PEF assisted green solvent extraction of high–added value compounds from agri-food by-products

The recovery of valuable compounds (natural colorants or nutraceuticals) from food wastes and by-products, which have been matter of concern by the agri-food industries due to their environmental impact, is gaining increasing interest in recent years. However, traditional extraction methods are generally very time-consuming and require large quantities of solvents in order to achieve sufficiently high extraction yield of target compounds from agri-food products. Moreover, these methods may do not comply with criteria of green chemistry concept, since they may require application of toxic organic solvents for the selective recovery of target compounds. Consequently, demand is increasing for extraction techniques that improve yield, shorten the extraction time and reduce the use of organic solvents. Recently, the interest in Pulsed Electric Fields (PEF) treatment of plant material before extraction with solvent, has considerably grown, due to its ability to induce a selective permeabilization of the cytoplasmatic membranes (electroporation), facilitating the release of intracellular compounds from the plant cells. In this study the efficiency of PEF-assisted extraction of valuable compounds from food by-products derived from the industrial transformation of artichoke (external bracts, stems and leaves) was investigated, as an example of total-use concept of wastes. PEF treatments were carried out at field strengths in the range 0.25 - 5 kV/cm and energy input between 0.25 and 20 kJ/kg. The cell disintegration index (Zp) was used to identify the PEF processing conditions for the pre-treatment of the artichoke wastes before the extraction with water. The optimal PEF processing were defined, and the extraction yield of total phenolic compounds and antioxidant activity was determined. Results showed that, regardless the type of artichoke waste (external bracts, leaf, or stem), the permeabilisation effect induced by the application of PEF pre-treatments led to significantly higher total polyphenols content (+ 300% on average) and antioxidant power (+ 280% on average) of the aqueous extracts, as compared to the untreated samples. HPLC analyses revealed that the most abundant phenolic compound in the extract was chlorogenic acid. In conclusion, it was demonstrated that PEF can allow the green extraction of valuable compounds from artichoke wastes leading to a greater diversity of products and decreasing waste problems.