Agro-industrial by-products are important sources of potent bioactive phenolic compounds. These compounds are of extreme relevance for food and pharmacological industries due to their great variety of biological activities. Fermentation represents an environmentally clean technology for production and extraction of these bioactive compounds, providing high quality and high activity extracts, which can be incorporated in foods using coatings/films wax-based in order to avoid alterations in their quality. In this document is presented an overview about importance and benefits of solid-state fermentation, pointing out this bioprocess as an alternative technology for use agro-industrial by-products as substrates to produce valuable secondary metabolites and their applications as food quality conservatives.