Enhanced in vitro and in vivo antioxidant activities of olive pomace by solid- state fermentation using the yeast Kluyveromyces marxianus

Background: This study investigated the potential role of solid-state fermentation (SSF) to enhance the in vitro and in vivo antioxidant activities of olive pomace (OP, the environmentally polluting solid residue produced after olive oil extraction) using the GRAS (Generally Recognized As Safe) yeast Kluyveromyces marxianus . Fermented OP (FOP) was produced by SSF of OP by K. marxianus . Both unfermented OP (UFOP) and FOP were extracted using methanol. Results: FOP methanolic extract (FOPME) demonstrated significantly higher antioxidant activity than UFOP methanolic extract (UFOPME) in ABTS radical scavenging, metal chelating, H ₂ O ₂ scavenging, lipid peroxidation inhibition, reducing power, and total antioxidant capacity. On the other hand, UFOPME demonstrated slightly higher superoxide anion radical scavenging and RBCs-protecting activities than FOPME. Prophylactic and therapeutic antioxidant activities of UFOPME and FOPME were assessed in vivo against oxidative stress associated with diethylnitrosamine (DENA)-induced hepatocellular carcinoma (HCC) in rats. Relative to the normal group, the administration of DENA/CCl ₄ in the HCC group significantly increased hepatic nitric oxide and malondialdehyde and significantly decreased total antioxidant concentration. Both UFOPME and FOPME protected against and relieved the oxidative stress associated with DENA/CCl ₄ -induced HCC in rats. Conclusion: SSF of OP using the GRAS yeast K. marxianus significantly enhanced most of its in vitro antioxidant activities alongside demonstrating simultaneous protective/therapeutic effects against oxidative stress associated with DENA/CCl ₄ -induced HCC in rats.