Finally, the selection of the most appropriate downstream process for the obtained product is also crucial when SSF processes are performed. The product obtained by SSF may be recovered from the solid fermented mass by extraction with solvents (aqueous or other solvents mixtures). The type of solvent and its concentration, as well as the ratio of solvent to the solid and pH are important variables that influence in the product extraction. In addition, since the metabolites diffuse throughout the solid mass during the culturing, long extraction-times may be required for complete product recovery. The cost of purification depends on the quality of the obtained extract. For example, the presence and concentration of inert compounds in the extract increase the cost of purification and therefore the cost of recovery is increased. Particularly those secondary metabolites which are used in bulk in the pharmaceutical and health industry and whose purity is governed by stringent regulations need to go through specific purification strategy (Nigam, 2009).
3. Uses of SSF for bioactive phenolic compounds production
3.1. Phenolic content increase in food products
Food quality is not only a function of nutritional values but also of the presence of bioactive compounds exerting positive effects on human health (Cassano et al., 2008). Phenolic compounds, also referred as polyphenols, are considered to be natural antioxidants and represent an important group of bioactive compounds in foods (Dueñas et al., 2005). These compounds are present in all plant foods but their type and levels vary enormously depending on the plant, genetic factors and environmental conditions (Kris-Etherton et al., 2002).