Superior antioxidant activity of biotransformed citrus flavonoids in intestinal epithelial cells under challenge conditions

Citrus fruits contain flavonoids with potential health benefits for humans and animals, such as naringin and hesperidin. However, conjugation with sugar moieties prevents an efficient absorption in the small intestine and reduces the bioactivity of these flavonoids.
Here, we demonstrated that our new biotransformation approach, based on citric acid hydrolysis and fermentation by lactic acid bacteria, increased the concentrations of the aglycones naringenin and hesperetin in citrus extract and improved its bioactivity. We investigated the effects of citrus extracts before and after biotransformation on transport and uptake, oxidative stress, and cell migration of intestinal epithelial cells. In addition, we compared the antioxidant capacity of the glycosylated flavonoids naringin and hesperidin with their respective aglycones naringenin and hesperetin when applied at the same concentration.
First, we showed that aglycones were better absorbed and transported than glycosylated flavonoids. Thereby, a higher initial aglycone concentration, as provided in the biotransformed extract, resulted in significantly higher cellular uptake and transport, being advantageous for higher bioactivity. Consistent with this, the biotransformed extract showed a more powerful reduction of intracellular reactive oxygen species (ROS) formation than the non-transformed extract under challenge conditions. Since significantly higher ROS-reducing effects were also observed for pure aglycones compared to flavonoid glycosides, the antioxidant effects can be attributed to the higher aglycone content in citrus extract after biotransformation. Moreover, treatment with the biotransformed extract restored the cell migration capability of stressed cells and resulted in a faster wound closure.
In conclusion, increasing the concentrations of naringenin and hesperetin in citrus extract by citric acid hydrolysis and fermentation improved the antioxidant activity of the extract.