Oxygen influences in vitro assessment for phenolic compounds: Digestive stability, α-glucosidase inhibitory activity and bioavailability.

Phenolic compounds are popular in screening novel hypoglycemic agents, but the impact of oxidative degradation on the determination of α-glucosidase inhibitory activity and bioavailability is unclear. Here we showed 12 phenolic compounds structure-dependently degraded during standard simulated digestion, while in physiological hypoxia their retention rates were all over 87.89 %. This enhancement of digestive stability resulted in the biggest drop of 31.72 % in IC against α-glucosidase and a significant increase in bioavailability. Enzyme kinetic and multi-spectroscopic analysis confirmed oxygen weakened the affinity of compounds to α-glucosidase, but the mechanisms were not changed. Moreover, a two-chamber culture system was designed to meet conflicting demands for oxygen between epithelium and cavity, and better α-glucosidase inhibitory activities (51.61 % maximum reduction in glucose production) and absorption rates (up to 1.10 % from undetectable) were obtained than those of uncontrolled oxygen. Hence, the oxygen level should be monitored to assess the activities of phenolic compounds in vitro.