Extraction of proteins and residual oil from flax ( Linum usitatissimum ), camelina ( Camelina sativa ), and sunflower ( Helianthus annuus ) oilseed press cakes

The oilseed pressing process for the production of vegetable oils creates large amounts of cakes as by-products that contain high-added-value substances such as proteins and lipids. This work targets the chemical characterization of flax cake (FC), camelina cake (CC), and sunflower cake (SC) in order to evaluate the composition of proteins and residual oil, which are two of the main components, and to assess further technological applications of these biowastes. The use of a deep eutectic solvent (DES) was developed for protein extraction as a green alternative to conventional organic solvents. The lipid component, on the contrary, was extracted with n-hexane, which is typically used in oil industries. Several analytical techniques were used to characterize the cakes and the extracts (thermogravimetric analysis, attenuated total reflectance-Fourier transform infrared spectroscopy, elemental analysis; HPLC-ESI-Q-TOF/MS). In general, proteins were extracted with DES and precipitated with water, obtaining a higher yield for FC and CC. An improvement in extraction was obtained by increasing the temperature of the treatment. Different acyl glycerides profiles were identified in the residual oils obtained by solvent extraction from the cakes.