dependent; for example, aglycones are more effective antioxidants than their corresponding glycosides (Yuan et al, 2022), and flavonoids with free 3-OH groups are excellent antioxidants (Tao et al, 2023). Extensive research has been conducted on rutin, quercetin, isorhamnetin, and kaempferol in FS (Liu et al, 2016;Li et al, 2022;Zhang et al, 2023); however, few studies have been conducted on the other flavonoid components of FS due to their low content and more intricate structures.…”