Moisture in Rehydrated Olive Paste Affects Oil Extraction Yield and Phenolic Compound Content and Profile of Extracted Olive Oil

The effect of olive paste moisture on both oil extraction yield and phenolic content and profile from extractable olive oil is studied at the lab‐scale by stressing physical and biochemical phenomena through gradual dilution of freeze‐dried olive paste at a wide range of moisture levels. Olive fruits of Frantoio and Leccio del Corno cultivars are freeze‐dried immediately after harvesting and then milled. Gradual dilution of the obtained freeze‐dried olive pastes allows obtaining olive pastes at moisture 0–60%, from which olive oil samples are immediately extracted. The experiments show that oil extraction yield and phenolic transfer yield increase in extractable oil and reach a maximum (i.e., phenols up to ≈1200 mg kg−1 for Frantoio cultivar) at olive paste moisture values lower than typical values of the olive paste during milling of whole olive fruits. Then, these yields decrease when the olive paste moisture gradually continues to ride above that value. The data also indicate that olive paste moisture plays a crucial role on enzymatic phenomena affecting phenolic profile of the extracted oils and confirms the hypothesis that lignans, absent or linked to other molecules into the fruits, are released or biosynthesized during oil extraction thanks to the co‐presence of enzymes and water. Practical Applications: The results point out that olive paste moisture appears to be as essential in controlling extra virgin olive oil processing as time, temperature and air exposure. Processing procedures along the olive oil chain able to reduce the olive fruit's moisture, may complement the technological innovations for improving oil extraction and phenolic transfer yields. For example, suitable blends of olive batches with different moisture content could be used to control the olive paste moisture and, consequently, the extra virgin olive oil quality. Small mills able to produce express olive oil from olive paste waffles of ≈1 kg, were recently proposed in the market: results of this study also suggest the possibility to dry olives for obtaining dried olive paste waffles suitable to produce small amounts of express olive oils with the selected qualitative characteristics after rehydrating them at the suitable moisture content.