# Recovery of Polyphenols from Agri-Food By-Products: The Olive Oil and Winery Industries Cases
## 5 From Agri-Food Wastes to Polyphenols: Processing Techniques
### Extraction Processes
It is well known that conventional extraction is easy to implement in industry, its main drawbacks being solvent consumption and extraction time. In this sense, modern technologies are much more attractive, since solvent consumption is reduced to a significant degree, extraction time is also reduced, and they provide higher yields. In certain instances, the combination of more than one technique can also be considered, either sequentially or hyphenated, such as UAE-SFE, UAE-MAE, EAE-PLE, or PEF-UAE. However, there are scarce applications of modern extraction techniques at an industrial scale, even at a pilot scale [104]. Scaling up from laboratory to industrial scale is not a trivial issue. Hence, the most mature techniques would be UAE or SFE. Conditioning of Polyphenol Extracts: From Particulate Matter and Colloidal Removal to Volume Size Reduction and Concentration  
After the extraction process, extracts of great complexity are obtained, so it is necessary to subject these extracts to a purification stage. This can be accomplished by membrane separation technology, adsorption-desorption, or a combination of both, which leads to obtaining a final product rich in polyphenols, with a higher quality, which can be subsequently used in the food, cosmetic and pharmaceutical industries. Membrane separation processes can be used at large scale, with three main objectives: (i) to remove suspended and colloidal matter in the extraction stage by using pressure-driven membrane techniques as microfiltration (MF 0.1-5 \(\upmu\)m, 1-10 bar) and/or ultra-filtration (UF 0.5-100 nm, 1-10 bar); (ii) to selectively separate polyphenols from other families of compounds co-extracted in the extraction (e.g., sugars, proteins, lipids) by using pressure-driven membrane techniques as ultrafiltration (UF) and/or nanofiltration (NF) and; (iii) to reduce the volume of the polyphenols rich streams by using pressure-driven membrane techniques as nanofiltration (NF 5-10 nm, 10-30 bar) and/or reverse osmosis (RO < 0.5 nm, 35-100 bar) [105; 106; 107; 108; 109; 110; 111; 112; 113]. Membranes are selective barriers that allow compounds to pass particulate matter (e.g., MF, UF), or dissolved solutes according to their molecular weight cut-off (MWCO) (e.g., UF) or according to the solute properties and active layer (e.g., NF and RO) [110]. Membrane operations separate a solution (feed) into two fractions that are the permeate or filtrate and the retentate or concentrate. The permeated liquid consists of the solvent and solutes that pass through the MWCO of the membrane. The retentate or concentrate contains particles and dissolved compounds partially retained by the membrane, as represented in Figure 8 [4; 6]. The separation efficiency of these methodologies depends on a series of factors: membrane characteristics (material, configuration of the separation module, pore size); physical-chemical composition of the solution (type, weight, polarity, solute load), and operating parameters (feed flow rate, trans-membrane pressure, temperature, permeate flow), among others [6]. Membrane technologies' advantages are low-temperature operation and energy consumption, high separation efficiency, simple equipment, easy scale-up, simple operation, high productivity in terms of permeate flows, and absence of phase transition [4; 6]. Compared with traditional concentration methods (evaporation, spray drying, etc. ), by membrane processes, the product is not subjected to high temperatures and there is no change in the physical state of the solvent, which means that the functional properties of the compounds of interest are preserved [105]. The integration of membrane processes allows the recovery of purified polyphenol streams and high-quality water for reuse purposes. MF is used to remove suspended solids and prevent the early fouling of membranes in the posterior steps. UF membranes separate the polyphenols in the permeate stream from the macromolecules that remain in the retentate (e.g., sugars, lipids, proteins).