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 (alpha-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.(c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.