Impact of simulated <i>in vitro</i> gastrointestinal digestion on phenolic compounds and the antioxident potential of olive pomace

The study’s aim was to investigate the impact of laboratory-imitated digestion, including mouth, gastric, and intestinal phases of olive pomace on the stability, bioaccessibility, and recovery of phenolic compounds as well as antioxidant ability. The total flavonoid content (TFC) and total polyphenol content (TPC) were extracted using water or 50% and 100% methanol, ethanol, and acetone. The digested mixture after each phase of digestion was centrifuged and used to assess recovery, bioaccessibility, and polyphenolic stability. Compared to other solvents, 100% methanol and ethanol extracts showed the highest values of TPC, TFC, half-maximal inhibitory concentration (IC50) of 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) IC50. The recovery rates of TPC, TFC, DPPH IC50, and ABTS IC50 decreased in a descending order during the gastrointestinal phases as follows: mouth > stomach > intestines. After gastric (27.20%) and intestinal (26.79%) phases, the TPC bioaccessibility index in olive pomace increased significantly, which was statistically similar to the oral phase (21.20%). For TFC, the bioaccessibility rate did not change significantly after mouth and intestinal phases. There were no significant differences in flavonoids and antioxidant scavenging activities among the three phases of digestion. The pellet fractions had higher phenolic levels and better free radical scavenging activity in all phases of digestion than chyme-soluble fractions. TPC or TFC had a significant and positive relationship with Pearson correlation coefficient (r = 0.891–0.994) with DPPH and ABTS scavenging rates in oral, gastric, and intestinal digestion phases. Overall, our research could pave way for the industrial application of olive pomace waste as a possible food ingredient to generate functional foods with beneficial health effects.