Energy analysis in the screw pressing of whole and dehulled flaxseed

Specific Mechanical Energy (SME) is an important parameter of screw press design and performance. Analysis of SME and its dissipation will improve our understanding of temperature increase during screw pressing, and will in turn lead to better protection of heat sensitive materials, such as alpha-linolenic acid in flaxseed oil. SME, net enthalpy change, and heat loss were estimated from steady state data for screw pressing whole flaxseed and flaxseed with different fraction of hull removal (FHR). 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 6.3%. SME when pressing whole flaxseed was significantly higher than when pressing dehulled flaxseed.