Nitrogen extractability and buffer capacity of defatted linseed (Linum usitatissimum L.) flour

Defatted linseed flour was prepared from cold‐pressed seed meal via hexane extraction of the residual oil, followed by removal of the major portion of the hulls through grinding and sieving (sieve size 0.25 mm). The resulting flour had 50% protein on a dry basis compared with 40% contained by the whole seed on an oil‐free dry basis. Nitrogen extractability of the defatted flour in water was not influenced by the length of the extraction period but an increased extraction was observed at higher solid:liquid ratios up to the studied limit of 1:40. The smallest amount of nitrogen (20%) was extracted in the pH range 4.0–4.6 and the greatest (80%) at pH 12.0. Addition of NaCl (0.1–1.0 M) broadened the pH range of minimum nitrogen extractability and shifted it towards lower pH region. At higher concentrations (0.6 and 1.0 M) NaCl markedly increased nitrogen extractability in the pH range of 4.0 to 8.0. Precipitation of protein from an extract at pH 10.0 was maximum (77%) at pH 4.1. A higher buffer capacity of the flour was observed in the acidic medium (0.204 mmol HCl g −1 flour) than in the alkaline medium (0.096 mmol NaOH g −1 flour).