Phenolic compounds and antioxidant activity of Lippia graveolens Kunth residual leaves fermented by two filamentous fungal strains in solid-state process

The residual leaves from essential oil extraction from Mexican oregano (Lippia graveolens) have a potential as a source of bioactive molecules (e.x. flavonoids) that could be extracted by solid state fermentation (SSF) process. In this study, the residual leaves were subjected to a SSF (120 h) by two microorganism Trichoderma harzianum and Rhizopus oryzae evaluating the phenolic compounds (Total polyphenols and flavonoids), the antioxidant activity (DPPH● / FRAP), the bioactivities (α-amylase inhibition and antimicrobial against Escherichia coli), the cytotoxic effect (erythrocytes) and a characterization (HPLC-MS). The results showed that the total polyphenols for T.harzarium did not show statistical differences (first 48 h), and R. oryzae fermentation obtained a higher context (48 h). Also, the higher flavonoid release was present at 48 and 96 h (T. harzianum and R. oryzae). The antioxidant activity decreased in the last fermentation hours, the a-amylase reported a higher inhibition value (29.97 ± 1.97 %) and antimicrobial capacities; R. oryzae (96 h) did not register a cytotoxic effect. The characterization determined the presence of valuable molecules as ferulic acid 4-O-glucoside, phloridzin and luteolin. The fermentation allowed the recovery of bioactive phenolic compounds that could be an alternative for the revalorization of oregano waste.