A small-scale in vitro digestion model to examine the stability of flavonoid C-glycosides, O-glycosides, and their aglycons

Flavonoids are widespread secondary plant metabolites and exhibit a broad range of biological activities, thus, they are of great interest for medical applications. In plants, flavonoids often occur as O- or C- glycosides since glycosylation improves their water solubility and stability. A small-scale in vitro digestion model modified according to Brodkorb et al. (2019) was applied to examine the impact of glycosylation on the stability of flavonoids upon oral application until resorption in the small intestine. The model consists of three different phases: oral, gastric, and intestinal digestion. In the oral phase, substances are incubated with simulated salivary fluid and 75 U/mL of α-amylase, followed by incubation with simulated gastric fluid and 2000 U/mL of pepsin. In the last step, the substances are incubated in simulated intestinal fluid and a mixture of different excretory digestive enzymes of the pancreas, such as lipases, amylases, and proteases (pancreatin). The amount of pancreatin added is based on the measured trypsin activity of 100 U/mL. The proportion of flavonoids stable against digestive fluids and enzymes was determined by subsequent HPLC- DAD analysis. As [Fig. 1] illustrates, compared to apigenin 8-C- and 6-C-glycosylated derivatives (vitexin and isovitexin) showed greatly increased stability. In comparison to luteolin, only a slight increase in stability was observed for the 8-C- and 6-C-glycosides orientin and isoorientin. Moreover, no positive impact on stability was observed for the O-glycosides apigenin-7-glucoside and luteolin-7-glucoside. These differences in the stability of flavonoids against digestive fluids and enzymes must be considered in subsequent studies on resorption, and metabolism.

Fig. 1 Stability of apigenin, luteolin, and their O- and C-glycosides in a small-scale in vitro digestion model. To investigate the stability of the flavonoids a small-scale in vitro digestion model was applied. The substances were incubated in three simulated digestion steps: oral, gastric, and intestinal phase, followed by HPLC-DAD analysis. The proportions of stable flavonoids are indicated as mean values of three independent measurements (n=3) and the error bars declare the standard error of mean.

Publication History

Article published online:
16 November 2023