Towards a green and sustainable recovery of phenolic compounds from food by-products

Food wastes or food by-products have long been matter of concern due to their environment, economic, ethical and social impact. However, nowadays the approach towards this material is changing since they are considered as a cheap source of valuable components. Among food by-products, grape pomace (skins and seeds) and germ and bran of wheat represent a rich source of polyphenols, proteins, fatty acids, oil, vitamins, and fibers that could be extracted and further used as functional additives in food, cosmetic or pharmaceutic products. In this work, the influence of pulsed electric field (PEF) pre-treatment of grape skin and seeds as well as of germ and bran of wheat on extraction yield of different compounds (polyphenols, proteins, carbohydrates) during the subsequent extraction with solvent was investigated. PEF treatments were carried out at 1, 3, and 5 kV/cm with a constant energy input of 10 kJ /kg and at 3 kV/cm with two different energies of 10 and 20 kJ/kg. Kinetics and concentrations of total polyphenols extracted were evaluated in different solvents (aqueous-ethanol and dimethyl sulfoxide) for up to 24 h and optimum parameters were defined. The composition of phenolic extracts obtained under the optimum processing conditions were determined by metabolomics analyses (UHPLC-MS/MS, GC/MS/MS, UPLC-Q-TOF-MS-ORBITRAP). The results demonstrate that mild PEF assisted extraction has the potential to increase the extraction kinetics and yield of phenolic compounds from both grape and flour by-products. Moreover, this eco friendly or "green" process (due to modalities of PEF with low energy consumptions and utilization of eco-solvents) has increased the extraction rates of proteins from wheat in compar-ison with the use of solvent alone.