Flaxseed milling and the stability of milled flaxseed

Flaxseed (Linum usitatissimum L.) producers are interested in milling flaxseed to add value to their crop. This research was conducted to help create a base of information that could be used to establish and advance flaxseed milling operations.;Four types of commonly used mills were compared to determine their effectiveness for milling flaxseed to a fine particle size in a single pass without processing difficulties. Fine-particle yields (particles <600 microns) of milled flaxseed were 23, 29, 44, and 54%, for the burr mill, roller mill, hammer mill, and centrifugal cutting mill, respectively. Agglomeration and adhesion of milled flaxseed particles to mill surfaces were encountered on all mills. The hammer mill and centrifugal cutting mill showed the greatest potential to mill flaxseed to a fine particle size.;The effect of moisture content on the yield and chemical composition of milled flaxseed particle size fractions was determined. Flaxseed was milled at 5.5, 8, and 10.5% moisture contents. Milled flaxseed was finest when flaxseed was milled at 5.5 and coarsest when milled at 10.5% moisture contents. Generally, milled product temperature was greater at high than at low flaxseed moisture content. Flaxseed milled at low moisture content resulted in minimal differences in chemical composition among coarse (>600 microns) and fine particle (<600 microns) fractions and whole milled flaxseed when compared to flaxseed milled at high moisture content.;Storage studies were designed to promote lipid oxidation to compare the oxidation at different sample depths and between coarse and fine particle fractions. Milled flaxseed samples were stored at depths of 1-2 cm and exposed to air for up to 84 d at 50°C. Lipid oxidation predominated at the pile surface of milled flaxseed and coincided with the formation of an adhered layer of flaxseed particles. The fine flaxseed fraction oxidized more than did the coarse flaxseed fraction.;The oil qualities of immature (green), off-colored and normal flaxseed were compared. Immature and off-colored flaxseed had higher peroxide value and free fatty acid content, and lower alpha linolenic acid content than did normal flaxseed. The selective removal of visibly defective seed improved flaxseed quality.