Impact of Pressing Process on the Chemical and Nutritional Characteristics of Flaxseed and Hempseed Cakes

Abstract

The increasing demand of high-quality plant-derived oils has generated large quantities of press cakes as by-products of mechanical extraction. This study investigates the impact of screw-pressing conditions on the chemical, nutritional and functional properties of flaxseed and hempseed cakes. Whole flaxseeds and hempseeds were mechanically pressed at two rotor velocities (20% and 80%), and unprocessed seeds and their press cakes, were analyzed for proximate composition, fatty acid profile, total phenolic content (TPC), antioxidant activity (AA) through DPPH assay with QUENCHER method, and individual phenolic compounds by HPLC-DAD. Press cakes exhibited significantly higher protein and fiber content compared to the whole seeds. Flaxseed press cakes reached up to approximately 36% protein versus 22.7% in whole flaxseed, and 35.8% of fiber for both flaxseed cakes. Hempseed press cakes presented a higher fiber component in the range of 45-50%. AA increased markedly in all press cakes, particularly in flaxseed cakes obtained at high velocity, which showed 34.2 µmol TE/g compared to 14.8 in whole flaxseed. TPC and HPLC analyses revealed that lower pressing velocity preserved more free phenolic compounds, while higher velocity occasionally led to degradation, especially of heatsensitive molecules. Finally, despite the reduced oil fraction, the residual lipid fraction is characterized by favorable fatty acid profiles, dominated by α-linolenic acid (ω-3) in flax and linoleic acid (ω-6) in hemp, maintaining balanced ω-6/ω-3 ratios. These findings highlight the potential of flaxseed and hempseed press cakes as functional food ingredients and emphasize the role of pressing conditions in determining their nutritional and antioxidant properties.