# Recovery of Polyphenols from Agri-Food By-Products: The Olive Oil and Winery Industries Cases
## 2 Polyphenols from Olive Oil Production Wastes: Source and Applications  
Olive oil is defined as the oil obtained from the olive, which comes from the _Olea europaea_ L. tree. It is an edible oil of high consumption, with volumes that have increased steadily since 2005. In the last decade, the production of olive oil has increased by about 40% worldwide. The main olive oil producers are Spain, Italy, Greece, and Portugal. The growing popularity of olive oil is predominantly attributed to its content of oleic acid and phenolic compounds, being considered a valuable source of antioxidants in the human diet. Nevertheless, during its production, a considerable amount of phenolic compounds remains in olive oil by-products and waste [12; 13]. The olive oil industry generates large amounts of solid and liquid wastes, olive pomace and olive mill wastewater being the main ones. All of them have a high load of lipids, organic acids, and phenolic compounds. Figure 3 shows the main olive oil processing schemes and the main streams of interest as a source of polyphenols. The chemical composition of waste depends on several factors, such as cultivation, origin, maturation of the olive, climatic conditions, and olive oil extraction procedure. Several studies have shown the negative effects of waste on microbial populations of the soil, aquatic ecosystems, and the air through the emissions of phenol and sulfur dioxide, so that waste constitutes a major environmental problem in the main producing countries of olive oil from the Mediterranean region [1; 12]. One of the main approaches for the valorization of these residues is the extraction of valuable phytochemical compounds, such as polyphenols, with interesting properties for the pharmaceutical, cosmetic, and food industries [12]. The main phenolic compounds identified in residues of olive oil production are shown in Table 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Identified Phenolic Compounds** & **Concentration** & **Reference** \\ \hline \multirow{8}{*}{Olive pomaces} & Hydroxyytrosol & 5.3–512.6 mg kg\({}^{-1}\) dw \\  & Tyrosol & 886.7 mg kg\({}^{-1}\) dw \\  & Oleuropein & \textless{}0.5–162.9 mg kg\({}^{-1}\) dw \\  & 3,4-dihydroxybenzoic acid & 37.2 mg kg\({}^{-1}\) dw \\  & Vanillic acid & 21.6 mg kg\({}^{-1}\) dw \\  & Homovanillic acid & 12.5 mg kg\({}^{-1}\) dw \\  & \(p\)-hydroxybenzoic acid & 3.3 mg kg\({}^{-1}\) dw \\  & Luteolin & 32.9–410.9 mg kg\({}^{-1}\) dw \\  & Ruitin & 1.3–354.2 mg kg\({}^{-1}\) dw \\  & Caffe acid & 0.7–876.2 mg kg\({}^{-1}\) dw \\  & Chlorogenic acid & 9.7–47.7 mg kg\({}^{-1}\) dw \\  & Ferulic acid & 6.1–34.6 mg kg\({}^{-1}\) dw \\  & \(p\)-coumaric acid & 8.0–67.1 mg kg\({}^{-1}\) dw \\  & Quercetin & 0.5–36.6 mg kg\({}^{-1}\) dw \\  & Naringenin & 0.9–3.3 mg kg\({}^{-1}\) dw \\  & Hydroxyytrosol & 102–1409 mg L\({}^{-1}\) \\  & Tyrosol & 14–425 mg L\({}^{-1}\) \\  & Caffe acid & 1–4 mg L\({}^{-1}\) \\  & Elenolic acid & 87–1884 mg L\({}^{-1}\) \\  & Salidroside & 33–265 mg L\({}^{-1}\) \\ Olive mill wastewaters & Comselogoside & 1–2 mg L\({}^{-1}\) \\  & Hydroxyytrosol 4-O-Glucoside & 54–3150 mg L\({}^{-1}\) \\  & Hydroxyytrosol 1-O-Glucoside & 23–27 mg L\({}^{-1}\) \\  & Hydroxyytrosol Glycol & 132–325 mg L\({}^{-1}\) \\  & Ester of caffeic & 1 mg L\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Phenolic compounds in olive mill wastes. Figure 3: Olive oil processing schemes: i) traditional as discontinuous process and ii) continuous processes by three phases or two phases (adapted from [12]). Reproduced with permission from [PERSON], et al. Process Biochemistry; published by Elsevier, 2013. As can be seen in Figure 3, olive pomace and olive mill wastewater are produced as by-products, regardless of the processing scheme followed. Olive pomace is a semi-solid waste, composed of olive skin, pulp, and bone. The main components are polysaccharides, proteins, fatty acids, pigments, and polyphenols, and thus it is considered a source of compounds with antioxidant activity [17].