Characterization of Solid By-Products Derived From Olive Oil Production Using Olive Pitting Technique

In the present study, the effect of the olive pitting technique on the quality of produced solid olive wastes (pulp and stone) were investigated within the framework of the circular economy. Two olive species from three regions of Greece were collected in autumn 2023, "Koroneiki" and "Chondrolia" from Crete, "Koroneiki" and "Kolireiki" from Peloponnese, and "Adramytini" and "Kolovi" from Lesvos. Olive oil was produced with and without pitting the olives before pressing. A total of 12 solid olive pulp samples were collected (from pitted olives and unpitted olives), and characterized for proteins, lipids and starch content. They were also characterized for bioactive substances (total hydroxytyrosol (Hydr.) and derivatives and total phenolic content), pigments (tocopherols, β-carotene, chlorophylls), lutein, and squalene. Moreover, the Higher Heating Value (HHV) of the six olive stones produced from pitted olives were determined. The results showed that olive pulps had a high average lipid content of 30.7 % ± 9.4 %, with the majority of pitted samples exhibiting higher lipid content. In addition, they presented low protein and carbohydrates contents of 6.2% ± 2.6% and 2.5% ± 0.5%, respectively. No difference between the same samples with and without pitting was observed. Olive pulps were characterized, in order of abundance, by high concentrations of total phenolic content 689 ± 255 mg/kg (740 ± 299 mg/kg pitted, 637 ± 217 mg/kg unpitted), squalene 281 ± 175 mg/kg (388 ± 188 mg/kg pitted, 173 ± 64 mg/kg unpitted), total hydrotyrosol and derivatives 171 ± 72 mg/kg (191 ± 85 mg/kg pitted, 151 ± 55 mg/kg unpitted), a-tocopherol (E vitamin) 27.8 ± 14.1 mg/kg (36 ± 14 mg/kg pitted, 18 ± 5 mg/kg unpitted), b-chlorophyll 20.3 ± 21.4 mg/kg (27 mg/kg pitted, 14 mg/kg unpitted), b- carotene 19.2 ± 15 mg/kg (25 ± 18 mg/kg pitted, 14 ± 10 mg/kg unpitted), a-chlorophyll 6.7 ± 7.2 mg/kg (9 mg/kg pitted, 5 mg/kg unpitted) and lutein 5.4 ± 4.1 mg/kg (7 ± 5 mg/kg pitted, 4 ± 3 mg/kg unpitted). It is concluded that olive pulp from pitted olives resulted in significantly higher contents of bioactive compounds (total hydrotyrosol and derivatives and total phenolic content) and squalene, α-tocopherol or vitamin E at a concentration close to the legislation limit 30 mg/kg for the contribution to human health, as well as pigments and lutein, which makes them suitable for animal feed or as a food supplement with significant health benefits. Finally the pitting technique results in the production of olive stones or olive cores with high HHV with an average value of 20.8 ± 0.7 MJ/kg which could be used as a low-cost solid fuel.