Enrichment and bioactivities of polyphenols of crude extract by deep eutectic solvent extraction from foxtail millet bran

The adsorption and desorption capabilities of eight types of macroporous adsorption resins (MARs) for polyphenols from foxtail millet bran (FMB) extract were investigated. The D101 resin demonstrated the highest adsorption and desorption capacity, followed by the AB-8, DM301 and ADS-17 resins. The reaction kinetics for the adsorption of FMB polyphenols onto MARs accorded with a pseudo-first-order model (R2 > 0.99), with an apparent adsorption rate constant (K) of 1.225 × 10−2 g/mg·min. The adsorption process of FMB polyphenols onto D101 resin could be best described with the Langmuir adsorption isotherm (R2 > 0.99). The phenolic fractions were separated using silica gel column chromatography, and their total phenolic content (TPC), antioxidant activity, total flavonoid content (TFC), anti-glycosylation activity and acetylcholinesterase and α-glucosidase inhibitory activities were compared. Fraction 4 had the highest abundance of phenolic compounds, with N′-p-coumaroyl-N″-feruloylspermidine (461.65 ± 0.79 μg/g) and N′,N″-di-feruloylspermidine (578.46 ± 2.56 μg/g) being the predominant phenolics, the best acetylcholinesterase inhibitory activity and anti-glycosylation activity. Fraction 5 contained the highest apigenin-C-dihexoside, and therefore showed the best performance of α-glucosidase inhibitory activity. Fractions 4 and 5 displayed high antioxidant, acetylcholinesterase inhibitory activity and anti-diabetic potential, indicating that these two fractions should be targeted for further high-value utilisation of free polyphenols from FMB

Green extraction of phenolic compounds from foxtail millet bran by ultrasonic-assisted deep eutectic solvent extraction: Optimization, comparison and bioactivities

An ultrasonic-assisted extraction (UAE) protocol using deep eutectic solvent (DES) was employed to extract phenolic compounds from foxtail millet bran (FMB). DES composed with betaine and glycerol in a 1:2 M ratio was selected basing on the total phenolic content (TPC) extraction yield, with the optimal extraction technology investigated using response surface methodology (RSM) with Box-Behnken design (BBD). The optimized process obtained was as follows: DESs with water content of 29 mL/100 mL, ultrasonic power at 247 W, extraction temperature of 61 °C, and extraction time of 31 min. The TPC of the extract was 7.80 ± 0.09 mg ferulic acid equivalent (FAE)/g under the optimum extraction conditions, with the result corresponding well with the model prediction. DES-based UAE produced higher total phenolics, total flavonoids, in vitro antioxidant activity and acetylcholinesterase inhibitory activity than the conventional solvent extraction. The phenolic extract from FMB with DES-based UAE was mainly composed of fifteen phenolic compounds, with p-coumaric acid, apigenin-C-dihexoside, and N′, N″-di-p-coumaroylspermidine being the predominant phenolic compounds. Additionally, 1-O-p-coumaroylglycerol was detected for the first time in FMB. The microstructure differences of the FMB samples following extraction were confirmed using scanning electron microscopy (SEM)