Leveraging the use of oxylipin measurements to elucidate the integrated impact of greener extraction and recovery methods on almond oil quality

Abstract: Aqueous (AEP) and enzymatic extraction processes (EAEP) enable the simultaneous extraction of oil and proteins from almond flour without the use of flammable solvents. However, most of the extracted oil is entrapped in an emulsion that needs to be demulsified for subsequent oil recovery. In this study, a lipidomic approach was applied to better understand the impact of AEP and EAEP and chemical and enzymatic demulsification strategies on almond oil quality. Extraction conditions for the AEP were 1:10 solids-to-liquid ratio, pH 9.0, 50 ^oC, for 60 min, while the EAEP involved the addition of 0.5% of neutral protease to assist the extraction. A hexane-extracted oil was used as a control. Chemical destabilization was performed by adjusting the emulsion pH to the protein isoelectric point while enzymatic demulsification was achieved by the addition of a protease to destabilize the emulsion. Liquid chromatography coupled with mass spectrometry (LC-MS/MS) and conventional oxidation markers (peroxide value, p-anisidine) were applied to identify the integrated impact of extraction and recovery methods on the lipid oxidation state and fatty acid profile of the oil. Conventional oxidation markers such as peroxide value (1.8-2.0 mEq/kg oil) and p-anisidine (0.1-0.4), along with the fatty acid composition of the oils (C18:1 - 72-75%, C18-2 - 22-25%, C16:0 - 4-5%) were not able to detect significant changes based on the extraction and recovery methods used. However, oxylipins measured by LC-MS/MS demonstrated that the solvent-extracted oil had significantly higher levels of 13-hydroxyoctadecadienoic acid (13-HODE) and 12(13)-epoxyoctadecenoic acid (12(13)-EpOME) than AEP and EAEP oils, regardless of the demulsification strategy. Principal component analysis demonstrated that the solvent-extracted oil can be separated from the green-extracted almond oils by using oxylipins as markers of lipid oxidation. Oxylipins quantification was successful in detecting early lipid oxidation and differences in oils extracted by solvent and green extraction processes.