Effect of Simulated Gastrointestinal Digestion on the Phenolic Composition and Bioactivity of Cymbopogon flexuosus Extracts

This study characterized leaf extracts of <i>Cymbopogon flexuosus</i> (Ryukyu Lemongrass Corporation, Okinawa, Japan) and evaluated the bioaccessibility and bioactivities of phenolic compounds following a simulated in vitro gastrointestinal model of digestion (in vitro GID) of plant material. Undigested (controls, AqC, EtC) and digested aqueous (AqD) and ethanolic (EtD) extracts were analyzed. Control extracts contained higher total phenolics and flavonoids than digested ones, with EtC showing the highest values. UHPLC-QToF-MS (ultra-high-performance liquid chromatography system coupled to a quadrupole time-of-flight mass spectrometer) identified 32 compounds, including phenolic acids, flavone aglycones, C-glycosides, and derivatives. Hydroxybenzoic acids, coumaric acid, caffeic esters, flavones, tricin derivatives, vitexin, and isoorientin exhibited reduced recovery, while coumaric acid hexoside, ferulic acid hexoside, and isoschaftoside/schaftoside exceeded 100% recovery, suggesting release from the matrix. Some compounds were absent from AqD, and many were found in the pellet, indicating potential colonic metabolism. Antioxidant activity (DPPH, reducing power, β-carotene/linoleic acid) was stronger in controls but always weaker than BHT/ascorbic acid. Extracts mildly inhibited α-amylase but more strongly inhibited α-glucosidase as shown with applied enzyme inhibition assays, especially EtD (76.93% at a concentration of 10 mg/mL), which showed stronger activity than controls but remained below acarbose (87.74% at 1 mg/mL). All extracts promoted HaCaT keratinocyte growth and reduced HCT-116 colon cancer cell viability at 250 µg/mL, with the strongest effects in AqC and AqD. Overall, GID decreased antioxidant activity but enhanced antidiabetic potential, confirming the safety and selective anticancer effects of <i>C. flexuosus</i> extracts.