Biotransformation of Rice Husk into Phenolic Extracts by Combined Solid Fermentation and Enzymatic Treatment

Biotechnology is essential for developing profitable and productive techniques to obtain metabolites. Two technologies can be used: solid or liquid fermentation and enzymatic treatments. In this context, the objective of this work was to evaluate the use of rice husk, a lignocellulosic material, to obtain bioactive compounds by lignin oxidative transformation and demethoxylation, respectively, through enzymatic treatments of P. chrysosporium and G. trabeum. In the first step, solid fermentation was used to obtain the enzyme Lig. Peroxidase and methoxyl hydrolase were quantified as 80 UE and 50 UE, respectively. This enzyme concentrate was lyophilized and used to prepare an enzymatic consortium (240 UE LigP and 150 UE metH) applied in the second phase of enzymatic treatment. The overall process involved 20 days in the solid fermentation step and 2 h for the enzymatic treatment. The obtained products were characterized by having veratryl alcohol and veratryl aldehyde at contents of 70.4 ± 0.1 and 23.3 ± 0.3 mg/g, respectively. Moreover, the analyzed products did not show cytotoxicity but revealed antioxidant and bacteriostatic activities. No anti-inflammatory activity was detected. In the context of circular economy, the obtained results pointed out the use of combined solid fermentation and enzymatic treatment as a viable strategy to valorize rice husk. The applications of these bioactive compounds presenting bactericidal and bacteriostatic activity and not showing toxicity are very common in medicine, agriculture, and environmental health, among others, and can be incorporated both in free systems and immobilized in spheres, capsules or biopolymer films, which is an important input for obtaining functionalized materials that are in high demand today.