Effect of extraction conditions on composition, surface activity and rheological properties of protein isolates from flaxseed (Linum usitativissimum L)

Flaxseed protein isolates were prepared by micellisation (FM) and isoeletric precipitation (FI). The influence of preparation conditions on composition and functional properties was investigated. Contents of 0.6% phytic acid and 2.3% pentosans were found for FI, whereas FM was almost phytic acid-free and had a low content of pentosans (0.6%). Chromatography and electrophoresis identified the 1 IS globulin (linin) as the main protein fraction in both isolates. Protein solubility, water- and oil-binding capacities, emulsification and rheological properties of dispersions and gels were measured at pH 8 and 3. For the latter, interactions of protein with phytic acid and pentosans are highly probable. FI possesses a lower solubility (about 40-50%) and an overall higher water-binding capacity than FM. For FI dispersions a higher storage modulus G' than loss modulus G was measured, clearly pointing to the formation of protein networks. Moreover, FI formed stronger gels than FM (G' about fivefold). The emulsifying activity, however, was distinctly lower for FI. These results point to enhanced complexation and aggregation of the isoelectric-precipitated protein isolate. (C) 2002 Society of Chemical Industry.