Screw pressing of whole and dehulled flaxseed for organic oil rich in omega-3 fatty acids

Flaxseed oil is a rich source of dietary omega-3 fatty acids and is commonly obtained by cold pressing whole seed. Furthermore, flaxseed hulls are emerging as a valuable lignan-rich product for functional food use; therefore, the pressing characteristics of dehulled seed should be understood. Screw press performance was measured for pressing whole and dehulled flaxseed with different fraction of hull removal (FHR). Steady-state energy analysis was carried out to calculate the specific mechanical energy (SME). The influence of extraction and pretreatment methods on the quality of flaxseed oil was also measured.; When whole Omega flaxseed was pressed through a 6 choke, an inverse relationship between seed moisture content (6.1 to 11.6% range) and oil recovery (70.1 to 85.7%) was observed. However, the oil recovery from pressing dehulled Omega flaxseed was low at both moisture content extremes. Although oil recovery from dehulled Omega flaxseed was lower than from whole Omega flaxseed, the weight of oil produced from dehulled Omega flaxseed per unit time was higher.; The decrease of moisture content and FHR all resulted in significant increases of both oil and meal temperature and net enthalpy change. Conduction dissipated up to half of the mechanical energy input while convection was low. SME increased significantly from 81.1 to 104.7 kJ/kg when the moisture content of whole flaxseed decreased from 12.6 to 6.30 (dry basis). SME when pressing whole flaxseed was significantly higher than when pressing dehulled flaxseed.; The oil recovery from pressing uncooked, dehulled flaxseed averaged 56.7% and was significantly higher than that from pressing corresponding samples cooked at 100°C or 120°C for 10 min. The oil sampled from pressing dehulled flaxseed that was cooked at 100°C for 10 minutes had the highest peroxide value at an average of 5.63 meq peroxide/kg oil. Oil from screw pressing whole uncooked flaxseed had the lowest peroxide value of 0.15 meq peroxide/kg oil compared with solvent extraction oil or pressed oil with dehulling or cooking pretreatment.; Therefore, pressing dehulled flaxseed appears to offer advantages in organic flaxseed oil production. Thermal pretreatment is not recommended in pressing flaxseed oil.